ISSN 0252-1075 Contribution from IITM

Research Report No. RR-124       

Determination of Onset and Withdrawal Dates of Summer Monsoon across India using

NCEP/NCAR Re-analysis

Nityanand Singh

and Ashwini A. Ranade

JANUARY 2010

Indian Institute of Tropical Meteorology Dr. Homi Bhabha Road, Pashan Pune - 411 008

Maharashtra, India

E-mail : lip@tropmet.res.in Fax : 91-020-25893825 Web : http://www.tropmet.res.in Telephone : 91-020-25904200

CONTENTS

Abstract

1. Introduction 1 2. Data used 5 3. Objective criteria for determination of yearly onset and withdrawal dates 5

3.1. Definition 6

3.1. Local hydrometeorological index (LHMI) 6

3.2. General and regional atmospheric circulation intensity index (GARACII) 7

4. Results 10

4.1. Onset dates 10

4.2. Withdrawal dates 12

4.3. The onset and withdrawal over the subregions 13

5. Limitations 21 6. Summary and conclusion 22 Acknowledgements 22 References 23 Annexure I 25 Tables 26 Figures 58

Abbreviation/Acronym used in this research report AAMCZ Asia-Australia monsoon convergence zone ASM Asian summer monsoon CACSP central Australia-central South Pacific CAS Central Arabian Sea CC Correlation coefficient CME central Middle East DMI Dynamic monsoon index EWPO Equatorial western Pacific Ocean GAC General Atmospheric Circulation GR Golden Ratio GARACI General and regional atmospheric circulation intensity GARACII General and regional atmospheric circulation intensity index HOWI Hydrological onset and withdrawal index IGPs Indo-Gangetic Plains IMD India Meteorological Department IMMC Indonesia-Malaysia maritime continent ITCZ Inter-Tropical Convergence Zone KJNWNP Korea-Japan-northwest North Pacific LHMC Local hydrometeorological condition LHMI Local Hydrometeorological Index MCICP Myanmar-central Indo-China peninsula ME Moderately early ML Moderately late MSLP Mean Sea Level Pressure N Normal NNWI northern northwest India NLM northern limit of monsoon OD Objectively determined OLR Outgoing Longwave Radiation P Precipitation PW Precipitable water RSMC Regional Satellite Meteorology Centre SC Somali Coast SA South Asia SCSSM South China Sea summer monsoon SR Subregion TCC Total cloud cover THIKHIHILs Tibet-Himalaya-Karakoram-Hindukush highlands VE Very early VL Very late VIMT Vertically integrated moisture transport

Determination of Onset and Withdrawal Dates of

Summer Monsoon across India using

NCEP/NCAR Re-analysis

Nityanand Singh and Ashwini A. Ranade

Indian Institute of Tropical Meteorology, Pune

ABSTRACT

Following a unified approach, an objective criterion has been developed for the determination of yearwise onset and withdrawal dates of the summer monsoon over the 19 subregions across India. In total 14 meteorological parameters are considered in the development of the objective criteria, two of which represent heating over south Asia-Middle East sector and Tibet-Himalaya-Karakoram-Hindukush Highlands (THIKHIHILS), two intensity of the general atmospheric circulation (GAC) over eastern hemisphere, three intensity of regional circulations and seven local hydro-meteorological conditions. The period of study is 1951-2007. The results are excellent to very good for the peninsula where relationship of monsoon activities with circulation parameters can be visualized relatively easily, and satisfactory for the remaining parts. Rainfall activities at the time of onset over different subregions are different. They are categorized as abrupt, gradual and feeble. An arbitrary definition for the categories is as: if more than 40% of the 30-day rainfall at the time of onset occurs in the last 5 days (including onset date), the onset is regarded as abrupt, between 40% and 25% as gradual and less than 35% as feeble. For the whole country, the frequency of the abrupt, gradual and feeble onset is ~42%, ~22% and ~36% respectively. The error is least in the determination of normal and moderately early-late onset dates (~5 days) and large that of very early-late onset (7.1-7.8 days), and least error in abrupt onset (4.5 days) and large in gradual (6.3 days) and feeble (7.4 days).

Rainfall activities at the time of withdrawal can be also categorized as abrupt, gradual and feeble. Similar to onset date an arbitrary definition for the categories is as: if more than 40% of the 30-day rainfall at the time of withdrawal occurs in the first 5 days (including onset date), the withdrawal is regarded as abrupt, between 40% and 25% as gradual and less than 35% as feeble. For the whole country, the frequency of abrupt, gradual and feeble withdrawal is ~30%, ~15% and ~55% respectively. For determining the normal and moderately early-late withdrawal dates the error is least (5.6-7.1 days) and large for very early-late withdrawals (8.9-9.6 days). Further, the error is least for abrupt withdrawal (6.7 days) and large for gradual and feeble withdrawal dates (7.3-7.8 days). Information related to withdrawal date is not very reliable but is given here as an appraisal to the researchers interested to take up the problem in the future.

In general, the objective determination is best when the occurrence of the onset-withdrawal is abrupt and worst when feeble. Limitations of the objective approach for the determination of onset and withdrawal dates of the Indian summer monsoon are indicated.

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1. Introduction During boreal (northern hemisphere) summer, cool dry southeast trades of the Indian and Pacific Oceans cross the equator and become warm moist wind system which produces frequent rains/rainspells over the Asia-Pacific region (Eq.-45°N; 40-170°E) is popularly known as the summer monsoon. The Tibet-Himalaya-Karakoram-Hindukush highlands (THIKHIHILS), in the middle of the eastern hemisphere with contiguous landmass on the west and north and water bodies on the east and south, act as elevated heat source during boreal summer. In response to deep tropospheric heating, an inward intense pressure gradient in the lower layers and outward pressure gradient in the upper troposphere develop in and around the THIKHIHILS facilitating unusual lower level convergence, upper level divergence, air-sea interaction and tropical-extratropical interaction. Intensity and geographical location of the different components of the general atmospheric circulation (e.g. polar highs, sub polar lows, temperate westerlies, subtropical highs, tropical easterlies and equatorial lows/convergence zone) show a large seasonality following north-south annual migration of the Sun with a lag of 20-40 days. Even different components show different seasonality over land and ocean and over lower and upper troposphere. The equatorial lows (or Inter-Tropical Convergence Zone; the ITCZ) show only a small spatial shift across the equator over the Atlantic and the Pacific oceans but a large shift over continents of Africa, South America, Australia and Asia. Largest pole-ward stretching of the ITCZ occurs in the marine environment between the Afro-Asian landmass on the west and the Indo-Pacific water-body on the east. The maritime environment from equatorial Indian Ocean to western/northwestern North Pacific and eastern flank of the Afro-Asian land mass experience climatic conditions of the equator, the tropic, the sub-tropic and the temperate zones and their interannual and intra-seasonal variability. During each boreal summer, the ITCZ sweeps this part of the globe. The southeasterly trades after crossing the equator between the Somali Coast and the Indonesia-Malaysia maritime continents (popularly as the monsoon winds/currents) blow from southerly, southwesterly, westerly and even easterly directions in the different areas. The monsoon winds are charged with moisture while blowing over equatorial and tropical Indian and Pacific Oceans. Different types of rain-producing weather systems such as circular systems (low-pressure area, cyclone, depression etc.), line systems (trough, convergence zone, squall line etc.) and wave disturbances (easterly and westerly waves) develop in the monsoon flows due to following factors:

1. net radiation over the Tibetan-Himalaya-Karakoram-Hindukush highlands (THIKHIHILS) and the surrounding Afro-Eurasian land mass;

2. the SST conditions of the Indian and Pacific Oceans; 3. the speed and depth with which northwesterlies and southwesterlies converge-merge

into the ITCZ over the central Arabian Sea and the combined flow approaches the Indian landmass and further over the Bay of Bengal;

4. the speed and depth with which the westerlies/southwesterlies from the Arabian Sea, the cross-equatorial flows from the Australian high and the easterlies from equatorial Pacific meet and merge over the southern Bay of Bengal and the Indo-China peninsula;

5. branching of the combined flow over the head Bay of Bengal into easterlies blowing over the Indo-Gangetic Plains (IGPs) and southerlies blowing over the Indo-China and eastern China;

6. convergence of the easterlies into ‘heat low’ over the central Middle East and the southerlies into the Asian continental low;

7. rising motion from the two lows, divergence from the THIKHIHILS anticyclone, outflows towards east and south and subsidence over the North and South Pacific Oceans and Indian Ocean highs;

8. return-flows towards Asian summer monsoon regime; and 9. the orographic effect of the West Coast, the central highlands and the THIKHIHILS.

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The warm, moist monsoon flow frequently produces rain-spells across India during its period of occurrence, popularly known as monsoon season. The monsoon rains are of great significance for natural and anthropogenic ecosystems of the country. Normally, the monsoon onset occurs around 1 June over extreme south peninsula and advances over extreme northwest India around 15 July. The withdrawal starts from northwest around 1 September and from extreme south peninsula 15 October. However, the onset and withdrawal of the monsoon across the country exhibit large interannual variation. Therefore, determining onset and withdrawal dates using objective criteria, and understanding their variability is an important area of the monsoon research.

Reliable determination of the onset and withdrawal dates of the summer monsoon across India on real-time basis is important information for science, society and services. The higher tropospheric (surface-200 hPa) temperature compared to the nearest equatorial region determines the period and place of meridional (pole-ward) extension of the ITCZ. Though the Sun’s declination remains almost invariant from one year to another, different phases of the seasonally occurring summer monsoon circulation (onset, northward progression, establishment, southward retreat and withdrawal) and associated rainfall show large variability due to complex internal dynamics of the global climate system. From 21 March, the Sun’s declination increases northward and the northward migration of belt of maximum temperature and convection follows with a lag of 20 to 40 days. On 21 June, the Sun is over the Tropic of Cancer, thereafter the Sun starts receding towards equator but the ITCZ continues to move northward. The monsoon advances over northwest India and Pakistan due to positive radiation balance and continued warming tendency of the northern hemisphere. During last pentad of July and third pentad of August (P42-P45), warming of the northern hemisphere and most parameters representing general and regional circulations attain their highest values. The seventy-three 5-day periods from 1 January to 31 December refer to as 73 pentads or P1 through P73 in order (Annexure I). Winter cooling of the atmosphere over south Asia begins during fourth pentad of August and third pentad of September (P46-P51). The ITCZ starts receding from extreme northwest India by pentad P52 and the process is complete from the extreme south peninsula by the pentad P59.

With the annual north-south oscillation of the Sun, the Inter-tropical Convergence Zone (ITCZ) is stretched pole ward over continents of Australia and Asia and the maritime continents between Indian and Pacific Oceans. During respective summer, the surface temperatures are higher compared to the surrounding oceans-seas, and the low mean sea level pressure relatively more intense and organized over the continents and the maritime continents. Outflows from the surrounding subtropical highs converge into this low-pressure area and give rise to heavy rainfall in and around the area. The position of the low-pressure area changes during the course of the year. During January through March, it is located over northern Australia, Indonesia and northwestern South Pacific, during April over Malaysia, during May over southern Myanmar-South China Sea-Indo-China-Philippines region, during June over Myanmar-Northeast India-Bangladesh, during July-September around the Tibetan-Himalaya-Karakoram-Hindukush highlands (THIKHIHILS) and during October through December return to northern Australia. As the geographical location of the ‘low’ changes, the direction of the converging airflows into the low changes giving rise to different nomenclature to the airflows (monsoon) in different countries. Understanding meteorology of this low is critical to understand dynamics of the monsoons and monsoon rainfall of the Asia-Indian Ocean-Pacific Ocean-Australia region. The

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‘low’ will be referred to as the Asia-Australia Monsoon Convergence Zone (AAMCZ). The moist/humid maritime airflows converging or tending to converge into the AAMCZ are the monsoon wind, the direction of the wind will be nearly opposite for the same position of the AAMCZ when it is advancing northwestward to Asia than it is retreating to Australia. Outflows from southern subtropical highs (Mascarene, Australia and South Pacific) and North Pacific High that converge into the AAMCZ approach different countries in the Indo-Pacific region (south, southeast and east Asia, northern Australia and the maritime continents between the two Oceans) from different directions (east, south, southwest and west) hence the different names are given to the moist monsoon winds. During the retreat of the AAMCZ, the outflows from the Siberian High converge into the AAMCZ mostly from northeast and over some areas from northwest such as Papua New Guinea, and the monsoon wind bears the respective name. During April when the AAMCZ is over Malaysia, cross-equatorial flows occur, albeit feeble, along Somali Coast and eastern equatorial Indian Ocean. The convergence is close to and on both sides of the equator. The cross-equatorial flows intensify during May when the AAMCZ is located between 10°N and 20°N latitudes over northern Andaman and Nicobar Islands-Philippines sector. At this time, Andaman and Nicobar Islands experience monsoonal rainfall and extreme south Indian peninsula and northeast India thunderstorm associated rainfall because of their location on the hotter continent on the left bank of the monsoon flow. For the first time in 1943, the India Meteorological Department (IMD) determined the normal onset and withdrawal dates of the summer monsoon at 180 raingauge stations across British India (present day India, Pakistan, Bangladesh, Myanmar and Sri Lanka) from ‘characteristic monsoon rise/fall in pentad rainfall’, and prepared charts showing normal onset and withdrawal dates across the Indian subcontinent (IMD, 1943). For determining onset over Kerala State (extreme southwest peninsula) by the operational meteorologists Ananthakrishnan et al. (1967) suggested an objective criterion, ‘beginning from 10 May if at least five out of the seven stations report 24-hourly rainfall 1 mm or more for two consecutive days the forecaster should declare on the second day that the monsoon has advanced over Kerala’. Later Ananthakrishnan and Soman (1988) suggested improved objective criterion for declaring onset date over Kerala State, ‘when rainfall on the day and mean rainfall in the following 5 days period exceeded 10 mm’. Presently, the IMD uses the following criteria (Joseph et al. (2006) for declaring operationally the arrival of monsoon over Kerala (Pai and Rajeevan, 2009).

i. If after 10 May, 60% of the available 14 selected stations viz. Minicoy, Amini Divi, Thiruvananthapuram, Punalur, Kollam, Allapuzha, Kottayam, Kochin, Trissur, Kozhikode, Talassery, Cannur, Kasargode and Mangalore report rainfall of 2.5mm or more for two consecutive days, the onset of monsoon over Kerala may be declared on the second day, provided the following conditions are also met.

ii. Depth of westerlies should be maintained up to 600 hPa, in the box equator to latitude 10°N and longitude 55°-80°E. The zonal wind speed over the area bounded by parallels 5°N and 10°N, and meridians 70°E and 80°E should be of the order of 15-20 knots at 925 hPa. The source of data can be RSMC New Delhi wind analysis/satellite derived winds.

iii. INSAT derived OLR value should be less than 200 Wm-2 over the area bounded by parallels 5° N and 10° N and meridians 70°E and 75°E.

Researchers across the world have attempted numerous quantitative approaches to determine onset (sometimes withdrawal) of the summer monsoon over India and other countries

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of Southeast Asia and East Asia. Taniguchi and Koike (2006) have used three variables (vertically integrated water vapor, moisture transport and low-level wind) in an objective manner to determine the Indian summer monsoon onset date. Zeng and Lu (2004) calculated Livio’s Golden Ratio (GR) with daily normalized precipitation data globally available for 1° grid cells and applied unified threshold to the GR (=0.618) to determine onset and retreat dates of the different summer monsoons. Zhang et al (2004) proposed the following two conditions for the monsoon onset over the tropical Asian region (south of 20°N):

i. Establishment of a zonal vertical shear, with low-level (e.g. 850 hPa) westerlies and upper level (e.g. 200 hPa) easterlies.

ii. A pentad means OLR < 240 W m-2. Different evolutionary features of the Asian summer monsoon are considered in developing the objective criteria, such as low-level flow and cyclonic vortices, low-level zonal wind and stability, upper level flow and geopotential height, upper level meridional gradient of temperature, upper level diabatic heating and upper level adiabatic warming. Flateau et al (2001) have examined behavior of the following three parameters to study the problem of actual and double/multiple monsoon onsets.

i. kinetic energy of the surface winds averaged over 5°-20°N, 40°-110°E; ii. dynamic monsoon index (DMI) defined as the shear between 850 and 200-hPa zonal

winds, averaged over 5°-20°N and 40°-110°E; and iii. monsoon circulation index (MH) based on the strength of the local Hadley Cell and

defined as the shear between 850- and 200-hPa meridional winds, averaged over 10°-30°N and 70°-110°E.

Fasullo and Webster (2003) developed hydrological onset and withdrawal index (HOWI) for the Indian monsoon from the vertically integrated moisture transport (VIMT). Normalized VIMT is greater than zero during monsoon period and less than zero during remaining period of the year. They believe that the HOWI meets several requirements such as,

i. associated with the establishment of the large-scale processes that drive the monsoon circulation;

ii. relatively insensitive to individual synoptic disturbances, bogus monsoon onsets, and active-break transitions that occur within the monsoon season;

iii. based on fields that have been well observed over an extended period so that the method can be employed over an extended climatology; and

iv. based on fields that experience large and rapid variability during the monsoon onset and withdrawal.

Fleux and Stommel (1977) identified three types of onset of the southwest monsoon over the Arabian Sea, single onsets, multiple onsets and gradual onsets. The dates of single onsets are determined by the time when the wind has reached about one-half of its full monsoon strength. The single onset rises to full strength in a little less than one week. The multiple onsets are characterized by an early beginning of the southwest winds followed by a lull in the monsoon with partial failure of the winds, and then resumption of full strength. The gradual onsets are characterized by their early start, slow growth to full strength without a massive failure of the wind and late attainment of full strength. A large number of indices with objective and subjective criteria have been proposed to define the onset of the SCSSM (Wang et al. 2004). These indices include precipitation or its proxies:

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• outgoing longwave radiation (OLR), upper-tropospheric water vapor brightness temperature, high cloud amount, highly reflective cloud (Tanaka 1992; Chen et al. 1996; Yan 1997; Lin and Lin 1997; Zhu et al. 2001);

• low-level or surface winds (Yan 1997; Zhang et al. 2001), low-level relative vorticity (Lu et al. 2000);

• low-level meridional winds (Lu and Chan 1999); • equivalent potential temperature (Gao et al. 2001); • vertical zonal wind shear (Li and Wu 2000); • differential geopotential heights (He et al. 2001); or • combined measures of convection and low-level winds (Wang and Wu 1997; May 1997;

Xie et al. 1998; Liang et al. 1999; Kuch and Lin 2001).

Literature provides documentation of elaborate but qualitative description of the general circulation of the atmosphere and the southwest monsoon circulation. There does not seem to exist any unified objective criterion for declaring onset and withdrawal of the southwest monsoon across the country. In the era of global warming, it a curiosity to understand nature of variability of onset and withdrawal dates of the monsoon in different parts the country.

The main motivation of the present study is to explore utilization of the circulation parameters for determining different phases of onset and withdrawal of the summer monsoon over the 19 subregions across India (Figure 1; Singh and Ranade, 2009). The three main objectives of the present study are:

1. To develop objective criteria for the determination of yearwise onset and withdrawal dates over the subregions of India by considering parameters crucial to monsoon circulation- intensity of the general atmospheric circulation over the eastern hemisphere and regional circulations, and the local hydro-meteorological conditions;

2. To provide detailed description of the circulation features and hydrometeorologica conditions at the time of onset and withdrawal of the monsoon over different subregions across the country; and

3. To understand limitations of the objective criteria in determining onset and withdrawal dates over different subregions of the country.

2. Data Used The following two sets of data are utilized in the present study.

1. Daily rainfall of 1o grid cells over India for the period 1951-2003 is provided by the India Metrological Department (IMD) (Rajeevan et. al., 2006); and

2. Daily meteorological data (MSLP, PW, TCC, OLR, and temperature, geopotential, U and V of standard isobaric levels within troposphere) for 2.5o grid cells over the globe for the period 1951-2007 is obtained from the NCEP/NCAR website http://iridl.ldeo.columbia.edu/SOURCES/.NOAA/.NCEP NCAR/.CDAS 1/.DAILY (Kalnay et. al., 1996).

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3. Objective Criteria for Determination of Yearly Onset and Withdrawal Dates

3.1. Definition With the start of boreal summer, the temperature of the troposphere over northern hemisphere begins to rise and that over southern hemisphere to fall. Seasonal changes in geographical location, and shape, size and intensity in different components of the general atmospheric circulations (pole-to-pole and surface to tropopause) follow the global temperature changes. Anomalous changes in the atmospheric conditions (highest surface air temperature, lowest mean sea level pressure etc.) are seen over the maritime continents and boarder regions between the Afro-Asian landmass on the west and the north and the Indo-Pacific Oceans on the east and the south. Further, presence of the THIKKHIHILS in the subtropical Asia which act like elevated heat source, and is a gainful factor in the occurrence of low-level convergence over the central Middle East (CME; northwest India to Saudi Arabia) and upper level divergence over the THIKHIHILS. In general, the intensity of the general and regional atmospheric circulations in and around the Asian summer monsoon regime increases with a lag of 20 to 40 days. There are three stages in the occurrence of the onset process: arrival of the ITCZ, onset of the moist monsoon winds and start of the rains from the monsoon flow. Sometimes the three processes occur in quick succession and sometimes wide apart. Generally, the specialists and the society regard the start of the rains along extreme southwest peninsula (ESWP) as the onset of the monsoon alike. Researchers have attempted to determine the onset date with ample rainfall along the ESWP using regional and local meteorological parameters. On the other hand, the withdrawal is a single stage phenomenon that is equator-ward return of the ITCZ. In the present study, the onset and withdrawal of the monsoon would be interpreted as start and end of the monsoon rains respectively.

The onset of the summer monsoon (specified local hydro-meteorological condition) over the ESWP occurs when the intensity of the general and regional circulations exceeds the specified limit. The monsoon advances northward as the intensity of the circulations increases. The value of the parameters on climatological onset date is used to decide the limit of the local hydro-meteorological condition (LHMC) and general and regional atmospheric circulation intensity (GARACI) for yearwise determination of the onset date. The withdrawal of the monsoon occurs when the combined intensity of local hydro-meteorological condition and the general and the regional atmospheric circulations falls below the specified limit determined from the value of different parameters on climatological withdrawal date. Normally, the withdrawal begins from extreme northward India, and the date gradually progresses southwards. Therefore, two indices have been developed, one would represent meteorological and hydrological (rainfall) conditions over the area of interest, and another the intensity of the general and regional atmospheric circulations. 3.2. Local Hydro-Meteorological Index (LHMI)

Computational steps for the development of local hydro-meteorological index (LHMI) for determining onset and withdrawal dates for the particular subregion are as follows: 1. Calculate climatology of daily rainfall (P) based on data of the period 1951-2007; 2. Find 30 days total rainfall up to the normal onset date (30 days includes onset date) and

use it as rainfall threshold (P30); 3. Calculate yearwise 30-day running total rainfall and assign it against the 30th day; 4. Normalize the 30-day running total rainfall by dividing by the threshold value (P30);

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5. Find out yearwise normalized value of 30-day running mean of other parameters by repeating the steps 1 to 4;

6. Find out mean of normalized value of the selected parameters to get the local hydro-meteorological index (LHMI); and

7. Determine tentative onset date of particular year when the LHMI equaled or exceeded 1.0, and the withdrawal date when it fell below the specified threshold.

The choice of 30-day window-width is to take into account lags of about 30 days of maximum-minimum temperature (and convective activities) from maximum-minimum solar radiation (Trewartha and Horn, 1980). The threshold for the seven parameters of the LHMI at the time of onset and that at the time of withdrawal over the 19 subregions is given in Table 1. Table 2 gives hydro-meteorological parameters actually considered for the development of the LHMI for determination of onset and withdrawal dates for the 19 subregions. 3.3. General and Regional Atmospheric Circulation Intensity Index (GARACII)

Another index has been developed as representative of combined intensity of the seven circulation parameters out of the 10 parameters conformed to the objective criterion. The index has been developed by linearly combining intensity of the different circulations. 1. Calculate daily climatology of the parameter; 2. Calculate 30-day running means of the climatological daily value of the parameter; 3. Normalize the running means by dividing them by the respective 30-day mean of the

onset phase (3 May-1 June; the 30-day period at the time of climatological onset over Kerala); and

4. Calculate arithmetic mean of normalized value of the seven circulation parameters to get the desired index, the GARACII; and

5. Find out the threshold of the GARACII at the time of onset over each of the 19 subregions.

The threshold for the seven parameters of the GARACII at the time of onset over extreme southwest peninsula (SR1) is given in Table 3, and the threshold to GARACII at the time of onset and withdrawal over the 19 subregions in Table 4. The onset date is determined when the LHMI exceeded 1.0 and the GARACII the specified threshold. For withdrawal date, the arithmetic mean of the LHMI and GARACHI is calculated and when the mean fell below the specified threshold the first day of the 30-day period is taken as the withdrawal date.

Some features of the General Atmospheric Circulation (GAC) over eastern hemisphere display strong seasonality closely paralleling the seasonality of the Asian summer monsoon. The main motivation of the present study is to understand quantitative relationship between annual cycle of the selected GAC parameters and the onset and the withdrawal dates of the summer monsoon across India. The annual weather cycle over India has been divided into six sub-periods- winter (P72-P16; 22 December-21 March), summer (P17-P30; 22 March-30 May), onset (P31-P38; 31 May-9 July), establishment (P39-P51; 10 July-12 September) and withdrawal (P52-P59; 13 September - 22 October) phases of the summer monsoon and post-monsoon (P60-P71; 23 October - 21 December). A brief description of the annual cycle of general circulation over eastern hemispheric and regional circulation parameters in relation to different phases of the Indian summer monsoon is in order. For selected pentads (P31, P38, P45 and P55) the climatology of some circulation parameters (surface air temperature, mean sea level pressure,

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lower troposphere (850-500 hPa) temperature and thickness, upper troposphere (500-200 hPa) temperature and thickness and geopotential height of 850 and 200 hPa isobaric levels) are shown in Figures 2 to 9 in order. The streamlines for two layers of the troposphere-tropopause for eight phases of the AAMCZ are given in Figures 10 to 17 in order to understand the changes in the geographical location of the low-level convergence and upper level divergence. The two layers are: surface layer (1000-850 hPa) and tropopause (200-100 hPa); and the eight phases of the AAMCZ: P22-P25 (16 April-5 May; southeast trades enter into the northern hemisphere over equatorial Indian Ocean), P29-P32 (25 May- 9 June; beginning of the onset phase summer monsoonover Indian subcontinent), P33-P36 (10 June-29 June; middle of the northward advance), P38-P41 (5 July-24 July; end of advance over northwest India and onset over Pakistan), P48-P51 (24 August-12 September; established phase), P54-P57 (23 September-12 October; middle of withdrawal phase from India), P60-P63 (23 October-11 November; end of the boreal monsoon), and P72-P2 (22 December-10 January; peak of Australian monsoon). The following judgmental approach has been applied for the selection of the 10 circulation parameters. i. Understandably the parameter is a part of the Asian summer monsoon (ASM) circulation

system i.e. it should represent any of the four components: a) heating over the Tibet-Himalaya-Karakoram-Hindukush Highlands (THIKHIHILs), b) divergence from subtropical anticyclone over the THIKHIHILs and upper tropospheric airflows over eastern hemisphere, and c) lower tropospheric airflows over eastern hemisphere and convergence into the heat-low over middle-east and the Asian Continental Low (ACL) over the China-Mongolia area;

ii. Climatology of the intra-annual cycle of the parameter should show close parallelism with the seasonality of the ASM, i.e. drastic change from winter to established phase of the monsoon;

iii. It should show increase from P31 to P38, and decrease from P52 to P59; and iv. It should represent meteorological conditions conducive for rainfall occurrences and the

rainfall amount over the particular subregion. The Table 5 gives the climatology (1951-2007) of the 10 selected parameters for the six sub-periods, Table 6 for the eight pentads of the onset and withdrawal phases of the Indian summer monsoon. Geographical location of the parameters is shown in Figure 18. During the summer monsoon period (P31-P38), the temperature of the lower (upper) troposphere over the NH is higher by 7.8°C (5.5°C) compared to the SH (Table 7), and the thickness larger by 122.1m (157.9m) (Table 11). Over the central Middle East (CME) the temperature (thickness) of the lower troposphere is higher (larger) by 8.8°C (131.3m) compared to the NH, and over the THIKHIHILs the temperature (thickness) of the upper troposphere by 7.2°C (200.4m). During the onset over the extreme southwest peninsula (P31), the temperature of the lower (upper) troposphere over the NH is higher by 5.9°C (3.8°C) compared to the SH (Table 8), and the thickness larger by 92.7m (112.4m) (Table 11). Over the Middle East the temperature (thickness) of the lower troposphere is higher (larger) by 8.1°C (123.7m) compared to the NH, and over the THIKHIHILs the temperature (thickness) of the upper troposphere by 5.4°C (150.1m). And during the onset over northern northwest India (P38), the temperature of the lower (upper) troposphere over the NH is higher by 9.3°C (6.8°C) compared to the SH, and the thickness larger by 145.7m (196.4m). Over the CME the temperature (thickness) of the lower troposphere is higher (larger) by 9.0°C (134.9m) compared to the NH, and over the THIKHIHILs the temperature (thickness) of the upper troposphere by 7.8°C (221.1m).

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During the withdrawal from northern northwest India (P53), the temperature of the lower (upper) troposphere over the NH is higher by 6.4°C (4.6°C) compared to the SH (Table 9), and the thickness larger by 100.7m (135.3m) (Table 12). Over the CME the temperature (thickness) of the lower troposphere is higher (larger) by 7.3°C (106.3m) compared to the NH, and over the THIKHIHILs the temperature (thickness) of the upper troposphere by 5.8°C (166.0m). And during the withdrawal from extreme south peninsula (P59), the temperature of the lower (upper) troposphere over the NH is higher by 2.8°C (1.8°C) compared to the SH, and the thickness larger by 44.1m (56.9m). Over the CME the temperature (thickness) of the lower troposphere is higher (larger) by 5.5°C (79.3m) compared to the NH, and over the THIKHIHILs the temperature (thickness) of the upper troposphere by 3.3°C (92.6m).

A description of seasonality in selected circulation parameters is in order: from winter (P72-P16) to established phase of the summer monsoon (P39-P51), the thickness of lower troposphere over Middle East (25°-35°N; 40°-75°E) increases from 4418.0m to 4416.8m and upper troposphere thickness over the THIKHIHILs (25°-45°N; 40°-100°E) from 6317.0m to 6692.1m; the U200 over the Korea-Japan-northwest North Pacific (KJNWNP) (30°-40°N; 120°-160°E) decreases from 61.8 m/s to 11.0 m/s; the U200 over the central Australia-central South Pacific (CACSP) (20°-30°S; 120°-180°E) increases from 17.2 m/s to 43.7 m/s; the U850 over the equatorial western Pacific Ocean (EWPO) (10°S-10°N; 150°-180°E) increases from -2.5 m/s to -4.0 m/s; the V850 along the Somali Coast (SC) (5°S-10°N; 45°-55°E) changes from a weak northerly (-2.0 m/s) to a strong southerly (7.9 m/s); the V850 over the Indonesia-Malaysia maritime continent (IMMC) (5°S-5°N; 100°-150°E) from a weaker northerly (-1.6 m/s) to a weak southerly (2.0 m/s); the U850 over the central Arabian Sea (CAS) (5°-15°N; 55°-70°E) changes from a moderate easterly (-4.7 m/s) to a strong westerly (13.3 m/s); the V850 over the Myanmar and central Indo-China peninsula (MCICP) (10°-30°N; 90°-100°E) changes from a weak southerly (0.3 m/s) to a moderate southerly (2.8 m/s); and the Z200 over the South Asia (SA) (25°-35°N; 50°-100°E) increases from 12008.7m to 12541.2m. Seasonality in seven of the 10 circulation parameters showed close parallelism with occurrence/non-occurrence of the summer monsoon over India. These parameters are combined suitably to produce an index, which has been used in determining the onset and withdrawal dates. Either the remaining three parameters showed opposite behavior or first increase then decrease and/or again increase are ignored.

Onset phase The southeasterly trades after crossing the equator along Somali Coast approach as southwesterly monsoon winds at the earliest over extreme south peninsula (SR1 & 2) during P31 and latest over northern northwest India (NNWI; SR15) during P38. From P31 to P38 the changes in circulation, meteorological condition and rainfall are as: temperature of the lower troposphere (1000-500 hPa thick layer) around the THIKHIHILs increases from 13.3°C to 16.7°C (0.5°C/pentad) and the upper troposphere from -37.6°C to -32.6°C (0.8°C/pentad); thickness of lower troposphere over the CME increases from 4381.6m to 4429.1m (6.8m/pentad); thickness of upper troposphere over the THIKHIHILs increases from 6574.5m to 6701.2m (18.1m/pentad); the U200 over the KJNWNP sector decreases from 34.2m/s to 17.7m/s (~2.4m/s/pentad); the U200 over the CACSP sector increases from 41.1m/s (P31) to 46.2m/s (P34) and again decreases to 43.6m/s; the U850 over the EWPO remains about -4.4m/s; the

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V850 along the SC increases from 5.5m/s to 8.1m/s (0.4m/s/pentad); the V850 over the IMMC decreases from 1.1m/s to 1.8m/s (-0.7m/s/pentad); the U850 over the CAS increases from 8.3m/s to 14.5m/s (0.9m/s/pentad); the V850 over the MCICP increases from 2.8m/s (P31) to 4.0m/s (P35) and again decreases to 3.4m/s (P38); and the Z200 over the SA increases from 12404.2m to 12547.4m (20.4m/pentad). Establishment phase Compared to the onset phase (P31-P38), during the establishment phase (P39-P51) the temperature of the lower troposphere over the THIKHIHILs increases from 15.3°C to 16.1°C and that of the upper troposphere from -34.2°C to -32.2°C. Notable changes in the general and regional circulation parameters during these phases are: thickness of lower troposphere over the CME increases by 7.2m and that of upper troposphere over the THIKHIHILs by 36.2m, the V850 along the Somali Coast by 0.4m/s, the V850 over the IMMC by 0.5m/s, the U850 over the CAS by 0.1m/s, and the Z200 over the SA by 48.5m; while the U200 over the KJNWNP decreases by -16.3m/s, the U200 over central the CACSP by -1.1m/s, the U850 over the EWPO by -0.5m/s, and the V850 over the MCICP by -0.8m/s. Withdrawal phase Compared to the establishment phase (P39-P51) during the withdrawal phase (P52-P59) the temperature of the lower troposphere decreases from 16.1°C to 9.5°C and that of the upper troposphere from -32.2°C to -38.9°C. During withdrawal phase, the U200 over the KJNWNP increases from 11.0m/s to 30.8m/s (19.8m/s). The other parameters show considerable decrease- the thickness of lower troposphere over Middle East from 4416.8m to 4334.3m (-82.5m), the thickness of upper troposphere over the THIKHIHILs from 6692.1m to 6544.7m (-147.4m), the U200 over the CACSP from 43.7m/s to 38.3m/s (-5.4m/s), the U850 over the EWPO from -4.0m/s to -3.4m/s (-0.6m/s), the V850 along the Somali Coast from 7.9m/s to 2.4m/s (-5.5m/s), the V850 over the IMMC from 2.0m/s to 1.3m/s (-0.7m/s), the U850 over the CAS from 13.3m/s to 3.5m/s (-9.8m/s), the V850 over the MCICP from 2.8m/s to 1.7m/s (-1.1m/s), and the Z200 over the South Asia from 12541.2m to 12370.0m (-171.2m).

During the entire period of summer monsoon activities temperature and thickness of the lower and upper troposphere over the THIKHIHILs are higher-larger than that over the northern hemisphere. The normal onset and withdrawal dates are across the country are shown in Figure 19. 4. Results 4.1. Onset Dates

Actual onset and withdrawal dates and those obtained after the application of the objective criterion are shown in Figures 20 and 21 for the 19 subregions in order. The correlation coefficient between actual and objectively determined onset dates is excellent along West Coast (0.79-0.83) and peninsula (0.71-0.78); very good in central India and east coast (0.49-0.60); and fairly good in northern and northwestern India (0.36-0.47). The West Coast receives ample orographic rainfall in addition to heavy rainfall associated with tropical and oceanic influences. Due to leeward effect though the intensity is low (2.6 to 5.7mm/day; Singh and Ranade, 2009) over the peninsula, there are relatively frequent rainfall activities over the area (7 to 11 wet spells per year). Over these areas, it is relatively easy to visualize relationship between regional and general circulation parameters and the monsoon activities. Over northern and northwestern parts, the monsoon flow is frequently affected by the extra-tropical disturbances, thus the CC is weakest over the area. The parameters representing extra-tropical influences are not considered in the present objective criteria.

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A frequency distribution analysis shows that onset in 30.4% of years is normal (mean ± ½ σ), 14.8% moderately early (between -1/5 σ and -1 σ), 14.0% moderately late (between +1/2 σ and + 1σ), 16.2% very early (earlier than -1 σ) and 16.6% very late (later than + 1σ) (Table 13). The frequency distribution of withdrawal date in order is 38.1%, 15.0%, 14.9%, 15.8% and 16.3% (Table 15). Rainfall activities at the time of onset are different over different subregions. They can be categorized as abrupt, gradual and feeble. An arbitrary definition for the categories is as: if more than 40% of the 30-day rainfall at the time of onset occurs in the last 5 days (including onset date), the onset is regarded as abrupt, between 40% and 25% as gradual and less than 25% as feeble. For the whole country, percentage frequency of the abrupt, gradual and feeble onsets is ~42%, ~22% and ~36% respectively (Table 14). The error is least in the determination of normal, moderately early and moderately late onset dates (~5 days) and large that of very early and very late onset (7.1-7.8 days) (Table 13), and further it is least in abrupt onset (4.5 days) and large in gradual (6.3 days) and feeble (7.4 days) (Table 14).

• Along West Coast and central and northwest India (SRs 1, 3, 5, 8, 9, 11, 12, 13, 15 & 16) the onset is mostly abrupt (percentage frequency > 60%), gradual 19% and feeble 21%. The frequency of abrupt onset is highest (82%) over SR-8, followed by SR-5 (74%), SR-9 (70%), SR-3 (67%) and SR-12 (61%). The rain-producing weather systems at the time of onset over western parts of the country are: onset vortex, off-shore trough along the West Coast, monsoon convergence zone over central India, monsoon trough over Indo-Gangetic Plains and mid-tropospheric cyclone over the Gujarat region (SRs 8 and 11).

• Over south peninsula (excluding West Coast), northeast and extreme north (SRs 2, 4, 6, 7, 10, 14, 17, 18 and 19) in majority of cases the onset is feeble (percentage frequency 54%), 24% gradual and 22% abrupt.

• Over Tamilnadu State (SRs 2 & 4), the frequency distribution of onset date is similar to all-India (14.04%, 14.9%, 40.3%, 16.7% and 14.04%) but the type of rainfall activities at the time of onset is mostly feeble (78.9%) followed by gradual (13.2%) and very few (7.9%) abrupt. The error in determining onset date in different classes (early, normal, late etc.) is 2.7-7.4days, and with categories of rainfall (abrupt, gradual and feeble) 2.8-5.2 days (Table 18).

• Over northeast India (SR 18), the frequency distribution of onset date is 10.53%, 22.81%, 36.84%, 14.04% and 15.78%, slightly bulged towards left compared to all-India frequency distribution. Majority of onset is feeble (49.12%), followed by gradual (45.61%) and least abrupt (only 5.26%). The error is least in determining the very early onset (3.9 days) and most the very late (6.4 days). Further, it is least for abrupt onset (3.5 days) and most for feeble (7.1 days).

• Over West Bengal and neighborhood (SR 14), the frequency distribution of onset date is 14.04, 15.79, 36.84, 14.04 and 19.30 percent, slight right skewed compared all-India distribution. Majority of onset is feeble (49.1%), followed by abrupt (40.4%) and least gradual (10.5%). The error is ~6 days in determining the onset in different classes. Further the error is least in case of abrupt onset (2.4 days) and most for feeble onset (7.5 days).

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• Over northern central Indo-Gangetic Plains (IGPs) (SR 17), the frequency distribution of onset date is 24.56, 14.04, 29.82, 24.56 and 14.04 percent; slight platykurtic and right skewed compared to all-India frequency curve. Majority of onset is abrupt (45.7%), followed by feeble (36.8%) and least gradual (17.5%). The error is least in determining moderately early and moderately late onset (5.6 days) and most very late onset (11 days). Further, the error is least for abrupt onset (4.9 days) and most feeble onset (8.7 days).

• Over western IGPs (SR 16), the frequency distribution of onset date is 12.28, 19.3, 42.11, 12.28 and 14.04 percent; mostly comparable to all-India curve. Majority of onset is abrupt (42.11%), followed by feeble (33.33%) and least gradual (24.56%). The error is least in determining moderately late onset (6.3 days) and most very early onset (12.8 days). Further, the error is least for abrupt onset (5.3 days) and most feeble onset (10.5 days).

• Over extreme northern India (SR 19), the frequency distribution of onset date is 8.77, 21.05, 43.86, 12.28 and 14.04 percent; central lyptokurtic and left platykurtic comapared to all-India distribution. Majority of onset is feeble (38.6%), followed by gradual (36.84%) and least abrupt (24.56%). The error is least in determining moderately early onset (6.3 days) and most very late onset (13.2 days). Further, the error is least for abrupt onset (3.3 days) and most gradual onset (10.9 days).

• Forty two percent of the normal/early/late onset is abrupt, 23% gradual and 35% feeble. But along West Coast and over central and northern India, the occurrence of onset in different classes (normal, early or late) is mostly abrupt (59.4%) followed by feeble (21.3%) and gradual (19.3%) and over peninsula, east coast and northeast the onset is mostly feeble (52%) followed by abrupt (26.3%) and gradual (21.7%).

4.2. Withdrawal Dates

The CC between actual and objectively determined withdrawal dates is comparatively better over peninsula and poor over northern and northwestern regions for the same reasons of onset dates. The frequency distribution of withdrawal date is in order: 15.8% (normal), 15.0% (moderately early), 38.1% (moderately late), 14.9% (very early) and 16.3% (very late) (Table 15). Rainfall activities at the time of withdrawal over different subregions can also be categorized as abrupt, gradual and feeble. Similar to onset date an arbitrary definition for the categories is as: if more than 40% of the 30-day rainfall at the time of withdrawal occurred in the first 5 days (including withdrawal date), the withdrawal is regarded as abrupt, between 40% and 25% as gradual and less than 35% as feeble. For the whole country, percentage frequency of the abrupt, gradual and feeble onsets is ~30%, ~15% and ~55% respectively (Table 16). For determining the normal, moderately early and late withdrawal dates the error is least (5.6-7.1 days) and large for very early and very late withdrawals (8.9-9.6 days) (Table 16). Further, the error is least for abrupt withdrawal (6.7 days) and large for gradual and feeble withdrawal dates (7.3-7.8 days) (Table 16). Over West Coast, central India and northern India (SRs 5,8,11,12,13,14,15,16,17 and 19) the withdrawal is generally feeble (50.9%) or abrupt (34.1%) and rarely gradual (15.0%); and over south peninsula, east coast and north east the withdrawal is generally feeble (58.2%) followed by abrupt (27.2%) and rarely gradual (14.6%). The information related to withdrawal date is not very reliable, but is given here as an appraisal to the researchers interested to take up the problem for detailed study.

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In general, the objective determination is best when the occurrence of the onset and withdrawal is abrupt and worst when feeble. The objectively determined (OD) onset and withdrawal dates for the period 1951-2007 for the 19 subregions are given in Tables 17 to 35 in order, which also gives the dates available from the IMD charts.

4.3. The Onset and Withdrawal over the Subregions Extreme Southwest Peninsula (ESWP; SR1) Onset date - Mean onset is 1 June (σ, 8.6 days); frequency distribution 15.79% (VE), 14.04% (ME), 43.86% (N), 8.77% (ML) and 17.54% (VL); error in the determination of onset date in different classes 6.3, 3.9, 2.8, 4.6 and 6.2 days respectively; onset is 43.86% abrupt, 22.81% gradual and 33.33% feeble; and error in the determination of abrupt onset is 3.8 days, gradual 5.8 days and feeble 5.2 days. At the time of onset over ESWP (SR1; Kerala State) the thickness of lower troposphere over the CME is 4381.6m, the thickness of upper troposphere over the THIKHIHILs 6574.5m, the U200 over the KJNWNP 34.2 m/s, the U200 over the CACSP 41.1m/s, the U850 over the EWPO -4.3m/s, the V850 along the Somali Coast 5.5m/s, the V850 over the IMMC 1.1m/s, the U850 over the CAS 8.3m/s, the V850 over the MCICP 2.8m/s and the Z200 over south Asia 12404.2m (GARACII= 1.0). The local hydrometeorological condition (LHMC) is as: 30-day total rainfall 240.8mm, precipitable water (PW) 41.3mm, total cloud cover (TCC) 57.4%, U850 4.0m/s, U200 -6.5m/s, Z850 1492.4m and the Z200 12462.3m. Withdrawal date – The mean date is 19 October (σ, 6.0 days). The frequency distribution of withdrawal date is 17.5% (VE), 8.8% (ME), 40.4% (N), 17.5% (ML) and 15.8% (VL); 15.8% of the withdrawal is abrupt, 17.5% gradual and 66.7% feeble. The value of GARACII is 1.035. During monsoon period, five wet spells occur, each of duration 9.5 days and rainfall intensity (RI) 27.6mm/day- the duration of each of the intervening dry spell is 15.2 days and the RI 5.8mm/day (Singh and Ranade, 2009). Extreme Southeast Peninsula (ESEP; SR2) Onset date - Mean onset is 2 June (σ, 7.0 days); frequency distribution 14.04% (VE), 17.54% (ME), 38.6% (N), 15.79% (ML) and 14.04% (VL); error in the determination of onset date in different classes 4.3, 5.6, 3.7, 4.3 and 6.4 days respectively; onset is 8.77% abrupt, 15.79% gradual and 75.44% feeble; and error in the determination of abrupt onset is 5.2 days, gradual 3.7 days and feeble 4.9 days. Features of the general atmospheric circulation and that of regional circulation are the same as that over the SR1 (GARACII= 1.03; 3% higher than that for the SR1). The LHMC is: 30-day total rainfall 53.8mm, the PW 40.9mm, the TCC 52.5%, the U850 4.5m/s, the U200 -7.2m/s, the Z850 1487.8m and the Z200 12462.6m. Withdrawal date – The mean date is 19 October (σ, 6.0 days). The frequency distribution of withdrawal date is 14.0% (VE), 15.8% (ME), 35.1% (N), 19.3% (ML) and 15.8% (VL); 12.3% of the withdrawal is abrupt, 17.5% gradual and 70.2% feeble. The value of GARACII is 1.035. During monsoon period, five wet spells occur, each of duration 9.4 days and rainfall intensity (RI) 7.6mm/day- the duration of each of the intervening dry spell is 17.8 days and the RI 0.8mm/day.

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Southern Central West Coast (SCWC; SR3) Onset date - Mean onset is 5 June (σ, 7.0 days); frequency distribution 17.54% (VE), 12.28% (ME), 38.60% (N), 10.53% (ML) and 21.05% (VL); error in the determination of onset date in different classes 7.6, 1.7, 2.2, 3.7 and 3.7 days respectively; onset is 66.67% abrupt, 24.56% gradual and 8.77% feeble; and error in the determination of abrupt onset is 3.3 days, gradual 5.0 days and feeble 5.4 days. At the time of onset over the SCWC (SR3) the thickness of lower troposphere over the CME is 4395.8m, the thickness of upper troposphere over the THIKHIHILs 6605.9m, the U200 over the KJNWNP 30.4m/s, the U200 over the CANWSP 44.9m/s, the U850 over the EWPO -4.9m/s, the V850 along the Somali Coast 6.6m/s, the V850 over the IMMC 1.2m/s, the U850 over the CAS 11.5m/s, the V850 over the MCICP 3.0m/s and the Z200 over south Asia 12439.7m (GARACII= 1.123; 12.3% higher than that for the SR1). The LHMC is: 30-day total rainfall 201.4mm, the PW 36.9mm, the TCC 52.6%, the U850 3.4m/s, the U200 -4.3m/s, the Z850 1487.3m and the Z200 12468.8m. Withdrawal date – The mean date is 19 October (σ, 6.0 days); the frequency distribution of withdrawal date is 17.5% (VE), 15.8% (ME), 35.1% (N), 19.3% (ML) and 12.3% (VL); the error in the determination of withdrawal date in different classes is 7.9, 5.8, 7.6, 3.6 and 7.5 days respectively; 26.3% of the withdrawal is abrupt, 22.8% gradual and 50.9% feeble; and the error in the determination of different types of the withdrawal 4.7, 8.0 and 5.9 days respectively. The value of GARACII is 1.084. During monsoon period, five wet spells occur, each of duration 11.5 days and rainfall intensity (RI) 36.9mm/day- the duration of each of the intervening dry spell is 12.7 days and the RI 9.8mm/day. Central Southeast Peninsula (CSEP; SR4) Onset date - Mean onset is 6 June (σ, 7.0 days); frequency distribution 14.04% (VE), 12.28% (ME), 42.11% (N), 17.54% (ML) and 14.04% (VL); error in the determination of onset date in different classes 7.4, 2.7, 4.4, 4.5 and 2.9 days respectively; onset is 7.02% abrupt, 10.53% gradual and 82.46% feeble; and error in the determination of abrupt onset is 3.8 days, gradual 2.8 days and feeble 5.0 days. Features of the general atmospheric circulation and that of regional circulation are the same as that over the SR3 (GARACII= 1.157; 15.7% higher than that for the SR1). The LHMC is: 30-day total rainfall 68.8mm, the PW 38.5mm, the TCC 45.2%, the U850 3.4m/s, the U200 -6.8m/s, the Z850 1479.6m and the Z200 12469.8m. Withdrawal date – The mean date is 17 October (σ, 6.0 days); the frequency distribution of withdrawal date is 19.3% (VE), 8.8% (ME), 40.4% (N), 15.8% (ML) and 15.8% (VL); the error in the determination of withdrawal date in different classes is 5.8, 9.5, 3.9, 2.0 and 7.6 days respectively; 7.0% of the withdrawal is abrupt, 21.1% gradual and 71.9% feeble; and the error in the determination of different types of the withdrawal 6.5, 6.8 and 5.6 days respectively. The value of GARACII is 1.084. During monsoon period, six wet spells occur, each of duration 8.9 days and rainfall intensity (RI) 8.2mm/day- the duration of each of the intervening dry spell is 16.9 days and the RI 1.1mm/day. Northern Central West Coast (NCWC; SR5) Onset date - Mean onset is 9 June (σ, 7.0 days); frequency distribution 15.79% (VE), 15.79% (ME), 35.09% (N), 10.53% (ML) and 22.81% (VL); error in the determination of onset date in different classes 6.3, 4.9, 2.6, 1.9 and 3.6 days respectively; onset is 73.68% abrupt, 15.79% gradual and 10.53% feeble; and error in the determination of abrupt onset is 2.4 days,

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gradual 5.6 days and feeble 7.8 days. Features of the general atmospheric circulation and that of regional circulation are the same as that over the SRs 3 & 4 (GARACII= 1.264; 26.4% higher than that for the SR1). The LHMC is: 30-day total rainfall 130.5mm, the PW 35.5mm, the TCC 46.1%, the U850 3.4m/s, the U200 -2.3m/s, the Z850 1482.1m and the Z200 12473.7m.

Withdrawal date – The mean date is 13 October (σ, 5.0 days); the frequency distribution of withdrawal date is 10.5% (VE), 15.8% (ME), 49.1% (N), 12.3% (ML) and 12.3% (VL); the error in the determination of withdrawal date in different classes is 12.0, 5.3, 4.2, 5.9 and 6.3 days respectively; 31.6% of the withdrawal is abrupt, 21.1% gradual and 47.4% feeble; and the error in the determination of different types of the withdrawal 4.5, 6.0 and 6.7 days respectively. The value of GARACII is 1.189. During monsoon period, five wet spells occur, each of duration 10.9 days and rainfall intensity (RI) 30.1mm/day- the duration of each of the intervening dry spell is 14 days and the RI 7.2mm/day.

Southern Central Peninsula (SCP; SR6) Onset date - Mean onset is 11 June (σ, 6.0 days); frequency distribution 17.54% (VE), 14.04% (ME), 38.60% (N), 12.28% (ML) and 17.54% (VL); error in the determination of onset date in different classes 5.6, 5.9, 3.6, 4.1 and 5.6 days respectively; onset is 29.82% abrupt, 19.30% gradual and 50.88% feeble; and error in the determination of abrupt onset is 4.5 days, gradual 4.8 days and feeble 5.0 days. At the time of onset over the SCP (SR6) the thickness of lower troposphere over the CME is 4399.3m, the thickness of upper troposphere over the THIKHIHILs 6637.4m, the U200 over the KJNWNP 30.1m/s, the U200 over the CACSP 46.0m/s, the U850 over the EWPO -4.6m/s, the V850 along the Somali Coast 7.6m/s, the V850 over the IMMC 1.1m/s, the U850 over the CAS 12.8m/s, the V850 over the MCICP 4.2m/s and the Z200 over the South Asia 12470.6m (GARACII= 1.336; 33.6% higher than that for the SR1). The LHMC is: 30-day total rainfall 63.4mm, the PW 35.5mm, the TCC 49.0%, the U850 4.2m/s, the U200 -4.1m/s, the Z850 1475.7m and the Z200 12475.9m. Withdrawal date – The mean date is 14 October (σ, 6.0 days); the frequency distribution of withdrawal date is 12.3% (VE), 22.8% (ME), 38.6% (N), 10.5% (ML) and 15.8% (VL); the error in the determination of withdrawal date in different classes is 9.8, 5.0, 5.0, 7.2 and 6.9 days respectively; 24.6% of the withdrawal is abrupt, 7.0% gradual and 68.4% feeble; and the error in the determination of different types of the withdrawal 7.1, 7.3 and 5.7 days respectively. The value of GARACII is 1.162. During monsoon period, five wet spells occur, each of duration 7.9 days and rainfall intensity (RI) 8.9mm/day- the duration of each of the intervening dry spell is 14.6 days and the RI 1.3mm/day. Central East Coast (CEC; SR7) Onset date - Mean onset is 12 June (σ, 6.0 days); frequency distribution 17.79% (VE), 15.79% (ME), 40.35% (N), 10.53% (ML) and 17.54% (VL); error in the determination of onset date in different classes 6.7, 3.0, 3.9, 2.4 and 5.3 days respectively; onset is 20.07% abrupt, 28.07% gradual and 43.86% feeble; and error in the determination of abrupt onset is 3.2 days, gradual 4.3 days and feeble 5.5 days. Features of the general atmospheric circulation and that of regional circulation are the same as that over the SR6 (GARACII= 1.373; 37.3% higher than that for the SR1). The LHMC is: 30-day total rainfall 61.8mm, the PW 40.7mm, the TCC 53.3%, the U850 4.2m/s, the U200 -6.0m/s, the Z850 1469.1m and the Z200 12478.7m.

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Withdrawal date – The mean date is 15 October (σ, 7.0 days); the frequency distribution of withdrawal date is 17.5% (VE), 10.5% (ME), 35.1% (N), 21.1% (ML) and 15.8% (VL); the error in the determination of withdrawal date in different classes is 19.0, 12.7, 3.7, 8.3 and 10.8 days respectively; 17.5% of the withdrawal is abrupt, 17.5% gradual and 64.9% feeble; and the error in the determination of different types of the withdrawal 11.3, 4.4 and 13.2 days respectively. The value of GARACII is 1.135. During monsoon period, six wet spells occur, each of duration 7.4 days and rainfall intensity (RI) 11.6mm/day- the duration of each of the intervening dry spell is 14.8 days and the RI 2.2mm/day. Northern West Coast (NWC; SR8) Onset date - Mean onset is 13 June (σ, 6.0 days); frequency distribution 14.04% (VE), 17.54% (ME), 40.35% (N), 10.53% (ML) and 17.54% (VL); error in the determination of onset date in different classes 4.3, 2.7, 3.6, 1.8 and 5.5 days respectively; onset is 82.46% abrupt, 8.77% gradual and 8.77% feeble; and error in the determination of abrupt onset is 3.2 days, gradual 6.1 days and feeble 6.2 days. Features of the general atmospheric circulation and that of regional circulation are the same as that over the SRs 6 & 7 (GARACII= 1.409; 40.9% higher than that for the SR1). The LHMC is: 30-day total rainfall 81.5mm, the PW 33.5mm, the TCC 35.5%, the U850 4.0m/s, the U200 -0.3m/s, the Z850 1477.3m and the Z200 12478.7m. Withdrawal date – The mean date is 7 October (σ, 8.0 days); the frequency distribution of withdrawal date is 22.8% (VE), 12.3% (ME), 31.6% (N), 17.5% (ML) and 15.8% (VL); the error in the determination of withdrawal date in different classes is 9.1, 11.0, 3.8, 5.5 and 7.9 days respectively; 38.6% of the withdrawal is abrupt, 15.8% gradual and 45.6% feeble; and the error in the determination of different types of the withdrawal 6.2, 3.8 and 9.2 days respectively. The value of GARACII is 1.339. During monsoon period, six wet spells occur, each of duration 9.7 days and rainfall intensity (RI) 28.7mm/day- the duration of each of the intervening dry spell is 13.2 days and the RI 6.2mm/day. Northern Central Peninsula (NCP; SR9) Onset date - Mean onset is 15 June (σ, 6.0 days); frequency distribution 17.54% (VE), 12.28% (ME), 33.33% (N), 19.30% (ML) and 17.54% (VL); error in the determination of onset date in different classes 7.6, 3.9, 3.7, 4.5 and 6.9 days respectively; onset is 70.18% abrupt, 19.30% gradual and 10.53% feeble; and error in the determination of abrupt onset is 5.5 days, gradual 4.5 days and feeble 7.9 days. At the time of onset over the NCP (SR9) the thickness of lower troposphere over the CME is 4407.3m, the thickness of upper troposphere over the THIKHIHILs 6660.7m, the U200 over the KJNWNP 29.1m/s, the U200 over the CACSP 46.2m/s, the U850 over the EWPO -4.5m/s, the V850 along the Somali Coast 7.8m/s, the V850 over the IMMC 1.4m/s, the U850 over the CAS 14.3m/s, the V850 over the MCICP 3.8m/s and the Z200 over the South Asia 12493.1m (GARACII= 1.478; 47.8% higher than that for the SR1). The LHMC is: 30-day total rainfall 60.4mm, the PW 34.9mm, the TCC 46.4%, the U850 4.5m/s, the U200 -2.3m/s, the Z850 1467.5m and the Z200 12483.2m. Withdrawal date – The mean date is 8 October (σ, 7.0 days); the frequency distribution of withdrawal date is 17.5% (VE), 12.3% (ME), 38.6% (N), 12.3% (ML) and 19.3% (VL); the error in the determination of withdrawal date in different classes is 7.3, 11.5, 5.3, 5.7 and 6.8 days respectively; 29.8% of the withdrawal is abrupt, 17.5% gradual and 52.6% feeble; and the error in the determination of different types of the withdrawal 2.4, 11.4 and 6.9 days respectively. The

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value of GARACII is 1.318. During monsoon period, six wet spells occur, each of duration 8.6 days and rainfall intensity (RI) 13.5mm/day- the duration of each of the intervening dry spell is 13.3 days and the RI 2.9mm/day. Northern East Coast (NEC; SR10) Onset date - Mean onset is 16 June (σ, 6.0 days); frequency distribution 21.05% (VE), 12.28% (ME), 35.09% (N), 10.53% (ML) and 21.05% (VL); error in the determination of onset date in different classes 6.9, 5.5, 5.2, 5.5 and 4.9 days respectively; onset is 36.84% abrupt, 15.79% gradual and 47.37% feeble; and error in the determination of abrupt onset is 3.1 days, gradual 4.4 days and feeble 6.9 days. Features of the general and regional atmospheric circulations are the same as that over the SR 9 (GARACII= 1.511; 51.1% higher than that for the SR1). The LHMC is: 30-day total rainfall 60.4mm, the PW 34.9mm, the TCC 46.4%, the U850 4.5m/s, the U200 -2.3m/s, the Z850 1467.5m and the Z200 12483.2m. Withdrawal date – The mean date is 12 October (σ, 6.0 days); the frequency distribution of withdrawal date is 12.3% (VE), 21.1% (ME), 40.4% (N), 5.3% (ML) and 21.1% (VL); the error in the determination of withdrawal date in different classes is 9.6, 4.3, 3.9, 7.3 and 3.7 days respectively; 22.8% of the withdrawal is abrupt, 10.5% gradual and 66.7% feeble; and the error in the determination of different types of the withdrawal 3.6, 10.6 and 4.8 days respectively. The value of GARACII is 1.216. During monsoon period, six wet spells occur, each of duration 6.9 days and rainfall intensity (RI) 16.2mm/day- the duration of each of the intervening dry spell is 11.1 days and the RI 4.0mm/day. Southern Northwest India (SNWI; SR11) Onset date - Mean onset is 23 June (σ, 9.0 days); frequency distribution 12.28% (VE), 17.54% (ME), 47.37% (N), 7.02% (ML) and 15.79% (VL); error in the determination of onset date in different classes 8.4, 4.5, 6.6, 7.3 and 11.1 days respectively; onset is 15.14% abrupt, 14.04% gradual and 29.82% feeble; and error in the determination of abrupt onset is 7.4 days, gradual 6.1 days and feeble 9.1 days. At the time of onset over the SNWI (SR11) the thickness of lower troposphere over the CME is 4415.3m, the thickness of upper troposphere over the THIKHIHILs 6676.6m, the U200 over the KJNWNP 28.8m/s, the U200 over the CACSP 44.2m/s, the U850 over the EWPO -4.2m/s, the V850 along the Somali Coast 7.8m/s, the V850 over the IMMC 1.5m/s, the U850 over the CAS 14.4m/s, the V850 over the MCICP 4.0m/s and the Z200 over the South Asia 12514.0m (GARACII= 1.728; 72.8% higher than that for the SR1). The LHMC is: 30-day total rainfall 48.4mm, the PW 35.6mm, the TCC 30.5%, the U850 5.0m/s, the U200 -0.5m/s, the Z850 1462.1m and the Z200 12496.0m. Withdrawal date – The mean date is 28 September (σ, 6.0 days); the frequency distribution of withdrawal date is 12.3% (VE), 21.1% (ME), 31.6% (N), 14.0% (ML) and 21.1% (VL); the error in the determination of withdrawal date in different classes is 10.6, 4.9, 3.2, 1.2 and 6.9 days respectively; 50.9% of the withdrawal is abrupt, 7.0% gradual and 42.1% feeble; and the error in the determination of different types of the withdrawal 3.8, 7.5 and 6.8 days respectively. The value of GARACII is 1.512. During monsoon period, four wet spells occur, each of duration 8.8 days and rainfall intensity (RI) 13.5mm/day- the duration of each of the intervening dry spell is 17.2 days and the RI 1.5mm/day.

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Western Central India (NCI; SR12) Onset date - Mean onset is 21 June (σ, 8.0 days); frequency distribution 21.05% (VE), 8.77% (ME), 33.33% (N), 24.56% (ML) and 12.28% (VL); error in the determination of onset date in different classes 5.4, 1.3, 8.5, 4.7 and 9.4 days respectively; onset is 61.40% abrupt, 15.79% gradual and 22.80% feeble; and error in the determination of abrupt onset is 6.8 days, gradual 5.6 days and feeble 8.8 days. Features of the general and regional atmospheric circulations are the same as that over the SR11 (GARACII= 1.665; 66.5% higher than that for the SR1). The LHMC is: 30-day total rainfall 64.4mm, the PW 35.1mm, the TCC 48.5%, the U850 4.3m/s, the U200 1.5m/s, the Z850 1449.0m and the Z200 12491.7m. Withdrawal date – The mean date is 3 October (σ, 6.0 days); the frequency distribution of withdrawal date is 17.5% (VE), 21.1% (ME), 28.1% (N), 12.3% (ML) and 21.1% (VL); the error in the determination of withdrawal date in different classes is 8.2, 6.7, 5.4, 3.8 and 7.2 days respectively; 43.9% of the withdrawal is abrupt, 14.0% gradual and 42.1% feeble; and the error in the determination of different types of the withdrawal 7.1, 3.1 and 6.5 days respectively. The value of GARACII is 1.42. During monsoon period, five wet spells occur, each of duration 10.1 days and rainfall intensity (RI) 15.8mm/day- the duration of each of the intervening dry spell is 11.8 days and the RI 3.8mm/day. Eastern Central India (ECI; SR13) Onset date - Mean onset is 20 June (σ, 7.0 days); frequency distribution 26.32% (VE), 3.51% (ME), 35.09% (N), 15.79% (ML) and 19.30% (VL); error in the determination of onset date in different classes 3.9, 10.3, 5.7, 4.7 and 6.3 days respectively; onset is 52.63% abrupt, 29.82% gradual and 17.54% feeble; and error in the determination of abrupt onset is 3.4 days, gradual 6.6 days and feeble 8.8 days. Features of the general and regional atmospheric circulations are the same as that over the SRs 11 & 12 (GARACII= 1.634; 63.4% higher than that for SR1). The LHMC is: 30-day total rainfall 83.5mm, the PW 38.5mm, the TCC 45.7%, the U850 2.7m/s, the U200 3.8m/s, the Z850 1440.4m and the Z200 12490.8m. Withdrawal date – The mean date is 7 October (σ, 6.0 days); the frequency distribution of withdrawal date is 17.5% (VE), 17.5% (ME), 35.1% (N), 12.3% (ML) and 17.5% (VL); the error in the determination of withdrawal date in different classes is 4.7, 5.1, 6.8, 5.1 and 10.8 days respectively; 36.8% of the withdrawal is abrupt, 5.3% gradual and 57.9% feeble; and the error in the determination of different types of the withdrawal 6.9, - and 6.5 days respectively. The value of GARACII is 1.339. During monsoon period, six wet spells occur, each of duration 9.2 days and rainfall intensity (RI) 15.9mm/day- the duration of each of the intervening dry spell is 10.3 days and the RI 4.4mm/day. Eastern Indo-Gangetic Plain (EIGP; SR14) Onset date - Mean onset is 13 June (σ, 6.0 days); frequency distribution 14.04% (VE), 15.79% (ME), 36.84% (N), 14.04% (ML) and 19.30% (VL); error in the determination of onset date in different classes 6.8, 6.3, 6.3, 5.4 and 6.0 days respectively; onset is 19.30% abrupt, 45.61% gradual and 35.09% feeble; and error in the determination of abrupt onset is 2.4 days, gradual 5.4 days and feeble 7.5 days. Features of the general atmospheric circulation and that of regional circulation are the same as that over the SRs 6, 7 & 8 (GARACII= 1.409; 40.9% higher than that for the SR1). The LHMC is: 30-day total rainfall 123.8mm, the PW 41.7mm, the TCC 38.4%, the U850 2.3m/s, the U200 7.3m/s, the Z850 1447.7m and the Z200 12477.8m.

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Withdrawal date – The mean date is 10 October (σ, 6.0 days); the frequency distribution of withdrawal date is 21.1% (VE), 10.5% (ME), 38.6% (N), 17.5% (ML) and 12.3% (VL); the error in the determination of withdrawal date in different classes is 5.7, 5.3, 4.9, 4.3 and 10.6 days respectively; 40.4% of the withdrawal is abrupt, 10.5% gradual and 49.1% feeble; and the error in the determination of different types of the withdrawal 5.3, 11.5 and 5.1 days respectively. The value of GARACII is 1.269. During monsoon period, seven wet spells occur, each of duration 7.7 days and rainfall intensity (RI) 16.8mm/day- the duration of each of the intervening dry spell is 11.3 days and the RI 4.5mm/day. Northern Northwest India (NNWI; SR15) Onset date - Mean onset is 8 July (σ, 8.0 days); frequency distribution 17.54% (VE), 15.79% (ME), 38.60% (N), 15.79% (ML) and 12.28% (VL); error in the determination of onset date in different classes 11.5, 11.3, 9.8, 9.5 and 24.4 days respectively; onset is 54.39% abrupt, 12.28% gradual and 33.33% feeble; and error in the determination of abrupt onset is 10.7 days, gradual 18.3 days and feeble 12.0 days. At the time of onset over the NNWI (SR15) the thickness of lower troposphere over the CME is 4429.1m, the thickness of upper troposphere over the THIKHIHILs 6701.2m, the U200 over the KJNWNP 17.7m/s, the U200 over the CACSP 43.6m/s, the U850 over the EWPO -4.3m/s, the V850 along the Somali Coast 8.1m/s, the V850 over the IMMC 1.8m/s, the U850 over the CAS 14.5m/s, the V850 over the MCICP 3.4m/s and the Z200 over the South Asia 12547.4m (GARACII= 2.051; 105.1% higher than that for the SR1). The LHMC is: 30-day total rainfall 55.7mm, the PW 39.8mm, the TCC 33.4%, the U850 3.1m/s, the U200 3.1m/s, the Z850 1423.8m and the Z200 12527.6m. Withdrawal date – The mean date is 19 September (σ, 8.0 days); the frequency distribution of withdrawal date is 17.5% (VE), 10.5% (ME), 38.6% (N), 21.1% (ML) and 12.3% (VL); the error in the determination of withdrawal date in different classes is 13.0, 7.8, 9.2, 11.9 and 18.1 days respectively; 35.1% of the withdrawal is abrupt, 12.3% gradual and 52.6% feeble; and the error in the determination of different types of the withdrawal 16.6, 9.2 and 9.9 days respectively. The value of GARACII is 1.681. During monsoon period, three wet spells occur, each of duration 7.7 days and rainfall intensity (RI) 9.2mm/day- the duration of each of the intervening dry spell is 19.0 days and the RI 0.6mm/day. Western Indo-Gangetic Plain (WIGP; SR16) Onset date - Mean onset is 30 June (σ, 8.0 days); frequency distribution 12.28% (VE), 19.03% (ME), 42.11% (N), 12.28% (ML) and 14.04% (VL); error in the determination of onset date in different classes 12.8, 6.8, 7.5, 6.3 and 10.2 days respectively; onset is 42.11% abrupt, 24.56% gradual and 33.33% feeble; and error in the determination of abrupt onset is 5.3 days, gradual 9.6 days and feeble 10.5 days. At the time of onset over the WIGP (SR16) the thickness of lower troposphere over the CME is 4426.3m, the thickness of upper troposphere over the THIKHIHILs 6699.8m, the U200 over the KJNWNP 21.8m/s, the U200 over the CACSP 46.2m/s, the U850 over the EWPO -4.4m/s, the V850 along the Somali Coast 8.3m/s, the V850 over the IMMC 1.6m/s, the U850 over the CAS 14.9m/s, the V850 over the MCICP 3.6m/s and the Z200 over south Asia 12541.0m (GARACII= 1.915; 91.5% higher than that for the SR1). The LHMC is: 30-day total rainfall 68.0mm, the PW 33.7mm, the TCC 32.5%, the U850 3.9m/s, the U200 7.4m/s, the Z850 1434.6m and the Z200 12500.5m.

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Withdrawal date – The mean date is 27 September (σ, 8.0 days); the frequency distribution of withdrawal date is 8.8% (VE), 17.5% (ME), 49.1% (N), 10.5% (ML) and 14.0% (VL); the error in the determination of withdrawal date in different classes is 6.8, 5.7, 9.0, 6.9 and 5.6 days respectively; 35.1% of the withdrawal is abrupt, 14.0% gradual and 50.9% feeble; and the error in the determination of different types of the withdrawal 9.1, 4.2 and 6.9 days respectively. The value of GARACII is 1.531. During monsoon period, five wet spells occur, each of duration 9.4 days and rainfall intensity (RI) 11.9mm/day- the duration of each of the intervening dry spell is 12.0 days and the RI 2.6mm/day. Central Indo-Gangetic Plain (CIGP; SR17) Onset date - Mean onset is 21 June (σ, 7.0 days); frequency distribution 24.56% (VE), 14.04% (ME), 29.82% (N), 24.56% (ML) and 14.04% (VL); error in the determination of onset date in different classes 5.7, 5.6, 5.7, 5.6 and 11.0 days respectively; onset is 38.60% abrupt, 21.05% gradual and 40.35% feeble; and error in the determination of abrupt onset is 4.9 days, gradual 5.5 days and feeble 8.7 days. Features of the general atmospheric circulation and that of regional circulation are the same as that over the SRs 11, 12, 13 & 17 (GARACII= 1.665; 66.5% higher than that for the SR1). The LHMC is: 30-day total rainfall 95.3mm, the PW 32.9mm, the TCC 33.4%, the U850 3.1m/s, the U200 8.9m/s, the Z850 1440.4m and the Z200 12480.4m. Withdrawal date – The mean date is 3 October (σ, 6.0 days); the frequency distribution of withdrawal date is 10.5% (VE), 28.1% (ME), 24.6% (N), 19.3% (ML) and 17.5% (VL); the error in the determination of withdrawal date in different classes is 6.5, 5.8, 5.3, 3.9 and 10.4 days respectively; 45.6% of the withdrawal is abrupt, 17.5% gradual and 36.8% feeble; and the error in the determination of different types of the withdrawal 6.4, 7.6 and 5.9 days respectively. The value of GARACII is 1.42. During monsoon period, six wet spells occur, each of duration 7.1 days and rainfall intensity (RI) 16.8mm/day- the duration of each of the intervening dry spell is 10.5 days and the RI 3.4mm/day. Northeast India (NEI; SR18) Onset date - Mean onset is 6 June (σ, 6.0 days); frequency distribution 10.53% (VE), 22.81% (ME), 36.84% (N), 14.04% (ML) and 15.79% (VL); error in the determination of onset date in different classes 3.9, 4.9, 6.4, 5.7 and 6.4 days respectively; onset is 5.26% abrupt, 45.61% gradual and 49.12% feeble; and error in the determination of abrupt onset is 3.5 days, gradual 4.4 days and feeble 7.1 days. Features of the general atmospheric circulation and that of regional circulation are the same as that over the SRs 3, 4 & 5 (GARACII= 1.157; 15.7% higher than that for the SR 1). The LHMC is: 30-day total rainfall 269.4mm, the PW 33.7mm, the TCC 47.7%, the U850 2.3m/s, the U200 14.6m/s, the Z850 1461.1m and the Z200 12452.3m. Withdrawal date – The mean date is 15 October (σ, 5.0 days); the frequency distribution of withdrawal date is 17.5% (VE), 8.8% (ME), 40.4% (N), 17.5% (ML) and 15.8% (VL); the error in the determination of withdrawal date in different classes is 13.1, 5.3, 5.3, 5.7 and 5.8 days respectively; 21.1% of the withdrawal is abrupt, 12.3% gradual and 66.7% feeble; and the error in the determination of different types of the withdrawal 5.3, 12.2 and 6.1 days respectively. The value of GARACII is 1.135. During monsoon period, seven wet spells occur, each of duration 7.5 days and rainfall intensity (RI) 18.2mm/day- the duration of each of the intervening dry spell is 12.3 days and the RI 5.6mm/day.

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Extreme Northern India (ENI; SR19) Onset date - Mean onset is 1 July (σ, 8.0 days); frequency distribution 8.77% (VE), 21.05% (ME), 43.86% (N), 12.28% (ML) and 14.04% (VL); error in the determination of onset date in different classes 12.8, 6.3, 6.7, 10.2 and 13.2 days respectively; onset is 24.56% abrupt, 36.84% gradual and 38.60% feeble; and error in the determination of abrupt onset is 3.3 days, gradual 10.9 days and feeble 9.0 days. Features of the general atmospheric circulation and that of regional circulation are the same as that over the SR16 (GARACII= 1.938; 93.8% higher than that for the SR1). The LHMC is: 30-day total rainfall 102.1mm, the PW 22.9mm, the TCC 20.6%, the U850 1.4m/s, the U200 16.7m/s, the Z850 1448.9m and the Z200 12463.8m. Withdrawal date – The mean date is 23 September (σ, 9.0 days); the frequency distribution of withdrawal date is 15.8% (VE), 5.3% (ME), 54.4% (N), 7.0% (ML) and 17.5% (VL); the error in the determination of withdrawal date in different classes is 14.3, 8.9, 9.5, 8.4 and 13.0 days respectively; 38.6% of the withdrawal is abrupt, 21.1% gradual and 40.4% feeble; and the error in the determination of different types of the withdrawal 6.3, 11.0 and 13.0 days respectively. The value of GARACII is 1.607. During monsoon period, four wet spells occur, each of duration 8.2 days and rainfall intensity (RI) 10.3mm/day- the duration of each of the intervening dry spell is 17.2 days and the RI 2.8mm/day. 5. Limitations There are some limitations of this study, which must be borne in mind before taking any new study in the future. i. The IMD subjectively draws the line of the ‘Northern Limit of Monsoon; NLM’ to

demarcate the limit of northward propagation of the monsoon after the onset over the Kerala Coast and similarly subjective lines are drawn to demarcate the southward retreat of the monsoon;

ii. From these subjectively drawn IMD charts, yearwise onset and withdrawal dates have been picked up subjectively for the 19 subregions of the country;

iii. Area-averaged rainfall is considered as uniform mean rainfall amount for the subregion, but for the same rainfall amount spatial variability could be quite different and thus the regional circulations and the local meteorological conditions;

iv. A unified approach has been attempted for the 19 subregions with diverse meteorological conditions – perhaps subregion specific criteria can give better results;

v. There is some biasedness of the present objective criteria – the objectively determined onset date occurs ~4 days later than the IMD date, and the withdrawal date ~5 days earlier (the RMSE reported here is after correction for bias);

vi. Extra-tropical parameters should be considered to obtain satisfactory results for northern and northwestern parts of the country;

vii. The monsoon onset and withdrawal over the particular subregion does not occur with the same intensity every year – both phases of the monsoon occurrences can be categorized as feeble, gradual and abrupt; and

viii. There are limitations of the NCEP/NCAR reanalyzed data also.

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6. Summary and Conclusion 1. The two heating parameters in and around the Tibet-Himalaya-Karakoram-Hindukush

highlands (THIKHIHILs), two general circulation parameters over eastern hemisphere, three regional circulation parameters around summer monsoon circulation system that show steady increase from summer to the monsoon onset period and decrease from established to withdrawal period are used along with seven local hydro-meteorological conditions to determine yearwise the onset and withdrawal dates of summer monsoon over 19 subregions of India.

2. The determination of onset date is excellent to very good along West Coast and over central and northern India and satisfactory over remaining parts.

3. The determination of withdrawal date is very good over peninsular India, east coast and northeast India.

4. Rainfall activities at the time of onset and withdrawal are generally abrupt along West Coast and over central and northern India and feeble over peninsula, east coast and northeast.

5. Information related to withdrawal date is not very reliable, but it is given here as an appraisal to the researchers interested to take up the problem for detailed study.

There is some biasedness in the determination of the onset and withdrawal dates, the present objective criteria can be adopted for operational purposes after necessary research and development work. As the linkages between circulation parameters and onset and withdrawal dates provide vital scientific information, they will be explored for prediction of summer monsoon onset and withdrawal across the country. Acknowledgements. The authors are extremely grateful to Prof. B.N.Goswami, Director, Indian Institute of Tropical Meteorology, Pune (INDIA) for necessary facilities to pursue this study, and to Dr. P.N. Mahajan, R.M. Khaladkar and S.S. Dugam for critically reviewing the manuscript offering valuable suggestions for modifying the manuscript. The 1-degree raster data of daily rainfall of the period 1951-2007 for the country was provided by the India Meteorological Department, Pune which is thankfully acknowledged.

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23

 

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Zhu, Y., Y. Li, and W. Qian, 2001: Comparison of the SCS summer monsoon onset, characteristics derived from different datasets. J. Trop. Meteor., 17, 34-44.

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25

 

Annexure I Pentad numbers and the corresponding calendar dates

Pentad No. Dates Pentad No. Dates Pentad No. Dates

1  1-5 Jan 26  6-10 May 51  8-12 Sept

2  6-10 Jan 27  11-15 May 52  13-17 Sept

3  11-15 Jan 28  16-20 May 53  18-22 Sept

4  16-20 Jan 29  21-25 May 54  23-27 Sept

5  21-25 Jan 30  26-30 May 55  28 Sept-2 Oct

6  26-30 Jan 31  31 May-4 Jun 56  3-7 Oct

7  31 Jan-4 Feb 32  5-9 Jun 57  8-12 Oct

8  5-9 Feb 33  10-14 Jun 58  13-17 Oct

9  10-14 Feb 34  15-19 Jun 59  18-22 Oct

10  15-19 Feb 35  20-24 Jun 60  23-27 Oct

11  20-24 Feb 36  25-29 Jun 61  28 Oct -1 Nov

12  25 Feb- 1 Mar 37  30 Jun-3July 62  2-6 Nov

13  2-6 Mar 38  4-9 July 63  7-11 Nov

14  7-11 Mar 39  10-14 July 64  12-16 Nov

15  12-16 Mar 40  15-19 July 65  17-21 Nov

16  17-21 Mar 41  20-24 July 66  22-26 Nov

17  22-26 Mar 42  25-29 July 67  27 Nov -1 Dec

18  27-31 Mar 43  30 July- 3 Aug 68  2-6 Dec

19  1-5 Apr 44  4-8 Aug 69  7-11 Dec

20  6-10 Apr 45  9-13 Aug 70  12-16 Dec

21  11-15 Apr 46  14-18 Aug 71  17-21 Dec

22  16-20 Apr 47  19-23 Aug 72  22-26 Dec

23  21-25 Apr 48  24-28 Aug 73  27-31 Dec

24  26-30 Apr 49  29 Aug-2 Sept ‐  -

25  1-5 May 50  3-7 Sept ‐  -

 

 

 

26

Table 1. The threshold to 30-day mean rainfall and other meteorological parameters at the time of summer monsoon onset and withdrawal (in bracket) over the particular subregion of the country.

Sub-

region Name of the

subregion Rainfall

(mm) PPW (mm)

TCC (%)

U850 (m/s)

U200 (m/s)

Z850 (m)

Z200 (m)

SR 1 Extreme southwest peninsula (ESWP)

240.8 (213.3)

41.3 (42.8)

57.4 (59.2)

4.0 (-1.1)

- 6.5 (-8.3)

1492.4 (1503.1)

12462.3 (12424.6)

SR 2 Extreme southeast peninsula (ESEP)

53.8 (235.6)

40.9 (43.0)

52.5 (63.4)

4.5 (-1.4)

-7.2 (-9.3)

1487.8 (1501.3)

12462.6 (12425.3)

SR 3 Southern central West Coast (SCWC)

201.4 (116.3)

36.9 (37.8)

52.6 (56.5)

3.4 (-3.3)

-4.3 (-3.3)

1487.3 (1505.3)

12468.8 (12430.7)

SR 4 Central southeast peninsula (CSEP)

68.8 (176.0)

38.5 (40.5)

45.2 (57.4)

3.4 (-3.5)

-6.8 (-4.7)

1479.6 (1502.5)

12469.8 (12433.3)

SR 5 Northern central West Coast (NCWC)

130.5 (62.1)

35.5 (35.1)

46.1 (47.8)

3.4 (-3.8)

-2.3 (1.14)

1482.1 (1506.5)

12473.7 (12432.0)

SR 6 Southern central peninsula (SCP)

63.4 (58.4)

35.5 (34.4)

49.0 (48.1)

4.2 (-4.0)

-4.1 (0.5)

1475.7 (1506.2)

12475.9 (12433.2)

SR 7 Central East Coast (CEC)

61.8 (142.6)

40.7 (40.1)

53.3 (54.4)

4.2 (-3.9)

-6.0 (-0.5)

1469.1 (1504.2)

12478.7 (12437.7)

SR 8 Northern West Coast (NWC)

81.5 (48.1)

33.5 (31.9)

35.5 (40.8)

4.0 (-3.4)

-0.3 (4.6)

1477.3 (1509.1)

12478.7 (12433.3)

SR 9 Northern central peninsula (NCP)

60.4 (148.5)

34.9 (33.2)

46.4 (43.7)

4.5 (-3.2)

-2.3 (4.0)

1467.5 (1508.0)

12483.2 (12436.1)

SR 10 Northern East Coast (NEC)

110.9 (104.1)

39.6 (34.1)

55.9 (43.4)

3.8 (-1.9)

-1.6 (8.5)

1456.2 (1508.9)

12487.6 (12429.7)

SR 11 Southern northwest India (SNWI)

48.4 (21.4)

35.6 (20.7)

30.5 (23.8)

5.0 (-1.4)

-0.5 (8.2)

1462.1 (1509.7)

12496.0 (12434.4)

SR 12 Western central India (WCI)

64.4 (33.1)

35.1 (28.9)

48.5 (33.7)

4.3 (-0.8)

1.5 (11.7)

1449.0 (1504.4)

12491.7 (12424.9)

SR 13 Eastern central India (ECI)

83.5 (37.1)

38.5 (29.1)

45.7 (29.3)

2.7 (0.1)

3.8 (17.4)

1440.4 (1504.8)

12490.8 (12408.9)

SR 14 Eastern Indo Gangetic Plain (EIGP)

123.8 (45.9)

41.7 (32.4)

38.4 (29.9)

2.3 (0.1)

7.3 (18.5)

1447.7 (1505.1)

12477.8 (12406.2)

SR 15 Northern northwest India (NNWI)

55.7 (16.1)

39.8 (26.6)

33.4 (20.0)

3.1 (-1.5)

3.1 (16.7)

1423.8 (1491.7)

12527.6 (12411.5)

SR 16 Western Indo Gangetic Plains(WIGP)

68.0 (36.7)

33.7 (23.7)

32.5 (20.5)

3.9 (0.9)

7.4 (22.4)

1434.6 (1502.2)

12500.5 (12376.9)

SR17 Central Indo Gangetic Plain (CIGP)

95.3 (44.4)

32.9 (25.0)

33.4 (25.5)

3.1 (0.5)

8.9 (23.1)

1440.4 (1506.9)

12480.9 (12381.6)

SR 18 Northeast India (NEI)

269.4 (71.3)

33.7 (27.3)

47.7 (37.1)

2.3 ( 0.5)

14.6 (25.4)

1461.1 (1510.5)

12452.3 (12375.8)

SR 19 Extreme northern India (ENI)

102.1 (46.8)

22.9 (17.3)

20.6 (17.1)

1.4 (0.2)

16.7 (28.1)

1448.9 (1508.6)

12463.8 (12310.5)

 

 

27

Table 2. Meteorological parameters used for development of the LHMI for the determination of onset and withdrawal dates of the 19 subregions. The CC indicates correlation coefficient between actual and objectively determined onset-withdrawal dates.

Sub region Onset date CC Withdrawal date CC

1 Rain, PPW, U200, U850, Z200, Z850 0.81 Rain, PPW, U200 -

2 Rain, PPW, U200, U850, Z200, Z850 0.78 Rain, PPW, U200 -

3 Rain, PPW, U850 0.83 Rain, PPW, U200 0.60

4 Rain, PPW, U850,Z850, TCC 0.78 Rain, PPW, U200, U850, Z200, Z850 0.58

5 Rain, PPW, U850, TCC 0.80 Rain, PPW, U200 0.44

6 Rain, PPW, U850,Z850, TCC 0.71 Rain, PPW, U200, U850, Z200, Z850 0.45

7 Rain, PPW, U850, TCC 0.71 Rain, PPW, Z850, TCC 0.40

8 Rain, PPW, Z850 0.79 Rain, PPW, U850 0.50

9 Rain, PPW, Z850 0.59 Rain, PPW, U200, TCC 0.48

10 Rain, PPW, U200, U850, Z200, Z850, TCC 0.53 Rain, PPW, U850, TCC 0.55

11 Rain, PPW, Z200, TCC 0.59 Rain, TCC 0.82

12 Rain, PPW, Z850 0.49 Rain, PPW, U200, Z850 0.56

13 Rain, PPW, Z850 0.60 Rain, PPW, TCC 0.48

14 Rain, PPW, U200, TCC 0.56 Rain, PPW, Z200, TCC 0.47

15 Rain, PPW, U850, TCC 0.47 Rain, PPW, TCC 0.15

16 Rain, PPW, U200, U850, Z200, Z850, TCC 0.36 Rain, PPW, U200 0.27

17 Rain, PPW, Z850 0.52 Rain, PPW, Z200 0.43

18 Rain, PPW, U200, TCC 0.55 Rain, PPW, U850, TCC 0.28

19 Rain, PPW, Z850 0.37 Rain, PPW, U200 0.21

 

 

28

Table 3. The threshold to 30-day mean of the GARACII parameters at the time of onset over the subregion 1 (SR 1; Kerala State).

Sr. No. General and regional atmospheric circulation parameters Threshold

value

1 Lower troposphere thickness over central Middle East

(CME; 25° -35°N; 40° -75°E) (m) 4348.1

2 Upper troposphere thickness over the Tibet-Himalaya –Karakoram-Hindukush Highlands (THIKHIHILs; 25°- 35°N; 60°- 95°E) (m)

6503.3

3 V850 along Somali Coast (SC; 5°S -10°N; 45° -55°E) (m/s) 2.82

4 V850 over Indonesia Malaysia maritime continent (IMMC; 5°S -5°N; 100° -150°E) (m/s) 0.78

5 U850 over central Arabian Sea (CAS; 5° -15°N; 55° -70°E) (m/s) 2.76

6 V850 over Myanmar and central Indo China peninsula (MCICP; 10°- 30°N; 90°- 100°E) (m/s)

2.09

7 Z200 over South Asia (SA; 25° -35°N; 50°- 100°E) (m) 12313.7

 

 

29

Table 4. The threshold to the GARACII at the time of onset and that at the time of withdrawal date of the summer monsoon over the 19 sub-regions.

Subregion The GARACII value at the time of Onset Withdrawal

1 1 1.035 2 1.029 1.035 3 1.123 1.084 4 1.157 1.084 5 1.264 1.189 6 1.336 1.162 7 1.373 1.135

8 1.409 1.339 9 1.478 1.318

10 1.511 1.216 11 1.728 1.512 12 1.665 1.419 13 1.634 1.339 14 1.409 1.269 15 2.051 1.681

16 1.915 1.531 17 1.665 1.420 18 1.157 1.135

19 1.938 1.607

 

 

30

Table 5. Climatological value of 10 selected general and regional atmospheric circulation parameters for the 6 subperiods of the annual weather cycle over India.

Sr. No. GAC parameter

Subperiods of the annual weather cycle

P72 -P16 P17- P30 P31- P38 P39 -P51 P52 -P59 P59- P71

1 Lower troposphere thickness over central Middle East (25°-35°N; 40°-75°E) (m)

4183.0 4303.6 4409.6 4416.8 4334.3 4239.1

2

Upper troposphere thickness over Tibet-Himalaya- Karakoram -Hindukush Highlands (25° -35°N; 60°-95°E) (m)

6317.0 6427.6 6655.9 6692.1 6544.7 6380.9

3 U200 over Korea-Japan -northwest North Pacific (30°- 40°N; 120°- 160°E) (m/s)

61.8 41.5 27.3 11.0 30.8 54.1

4 U200 central Australia- southwest South Pacific (20° -30°S; 120° -180°E) (m/s)

17.2 33.6 44.8 43.7 38.3 30.7

5 U850 over equatorial western Pacific Ocean (10°S -10°N; 150°- 180°E) (m/s)

-2.5 -3.5 -4.5 -4.0 -3.4 -1.7

6 V850 over Indonesia Malaysia maritime continent (5°S -5°N; 100° -150°E) (m/s)

-1.6 0.4 1.5 2.0 1.3 -0.1

7 V850 over Myanmar and central Indo China peninsula (10° -30°N; 90° -100°E) (m/s)

0.3 1.3 3.6 2.8 1.7 0.4

8 V850 along Somali Coast (5°S- 10°N; 45°- 55°E) (m/s) -2.0 0.9 7.5 7.9 2.4 - 1.9

9 U850 over central Arabian Sea (5°- 15°N; 55° -70°E) (m/s) -4.7 -1.1 13.2 13.3 3.5 -3.6

10 Z200 over South Asia (25° -35°N; 50° -100°E) (m) 12008.7 12212.5 12492.7 12541.2 12370.0 12142.6

 

 

31

Table 6. Climatological value of the 10 selected general and regional circulation parameters for the 8 pentads of the onset (withdrawal) phase of summer monsoon over India.

Sr. No GAC parameter

Pentads of the onset phase P31 (P52)

P32 (P53)

P33 (P54)

P34 (P55)

P35 (P56)

P36 (P57)

P37 (P58)

P38 (P59)

1

Lower troposphere thickness over central Middle East (25°-35°N; 40°-75°E) (m)

4381.6

(4375.0)

4395.8

(4362.4)

4399.3

(4353.5)

4407.3

(4339.9)

4415.3

(4328.3)

4421.8

(4314.5)

4426.3

(4304.5)

4429.1

(4296.0)

2

Upper troposphere thickness over Tibet-Himalaya- Karakoram -Hindukush Highlands (25° -35°N; 60°-95°E) (m)

6574.5

(6616.4)

6605.9

(6596.3)

6637.4

(6579.1)

6660.7

(6556.6)

6676.6

(6538.0)

6691.3

(6513.2)

6699.8

(6487.8)

6701.2

(6469.9)

3

U200 over Korea-Japan -northwest North Pacific (30°- 40°N; 120°- 160°E) (m/s)

34.2

(20.6)

30.4

(24.6)

30.1

(26.7)

29.1

(29.9)

28.8

(32.9)

25.8

(33.7)

21.8

(37.9)

17.7

(39.6)

4

U200 central Australia- southwest South Pacific (20° -30°S; 120° -180°E) (m/s)

41.1

(40.6)

44.9

(39.6)

46.0

(39.7)

46.2

(37.6)

44.2

(36.6)

45.7

(36.4)

46.2

(38.2)

43.6

(37.3)

5

U850 over equatorial western Pacific Ocean (10°S -10°N; 150°- 180°E) (m/s)

-4.3

(-3.4)

-4.9

(-3.5)

-4.6

(-3.9)

-4.5

(-4.1)

-4.2

(-3.3)

-4.1

(-2.6)

-4.4

(-3.1)

-4.3

(-3.1)

6

V850 over Indonesia Malaysia maritime continent (5°S -5°N; 100° -150°E) (m/s)

1.1

(1.9)

1.2

(1.3)

1.1

(1.2)

1.4

(1.1)

1.5

(1.2)

1.5

(1.1)

1.6

(0.9)

1.8

(0.9)

7

V850 over Myanmar and central Indo China peninsula (10° -30°N; 90° -100°E) (m/s)

2.8

(1.5)

3.0

(1.9)

4.2

(2.2)

3.8

(2.0)

4.0

(1.9)

3.6

(1.3)

3.6

(1.4)

3.4

(1.1)

8 V850 along Somali Coast (5°S- 10°N; 45°- 55°E) (m/s)

5.5

(4.8)

6.6

(4.4)

7.6

(3.5)

7.8

(3.2)

7.8

(2.1)

8.0

(1.3)

8.3

(0.2)

8.1

(-0.3)

9 U850 over central Arabian Sea (5°- 15°N; 55° -70°E) (m/s)

8.3

(7.2)

11.5

(6.6)

12.8

(5.8)

14.3

(4.5)

14.4

(2.7)

14.8

(1.2)

14.9

(0.0)

14.5

(-0.5)

10. Z200 over South Asia (25° -35°N; 50° -100°E) (m)

12404.2

(12460.4)

12439.7

(12434.3)

12470.6

(12415.7)

12493.1

(12385.8)

12514.0

(12362.1)

12532.0

(12328.2)

12541.0

(12298.0)

12547.4

(12275.9)

 

 

32

Table 7. Climatological value of the lower and upper tropospheric temperatures (˚C) over the whole globe and 5 climatic zones for the 6 subperiods of the annual weather cycle over India.

Sr. No. Region

Lower/ Upper

troposphere

Subperiods of the annual cycle P72 -P16

(S1) P17 -P30

(S2) P31-P38

(S3) P39- P51

(S4) P52- P59

(S5) P60 -P71

(S6)

1 Global LT - 4.3 -3.5 -2.3 -2.2 -3.3 -4.1 UT -41.5 -41.5 -40.9 -40.9 -41.7 -42.0

2 Northern hemisphere (NH)

LT - 6.8 -2.8 1.6 2.4 -0.8 -4.7 UT -43.6 -41.5 -38.2 -37.6 -39.9 -42.4

3 Southern hemisphere (SH)

LT - 1.8 -4.1 -6.2 -6.9 -5.8 -3.5 UT -39.4 -41.6 -43.7 -44.2 -43.4 -41.5

4 Extra tropical NH

LT -17.3 -11.1 -3.1 -1.5 -7.4 -14.0 UT -50.4 -46.7 -41.5 -40.3 -44.3 -48.4

5 Extra tropical SH

LT - 9.3 -13.3 -16.2 -17.1 -15.5 -11.9

UT -43.3 -47.3 -50.7 -51.6 -50.0 -46.6

6 Tropics LT 4.7 5.2 5.1 4.8 4.9 4.8 UT -36.2 -36.0 -35.8 -35.8 -36.1 -36.4

Table 8. Climatological temperature of the lower and upper troposphere (in ˚C) over the whole globe and the 5 climatic zones during 8 pentads of the onset phase of the summer monsoon across India.

Sr. No. Region

Lower/ Upper

troposphere

Pentads of the onset phase

P31 P32 P33 P34 P35 P36 P37 P38

1 Global LT - 2.7 -2.5 -2.4 -2.3 -2.2 -2.1 -2.1 -2.0 UT -41.2 -41.1 -41.0 -40.9 -40.9 -40.8 -40.8 -40.8

2 Northern hemisphere (NH)

LT 0.3 0.8 1.2 1.6 1.9 2.2 2.4 2.6 UT -39.3 -38.9 -38.6 -38.3 -38.0 -37.8 -37.6 -37.4

3 Southern hemisphere (SH)

LT -5.6 -5.8 -6.0 -6.2 -6.3 -6.4 -6.6 -6.7 UT -43.1 -43.3 -43.5 -43.6 -43.7 -43.9 -44.0 -44.2

4 Extra tropical NH LT -5.6 -4.8 -4.0 -3.3 -2.6 -2.0 -1.5 -1.0 UT -43.3 -42.7 -42.1 -41.7 -41.2 -40.7 -40.3 -39.9

5 Extra tropical SH LT -15.4 -15.7 -16.0 -16.1 -16.3 -16.5 -16.7 -16.8 UT -49.9 -50.2 -50.5 -50.7 -50.9 -51.1 -51.2 -51.5

6 Tropics LT 5.2 5.2 5.2 5.1 5.1 5.0 4.9 4.8 UT -35.8 -35.7 -35.7 -35.7 -35.7 -35.8 -35.8 -35.9

 

 

33

Table 9. Climatological value of the lower and upper tropospheric temperature (˚C) over the whole globe and 5 climatic zones for the 8 pentads of withdrawal phase of monsoon across India.

Sr. No.

Region Lower/ Upper

troposphere

Pentads of the withdrawal phase

P52 P53 P54 P55 P56 P57 P58 P59

1 Global LT -2.9 -3.0 -3.1 -3.3 -3.4 -3.5 -3.6 -3.7 UT -41.4 -41.5 -41.6 -41.7 -41.7 -41.8 -41.9 -41.9

2 Northern hemisphere (NH)

LT 0.6 0.2 -0.2 -0.6 -1.0 -1.5 -1.9 -2.3 UT -38.9 -39.2 -39.5 -39.8 -40.1 -40.3 -40.7 -41.0

3 Southern hemisphere (SH)

LT -6.4 -6.2 -6.1 -5.9 -5.8 -5.5 -5.3 -5.1 UT -43.9 -43.8 -43.7 -43.5 -43.4 -43.2 -43.0 -42.8

4 Extra tropical NH LT -4.8 -5.5 -6.3 -7.1 -7.8 -8.5 -9.3 -10.0 UT -42.7 -43.1 -43.6 -44.1 -44.5 -45.0 -45.6 -46.0

5 Extra tropical SH LT -16.4 -16.3 -16.0 -15.7 -15.5 -15.2 -14.8 -14.5 UT -50.9 -50.7 -50.5 -50.3 -50.0 -49.6 -49.3 -48.9

6 Tropics LT 4.9 4.9 4.9 4.8 4.8 4.9 4.8 4.8 UT -36.0 -36.0 -36.1 -36.1 -36.2 -36.2 -36.3 -36.3

Table 10. Climatological value of lower and upper tropospheric thicknesses (meters) over the

whole globe and 5 climatic zones for 6 subperiods of the annual weather cycle over India.

Sr. No. Region

Lower/ Upper

troposphere

Subperiods of the annual cycle

P72-P16 P17- P30 P31-P38 P39- P51 P52- P59 P59- P71

1 Global LT 4186.4 4198.2 4217.1 4217.9 4200.7 4189.0 UT 6352.5 6355.9 6376.3 6378.6 6356.1 6344.4

2 Northern hemisphere (NH)

LT 4148.0 4208.0 4278.3 4290.4 4239.5 4180.5 UT 6290.6 6357.5 6455.5 6476.0 6408.1 6331.4

3 Southern hemisphere (SH)

LT 4225.0 4188.6 4156.2 4145.7 4162.1 4197.7 UT 6414.8 6354.7 6297.6 6281.6 6304.4 6357.7

4 Extra tropical NH LT 3982.1 4078.2 4203.1 4228.6 4135.8 4033.6 UT 6071.0 6182.1 6342.7 6380.9 6261.7 6136.2

5 Extra tropical SH LT 4107.1 4044.2 3999.0 3984.7 4008.3 4065.5 UT 6274.4 6168.5 6076.3 6052.7 6094.9 6186.7

6 Tropics LT 4328.5 4335.4 4333.4 4329.4 4329.6 4328.7 UT 6532.7 6536.9 6543.6 6540.8 6534.3 6527.7

 

 

34

Table 11. Climatological value of lower and upper tropospheric thickness (meters) over the whole globe and 5 climatic zones for 8 pentads of onset phase of summer monsoon across India.

Sr. No.

Region Lower/ Upper

troposphere

Pentads of the onset phase

P31 P32 P33 P34 P35 P36 P37 P38

1 Global LT 4211.4 4213.4 4215.0 4217.0 4218.9 4219.8 4220.3 4221.3 UT 6368.1 6371.2 6373.6 6376.6 6378.7 6379.6 6380.9 6381.8

2 Northern hemisphere (NH)

LT 4257.9 4264.9 4271.2 4277.3 4282.7 4287.2 4290.8 4294.2 UT 6424.4 6434.7 6445.1 6453.9 6462.1 6468.6 6474.9 6480.2

3 Southern hemisphere (SH)

LT 4165.2 4162.1 4159.0 4156.9 4155.2 4152.6 4150.1 4148.5 UT 6312.0 6308.3 6302.7 6299.7 6295.7 6290.9 6287.3 6283.8

4 Extra tropical NH

LT 4163.6 4176.5 4188.6 4200.1 4210.9 4220.3 4228.8 4235.9 UT 6287.9 6305.3 6322.6 6337.6 6352.2 6365.6 6380.1 6390.5

5 Extra tropical SH

LT 4010.8 4006.8 4002.2 4000.1 3997.0 3994.4 3991.5 3989.6 UT 6098.3 6091.5 6082.7 6078.6 6072.7 6066.7 6062.5 6057.5

6 Tropics LT 4336.0 4335.3 4334.8 4334.1 4334.0 4332.5 4330.7 4330.0 UT 6543.4 6544.6 6545.2 6545.6 6545.4 6543.4 6541.0 6540.1

Table 12. Climatological value of lower and upper tropospheric thickness (meters) over the whole globe and 5 climatic zones for 8 pentads of withdrawal phase of summer monsoon across India.

Sr. No.

Region Lower/ Upper

troposphere

Pentads of the withdrawal phase

P52 P53 P54 P55 P56 P57 P58 P59

1 Global LT 4207.5 4205.6 4203.6 4201.5 4199.3 4198.0 4195.9 4194.5 UT 6365.0 6362.2 6359.2 6356.5 6354.6 6353.0 6349.8 6348.7

2 Northern hemisphere (NH)

LT 4262.1 4256.1 4249.5 4242.8 4236.3 4230.0 4223.0 4216.7 UT 6438.5 6430.0 6421.1 6412.5 6404.4 6396.0 6385.1 6377.3

3 Southern hemisphere (SH)

LT 4153.0 4155.4 4157.8 4160.4 4162.6 4166.1 4169.1 4172.6 UT 6292.0 6294.7 6297.5 6300.8 6305.0 6310.3 6314.8 6320.4

4 Extra tropical NH LT 4176.3 4165.2 4153.5 4141.5 4129.7 4118.7 4106.4 4095.5 UT 6312.3 6298.5 6283.4 6269.0 6255.2 6240.9 6223.5 6210.6

5 Extra tropical SH LT 3994.4 3997.3 4001.6 4006.0 4008.8 4014.1 4019.3 4024.9 UT 6071.5 6077.0 6083.1 6089.3 6096.1 6105.3 6114.0 6122.9

6 Tropics LT 4329.8 4330.2 4329.8 4329.5 4329.6 4329.8 4329.2 4329.1 UT 6538.6 6537.0 6535.4 6534.2 6533.9 6533.2 6531.2 6531.1

 

 

35

Table 13. Percentage frequency of the onset date occurrence in five specified class interval (very early, VE; moderately, ME; normal, N; moderately early, ME; and very late, VE), and the root mean square error (RMSE) in the objectively determined onset date in different class intervals for the 19 subregions.

Sub-

region

Very early (VE) Moderately early (ME) Normal (N) Moderately late (ML) Very late (VL) Freq. (%)

RMSE (days)

Freq. (%)

RMSE (days)

Freq. (%)

RMSE (days)

Freq. (%)

RMSE (days)

Freq. (%)

RMSE (days)

1 15.79 6.3 14.04 3.9 43.86 2.8 8.77 4.6 17.54 6.2 2 14.04 4.3 17.54 5.6 38.60 3.7 15.79 4.3 14.04 6.4 3 17.54 7.6 12.28 1.7 38.60 2.2 10.53 3.7 21.05 3.7 4 14.04 7.4 12.28 2.7 42.11 4.4 17.54 4.5 14.04 2.9 5 15.79 6.3 15.79 4.9 35.09 2.6 10.53 1.9 22.81 3.6 6 17.54 5.6 14.04 5.9 38.60 3.6 12.28 4.1 17.54 5.6 7 15.79 6.7 15.79 3.0 40.35 3.9 10.53 2.4 17.54 5.3 8 14.04 4.3 17.54 2.7 40.35 3.6 10.53 1.8 17.54 5.5 9 17.54 7.6 12.28 3.9 33.33 3.7 19.30 4.5 17.54 6.9

10 21.05 6.9 12.28 5.5 35.09 5.2 10.53 5.5 21.05 4.9 11 12.28 8.4 17.54 4.5 47.37 6.6 7.02 7.3 15.79 11.1 12 21.05 5.4 8.77 1.3 33.33 8.5 24.56 4.7 12.28 9.4 13 26.32 3.9 3.51 10.3 35.09 5.7 15.79 4.7 19.30 6.3 14 14.04 6.8 15.79 6.3 36.84 6.3 14.04 5.4 19.30 6.0 15 17.54 11.5 15.79 11.3 38.60 9.8 15.79 9.5 12.28 24.4 16 12.28 12.8 19.30 6.8 42.11 7.5 12.28 6.3 14.04 10.2 17 24.56 5.7 14.04 5.6 29.82 5.7 24.56 5.6 14.04 11.0 18 10.53 3.9 22.81 4.9 36.84 6.4 14.04 5.7 15.79 6.4 19 8.77 12.8 21.05 6.3 43.86 6.7 12.28 10.2 14.04 13.2

Mean (All

India) 16.2 7.1 14.8 5.1 38.4 5.2 14 5.1 16.6 7.8

 

 

36

Table 14. The percentage frequency of occurrence of abrupt, gradual and feeble onset, and root mean square error (RMSE) in determining the onset date different categories of the onset for the 19 sub-regions.

Subregion Abrupt Gradual Feeble

Freq. (%age)

RMSE (days)

Freq. (%age)

RMSE (days

Freq. (%age)

RMSE (days

1 43.86 3.8 22.8 5.8 33.33 5.2 2 8.77 5.2 15.79 3.7 75.44 4.9 3 66.67 3.3 24.56 5.0 8.77 5.4 4 7.02 3.8 10.53 2.8 82.46 5.0 5 73.68 2.4 15.79 5.6 10.53 7.8 6 29.82 4.5 19.30 4.8 50.88 5.0 7 20.07 3.2 28.07 4.3 43.86 5.5 8 82.46 3.2 8.77 6.1 8.77 6.2 9 70.18 5.5 19.30 4.5 10.53 7.9

10 36.84 3.1 15.79 4.4 47.37 6.9 11 56.14 7.4 14.04 6.1 29.82 9.1 12 61.40 6.8 15.79 5.6 22.8 8.8 13 52.63 3.4 29.82 6.6 17.54 8.8 14 19.30 2.4 45.61 5.4 35.09 7.5 15 54.39 10.7 12.28 18.3 33.33 12.0 16 42.11 5.3 24.56 9.6 33.33 10.5 17 38.60 4.9 21.05 5.5 40.35 8.7 18 5.26 3.5 45.61 4.4 49.12 7.1 19 24.56 3.3 36.84 10.9 38.60 9.0

Total 41.8 4.5 22.4 6.3 35.4 7.4

 

 

37

Table 15. The percentage frequency of the withdrawal date occurrence in five specified class interval (very early, VE; moderately, ME; normal, N; moderately early, ME; and very late, VE), and the root mean square error (RMSE) in the objectively determined withdrawal date in different class intervals for the 19 sub-regions.

Sub-region

Very early (VE) Moderately early (ME) Normal (N) Moderately late

(ML) Very late (VL)

Freq. (%)

RMSE (days)

Freq. (%)

RMSE (days)

Freq. (%)

RMSE (days)

Freq. (%)

RMSE (days)

Freq. (%)

RMSE (days)

1 17.5 8.8 40.4 17.5 15.8 2 14.0 15.8 35.1 19.3 15.8 3 17.5 7.9 15.8 5.8 35.1 7.6 19.3 3.6 12.3 7.5 4 19.3 5.8 8.8 9.5 40.4 3.9 15.8 2.0 15.8 7.6 5 10.5 12.0 15.8 5.3 49.1 4.2 12.3 5.9 12.3 6.3 6 12.3 9.8 22.8 5.0 38.6 5.0 10.5 7.2 15.8 6.9 7 17.5 19.0 10.5 12.7 35.1 3.7 21.1 8.3 15.8 10.8 8 22.8 9.1 12.3 11.0 31.6 3.8 17.5 5.5 15.8 7.9 9 17.5 7.3 12.3 11.5 38.6 5.3 12.3 5.7 19.3 6.8

10 12.3 9.6 21.1 4.3 40.4 3.9 5.3 7.3 21.1 3.7 11 12.3 10.6 21.1 4.9 31.6 3.2 14.0 1.2 21.1 6.9 12 17.5 8.2 21.1 6.7 28.1 5.4 12.3 3.8 21.1 7.2 13 17.5 4.7 17.5 5.1 35.1 6.8 12.3 5.1 17.5 10.8 14 21.1 5.7 10.5 5.3 38.6 4.5 17.5 4.3 12.3 16.0 15 17.5 13.0 10.5 7.8 38.6 9.2 21.1 11.9 12.3 18.1 16 8.8 6.8 17.5 5.7 49.1 9.0 10.5 6.9 14.0 5.6 17 10.5 6.5 28.1 5.8 24.6 5.3 19.3 3.9 17.5 10.2 18 17.5 13.1 8.8 5.3 40.4 5.3 17.5 5.7 15.8 5.8 19 15.8 14.3 5.3 8.9 54.4 9.5 7.0 8.4 17.5 13.0

Mean (All

India) 15.8 9.6 15.0 7.1 38.1 5.6 14.9 5.7 16.3 8.9

 

 

38

Table 16. The percentage frequency of occurrence of abrupt, gradual and feeble withdrawal, and root mean square error (RMSE) in determining withdrawal date different categories for the 19 sub-regions.

Subregion

Abrupt Gradual Feeble Freq.

(%age) RMSE (days)

Freq. %age

RMSE (days)

Freq. %age

RMSE (days)

1 15.8 - 17.5 - 66.7 - 2 12.3 - 17.5 - 70.2 - 3 26.3 4.7 22.8 8.0 50.9 5.9 4 7.0 6.5 21.1 6.8 71.9 5.6 5 31.6 4.5 21.1 6.0 47.4 6.7 6 24.6 7.1 7.0 7.3 68.4 5.7 7 17.5 11.3 17.5 4.4 64.9 13.2 8 38.6 6.2 15.8 3.8 45.6 9.2 9 29.8 2.4 17.5 11.4 52.6 6.9

10 22.8 3.6 10.5 10.6 66.7 4.8 11 50.9 3.8 7.0 7.5 42.1 6.8 12 43.9 7.1 14.0 3.1 42.1 6.5 13 36.8 6.9 5.3 57.9 6.5 14 40.4 5.3 10.5 11.5 49.1 5.1 15 35.1 16.6 12.3 9.2 52.6 9.9 16 35.1 9.1 14.0 4.4 50.9 6.9 17 45.6 6.4 17.5 7.6 36.8 5.9 18 21.1 5.3 12.3 12.2 66.7 6.1 19 38.6 6.3 21.1 11.0 40.4 13.0

Total 30.2 6.7 14.9 7.8 54.9 7.3

 

 

39

Table 17. Yearwise onset and withdrawal dates of southwest monsoon over the Subregion-1 as determine by the objective criteria and that extracted from IMD charts.

Year Onset date Withdrawal date

IMD charts Objective criteria IMD charts Objective criteria 1951 5 Jun 20 Oct 1952 5 Jun 19 Oct 1953 10 Jun 20 Oct 1954 5 Jun 17 Oct 1955 29 May 27 Oct 1956 16 May 24 Oct 1957 7 Jun 19 Oct 1958 21 May 26 Oct 1959 29 May 24 Oct 1960 14 May 25 May 31 Oct 1961 21 May 25 May 17 Oct 1962 17 May 26 May 15 Oct 1963 3 Jun 6 Jun 10 Oct 1964 6 Jun 10 Jun 22 Oct 1965 30 May 3 Jun 27 Sep 1966 3 Jun 6 Jun 22 Oct 1967 13 Jun 8 Jun 6 Oct 1968 8 Jun 15 Jun 6 Oct 1969 25 May 1 Jun 25 Sep 1970 27 May 29 May 16 Oct 1971 31 May 31 May 16 Oct 1972 19 Jun 17 Jun 15 Oct 1973 5 Jun 5 Jun 15 Oct 1974 29 May 1 Jun 11 Oct 1975 31 May 29 May 28 Oct 1976 31 May 6 Jun 26 Oct 1977 30 May 1 Jun 24 Oct 1978 28 May 27 May 6 Oct 1979 11 Jun 16 Jun 3 Oct 1980 1 Jun 5 Jun 11 Oct 1981 30 May 2 Jun 21 Oct 1982 29 May 11 Jun 26 Sep 1983 12 Jun 16 Jun 16 Oct 1984 31 May 2 Jun 7 Oct 1985 28 May 1 Jun 11 Oct 1986 4 Jun 10 Jun 5 Oct 1987 2 Jun 12 Jun 21 Oct 1988 26 May 2 Jun 8 Oct 1989 3 Jun 1 Jun 12 Oct 1990 19 May 25 May 22 Oct 1991 2 Jun 6 Jun 20 Oct 1992 5 Jun 13 Jun 18 Oct 1993 29 May 6 Jun 22 Oct 1994 29 May 2 Jun 17 Oct 12 Oct 1995 8 Jun 5 Jun 20 Oct 1996 3 Jun 13 Jun 16 Oct 1997 9 Jun 19 Jun 8 Oct 29 Sep 1998 2 Jun 7 Jun 20 Oct 24 Oct 1999 25 May 21 May 21 Oct 20 Oct 2000 1 Jun 28 May 25 Oct 11 Oct 2001 24 May 27 May 25 Oct 2002 30 May 22 May 13 Oct 2003 8 Jun 8 Jun 13 Oct 2004 18 May 20 May 26 Oct 2005 5 Jun 16 Jun 14 Oct 2006 26 May 29 May 8 Oct 2007 28 May 3 Jun 21 Oct Mean 31 May (±7) 3 June (±8) 18 oct (±6) 15 Oct (±8)

 

 

40

Table 18. Yearwise onset and withdrawal dates of southwest monsoon over the Subregion-2 as determine by the objective criteria and that extracted from IMD charts.

Year Onset date Withdrawal date

IMD charts Objective criteria IMD charts Objective criteria 1951 6 Jun 3 Oct 1952 6 Jun 18 Oct 1953 11 Jun 19 Oct 1954 6 Jun 17 Oct 1955 31 May 1 Nov 1956 17 May 27 Oct 1957 8 Jun 21 Oct 1958 18 May 24 Oct 1959 31 May 26 Oct 1960 14 May 31 May 1 Nov 1961 21 May 26 May 15 Oct 1962 18 May 27 May 13 Oct 1963 3 Jun 9 Jun 7 Oct 1964 6 Jun 11 Jun 19 Oct 1965 30 May 4 Jun 25 Sep 1966 5 Jun 6 Jun 14 Oct 1967 13 Jun 9 Jun 14 Oct 1968 8 Jun 16 Jun 4 Oct 1969 25 May 2 Jun 20 Sep 1970 27 May 29 May 13 Oct 1971 31 May 1 Jun 20 Oct 1972 19 Jun 18 Jun 15 Sep 1973 5 Jun 3 Jun 1 Oct 1974 29 May 2 Jun 9 Oct 1975 31 May 30 May 28 Oct 1976 31 May 7 Jun 20 Sep 1977 30 May 3 Jun 24 Oct 1978 28 May 31 May 22 Oct 1979 11 Jun 19 Jun 1 Oct 1980 1 Jun 7 Jun 9 Oct 1981 30 May 30 May 21 Oct 1982 29 May 13 Jun 25 Sep 1983 16 Jun 14 Jun 17 Oct 1984 4 Jun 7 Jun 4 Oct 1985 28 May 4 Jun 8 Oct 1986 4 Jun 10 Jun 16 Oct 1987 3 Jun 13 Jun 20 Oct 1988 26 May 2 Jun 5 Oct 1989 3 Jun 3 Jun 6 Oct 1990 20 May 25 May 20 Oct 1991 2 Jun 9 Jun 22 Oct 1992 5 Jun 13 Jun 13 Oct 1993 29 May 8 Jun 3 Nov 1994 29 May 4 Jun 17 Oct 19 Sep 1995 8 Jun 6 Jun 17 Oct 1996 3 Jun 11 Jun 15 Oct 1997 9 Jun 21 Jun 8 Oct 23 Sep 1998 2 Jun 3 Jun 20 Oct 31 Oct 1999 26 May 22 May 21 Oct 19 Oct 2000 1 Jun 31 May 25 Oct 8 Oct 2001 24 May 24 May 10 Oct 2002 30 May 31 May 24 Sep 2003 8 Jun 6 Jun 3 Oct 2004 18 May 20 May 25 Oct 2005 6 Jun 10 Jun 14 Oct 2006 26 May 29 May 4 Oct 2007 29 May 9 Jun 1 Oct Mean 31 May (±7) 4 Jun (±8) 18 Oct (±6) 12 Oct ±12)

 

 

41

Table 19. Yearwise onset and withdrawal dates of southwest monsoon over the Subregion-3 as

determine by the objective criteria and that extracted from IMD charts.

Year Onset date Withdrawal date IMD charts Objective criteria IMD charts Objective criteria

1951 8 Jun 18 Oct 1952 9 Jun 18 Oct 1953 17 Jun 19 Oct 1954 8 Jun 16 Oct 1955 3 Jun 24 Oct 1956 21 May 25 Oct 1957 10 Jun 19 Oct 1958 16 Jun 25 Oct 1959 3 Jun 21 Oct 1960 22 May 29 May 29 Oct 1961 21 May 28 May 18 Oct 1962 21 May 28 May 15 Oct 1963 4 Jun 5 Jun 11 Oct 1964 9 Jun 15 Jun 20 Oct 1965 6 Jun 8 Jun 29 Sep 1966 6 Jun 14 Jun 16 Oct 1967 13 Jun 12 Jun 7 Oct 1968 11 Jun 18 Jun 10 Oct 1969 28 May 4 Jun 8 Oct 1970 28 May 1 Jun 16 Oct 1971 31 May 3 Jun 18 Oct 1972 19 Jun 22 Jun 6 Oct 1973 6 Jun 7 Jun 15 Oct 1974 1 Jun 5 Jun 15 Oct 1975 2 Jun 3 Jun 27 Oct 26 Oct 1976 1 Jun 6 Jun 12 Oct 8 Oct 1977 7 Jun 10 Jun 12 Oct 10 Oct 1978 29 May 31 May 15 Oct 20 Oct 1979 16 Jun 18 Jun 15 Oct 6 Oct 1980 4 Jun 6 Jun 6 Oct 11 Oct 1981 1 Jun 4 Jun 14 Oct 18 Oct 1982 1 Jun 10 Jun 11 Oct 1 Oct 1983 16 Jun 17 Jun 19 Oct 20 Oct 1984 4 Jun 7 Jun 3 Oct 7 Oct 1985 30 May 4 Jun 24 Oct 14 Oct 1986 5 Jun 14 Jun 21 Oct 20 Oct 1987 4 Jun 9 Jun 24 Oct 18 Oct 1988 5 Jun 9 Jun 10 Oct 12 Oct 1989 4 Jun 5 Jun 13 Oct 11 Oct 1990 20 May 27 May 17 Oct 20 Oct 1991 4 Jun 9 Jun 12 Oct 15 Oct 1992 6 Jun 17 Jun 18 Oct 20 Oct 1993 4 Jun 10 Jun 19 Oct 20 Oct 1994 2 Jun 4 Jun 17 Oct 9 Oct 1995 10 Jun 11 Jun 18 Oct 1996 7 Jun 14 Jun 18 Oct 1997 11 Jun 19 Jun 8 Oct 27 Sep 1998 7 Jun 11 Jun 20 Oct 27 Oct 1999 1 Jun 24 May 15 Oct 21 Oct 2000 3 Jun 27 May 25 Oct 13 Oct 2001 6 Jun 29 May 15 Oct 25 Oct 2002 3 Jun 30 May 10 Oct 2003 11 Jun 15 Jun 14 Oct 2004 23 May 23 May 12 Oct 2005 7 Jun 17 Jun 16 Oct 2006 27 May 31 May 10 Oct 2007 8 Jun 15 Jun 21 Oct Mean 3 Jun (±7) 7 Jun (±8) 15 Oct (±6) 15 Oct (±7)

 

 

42

Table 20. Yearwise onset and withdrawal dates of southwest monsoon over the Subregion-4 as

determine by the objective criteria and that extracted from IMD charts.

Year Onset date Withdrawal date IMD charts Objective criteria IMD charts Objective criteria

1951 8 Jun 3 Oct 1952 10 Jun 12 Oct 1953 15 Jun 8 Oct 1954 9 Jun 12 Oct 1955 4 Jun 13 Oct 1956 22 May 16 Oct 1957 12 Jun 4 Oct 1958 2 Jun 21 Oct 1959 7 Jun 11 Oct 1960 22 May 8 Jun 12 Oct 1961 21 May 29 May 14 Oct 1962 18 May 30 May 7 Oct 1963 5 Jun 7 Jun 6 Oct 1964 9 Jun 16 Jun 13 Oct 1965 6 Jun 12 Jun 26 Sep 1966 10 Jun 10 Jun 28 Sep 1967 13 Jun 12 Jun 2 Oct 1968 11 Jun 18 Jun 4 Oct 1969 28 May 4 Jun 26 Sep 1970 28 May 2 Jun 8 Oct 1971 31 May 3 Jun 13 Oct 1972 19 Jun 20 Jun 28 Sep 1973 6 Jun 6 Jun 5 Oct 1974 1 Jun 6 Jun 13 Oct 1975 2 Jun 5 Jun 27 Oct 21 Oct 1976 1 Jun 9 Jun 12 Oct 26 Sep 1977 7 Jun 11 Jun 12 Oct 26 Sep 1978 29 May 5 Jun 15 Oct 5 Oct 1979 16 Jun 18 Jun 15 Oct 2 Oct 1980 4 Jun 8 Jun 6 Oct 28 Sep 1981 1 Jun 2 Jun 14 Oct 4 Oct 1982 1 Jun 15 Jun 11 Oct 26 Sep 1983 16 Jun 17 Jun 19 Oct 12 Oct 1984 4 Jun 12 Jun 3 Oct 2 Oct 1985 4 Jun 8 Jun 24 Oct 9 Oct 1986 14 Jun 9 Jun 21 Oct 1 Oct 1987 10 Jun 15 Jun 24 Oct 2 Oct 1988 8 Jun 7 Jun 12 Oct 9 Oct 1989 4 Jun 6 Jun 13 Oct 4 Oct 1990 21 May 28 May 17 Oct 8 Oct 1991 4 Jun 10 Jun 16 Oct 3 Oct 1992 16 Jun 20 Jun 18 Oct 11 Oct 1993 4 Jun 11 Jun 9 Oct 1994 4 Jun 10 Jun 17 Oct 29 Sep 1995 10 Jun 10 Jun 8 Oct 1996 7 Jun 14 Jun 11 Oct 1997 11 Jun 20 Jun 8 Oct 26 Sep 1998 7 Jun 13 Jun 20 Oct 20 Oct 1999 5 Jun 25 May 15 Oct 8 Oct 2000 3 Jun 31 May 25 Oct 9 Oct 2001 6 Jun 6 Jun 15 Oct 14 Oct 2002 3 Jun 3 Jun 28 Sep 2003 15 Jun 20 Jun 9 Oct 2004 23 May 23 May 3 Oct 2005 8 Jun 13 Jun 7 Oct 2006 27 May 1 Jun 5 Oct 2007 13 Jun 11 Jun 13 Oct Mean 4 Jun (±7) 8 Jun (±7) 15 Oct (±6) 6 Oct (±7)

 

 

43

Table 21. Yearwise onset and withdrawal dates of southwest monsoon over the Subregion-5 as determine by the objective criteria and that extracted from IMD charts.

Year Onset date Withdrawal date

IMD charts Objective criteria IMD charts Objective criteria 1951 10 Jun 12 Oct 1952 12 Jun 7 Oct 1953 18 Jun 15 Oct 1954 12 Jun 12 Oct 1955 9 Jun 20 Oct 1956 28 May 18 Oct 1957 15 Jun 8 Oct 1958 18 Jun 21 Oct 1959 5 Jun 15 Oct 1960 13 Jun 5 Jun 14 Oct 1961 25 May 1 Jun 13 Oct 1962 27 May 2 Jun 8 Oct 1963 6 Jun 7 Jun 7 Oct 1964 9 Jun 20 Jun 17 Oct 1965 10 Jun 13 Jun 27 Sep 1966 11 Jun 13 Jun 3 Oct 1967 18 Jun 18 Jun 4 Oct 1968 12 Jun 21 Jun 7 Oct 1969 2 Jun 8 Jun 30 Sep 1970 30 May 4 Jun 12 Oct 1971 31 May 6 Jun 12 Oct 1972 20 Jun 23 Jun 27 Sep 1973 7 Jun 9 Jun 7 Oct 1974 1 Jun 10 Jun 13 Oct 1975 7 Jun 10 Jun 16 Oct 21 Oct 1976 3 Jun 11 Jun 8 Oct 4 Oct 1977 10 Jun 15 Jun 12 Oct 5 Oct 1978 7 Jun 6 Jun 15 Oct 7 Oct 1979 19 Jun 20 Jun 6 Oct 5 Oct 1980 6 Jun 10 Jun 4 Oct 5 Oct 1981 5 Jun 4 Jun 12 Oct 12 Oct 1982 11 Jun 11 Jun 5 Oct 28 Sep 1983 18 Jun 20 Jun 14 Oct 13 Oct 1984 6 Jun 10 Jun 30 Sep 5 Oct 1985 4 Jun 6 Jun 17 Oct 12 Oct 1986 14 Jun 16 Jun 8 Oct 3 Oct 1987 8 Jun 11 Jun 9 Oct 6 Oct 1988 8 Jun 14 Jun 6 Oct 10 Oct 1989 7 Jun 7 Jun 6 Oct 7 Oct 1990 20 May 31 May 15 Oct 11 Oct 1991 5 Jun 12 Jun 7 Oct 10 Oct 1992 17 Jun 19 Jun 15 Oct 9 Oct 1993 12 Jun 13 Jun 15 Oct 14 Oct 1994 4 Jun 7 Jun 16 Oct 3 Oct 1995 16 Jun 18 Jun 9 Oct 10 Oct 1996 9 Jun 15 Jun 7 Oct 16 Oct 1997 13 Jun 20 Jun 8 Oct 26 Sep 1998 12 Jun 18 Jun 20 Oct 23 Oct 1999 10 Jun 1 Jun 15 Oct 15 Oct 2000 5 Jun 31 May 23 Oct 11 Oct 2001 8 Jun 5 Jun 15 Oct 16 Oct 2002 10 Jun 13 Jun 21 Oct 1 Oct 2003 15 Jun 17 Jun 13 Oct 8 Oct 2004 6 Jun 9 Jun 11 Oct 7 Oct 2005 18 Jun 19 Jun 10 Oct 11 Oct 2006 31 May 3 Jun 16 Oct 9 Oct 2007 15 Jun 16 Jun 15 Oct 19 Oct Mean 8 Jun (±7) 11 Jun (±6) 11 Oct (±5) 9 Oct (±6)

 

 

44

Table 22. Yearwise onset and withdrawal dates of southwest monsoon over the Subregion-6 as determine by the objective criteria and that extracted from IMD charts.

Year Onset date Withdrawal date

IMD charts Objective criteria IMD charts Objective criteria 1951 11 Jun 13 Oct 1952 14 Jun 11 Oct 1953 19 Jun 16 Oct 1954 14 Jun 13 Oct 1955 9 Jun 21 Oct 1956 28 May 19 Oct 1957 17 Jun 8 Oct 1958 17 Jun 23 Oct 1959 7 Jun 15 Oct 1960 13 Jun 8 Jun 14 Oct 1961 28 May 4 Jun 13 Oct 1962 28 May 7 Jun 9 Oct 1963 6 Jun 7 Jun 7 Oct 1964 9 Jun 22 Jun 19 Oct 1965 10 Jun 13 Jun 28 Sep 1966 11 Jun 19 Jun 4 Oct 1967 13 Jun 20 Jun 5 Oct 1968 15 Jun 23 Jun 7 Oct 1969 2 Jun 10 Jun 2 Oct 1970 30 May 5 Jun 14 Oct 1971 1 Jun 8 Jun 13 Oct 1972 20 Jun 25 Jun 29 Sep 1973 7 Jun 13 Jun 9 Oct 1974 7 Jun 12 Jun 13 Oct 1975 17 Jun 13 Jun 16 Oct 23 Oct 1976 4 Jun 12 Jun 6 Oct 5 Oct 1977 15 Jun 16 Jun 10 Oct 3 Oct 1978 7 Jun 7 Jun 15 Oct 11 Oct 1979 19 Jun 21 Jun 6 Oct 5 Oct 1980 6 Jun 11 Jun 4 Oct 6 Oct 1981 5 Jun 6 Jun 12 Oct 14 Oct 1982 11 Jun 16 Jun 5 Oct 30 Sep 1983 24 Jun 21 Jun 15 Oct 14 Oct 1984 6 Jun 15 Jun 30 Sep 6 Oct 1985 7 Jun 10 Jun 19 Oct 12 Oct 1986 14 Jun 14 Jun 9 Oct 12 Oct 1987 10 Jun 16 Jun 9 Oct 6 Oct 1988 9 Jun 14 Jun 6 Oct 11 Oct 1989 9 Jun 10 Jun 6 Oct 8 Oct 1990 31 May 1 Jun 15 Oct 12 Oct 1991 6 Jun 15 Jun 12 Oct 12 Oct 1992 17 Jun 22 Jun 16 Oct 11 Oct 1993 13 Jun 17 Jun 19 Oct 13 Oct 1994 6 Jun 14 Jun 16 Oct 5 Oct 1995 16 Jun 26 Jun 22 Oct 13 Oct 1996 9 Jun 15 Jun 9 Oct 17 Oct 1997 13 Jun 23 Jun 8 Oct 27 Sep 1998 12 Jun 19 Jun 20 Oct 24 Oct 1999 10 Jun 2 Jun 15 Oct 18 Oct 2000 5 Jun 4 Jun 23 Oct 11 Oct 2001 8 Jun 11 Jun 15 Oct 19 Oct 2002 10 Jun 5 Jun 21 Oct 2 Oct 2003 15 Jun 23 Jun 13 Oct 11 Oct 2004 6 Jun 4 Jun 11 Oct 8 Oct 2005 21 Jun 19 Jun 10 Oct 12 Oct 2006 6 Jun 4 Jun 16 Oct 7 Oct 2007 14 Jun 9 Jun 15 Oct 20 Oct Mean 9 Jun (±6) 12 Jun (±7) 12 Oct (±6) 10 Oct (±6)

 

 

45

Table 23. Yearwise onset and withdrawal dates of southwest monsoon over the Subregion-7 as determine by the objective criteria and that extracted from IMD charts.

Year Onset date Withdrawal date

IMD charts Objective criteria IMD charts Objective criteria 1951 12 Jun 4 Oct 1952 15 Jun 4 Oct 1953 20 Jun 13 Oct 1954 15 Jun 16 Oct 1955 10 Jun 19 Oct 1956 28 May 22 Oct 1957 18 Jun 30 Sep 1958 16 Jun 25 Oct 1959 10 Jun 16 Oct 1960 13 Jun 15 Jun 12 Oct 1961 28 May 6 Jun 19 Oct 1962 29 May 6 Jun 17 Oct 1963 7 Jun 10 Jun 15 Oct 1964 10 Jun 23 Jun 6 Oct 1965 14 Jun 16 Jun 29 Sep 1966 13 Jun 16 Jun 20 Sep 1967 13 Jun 22 Jun 30 Sep 1968 15 Jun 24 Jun 8 Oct 1969 5 Jun 12 Jun 20 Sep 1970 30 May 6 Jun 7 Oct 1971 1 Jun 9 Jun 13 Oct 1972 20 Jun 25 Jun 7 Oct 1973 8 Jun 12 Jun 14 Oct 1974 16 Jun 15 Jun 13 Oct 1975 17 Jun 11 Jun 27 Oct 21 Oct 1976 7 Jun 14 Jun 6 Oct 21 Sep 1977 15 Jun 17 Jun 10 Oct 3 Oct 1978 9 Jun 14 Jun 15 Oct 3 Oct 1979 19 Jun 21 Jun 6 Oct 5 Oct 1980 6 Jun 10 Jun 4 Oct 23 Sep 1981 5 Jun 16 Jun 12 Oct 2 Oct 1982 11 Jun 17 Jun 5 Oct 24 Sep 1983 24 Jun 22 Jun 19 Oct 12 Oct 1984 6 Jun 12 Jun 28 Sep 5 Sep 1985 7 Jun 10 Jun 19 Oct 10 Oct 1986 15 Jun 14 Jun 21 Oct 14 Sep 1987 12 Jun 18 Jun 13 Oct 25 Sep 1988 13 Jun 12 Jun 10 Oct 7 Oct 1989 9 Jun 10 Jun 13 Oct 1 Oct 1990 31 May 2 Jun 16 Oct 18 Oct 1991 7 Jun 16 Jun 12 Oct 22 Oct 1992 18 Jun 22 Jun 16 Oct 11 Oct 1993 13 Jun 15 Jun 15 Oct 1994 9 Jun 12 Jun 17 Oct 18 Oct 1995 17 Jun 17 Jun 22 Oct 14 Oct 1996 10 Jun 16 Jun 10 Oct 17 Oct 1997 13 Jun 23 Jun 8 Oct 1 Oct 1998 14 Jun 14 Jun 20 Oct 28 Oct 1999 12 Jun 1 Jun 15 Oct 13 Oct 2000 5 Jun 3 Jun 23 Oct 27 Sep 2001 8 Jun 4 Jun 15 Oct 19 Sep 2002 10 Jun 8 Jun 21 Oct 13 Sep 2003 15 Jun 18 Jun 17 Oct 2004 10 Jun 10 Jun 11 Oct 7 Oct 2005 21 Jun 23 Jun 16 Oct 2006 6 Jun 5 Jun 16 Oct 30 Sep 2007 15 Jun 16 Jun 12 Oct Mean 10 Jun (±6) 13 Jun (±6) 13 Oct (±7) 7 Oct (±11)

 

 

46

Table 24. Yearwise onset and withdrawal dates of southwest monsoon over the Subregion-8 as determine by the objective criteria and that extracted from IMD charts.

Year Onset date Withdrawal date

IMD charts Objective criteria IMD charts Objective criteria 1951 14 Jun 15 Sep 1952 15 Jun 15 Sep 1953 21 Jun 23 Sep 1954 17 Jun 5 Oct 1955 19 Jun 6 Oct 1956 30 May 7 Oct 1957 22 Jun 25 Sep 1958 21 Jun 8 Oct 1959 8 Jun 13 Oct 1960 13 Jun 13 Jun 5 Oct 1961 8 Jun 7 Jun 11 Oct 1962 31 May 8 Jun 28 Sep 1963 9 Jun 12 Jun 20 Sep 1964 11 Jun 23 Jun 30 Sep 1965 16 Jun 15 Jun 16 Sep 1966 13 Jun 17 Jun 17 Sep 1967 18 Jun 21 Jun 28 Sep 1968 15 Jun 25 Jun 1 Oct 1969 6 Jun 13 Jun 21 Sep 1970 3 Jun 7 Jun 26 Sep 1971 1 Jun 10 Jun 28 Sep 1972 21 Jun 25 Jun 15 Sep 1973 8 Jun 12 Jun 25 Sep 1974 28 Jun 26 Jun 7 Oct 1975 17 Jun 18 Jun 15 Oct 5 Oct 1976 3 Jun 15 Jun 1 Oct 22 Sep 1977 17 Jun 17 Jun 10 Oct 23 Sep 1978 9 Jun 12 Jun 9 Sep 22 Sep 1979 23 Jun 22 Jun 6 Oct 2 Oct 1980 6 Jun 11 Jun 25 Sep 21 Sep 1981 25 Jun 24 Jun 5 Oct 29 Sep 1982 17 Jun 17 Jun 30 Sep 24 Sep 1983 20 Jun 23 Jun 14 Oct 8 Oct 1984 12 Jun 13 Jun 25 Sep 20 Sep 1985 8 Jun 10 Jun 17 Oct 1 Oct 1986 15 Jun 16 Jun 8 Oct 20 Sep 1987 13 Jun 13 Jun 9 Oct 23 Sep 1988 9 Jun 16 Jun 30 Sep 5 Oct 1989 9 Jun 10 Jun 6 Oct 26 Sep 1990 4 Jun 2 Jun 15 Oct 9 Oct 1991 7 Jun 17 Jun 30 Sep 17 Sep 1992 19 Jun 21 Jun 15 Oct 19 Sep 1993 13 Jun 14 Jun 8 Oct 6 Oct 1994 10 Jun 10 Jun 1 Oct 19 Sep 1995 17 Jun 28 Jun 7 Oct 29 Sep 1996 12 Jun 16 Jun 7 Oct 27 Sep 1997 16 Jun 23 Jun 3 Oct 28 Sep 1998 15 Jun 15 Jun 7 Oct 14 Oct 1999 13 Jun 12 Jun 12 Oct 3 Oct 2000 7 Jun 4 Jun 29 Sep 18 Sep 2001 9 Jun 11 Jun 13 Oct 2 Oct 2002 12 Jun 15 Jun 30 Sep 16 Sep 2003 16 Jun 17 Jun 11 Oct 28 Sep 2004 10 Jun 15 Jun 8 Oct 3 Oct 2005 21 Jun 21 Jun 6 Oct 30 Sep 2006 6 Jun 6 Jun 9 Oct 8 Oct 2007 18 Jun 17 Jun 12 Oct 3 Oct Mean 12 Jun (±6) 15 Jun (±6) 5 Oct (±8) 28 Sept (±8)

 

 

47

Table 25. Yearwise onset and withdrawal dates of southwest monsoon over the Subregion-9 as determine by the objective criteria and that extracted from IMD charts.

Year Onset date Withdrawal date

IMD charts Objective criteria IMD charts Objective criteria 1951 20 Jun 25 Sep 1952 18 Jun 28 Sep 1953 22 Jun 2 Oct 1954 19 Jun 4 Oct 1955 18 Jun 10 Oct 1956 2 Jun 10 Oct 1957 21 Jun 28 Sep 1958 24 Jun 15 Oct 1959 9 Jun 9 Oct 1960 13 Jun 12 Jun 8 Oct 1961 4 Jun 9 Jun 11 Oct 1962 31 May 7 Jun 28 Sep 1963 9 Jun 11 Jun 1 Oct 1964 13 Jun 25 Jun 7 Oct 1965 18 Jun 18 Jun 22 Sep 1966 14 Jun 19 Jun 20 Sep 1967 18 Jun 23 Jun 29 Sep 1968 15 Jun 26 Jun 30 Sep 1969 6 Jun 20 Jun 26 Sep 1970 3 Jun 8 Jun 29 Sep 1971 1 Jun 11 Jun 2 Oct 1972 22 Jun 26 Jun 20 Sep 1973 11 Jun 14 Jun 30 Sep 1974 18 Jun 22 Jun 9 Oct 1975 18 Jun 16 Jun 15 Oct 13 Oct 1976 7 Jun 24 Jun 1 Oct 23 Sep 1977 17 Jun 19 Jun 6 Oct 26 Sep 1978 15 Jun 14 Jun 9 Sep 25 Sep 1979 23 Jun 23 Jun 6 Oct 2 Oct 1980 6 Jun 13 Jun 30 Sep 25 Sep 1981 21 Jun 21 Jun 5 Oct 1 Oct 1982 15 Jun 20 Jun 30 Sep 23 Sep 1983 26 Jun 24 Jun 14 Oct 9 Oct 1984 12 Jun 14 Jun 26 Sep 1 Oct 1985 15 Jun 9 Jun 17 Oct 5 Oct 1986 16 Jun 17 Jun 9 Oct 26 Sep 1987 16 Jun 15 Jun 9 Oct 2 Oct 1988 13 Jun 18 Jun 30 Sep 7 Oct 1989 10 Jun 11 Jun 6 Oct 27 Sep 1990 5 Jun 4 Jun 15 Oct 8 Oct 1991 8 Jun 19 Jun 30 Sep 29 Sep 1992 19 Jun 22 Jun 15 Oct 29 Sep 1993 14 Jun 17 Jun 6 Oct 6 Oct 1994 10 Jun 11 Jun 1 Oct 25 Sep 1995 18 Jun 21 Jun 9 Oct 9 Oct 1996 13 Jun 18 Jun 8 Oct 5 Oct 1997 16 Jun 25 Jun 8 Oct 24 Sep 1998 15 Jun 15 Jun 9 Oct 16 Oct 1999 12 Jun 11 Jun 12 Oct 5 Oct 2000 6 Jun 5 Jun 13 Oct 27 Sep 2001 9 Jun 10 Jun 13 Oct 6 Oct 2002 12 Jun 20 Jun 3 Oct 19 Sep 2003 17 Jun 22 Jun 11 Oct 1 Oct 2004 15 Jun 14 Jun 11 Oct 2 Oct 2005 24 Jun 24 Jun 7 Oct 5 Oct 2006 23 Jun 8 Jun 13 Oct 4 Oct 2007 18 Jun 14 Jun 12 Oct 4 Oct Mean 13 Jun (±6) 16 Jun (±6) 6 Oct (±7) 1 Oct (±6)

 

 

48

Table 26. Yearwise onset and withdrawal dates of southwest monsoon over the Subregion-10 as determine by the objective criteria and that extracted from IMD charts.

Year Onset date Withdrawal date

IMD charts Objective criteria IMD charts Objective criteria 1951 23 Jun 29 Sep 1952 18 Jun 28 Sep 1953 22 Jun 27 Sep 1954 20 Jun 2 Oct 1955 14 Jun 9 Oct 1956 3 Jun 7 Oct 1957 25 Jun 27 Sep 1958 23 Jun 14 Oct 1959 14 Jun 11 Oct 1960 16 Jun 16 Jun 7 Oct 1961 4 Jun 10 Jun 9 Oct 1962 9 Jun 11 Jun 29 Sep 1963 11 Jun 14 Jun 26 Sep 1964 18 Jun 25 Jun 3 Oct 1965 20 Jun 17 Jun 23 Sep 1966 14 Jun 19 Jun 18 Sep 1967 18 Jun 24 Jun 29 Sep 1968 15 Jun 27 Jun 30 Sep 1969 6 Jun 16 Jun 26 Sep 1970 4 Jun 11 Jun 25 Sep 1971 3 Jun 12 Jun 27 Sep 1972 23 Jun 27 Jun 28 Sep 1973 12 Jun 15 Jun 7 Oct 1974 17 Jun 24 Jun 29 Sep 1975 18 Jun 15 Jun 27 Oct 5 Oct 1976 28 Jun 18 Jun 6 Oct 25 Sep 1977 17 Jun 19 Jun 10 Oct 24 Sep 1978 17 Jun 13 Jun 12 Oct 30 Sep 1979 23 Jun 24 Jun 6 Oct 28 Sep 1980 16 Jun 17 Jun 4 Oct 27 Sep 1981 21 Jun 20 Jun 5 Oct 28 Sep 1982 14 Jun 20 Jun 30 Sep 22 Sep 1983 24 Jun 25 Jun 17 Oct 7 Oct 1984 10 Jun 10 Jun 26 Sep 16 Sep 1985 20 Jun 14 Jun 19 Oct 3 Oct 1986 16 Jun 19 Jun 20 Oct 2 Oct 1987 13 Jun 22 Jun 9 Oct 26 Sep 1988 11 Jun 12 Jun 10 Oct 3 Oct 1989 13 Jun 10 Jun 13 Oct 27 Sep 1990 13 Jun 5 Jun 16 Oct 5 Oct 1991 6 Jun 19 Jun 7 Oct 26 Sep 1992 18 Jun 24 Jun 15 Oct 22 Sep 1993 15 Jun 22 Jun 6 Oct 2 Oct 1994 11 Jun 15 Jun 15 Oct 25 Sep 1995 18 Jun 21 Jun 12 Oct 1 Oct 1996 19 Jun 20 Jun 8 Oct 22 Sep 1997 18 Jun 25 Jun 8 Oct 24 Sep 1998 14 Jun 16 Jun 9 Oct 2 Oct 1999 12 Jun 9 Jun 12 Oct 2 Oct 2000 6 Jun 7 Jun 13 Oct 27 Sep 2001 9 Jun 11 Jun 13 Oct 1 Oct 2002 12 Jun 21 Jun 17 Oct 22 Sep 2003 20 Jun 20 Jun 13 Oct 9 Oct 2004 13 Jun 5 Jun 11 Oct 3 Oct 2005 24 Jun 21 Jun 10 Oct 29 Sep 2006 23 Jun 10 Jun 13 Oct 6 Oct 2007 18 Jun 15 Jun 15 Oct 5 Oct Mean 15 Jun (±6) 17 Jun (±6) 11 Oct (±6) 30 Sept (±6)

 

 

49

Table 27. Yearwise onset and withdrawal dates of southwest monsoon over the Subregion-11 as determine by the objective criteria and that extracted from IMD charts.

Year Onset date Withdrawal date

IMD charts Objective criteria IMD charts Objective criteria 1951 27 Jun 2 Sep 1952 1 Jul 1 Sep 1953 29 Jun 12 Sep 1954 28 Jun 2 Oct 1955 27 Jun 28 Sep 1956 26 Jun 30 Sep 1957 28 Jun 13 Sep 1958 27 Jun 9 Oct 1959 26 Jun 12 Oct 1960 15 Jun 23 Jun 26 Sep 1961 10 Jun 23 Jun 4 Oct 1962 24 Jun 7 Jul 24 Sep 1963 15 Jun 26 Jun 17 Sep 1964 24 Jun 29 Jun 24 Sep 1965 4 Jul 10 Jul 11 Sep 1966 20 Jun 26 Jun 14 Sep 1967 18 Jun 27 Jun 19 Sep 1968 5 Jul 4 Jul 21 Sep 1969 7 Jun 30 Jun 18 Sep 1970 23 Jun 15 Jun 26 Sep 1971 2 Jun 18 Jun 23 Sep 1972 22 Jun 1 Jul 30 Aug 1973 13 Jun 21 Jun 21 Sep 1974 2 Jul 6 Jul 27 Sep 1975 20 Jun 23 Jun 11 Oct 6 Oct 1976 7 Jun 27 Jun 25 Sep 21 Sep 1977 22 Jun 24 Jun 30 Sep 20 Sep 1978 17 Jun 20 Jun 18 Sep 15 Sep 1979 26 Jun 27 Jun 29 Sep 13 Sep 1980 22 Jun 21 Jun 23 Sep 13 Sep 1981 27 Jun 27 Jun 3 Oct 28 Sep 1982 12 Jul 11 Jul 15 Sep 9 Sep 1983 26 Jun 30 Jun 5 Oct 6 Oct 1984 18 Jun 22 Jun 24 Sep 18 Sep 1985 14 Jul 12 Jul 19 Sep 13 Sep 1986 21 Jun 21 Jun 22 Sep 6 Sep 1987 7 Jul 1 Jul 21 Sep 12 Sep 1988 22 Jun 2 Jul 30 Sep 2 Oct 1989 13 Jun 15 Jun 2 Oct 21 Sep 1990 30 Jun 27 Jun 6 Oct 30 Sep 1991 10 Jun 12 Jul 21 Sep 12 Sep 1992 21 Jun 9 Jul 22 Sep 16 Sep 1993 16 Jun 26 Jun 29 Sep 1 Oct 1994 12 Jun 16 Jun 21 Sep 19 Sep 1995 12 Jul 12 Jul 21 Sep 16 Sep 1996 15 Jun 21 Jun 22 Sep 15 Sep 1997 20 Jun 30 Jun 22 Sep 22 Sep 1998 26 Jun 27 Jun 30 Sep 8 Oct 1999 19 Jun 11 Jun 7 Oct 3 Oct 2000 30 Jun 30 Jun 23 Sep 13 Sep 2001 12 Jun 14 Jun 24 Sep 4 Sep 2002 25 Jun 26 Jun 20 Sep 12 Sep 2003 18 Jun 26 Jun 1 Oct 25 Sep 2004 16 Jun 17 Jun 3 Oct 28 Sep 2005 26 Jun 25 Jun 1 Oct 28 Sep 2006 27 Jun 25 Jun 3 Oct 3 Oct 2007 24 Jun 22 Jun 2 Oct 2 Oct Mean 21 Jun (±9) 26 Jun (±7) 26 Sept (±6) 21 Sept (±10)

 

 

50

Table 28. Yearwise onset and withdrawal dates of southwest monsoon over the Subregion-12 as determine by the objective criteria and that extracted from IMD charts.

Year Onset date Withdrawal date

IMD charts Objective criteria IMD charts Objective criteria

1951 24 Jun 13 Sep 1952 27 Jun 12 Sep 1953 27 Jun 19 Sep 1954 26 Jun 30 Sep 1955 22 Jun 4 Oct 1956 17 Jun 2 Oct 1957 26 Jun 22 Sep 1958 26 Jun 7 Oct 1959 14 Jun 7 Oct 1960 18 Jun 22 Jun 3 Oct 1961 9 Jun 14 Jun 8 Oct 1962 12 Jun 6 Jul 26 Sep 1963 16 Jun 16 Jun 20 Sep 1964 24 Jun 28 Jun 27 Sep 1965 3 Jul 1 Jul 17 Sep 1966 18 Jun 24 Jun 14 Sep 1967 18 Jun 26 Jun 23 Sep 1968 5 Jul 1 Jul 26 Sep 1969 4 Jul 29 Jun 23 Sep 1970 14 Jun 13 Jun 23 Sep 1971 3 Jun 16 Jun 27 Sep 1972 23 Jun 30 Jun 15 Sep 1973 13 Jun 25 Jun 23 Sep 1974 29 Jun 3 Jul 5 Sep 1975 20 Jun 21 Jun 13 Oct 3 Oct 1976 7 Jun 25 Jun 25 Sep 21 Sep 1977 22 Jun 23 Jun 6 Oct 22 Sep 1978 17 Jun 19 Jun 4 Oct 14 Sep 1979 25 Jun 26 Jun 29 Sep 19 Sep 1980 21 Jun 16 Jun 25 Sep 17 Sep 1981 25 Jun 23 Jun 3 Oct 26 Sep 1982 12 Jul 21 Jun 20 Sep 19 Sep 1983 28 Jun 28 Jun 13 Oct 4 Oct 1984 14 Jun 15 Jun 25 Sep 14 Sep 1985 28 Jun 25 Jun 27 Sep 4 Oct 1986 21 Jun 21 Jun 8 Oct 18 Sep 1987 16 Jun 25 Jun 25 Sep 24 Sep 1988 22 Jun 24 Jun 30 Sep 2 Oct 1989 14 Jun 18 Jun 5 Oct 17 Sep 1990 20 Jun 15 Jun 13 Oct 30 Sep 1991 8 Jun 23 Jun 24 Sep 15 Sep 1992 23 Jun 1 Jul 22 Sep 18 Sep 1993 16 Jun 18 Jun 1 Oct 1 Oct 1994 13 Jun 14 Jun 23 Sep 18 Sep 1995 19 Jun 27 Jun 30 Sep 18 Sep 1996 18 Jun 28 Jun 7 Oct 21 Sep 1997 18 Jun 28 Jun 3 Oct 20 Sep 1998 16 Jun 26 Jun 5 Oct 30 Sep 1999 16 Jun 17 Jun 7 Oct 30 Sep 2000 8 Jun 10 Jun 27 Sep 16 Sep 2001 13 Jun 10 Jun 27 Sep 8 Sep 2002 22 Jun 21 Jun 30 Sep 16 Sep 2003 19 Jun 24 Jun 3 Oct 28 Sep 2004 17 Jun 16 Jun 3 Oct 29 Sep 2005 24 Jun 25 Jun 3 Oct 26 Sep 2006 29 Jun 28 Jun 9 Oct 5 Oct 2007 25 Jun 20 Jun 8 Oct 1 Oct Mean 19 Jun (±8) 22 Jun (±6) 1 Oct (±6) 23 Sept (±8)

 

 

51

Table 29. Yearwise onset and withdrawal dates of southwest monsoon over the Subregion-13 as determine by the objective criteria and that extracted from IMD charts.

Year Onset date Withdrawal date

IMD charts Objective criteria IMD charts Objective criteria 1951 20 Jun 25 Sep 1952 24 Jun 29 Sep 1953 26 Jun 30 Sep 1954 24 Jun 4 Oct 1955 26 Jun 11 Oct 1956 11 Jun 14 Oct 1957 28 Jun 29 Sep 1958 27 Jun 19 Oct 1959 13 Jun 14 Oct 1960 21 Jun 24 Jun 8 Oct 1961 8 Jun 13 Jun 14 Oct 1962 9 Jun 21 Jun 5 Oct 1963 15 Jun 15 Jun 12 Oct 1964 22 Jun 27 Jun 8 Oct 1965 28 Jun 27 Jun 28 Sep 1966 17 Jun 22 Jun 19 Sep 1967 18 Jun 29 Jun 27 Sep 1968 17 Jun 30 Jun 5 Oct 1969 1 Jul 21 Jun 27 Sep 1970 10 Jun 12 Jun 1 Oct 1971 5 Jun 15 Jun 6 Oct 1972 24 Jun 4 Jul 2 Oct 1973 14 Jun 24 Jun 8 Oct 1974 18 Jun 1 Jul 11 Oct 1975 19 Jun 24 Jun 14 Oct 12 Oct 1976 28 Jun 29 Jun 3 Oct 28 Sep 1977 20 Jun 22 Jun 10 Oct 3 Oct 1978 20 Jun 22 Jun 12 Oct 30 Sep 1979 25 Jun 28 Jun 6 Oct 4 Oct 1980 19 Jun 18 Jun 27 Sep 29 Sep 1981 23 Jun 22 Jun 5 Oct 30 Sep 1982 15 Jun 19 Jun 30 Sep 22 Sep 1983 28 Jun 27 Jun 14 Oct 10 Oct 1984 10 Jun 15 Jun 25 Sep 19 Sep 1985 26 Jun 26 Jun 19 Oct 9 Oct 1986 21 Jun 23 Jun 9 Oct 6 Oct 1987 5 Jul 3 Jul 27 Sep 8 Oct 1988 17 Jun 13 Jun 7 Oct 4 Oct 1989 15 Jun 15 Jun 5 Oct 29 Sep 1990 15 Jun 15 Jun 16 Oct 7 Oct 1991 8 Jun 22 Jun 30 Sep 29 Sep 1992 20 Jun 30 Jun 3 Oct 28 Sep 1993 23 Jun 21 Jun 4 Oct 6 Oct 1994 12 Jun 14 Jun 19 Sep 4 Oct 1995 18 Jun 26 Jun 4 Oct 30 Sep 1996 22 Jun 21 Jun 8 Oct 4 Oct 1997 22 Jun 28 Jun 3 Oct 7 Oct 1998 15 Jun 26 Jun 5 Oct 24 Oct 1999 14 Jun 12 Jun 11 Oct 7 Oct 2000 7 Jun 15 Jun 29 Sep 27 Sep 2001 13 Jun 14 Jun 13 Oct 6 Oct 2002 20 Jun 21 Jun 3 Oct 29 Sep 2003 23 Jun 24 Jun 11 Oct 13 Oct 2004 15 Jun 15 Jun 8 Oct 7 Oct 2005 24 Jun 28 Jun 5 Oct 11 Oct 2006 27 Jun 16 Jun 9 Oct 8 Oct 2007 25 Jun 20 Jun 10 Oct 8 Oct Mean 18 Jun (±7) 21 Jun (±6) 5 Oct (±6) 4 Oct (±7)

 

 

52

Table 30. Yearwise onset and withdrawal dates of southwest monsoon over the Subregion-14 as determine by the objective criteria and that extracted from IMD charts.

Year Onset date Withdrawal date

IMD charts Objective criteria IMD charts Objective criteria 1951 15 Jun 1 Oct 1952 15 Jun 2 Oct 1953 21 Jun 2 Oct 1954 17 Jun 8 Oct 1955 13 Jun 14 Oct 1956 30 May 17 Oct 1957 22 Jun 7 Oct 1958 21 Jun 21 Oct 1959 11 Jun 18 Oct 1960 18 Jun 9 Jun 10 Oct 1961 8 Jun 8 Jun 15 Oct 1962 1 Jun 12 Jun 6 Oct 1963 10 Jun 9 Jun 13 Oct 1964 17 Jun 23 Jun 9 Oct 1965 23 Jun 15 Jun 30 Sep 1966 13 Jun 18 Jun 29 Sep 1967 13 Jun 21 Jun 2 Oct 1968 11 Jun 25 Jun 8 Oct 1969 5 Jun 13 Jun 30 Sep 1970 3 Jun 9 Jun 6 Oct 1971 3 Jun 10 Jun 9 Oct 1972 22 Jun 25 Jun 4 Oct 1973 13 Jun 12 Jun 6 Oct 1974 7 Jun 16 Jun 11 Oct 1975 19 Jun 12 Jun 26 Oct 14 Oct 1976 9 Jun 15 Jun 10 Oct 3 Oct 1977 15 Jun 18 Jun 10 Oct 4 Oct 1978 17 Jun 10 Jun 12 Oct 6 Oct 1979 12 Jun 22 Jun 6 Oct 7 Oct 1980 8 Jun 11 Jun 4 Oct 9 Oct 1981 21 Jun 16 Jun 5 Oct 1 Oct 1982 11 Jun 16 Jun 30 Sep 25 Sep 1983 26 Jun 23 Jun 17 Oct 13 Oct 1984 6 Jun 7 Jun 25 Sep 1 Oct 1985 15 Jun 12 Jun 19 Oct 14 Oct 1986 20 Jun 19 Jun 16 Oct 8 Oct 1987 8 Jun 20 Jun 9 Oct 5 Oct 1988 9 Jun 12 Jun 10 Oct 9 Oct 1989 14 Jun 8 Jun 6 Oct 7 Oct 1990 15 Jun 2 Jun 16 Oct 10 Oct 1991 8 Jun 17 Jun 3 Oct 5 Oct 1992 18 Jun 22 Jun 15 Oct 7 Oct 1993 16 Jun 17 Jun 6 Oct 13 Oct 1994 10 Jun 13 Jun 29 Sep 4 Oct 1995 18 Jun 19 Jun 4 Oct 5 Oct 1996 8 Jun 18 Jun 8 Oct 8 Oct 1997 22 Jun 23 Jun 5 Oct 1 Oct 1998 15 Jun 15 Jun 6 Oct 25 Oct 1999 28 May 30 May 11 Oct 14 Oct 2000 5 Jun 4 Jun 4 Oct 1 Oct 2001 4 Jun 4 Jun 13 Oct 11 Oct 2002 11 Jun 12 Jun 10 Oct 30 Sep 2003 20 Jun 18 Jun 11 Oct 13 Oct 2004 13 Jun 6 Jun 11 Oct 10 Oct 2005 23 Jun 19 Jun 7 Oct 13 Oct 2006 6 Jun 6 Jun 9 Oct 12 Oct 2007 13 Jun 12 Jun 12 Oct 12 Oct Mean 12 Jun (±6) 14 Jun (±6) 8 Oct (±6) 8 Oct (±6)

 

 

53

Table 31. Yearwise onset and withdrawal dates of southwest monsoon over the Subregion-15 as determine by the objective criteria and that extracted from IMD charts.

Year Onset date Withdrawal date

IMD charts Objective criteria IMD charts Objective criteria 1951 26 Jul 26 Aug 1952 24 Jul 27 Aug 1953 30 Jul 8 Sep 1954 19 Jul 25 Sep 1955 13 Aug 18 Sep 1956 6 Aug 21 Sep 1957 15 Jul 8 Sep 1958 7 Jul 25 Sep 1959 2 Jul 22 Sep 1960 27 Jun 22 Jul 4 Sep 1961 21 Jun 14 Jul 18 Sep 1962 5 Jul 21 Jul 12 Sep 1963 14 Jul 4 Aug 15 Sep 1964 6 Jul 8 Jul 14 Sep 1965 17 Jul 20 Jul 1 Sep 1966 6 Jul 25 Jul 16 Sep 1967 2 Jul 6 Jul 14 Sep 1968 9 Jul 28 Jul 20 Aug 1969 15 Jul 23 Jul 2 Sep 1970 3 Jul 6 Jul 21 Sep 1971 2 Jul 28 Jul 6 Sep 1972 29 Jun 9 Jul 27 Aug 1973 5 Jul 27 Jul 8 Sep 1974 12 Jul 9 Aug 25 Aug 1975 30 Jun 10 Aug 23 Sep 24 Sep 1976 15 Jul 17 Jul 19 Sep 16 Sep 1977 29 Jun 4 Jul 23 Sep 16 Sep 1978 3 Jul 3 Jul 11 Sep 9 Sep 1979 15 Jul 29 Jul 16 Sep 24 Aug 1980 26 Jun 25 Jun 15 Sep 9 Sep 1981 10 Jul 12 Jul 3 Sep 22 Sep 1982 22 Jul 22 Jul 3 Sep 5 Sep 1983 18 Jul 13 Jul 13 Sep 19 Sep 1984 2 Jul 20 Jul 22 Sep 15 Sep 1985 14 Jul 17 Jul 11 Sep 3 Sep 1986 24 Jul 28 Jul 17 Sep 31 Aug 1987 15 Jul 28 Aug 12 Sep 8 Sep 1988 30 Jun 16 Jul 12 Sep 20 Sep 1989 2 Jul 20 Jul 14 Sep 15 Sep 1990 1 Jul 7 Jul 27 Sep 22 Sep 1991 16 Jul 26 Jul 18 Sep 10 Sep 1992 12 Jul 20 Jul 17 Sep 15 Sep 1993 27 Jun 8 Jul 21 Sep 14 Sep 1994 30 Jun 1 Jul 19 Sep 17 Sep 1995 13 Jul 16 Jul 15 Sep 12 Sep 1996 24 Jun 15 Jul 17 Oct 8 Sep 1997 12 Jul 17 Jul 18 Sep 4 Oct 1998 29 Jun 1 Jul 7 Sep 28 Sep 1999 12 Jul 22 Jul 21 Sep 30 Sep 2000 2 Jul 13 Jul 15 Sep 4 Sep 2001 24 Jun 27 Jun 14 Sep 29 Aug 2002 15 Jul 24 Aug 16 Sep 7 Sep 2003 5 Jul 7 Jul 19 Sep 10 Sep 2004 8 Jul 4 Jul 24 Sep 5 Sep 2005 29 Jun 4 Jul 28 Sep 22 Sep 2006 20 Jul 5 Jul 25 Sep 30 Sep 2007 30 Jun 27 Jun 30 Sep 21 Sep Mean 6 Jul (±8) 18 Jul (±14) 18 Sept (±8) 12 Sept (±10)

 

 

54

Table 32. Yearwise onset and withdrawal dates of southwest monsoon over the Subregion-16 as determine by the objective criteria and that extracted from IMD charts.

Year Onset date Withdrawal date

IMD charts Objective criteria IMD charts Objective criteria 1951 30 Jun 1 Sep 1952 8 Jul 3 Sep 1953 5 Jul 4 Sep 1954 7 Jul 19 Sep 1955 30 Jun 11 Sep 1956 3 Jul 3 Sep 1957 10 Jul 7 Sep 1958 3 Jul 8 Sep 1959 5 Jul 21 Sep 1960 23 Jun 3 Jul 8 Sep 1961 9 Jun 2 Jul 20 Sep 1962 24 Jun 15 Jul 5 Sep 1963 25 Jun 3 Jul 4 Sep 1964 1 Jul 5 Jul 9 Sep 1965 4 Jul 9 Jul 3 Sep 1966 20 Jun 11 Jul 5 Sep 1967 26 Jun 1 Jul 9 Sep 1968 5 Jul 7 Jul 31 Aug 1969 8 Jul 12 Jul 6 Sep 1970 29 Jun 22 Jun 12 Sep 1971 23 Jun 26 Jun 2 Sep 1972 25 Jun 6 Jul 27 Aug 1973 30 Jun 2 Jul 4 Sep 1974 11 Jul 25 Jul 26 Aug 1975 21 Jun 28 Jun 8 Oct 11 Sep 1976 11 Jul 3 Jul 22 Sep 7 Sep 1977 27 Jun 30 Jun 26 Sep 3 Sep 1978 23 Jun 26 Jun 26 Sep 2 Sep 1979 30 Jun 4 Jul 21 Sep 23 Aug 1980 21 Jun 22 Jun 13 Sep 30 Aug 1981 25 Jun 2 Jul 11 Sep 4 Sep 1982 14 Jul 16 Jul 15 Sep 5 Sep 1983 28 Jun 7 Jul 1 Oct 16 Sep 1984 18 Jun 20 Jun 22 Sep 4 Sep 1985 8 Jul 7 Jul 27 Sep 8 Sep 1986 24 Jun 30 Jun 18 Sep 3 Sep 1987 7 Jul 13 Jul 25 Sep 2 Sep 1988 23 Jun 30 Jun 30 Sep 7 Sep 1989 1 Jul 28 Jun 2 Oct 2 Sep 1990 28 Jun 29 Jun 1 Oct 12 Sep 1991 14 Jul 6 Jul 21 Sep 5 Sep 1992 3 Jul 14 Jul 22 Sep 7 Sep 1993 24 Jun 2 Jul 28 Sep 2 Sep 1994 25 Jun 27 Jun 21 Sep 10 Sep 1995 10 Jul 1 Jul 29 Sep 5 Sep 1996 23 Jun 25 Jun 24 Oct 3 Sep 1997 7 Jul 5 Jul 28 Sep 2 Sep 1998 16 Jun 29 Jun 28 Sep 5 Sep 1999 22 Jun 8 Jul 26 Sep 6 Sep 2000 23 Jun 29 Jun 23 Sep 5 Sep 2001 23 Jun 19 Jun 24 Sep 29 Aug 2002 15 Jul 25 Jun 26 Sep 1 Sep 2003 27 Jun 2 Jul 29 Sep 11 Sep 2004 5 Jul 20 Jun 27 Sep 4 Sep 2005 27 Jun 29 Jun 29 Sep 7 Sep 2006 10 Jul 26 Jun 27 Sep 17 Sep 2007 28 Jun 27 Jun 2 Oct 13 Sep Mean 28 Jun (±8) 2 Jul (±7) 26 Sept (±8) 6 Sept (±6)

 

 

55

Table 33. Yearwise onset and withdrawal dates of southwest monsoon over the Subregion-17 as determine by the objective criteria and that extracted from IMD charts.

Year Onset date Withdrawal date

IMD charts Objective criteria IMD charts Objective criteria 1951 21 Jun 15 Sep 1952 27 Jun 20 Sep 1953 27 Jun 29 Sep 1954 26 Jun 3 Oct 1955 22 Jun 4 Oct 1956 17 Jun 10 Oct 1957 27 Jun 23 Sep 1958 29 Jun 11 Oct 1959 14 Jun 11 Oct 1960 18 Jun 27 Jun 8 Oct 1961 8 Jun 15 Jun 12 Oct 1962 9 Jun 3 Jul 3 Oct 1963 17 Jun 16 Jun 29 Sep 1964 22 Jun 28 Jun 28 Sep 1965 28 Jun 29 Jun 27 Sep 1966 19 Jun 24 Jun 16 Sep 1967 25 Jun 26 Jun 26 Sep 1968 17 Jun 1 Jul 5 Oct 1969 1 Jul 23 Jun 27 Sep 1970 10 Jun 13 Jun 3 Oct 1971 6 Jun 16 Jun 3 Oct 1972 24 Jun 6 Jul 23 Sep 1973 14 Jun 19 Jun 1 Oct 1974 28 Jun 3 Jul 23 Sep 1975 20 Jun 21 Jun 13 Oct 2 Oct 1976 8 Jul 29 Jun 3 Oct 27 Sep 1977 20 Jun 8 Jul 6 Oct 2 Oct 1978 23 Jun 24 Jun 9 Oct 24 Sep 1979 26 Jun 29 Jun 21 Sep 26 Sep 1980 19 Jun 19 Jun 27 Sep 25 Sep 1981 23 Jun 28 Jun 3 Oct 30 Sep 1982 15 Jun 18 Jun 16 Sep 21 Sep 1983 28 Jun 1 Jul 5 Oct 11 Oct 1984 12 Jun 13 Jun 25 Sep 17 Sep 1985 28 Jun 27 Jun 27 Sep 8 Oct 1986 23 Jun 25 Jun 8 Oct 3 Oct 1987 7 Jul 2 Jul 27 Sep 11 Oct 1988 17 Jun 20 Jun 7 Oct 3 Oct 1989 21 Jun 15 Jun 4 Oct 26 Sep 1990 19 Jun 21 Jun 13 Oct 30 Sep 1991 10 Jun 23 Jun 30 Sep 23 Sep 1992 26 Jun 5 Jul 3 Oct 5 Oct 1993 23 Jun 21 Jun 4 Oct 1 Oct 1994 11 Jun 26 Jun 23 Sep 24 Sep 1995 18 Jun 25 Jun 30 Sep 25 Sep 1996 22 Jun 25 Jun 7 Oct 1 Oct 1997 24 Jun 28 Jun 3 Oct 26 Sep 1998 16 Jun 29 Jun 5 Oct 4 Oct 1999 14 Jun 12 Jun 7 Oct 8 Oct 2000 8 Jun 10 Jun 27 Sep 23 Sep 2001 17 Jun 10 Jun 27 Sep 28 Sep 2002 22 Jun 22 Jun 3 Oct 24 Sep 2003 25 Jun 24 Jun 3 Oct 28 Sep 2004 15 Jun 18 Jun 8 Oct 5 Oct 2005 24 Jun 29 Jun 5 Oct 8 Oct 2006 27 Jun 18 Jun 3 Oct 7 Oct 2007 25 Jun 20 Jun 2 Oct 6 Oct Mean 20 Jun (±7) 23 Jun (±7) 2 Oct (±6) 30 Sept (±7)

 

 

56

Table 34. Yearwise onset and withdrawal dates of southwest monsoon over the Subregion-18 as determine by the objective criteria and that extracted from IMD charts.

Year Onset date Withdrawal date

IMD charts Objective criteria IMD charts Objective criteria 1951 10 Jun 2 Oct 1952 10 Jun 26 Sep 1953 14 Jun 5 Oct 1954 9 Jun 20 Sep 1955 5 Jun 2 Oct 1956 20 May 25 Sep 1957 16 Jun 12 Oct 1958 22 May 21 Oct 1959 8 Jun 19 Sep 1960 31 May 3 Jun 4 Oct 1961 31 May 30 May 9 Oct 1962 27 May 8 Jun 19 Sep 1963 9 Jun 4 Jun 9 Oct 1964 11 Jun 16 Jun 13 Oct 1965 6 Jun 8 Jun 2 Oct 1966 5 Jun 10 Jun 1 Oct 1967 13 Jun 12 Jun 6 Oct 1968 10 Jun 18 Jun 10 Oct 1969 4 Jun 4 Jun 19 Sep 1970 2 Jun 4 Jun 6 Oct 1971 1 Jun 4 Jun 9 Oct 1972 13 Jun 20 Jun 2 Oct 1973 12 Jun 5 Jun 8 Oct 1974 1 Jun 6 Jun 10 Oct 1975 30 May 7 Jun 25 Oct 16 Oct 1976 9 Jun 8 Jun 12 Oct 5 Oct 1977 7 Jun 9 Jun 20 Oct 7 Oct 1978 9 Jun 1 Jun 12 Oct 6 Sep 1979 12 Jun 18 Jun 15 Oct 10 Oct 1980 4 Jun 9 Jun 9 Oct 4 Oct 1981 17 Jun 6 Jun 12 Oct 29 Sep 1982 11 Jun 13 Jun 9 Oct 3 Oct 1983 18 Jun 17 Jun 19 Oct 5 Oct 1984 6 Jun 3 Jun 26 Sep 3 Oct 1985 4 Jun 1 Jun 21 Oct 2 Oct 1986 16 Jun 12 Jun 21 Oct 9 Oct 1987 5 Jun 14 Jun 13 Oct 8 Oct 1988 30 May 28 May 10 Oct 9 Oct 1989 6 Jun 2 Jun 13 Oct 7 Oct 1990 4 Jun 31 May 17 Oct 5 Oct 1991 2 Jun 10 Jun 18 Oct 12 Oct 1992 13 Jun 20 Jun 18 Oct 12 Oct 1993 31 May 7 Jun 19 Oct 12 Oct 1994 3 Jun 5 Jun 15 Oct 5 Oct 1995 5 Jun 10 Jun 10 Oct 4 Oct 1996 31 May 16 Jun 10 Oct 4 Oct 1997 9 Jun 15 Jun 5 Oct 1 Oct 1998 1 Jun 12 Jun 7 Oct 30 Sep 1999 26 May 27 May 12 Oct 13 Oct 2000 2 Jun 1 Jun 13 Oct 4 Oct 2001 1 Jun 2 Jun 13 Oct 13 Oct 2002 6 Jun 9 Jun 17 Oct 30 Sep 2003 5 Jun 12 Jun 13 Oct 11 Oct 2004 21 May 5 Jun 11 Oct 11 Oct 2005 16 Jun 13 Jun 10 Oct 8 Oct 2006 27 May 1 Jun 16 Oct 7 Oct 2007 8 Jun 3 Jun 15 Oct 28 Sep Mean 5 Jun (±6) 7 Jun (±7) 13 Oct (±5) 4 Oct (±8)

 

 

57

Table 35. Yearwise onset and withdrawal dates of southwest monsoon over the Subregion-19 as determine by the objective criteria and that extracted from IMD charts.

Year Onset date Withdrawal date

IMD charts Objective criteria IMD charts Objective criteria 1951 28 Jul 11 Sep 1952 11 Jul 7 Sep 1953 8 Jul 15 Sep 1954 14 Jul 1 Oct 1955 2 Jul 27 Aug 1956 4 Jul 27 Sep 1957 13 Jul 19 Sep 1958 7 Jul 30 Sep 1959 1 Jul 3 Oct 1960 28 Jun 1 Jul 22 Sep 1961 9 Jun 3 Jul 29 Sep 1962 14 Jun 16 Jul 22 Sep 1963 7 Jul 21 Jul 18 Sep 1964 1 Jul 4 Jul 23 Sep 1965 4 Jul 7 Jul 9 Sep 1966 20 Jun 13 Jul 18 Sep 1967 27 Jun 2 Jul 20 Sep 1968 9 Jul 8 Jul 21 Sep 1969 12 Jul 14 Jul 18 Sep 1970 30 Jun 23 Jun 23 Sep 1971 23 Jun 28 Jun 11 Sep 1972 27 Jun 7 Jul 7 Sep 1973 5 Jul 3 Jul 18 Sep 1974 12 Jul 26 Jul 10 Sep 1975 23 Jun 29 Jun 25 Sep 19 Sep 1976 11 Jul 3 Jul 19 Sep 20 Sep 1977 29 Jun 1 Jul 23 Sep 23 Sep 1978 25 Jun 28 Jun 18 Sep 15 Sep 1979 11 Jul 8 Jul 21 Sep 5 Sep 1980 26 Jun 3 Jul 15 Sep 21 Sep 1981 27 Jun 4 Jul 3 Sep 16 Sep 1982 16 Jul 22 Jul 3 Sep 13 Sep 1983 29 Jun 8 Jul 20 Sep 29 Sep 1984 2 Jul 19 Jun 15 Sep 25 Aug 1985 12 Jul 5 Jul 11 Sep 1 Oct 1986 25 Jun 30 Jun 17 Sep 24 Sep 1987 8 Jul 22 Jul 21 Sep 18 Sep 1988 23 Jun 2 Jul 12 Sep 24 Sep 1989 29 Jun 11 Jul 27 Sep 16 Sep 1990 30 Jun 3 Jul 28 Sep 22 Sep 1991 14 Jul 13 Jul 18 Sep 16 Sep 1992 29 Jun 19 Jul 20 Sep 15 Sep 1993 24 Jun 7 Jul 21 Sep 21 Sep 1994 26 Jun 2 Jul 21 Sep 17 Sep 1995 10 Jul 1 Jul 20 Sep 15 Sep 1996 25 Jun 28 Jun 21 Oct 15 Sep 1997 29 Jun 7 Jul 23 Sep 5 Oct 1998 18 Jun 28 Jun 28 Sep 3 Oct 1999 5 Jul 15 Jul 26 Sep 22 Sep 2000 23 Jun 30 Jun 23 Sep 17 Sep 2001 22 Jun 20 Jun 20 Sep 10 Sep 2002 4 Jul 2 Jul 20 Sep 16 Sep 2003 27 Jun 2 Jul 27 Sep 19 Sep 2004 8 Jul 26 Jun 27 Sep 26 Sep 2005 29 Jun 4 Jul 29 Sep 27 Sep 2006 9 Jul 30 Jun 27 Sep 6 Oct 2007 26 Jun 27 Jun 2 Oct 30 Sep Mean 30 Jun (±8) 5 Jul (±8) 21 Sept (±9) 19 Sept (±9)

  

58

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59

   Figure 2. Spatial pattern of the

 clim

atology of surface air tem

perature (SA

T; unit: °K) of selected

 pen

tads in and arou

nd the

 Asian

 sum

mer 

mon

soon

 regim

e. M

igratio

n and locatio

n of the

 high SA

T may be no

ted. Location of the

 core area

 of highest tempe

rature is as: P31

 over IG

Ps; P38

 over Ra

jasthan‐eastern Saud

i Arabia; P45

 over southe

rn Pakistan‐Saud

i Arabia; and

 P55

 over trop

ical Indo

‐Pacific sector. 

  

60

   Figure 3.   Spatia

l pattern of the clim

atology of m

ean sea level p

ressure (M

SLP; unit: hPa) of selected pe

ntads in and

 aroun

d the Asian

 sum

mer 

mon

soon

 regim

e. M

igratio

n and locatio

n of th

e intense low M

SLP area

 (mon

soon

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vergen

ce zon

e; M

CZ) m

ay be no

ted. Location of 

core area of lowest MSLP is as: P31

 over IGPs; P

38 over Ra

jasthan‐Pakistan; P

45 over Ra

jasthan‐Pakistan; and

 P55

 over central Ind

ia‐

northw

estern Bay of B

engal. 

   

  

61

   Figure 4.  Spatia

l pattern of the clim

atology of lo

wer tropo

sphe

re tem

perature (85

0‐50

0 hP

a; unit: °K) of selected

 pen

tads in

 and

 aroun

d the 

Asian

 sum

mer m

onsoon

 regim

e. M

igratio

n and locatio

n of the

 high lower tropo

sphe

ric tempe

rature m

ay be no

ted. Location of the

 core area of low

est trop

osph

eric tem

perature is as:  P3

1 over sou

th Pakistan‐Arabia and eastern Tibe

t; P38

 over south Iran

 and

 eastern Tibe

t; P45

 over eastern Tibe

t; and

 P55

 over Arabia‐South Ch

ina Sea. 

  

62

   Figure 5. Spatial pattern of the

 clim

atology of low

er tropo

sphe

re thickne

ss (un

it: m

) of selected pe

ntads in and

 aroun

d the Asian

 sum

mer 

mon

soon

 regim

e. M

igratio

n and locatio

n of the

 large trop

osph

eric thickne

ss m

ay be no

ted. Location of la

rgest lower tropo

sphe

ric 

thickness is over the respectiv

e area

 of h

ighe

st lower trop

osph

eric te

mpe

rature. 

  

63

   Figure 6. S

patia

l pattern of the clim

atology of upp

er tropo

sphe

re tem

perature (un

it: °K) of selected

 pen

tads in

 and

 aroun

d the Asian

 sum

mer 

mon

soon

 regim

e. M

igratio

n and locatio

n of the

 high up

per trop

osph

eric tem

perature m

ay be no

ted. The

 core area

 of highest up

per 

trop

osph

eric te

mpe

rature is as: P31

 over eastern India ‐Myanm

ar; P

38 over IGPs; P45

 over western IG

Ps; and

 P55

 over eastern IGPs. 

  

64

   Figure 7.  Spatia

l pattern of the

 clim

atology of upp

er tropo

sphe

re thickne

ss (un

it: m

) of selected pe

ntads in and

 aroun

d the Asian

 sum

mer 

mon

soon

 regim

e. M

igratio

n and locatio

n of the

 large up

per trop

osph

eric thickne

ss m

ay be no

ted. Location of core area

 of highest 

largest u

pper trop

osph

eric th

ickness is over the respectiv

e  area

 of h

ighe

st upp

er trop

osph

eric te

mpe

rature. 

 

  

65

   Figure 8.  Spatial p

attern of the clim

atology of geo

potential h

eight of 850

 hPa

 (un

it: m

) of selected pe

ntads in and

 aroun

d the Asian

 sum

mer 

mon

soon

 regim

e. M

igratio

n and locatio

n of the

 high geop

oten

tial height of the

 850

‐hPa

 level m

ay be no

ted. Location of core area

 of 

lowest he

ight of  the 85

0 hP

a isob

aric level is as: P

31 over central P

akistan; P38

 over Afghanistan

‐IGP; P45

 Afghanistan

‐Pakistan; and

 P5

5 over east coast of Ind

ia‐NW Bay of B

engal. 

 

  

66

   Figure 9. Spatial p

attern of the clim

atology of geo

potential h

eight of 200

 hPa

 (un

it: m

) of selected pe

ntads in and

 aroun

d the Asian

 sum

mer 

mon

soon

 regim

e. M

igratio

n and locatio

n of the

 high geop

oten

tial he

ight of the 20

0‐hP

a level may be no

ted. Location of highe

st 

geop

oten

tial height of the

 200

 hPa

 level is as: P

31 over Myanm

ar‐sou

thwestern China; P

38 over Saud

i Arabia‐southw

estern China; P

45 

over sam

e as during P3

8; and

 P55

 over Myanm

ar‐cen

tral Indo

‐china. 

67

Figure 10. Streamlines at different layers of the troposphere during P22-P25 (16 April – 5

May; southeast trades enter into the northern hemisphere over equatorial Indian Ocean; unit: m/sec). The lower layer convergence is located over upper Yangtze River basin and Indo-China peninsula; and upper layer divergence over Indo-China peninsula.

68

Figure 11. Streamlines at different layers of the troposphere during P29-P32 (25 May – 9

Jun; beginning of the onset phase over Indian subcontinent; unit: m/sec). The lower layer convergence occurs over the upper Yangtze River basin and NE India-Bangladesh; and upper layer divergence over NE India-Bangladesh.

69

Figure 12. Streamlines at different layers of the troposphere during P33-P36 (10 Jun – 29

Jun; middle of the northward advance; unit: m/sec). Both the lower layer convergence over Pakistan and THIKHIHILS and upper layer divergence occurs over the Nepal-Himalaya.

70

Figure 13. Streamlines at different layers of the troposphere during P38-P41 (5 Jul – 24

Jul; end of advance-onset over northwest India and Pakistan; unit: m/sec). The lower layer convergence occurs over Pakistan-Afghanistan and western; the upper layer divergence over western Himalaya.

71

Figure 14. Streamlines at different layers of the troposphere during P48-P51 (24 August –

12 September; established phase; unit: m/sec). The lower layer convergence occurs over Pakistan-Afghanistan and eastern Tibet; and upper layer divergence over eastern Himalaya.

72

Figure 15. Streamlines at different layers of the troposphere during P54-P57 (23

September–12 October; middle of withdrawal phase; unit: m/sec). The lower layer convergence occurs over the south Indian peninsula-Bay of Bengal-South China Sea sector; and upper layer divergence over northeast India-western North Pacific sector.

73

Figure 16. Streamlines at different layers of the troposphere during P60-P63 (23

October–11 November; end of the boreal monsoon; unit: m/sec). The lower layer convergence occurs over Sri Lanka-western equatorial Pacific Ocean sector; and upper layer divergence over western North Pacific.

74

Figure 17. Streamlines at different layers of the troposphere during P72-P2 (22 December

– 10 January; peak of Australian monsoon; unit: m/sec). The lower layer convergence occurs over eastern equatorial Indian Ocean-northwest South Pacific; and upper layer divergence over western North Pacific.

  

75

Fi

gure

18.

Geo

grap

hica

l loc

atio

n fo

r eac

h of

the

10 g

ener

al a

nd re

gion

al c

ircul

atio

n pa

ram

eter

s tha

t are

con

side

red

I the

pre

sent

stud

y.

See

the

tabl

e of

Abb

revi

atio

n/A

cron

yms f

or fu

ll na

me

of th

e lo

catio

n

  

76

Fi

gure

19.

Geo

grap

hica

l loc

atio

n of

the

19 s

ubre

gion

s. Th

e bl

ue is

olin

es in

dica

te c

limat

olog

ical

ons

et d

ate

(a),

and

red

with

draw

al

date

(b)

. The

fig

ure

insi

de th

e ar

row

s is

the

GA

RA

CII

(G

ener

al a

nd R

egio

nal A

tmos

pher

ic C

ircul

atio

n In

tens

ity I

ndex

) va

lues

at t

he ti

me

of re

spec

tive

onse

t and

with

draw

al d

ates

.

  

77

13

5

14

0

14

5

15

0

15

5

16

0

16

5

17

0S

ub

regi

on 1

LE

GE

ND

Ob

jec

tive

ly d

ete

rmin

ed

o

ns

et

da

te A

ctu

al o

ns

et

da

te f

rom

I

MD

ch

art

s T

he

me

an

13

5

14

0

14

5

15

0

15

5

16

0

16

5

17

0

CC

=0

.78

CC

=0

.81

Yea

r

(onset date) Day-in-yearS

ub

regi

on 2

14

0

14

5

15

0

15

5

16

0

16

5

17

0

CC

=0

.83

Su

bre

gion

3

14

0

14

5

15

0

15

5

16

0

16

5

17

0

CC

=0

.78

Su

bre

gion

4

14

0

14

5

15

0

15

5

16

0

16

5

17

0

CC

=0

.80

Su

bre

gion

5

14

5

15

0

15

5

16

0

16

5

17

0

17

5

CC

=0

.71

Su

bre

gion

6

14

5

15

0

15

5

16

0

16

5

17

0

17

5

CC

=0

.71

Su

bre

gion

7

15

0

15

6

16

2

16

8

17

4

18

0

CC

=0

.79

Su

bre

gion

8

15

0

15

5

16

0

16

5

17

0

17

5

18

0

CC

=0

.59

Su

bre

gion

9

15

5

16

0

16

5

17

0

17

5

18

0

CC

=0

.53

Su

bre

gion

10

16

0

17

0

18

0

19

0

CC

=0

.59

Su

bre

gion

11

16

0

17

0

18

0

19

0

CC

=0

.49

Su

bre

gion

12

15

5

16

0

16

5

17

0

17

5

18

0

18

5

CC

=0

.60

Su

bre

gion

13

15

0

15

5

16

0

16

5

17

0

17

5

18

0

CC

=0

.56

Su

bre

gion

14

16

8

18

0

19

2

20

4

21

6

22

8

CC

=0

.47

Su

bre

gion

15

16

0

17

0

18

0

19

0

20

0

CC

=0

.36

Su

bre

gion

16

19

50

19

60

19

70

19

80

19

90

20

00

15

5

16

0

16

5

17

0

17

5

18

0

18

5

19

0

CC

=0

.52

Su

bre

gion

17

19

60

19

70

19

80

19

90

20

00

14

0

14

5

15

0

15

5

16

0

16

5

17

0

CC

=0

.55

Su

bre

gion

18

19

60

19

70

19

80

19

90

20

00

16

0

17

0

18

0

19

0

20

0

.

CC

=0

.37

Su

bre

gion

19

Fig

ure

20. A

ctua

l (re

d) a

nd o

bjec

tivel

y de

term

ined

(bla

ck; a

fter c

orre

ctin

g fo

r bia

s) o

nset

dat

es o

f the

sum

mer

mon

soon

for t

he 1

9

su

breg

ions

.

  

78

27

0

27

5

28

0

28

5

29

0

29

5

30

0

30

5

31

0

.

Su

breg

ion

1

LE

GE

ND

Ob

jec

tive

ly d

ete

rmin

ed

o

ns

et

da

te A

ctu

al o

ns

et

da

te f

rom

I

MD

ch

art

s T

he

me

an

26

52

70

27

52

80

28

52

90

29

53

00

30

53

10

31

5

Yea

r

(Withdrawal date) Day-in-yearS

ubr

egio

n 2

27

0

27

5

28

0

28

5

29

0

29

5

30

0

30

5

CC

=0.

60

Su

breg

ion

3

27

5

28

0

28

5

29

0

29

5

30

0

30

5

CC

=0

.58

Sub

regi

on 4

27

0

27

5

28

0

28

5

29

0

29

5

30

0

CC

=0

.44

Su

bre

gion

5

27

0

27

5

28

0

28

5

29

0

29

5

30

0

CC

=0

.45

Su

breg

ion

6

25

52

60

26

52

70

27

52

80

28

52

90

29

53

00

30

53

10

CC

=0

.40

Su

breg

ion

7

25

2

25

8

26

4

27

0

27

6

28

2

28

8

29

4

30

0

CC

=0.

50

Su

bre

gion

8

25

0

25

5

26

0

26

5

27

0

27

5

28

0

28

5

29

0

29

5

CC

=0

.48

Su

breg

ion

9

27

0

27

5

28

0

28

5

29

0

29

5

30

0

30

5

CC

=0

.55

Su

bre

gion

10

25

0

26

0

27

0

28

0

29

0

CC

=0

.82

Sub

regi

on 1

1

26

0

27

0

28

0

29

0

CC

=0

.56

Su

bre

gion

12

26

5

27

0

27

5

28

0

28

5

29

0

29

5

30

0

CC

=0

.48

Sub

regi

on 1

3

26

5

27

0

27

5

28

0

28

5

29

0

29

5

30

0

CC

=0

.47

Su

bre

gion

14

24

0

25

2

26

4

27

6

28

8

CC

=0

.15

Su

breg

ion

15

25

0

26

0

27

0

28

0

29

0

30

0

CC

=0

.27

Su

bre

gion

16

19

50

19

60

19

70

19

80

19

90

20

00

26

0

26

5

27

0

27

5

28

0

28

5

29

0

CC

=0

.43

Sub

regi

on 1

7

19

60

19

70

19

80

19

90

20

00

25

52

60

26

52

70

27

52

80

28

52

90

29

53

00

30

53

10

CC

=0

.28

Su

bre

gion

18

19

60

19

70

19

80

19

90

20

00

24

0

25

0

26

0

27

0

28

0

29

0

CC

=0

.21

Su

breg

ion

19

Fi

gure

21.

Act

ual (

red)

and

obj

ectiv

ely

dete

rmin

ed (b

lack

; afte

r cor

rect

ing

for b

ias)

with

draw

al d

ates

of t

he s

umm

er m

onso

on fo

r the

19

subr

egio

ns.