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02-03-2015 R. Ezhilraman, PGT-Social Science 1
R. Ezhilraman
PGT-Social Science
JNV Lepakshi
Subject: Geography
For Class: IX
What is Climate?
Climate is the characteristic condition of theatmosphere near the earth's surface at a certainplace on earth.
It refers to the sum total of weather conditions andvariation over a large area for a long period of time.
It is the long-term weather of that area whichremains at least 30 years.
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Weather refers to the state ofatmosphere over an area atany point of time. Theelements of both weatherand climate are same. It is thecombination of temperature,humidity, precipitation, wind,cloudiness and otheratmospheric conditions at aspecific time.
What is Weather?
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Monsoon
The word monsoon is derived from the Arabic word ‘mausim’which literally means season.
‘Monsoon’ refers to the seasonal reversal in the winddirection during a year.
The World is divided into a number of Climatic Regions. TheClimate of India is described as the ‘monsoon’ type. This typeof climate is found in South and Southeast Asia. But, there areperceptible regional variations in climatic conditions withinthe country.
Two important elements viz., temperature and precipitation,often vary from place to place and season to season.
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Difference in Temperature
In summer, the temperature in parts of Rajasthan Desert
is 50°C, and it is around 20°C in Pahalgam in J & K. On
a winter night, temperature at Drass in J & K may less
than -45°C, and at Tiruvananthapuram it may be of
22°C.
In some places temperature between day and
night temperature differs. In the Thar Desert, it rise to
50°C, in day and drop down to near 15°C in night. But
in the Andaman and Nicobar islands or in Kerala, there
is no much difference in day and night temperatures.
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Precipitation
Precipitation varies in its form, types and amount and
seasonal distribution. It is in the form of snowfall in the
upper parts of Himalayas, it rains over the rest of the
country. The annual precipitation varies from 400 cm in
Meghalaya to less than 10 cm in Ladakh and western
Rajasthan. Most parts of the country receive rainfall from
June to September. But Tamil Nadu coast gets rain during
October and November.
Rainfall generally decrease from east to west in the
Northern Plains. These variations have given rise to
variety in lives of people, their food, clothes and houses.
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Vegetation
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Vegetation can affect both temperature and
the precipitation patterns in an area.
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FACTORS AFFECTING CLIMATE
RELATED TO LOCATION RELATED TO AIR
PRESSURE & WIND
•Latitude
•The Himalayan Mt.
•Distribution of Land & water
•Altitude
•Distance from Sea
Surface pressure & wind
Upper air circulation
Western cyclones•Relief Features
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Latitude
Latitude is thedistance a placelies north orsouth of theequator and ismeasured by animaginary linecalled lines oflatitude.
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EQUATORIAL REGION
LATITUDE
High Temp
Low range
High range
of Temp
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Latitude
As latitude increases, the intensity of solar energy
decreases. Due to curvature of the Earth, the
amount of solar energy varies according to latitude.
In India, the Tropic of Cancer passes through the middleof the country from the Rann of Kuchchh in the west toMizoram in the east.
Almost half of the country, lying south of the Tropic ofCancer, belongs to the tropical area. All the remainingarea, north of the Tropic, lies in the sub-tropics.Therefore, India’s climate has characteristics of tropicalas well as subtropical climates.
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Tropical, Temperate and Polar Zones
• The tropical zone is between 23.5o north (the tropic of
Cancer) and 23.5o south (the tropic of Capricorn) of the
Equator. The Sun’s rays are most intense and the
temperatures are always warm.
• The temperate zones are between 23.5o and 66.5o
north and between 23.5o and 66.5o south of the
Equator. The Sun’s rays strike Earth at a smaller angle
than near the Equator.
• Polar zones are between 66.5o north and south
latitudes and the poles. The sun’s rays strike Earth at a
very small angle in the polar zones.
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Highland Climates
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In general, highland climates are cooler and wetter than
nearby areas at lower elevations.
Earth’s Major Climate Zones
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North Frigid Zone
Temperate Zone
Temperate Zone
South Frigid Zone
Torrid Zone
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AGRA
160C in Jan
DARJILING40C in January
ALTITUDE
HIGH ALTITUDE
LOW ALTITUDE
Temperature decreased from low to high altitude
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Air Temperature decreases with altitude.
As elevation increases, the air gets cooler because ofthe energy drawn from the surroundings.
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Factors That Affect Climate
Water Bodies
Large bodies of water such as lakes and oceans have an
important effect on the temperature of an area because
the temperature of the water body influences the
temperature of the air above it.
Atmospheric Circulation
Global winds are another factor that influences climate
because they distribute heat and moisture around Earth.
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Solar Activity
When the Sun is most active, it contains dark blemishes
called sunspots. The formation of sunspots appears to
correspond with warm periods in Europe and North
America.
Earth Motions
Geographic changes in Earth’s land and water bodies
cause changes in climate. Changes in the shape of
Earth’s orbit and the tilt of Earth on its axis are other
Earth motions that affect global climates.
Natural Processes That Change Climates
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Human Impact on Climate Changes
The Greenhouse Effect
The greenhouse effect is a natural warming of both
Earth’s lower atmosphere and Earth’s surface from solar
radiation being absorbed and emitted by the
atmosphere.
Global Warming
As a result of increased levels of carbon dioxide and
other greenhouse gases, global temperatures have
increased. This increase is called global warming.
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The Pressure and Surface Winds
The pressure and wind system of any area depend on the latitudeand altitude of the place. It influences the temperature and rainfallpattern.
The climate and weather conditions in India are governed by theatmospheric conditions like:
• Pressure and surface winds;
• Upper air circulation; and
• Western cyclonic disturbances and tropical cyclones.
India lies in the north easterly winds region. These winds originatefrom the subtropical high-pressure belt of the northernhemisphere. They blow south, get deflected to the right due to theCoriolis force and move towards equatorial low-pressure area.
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NORTH-EAST
TRADE WIND
SOUTH-EAST
TRADE WIND
INTER TROPICAL CONVERGENCE ZONE
SUB TROPICAL HIGH PRESSURE
SUB TROPICAL HIGH PRESSURE
SUB TROPICAL LOW PRESSURE
SUB TROPICAL LOW PRESSURE
POLAR HIGH
POLAR HIGH
SURFACE WIND
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AIR MASSES CIRCULATE GLOBALLY
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• At the Equator, temperatures are relativelyhigh. Land and water masses heat up and as aresult these warm the air over them.
• Air heated at the equatorial region rises tothe top of the atmosphere.
• More air rising beneath it forces the air massto spread north and south toward the poles.
Coriolis Effect
• The rotation of the Earth causes all movingobjects in the Northern Hemisphere,including air mass, to deflect to the right andthose in the Southern Hemisphere to move tothe left.
• This Coriolis effect is absent at the Equator.
• Coriolis Force- prevents a direct simple flowfrom the Equator to the Poles.
• This is also known as ‘Ferrel’s Law’.
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The Pressure and Surface Winds in India
The pressure and wind conditions in India is unique. During winter,there is a high-pressure in the north of the Himalayas. Cold drywinds blow from this region to the low-pressure areas over theoceans to the south. In summer, a low-pressure area develops overinterior Asia and in north-western India. This causes a completereversal of the direction of winds during summer. Air moves fromthe high-pressure area over the southern Indian Ocean, in a south-easterly direction, crosses the equator, and turns right towards thelow-pressure areas over the Indian subcontinent. These are knownas the Southwest Monsoon winds. These winds blow over thewarm oceans, gather moisture and bring widespread rainfall overthe mainland of India.
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ARABIAN
SEA
BAY OF
BENGAL
INDIAN OCEAN
LOW AND HIGH PRESSURE
HIGH PRESSURE
IN WINTER
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MUMBAI
CHENNAI
KOLKOTA
DELHI
SIMLA
DISTANCE FROM SEA
Coastal areas have equable climate where
as Interior parts have extreme climate.
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Relief
• Relief too plays a major role in determiningthe climate of a place. High mountains actas barriers for cold or hot winds; they mayalso cause precipitation if they are highenough and lie in the path of rain-bearingwinds. The leeward side of mountainsremains relatively dry.
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Receives high
rainfall
Receives low
rainfall
RELIEF
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RELIEF
The Rain Shadow Effect
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Jet Stream
• The upper air circulation in India is dominatedby a westerly flow, known as the jet stream.
• These are a narrow belt of high altitude (above12,000 m) westerly winds in the troposphere.Their speed varies from about 110 km/h insummer to about 184 km/h in winter.
• Many jet streams have been identified. Themost constant are the mid-latitude and the subtropical jet stream.
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TIBET
JET STREAM IN WINTER
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Jet Stream
Jet streams are located at 27°-30° north latitude, areknown as subtropical westerly jet streams. Over India,these jet streams blow south of the Himalayas, allthrough the year except in summer. The western cyclonicdisturbances experienced in the north and north-westernparts of the country are brought in by this westerly flow.In summer, the subtropical westerly jet stream movesnorth of the Himalayas with the apparent movement ofthe Sun. An easterly jet stream, called the tropicaleasterly jet stream blows over peninsular India,approximately over 14°N during the summer.
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JET STREAM IN SUMMER
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Western Disturbances
• The western cyclonic disturbances are weatherphenomena of the winter months brought in by thewesterly flow from the Mediterranean region. Theyusually influence the weather of the north and north-western regions of India. Tropical cyclones occur duringthe monsoon as well as in October - November, and arepart of the easterly flow. These disturbances affect thecoastal regions of the country.
• Thus very often the coast of Orissa and Andhra Pradeshare affected by those disasters.
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WESTERN DISTURBANCE
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OCEAN CURRENTS
Solar energy, wind, and Earth’s rotation creates Ocean currents
Current- the systematic patters of water movement.
Gyres- two great circular water motion.
Northern Hemisphere- the ocean current moves clockwise.
Southern Hemisphere- the ocean current move anti-clockwise.
Trade winds push warm surface waters westward at the equator.
As the waters encounter the continents, they split into north-and south-flowing currents along the eastern coast, formingnorth and south gyres.
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Surface Water blown by the winds at point A will weirs to theright of its initial path and continue eastward. Water at pointB weirs to the right and continues westward.
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Winds driven by uneven solar heating and Earth’s spin, drive themovement of the ocean’s surface currents. The prime movers are thepowerful westerlies and the persistent trade winds (easterlies)
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The Köppen climate classification system uses
mean monthly and annual values of temperature and
precipitation to classify climates. According to the Köppen classification, the earth can be
divided into several major climatic zones and bands:
The Köppen Climate Classification System
Tropical climate
Subtropical climate
Arid climate
Equatorial climate
Semiarid climate
Mediterranean climate
Temperate climate
Oceanic climate
Continental climate
Subarctic climate
Polar climate
Climate of Antarctica02-03-2015 R. Ezhilraman, PGT-Social Science 45
Tropical Climate
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Subtropical Climate
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Arid Climate
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Equatorial Climate
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Semiarid Climate
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Mediterranean Climate
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Temperate Climate
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Oceanic Climate
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Continental Climate
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Subarctic Climate
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Polar Climate
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Polar Climate02-03-2015 R. Ezhilraman, PGT-Social Science 57
Polar climates are those in which the mean temperature
of the warmest month is below 10oC.
Climate of Antarctica
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The Indian Monsoon
The climate of India is strongly influenced bymonsoon winds. The sailors who came to India inhistoric times were one of the first to have noticedthe phenomenon of the monsoon. They benefitedfrom the reversal of the wind system as they cameby sailing ships at the mercy of winds. The Arabs,who had also come to India as traders named thisseasonal reversal of the wind system ‘monsoon’.
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Atmospheric Conditions over the Indian Subcontinent
in the Month of January
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Atmospheric Conditions over the Indian Subcontinent
in the Month of June
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Facts of Mechanism of the Monsoons
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In India, the monsoons are experienced in the tropical area
roughly between 20°N and 20°S. The Following facts are the
Mechanism of the Monsoons.
(a) The differential heating and cooling of land and water
creates low pressure on the landmass of India while the
seas around experience comparatively high pressure.
(b) The shift of the position of Inter Tropical Convergence Zone
(ITCZ) in summer, over the Ganga plain (this is the equatorial
trough normally positioned about 5°N of the equator. It is also
known as the monsoon-trough during the monsoon season).
Inter Tropical Convergence Zone (ITCZ)
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The Inter Tropical Convergence Zone
(ITCZ) is a broad trough of low pressure
in equatorial latitudes. This is where the
northeast and the southeast trade winds
converge. This convergence zone lies
more or less parallel to the equator but
moves north or south with the apparent
movement of the sun.
Facts of Mechanism of the Monsoons
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(c) The presence of the high-pressure area, east of
Madagascar, nearly at 20°S over the Indian Ocean. The
intensity of this high-pressure area affects the Indian
Monsoon.
(d) The Tibetan plateau gets intensely heated during
summer, results in strong vertical air currents and the
formation of low pressure over the plateau at about 9 km
above sea level.
(e) The movement of the westerly jet stream to the
north of the Himalayas and the presence of the tropical
easterly jet stream over the Indian peninsula during
summer.
Southern Oscillation
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The changes in the pressure conditions over the southern
oceans also affect the monsoons. When the tropical eastern south
Pacific Ocean experiences high pressure, the tropical eastern Indian
Ocean experiences low pressure. But sometimes, there is a reversal in
the pressure conditions and the eastern Pacific has lower pressure in
comparison to the eastern Indian Ocean. This periodic change in
pressure conditions is known as the Southern Oscillation or SO.
The difference in pressure over Tahiti in Pacific Ocean and Darwin in
northern Australia of Indian Ocean is predicted the intensity of the monsoons.
If the pressure differences were negative, it would mean below average and
late monsoons. A feature connected with the SO is the El Nino, a warm ocean
current that flows past the Peruvian Coast, in place of the cold Peruvian
current, every 2 to 5 years. The changes in pressure conditions are connected
to the El Nino. Hence, the phenomenon is referred to as ENSO (El Nino
Southern Oscillations).
DarwinTahiti
SOUTHERN OSCILLATION
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Effect of El Niño
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El Nino is a name given to the
periodic development of a warm
ocean current along the coast of
Peru as a temporary replacement of
the cold Peruvian current. ‘El Nino’
is a Spanish word meaning ‘the
child’, and refers to the baby Christ,
as this current starts flowing during
Christmas. The presence of the El
Nino leads to an increase in sea-
surface temperatures and
weakening of the trade winds in the
region.
Homboldt Cold
Current
EL-NINO EFFECTS
1990
Delay in
Monsoon
Equatorial Warm
Current
El-Nino
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Beginning of the Monsoon
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The duration of the monsoon is between 100-120 days from
early June to mid-September.
During its arrival, the normal rainfall increases suddenly and
continues constantly for several days. This is known as the
‘burst’ of the monsoon, and can be distinguished from the
pre-monsoon showers.
The monsoon arrives at the southern tip of the Indian
peninsula generally by the first week of June.
Subsequently, it proceeds into two –
(i) the Arabian Sea branch and
(ii) the Bay of Bengal branch.
Beginning of the Monsoon
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The Arabian Sea branch reaches Mumbai about ten days later on
approximately the 10th of June. This is a fairly rapid advance.
The Bay of Bengal branch also advances rapidly and arrives in Assam
in the first week of June. The lofty mountains causes the monsoon
winds to deflect towards the west over the Ganga plains.
By mid-June the Arabian Sea branch of the monsoon arrives over
Saurashtra-Kuchchh and the central part of the country. The Arabian
Sea and the Bay of Bengal branches of the monsoon merge over the
north-western part of the Ganga plains.
Delhi generally receives the monsoon showers from the Bay of Bengal
branch by the end of June (tentative date is 29th of June). By the July
first week, western Uttar Pradesh, Punjab, Haryana and eastern
Rajasthan experience the monsoon. By mid-July, the monsoon reaches
Himachal Pradesh and the rest of the country.
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End of the Monsoon
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Withdrawal or the retreat of the monsoon is a more gradual
process. The withdrawal of the monsoon begins in north-western
states of India by early September. By mid-October, it withdraws
completely from the northern half of the peninsula. Then it
quickly withdraw from the southern half of the peninsula. By
early December, the monsoon has totally withdrawn from the
country.
The islands receive the very first monsoon showers, from south to
north, between the last week of April and the first week of May.
Then it withdraw from north to south during the first week of
December to the first week of January. By this time, the other
parts of the country is already influencing the winter monsoon.
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RHYTHM OF SEASONS
COLD WEATHER
RETREATING MONSOONHOT WEATHER
SOUTH WEST MONSOON
Let us discuss each of them individually
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76
The monsoon type of climate is characterised by a distinct
seasonal pattern. The weather conditions greatly change from one
season to the other. These changes are particularly noticeable in
the interior parts of the country. But, the coastal areas do not
experience much variation in temperature though there is variation
in rainfall pattern.
In India, Four main seasons can be identified:
(i) the cold weather season,
(ii) the hot weather season,
(iii)the advancing monsoon and(iv) the retreating monsoon with some regional variations.
COLD WEATHER SEASON
► It extends from
December to February.
►Vertical sun rays shift
towards southern
hemisphere.
►North India experiences
intense cold where as
this season is not well
defined in south India.
►Light wind blow makes
this season pleasant in
south India.
►Occasional tropical
cyclone visit eastern
coast in this season.
Tropical Cyclone
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78
The cold weather season begins from mid- November in northern India and
stays till February. December and January are the coldest months. The
temperature decreases from south to the north. The average temperature of
Chennai, on the eastern coast is between 24°-25° Celsius, while in the northern
plains, it ranges between 10°-15° Celsius. Days are warm and nights are cold.
Frost is common in the north and the higher slopes of the Himalayas experience
snowfall.
During winter, the northeast trade winds blow from land to sea. So, most part of
the country faces a dry season. Some amount of rainfall occurs on the Tamil
Nadu coast from these winds as, trade winds blow from sea to land.
In the northern part of the country, a feeble high-pressure region develops, with
light winds moving outwards from this area. Influenced by the relief, these
winds blow through the Ganga valley from the west and the northwest. The
weather is normally marked by clear sky, low temperatures and low humidity
and feeble, variable winds.
250
C
250
C 200
C
200
C
200
C
150
C200
C
100
C`
TEMPERATURE- JANUARY
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PRESSURE- JANUARY
101
4
HIGH
PRESSURE
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81
In the northern plains, there is the inflow of cyclonic
disturbances from the west and the northwest. These low-
pressure systems, from the Mediterranean Sea and western
Asia and move into India, along with the westerly flow. They
cause the winter rains (locally known as ‘mahawat’) over the
plains and snowfall in the mountains. Although the amount of
rainfall is small, it is more importance for cultivating the ‘rabi’
crops.
But, the peninsular region does not have a well-defined cold
season. There is rare seasonal change in temperature
pattern during winters due to the moderating influence of the
sea.
WIND DIRECTION- WINTER
Bay of Bengal
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WINTER RAINFALL
RAINFALL DUE
TO WESTERN
DISTURBANCES
RAINFALL DUE
TO NORTH EAST
WIND
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Winter is cold.
Children dress warmly to play in the snow.
Animals head to their winter homes.
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HOT WEATHER SEASON
► It extends from March to
May.
► Vertical sun rays shift
towards Northern
hemisphere.
► Temperature rises
gradually from south to
north.
► Highest Temperature
experiences in Karnataka
in March, Madhya
Pradesh in April and
Rajasthan in May.
March 300C
April 380C
May 480C
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86
Due to the apparent northward movement of the Sun, the global
heat belt shifts northward. So, from March to May, it is hot weather
season in India. In March, the highest temperature is about 38°C, in
Deccan plateau. In April, temperatures in Gujarat and Madhya
Pradesh are around 42°C. In May, 45°C temperature is common in
the north-western parts of the country. In peninsular India,
temperatures remain lower due to the moderating influence of the
oceans.
The summer months experience rising temperature and falling air
pressure in the northern part of the country. By the end of May, an
elongated low-pressure area develops in the region extending from
the Thar Desert in the northwest to Patna and Chotanagpur plateau
in the east and southeast. Circulation of air begins to set in around
this trough.
TEMPERATURE- JULY
250
C
300
C
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PRESSURE- JULY
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LOO
KALBAISAKHI
BARDOLI
CHHEERHA
MANGO
SHOWER
BLOSSOM
SHOWER
STORMS IN HOT WEATHER SEASON
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An important feature of the summer season is the ‘loo’. These are
strong, gusty, hot, dry winds blowing during the day, sometimes till
late evening over the north and North-western India. Direct
exposure to these winds may be harmful. Dust storms are very
common during May in northern India. These storms bring
temporary relief as they lower the temperature and may bring light
rain and cool breeze. This is also the season for localised
thunderstorms, associated with violent winds. In West Bengal,
these storms are known as the ‘Kaal Baisakhi’.
By close of the summer season, pre-monsoon showers are common
especially, in Kerala and Karnataka. They help in the early ripening
of mangoes, and are often referred to as ‘mango showers’.
Long, hot days.
Summer fruit and vegetables are ready to be picked.
You see many bees and butterflies fly flower to flower.
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Advancing Monsoon (The Rainy Season)
SOUTH WEST MONSOON SEASON
► It extends from June to
September.
► Intense heating in north
west India creates low
pressure region.
► Low pressure attract the
wind from the surrounding
region.
► After having rains for a
few days sometime
monsoon fails to occur for
one or more weeks is
known as break in the
monsoon.
HIGH TEMPERATURELOW PRESSURE
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INTER TROPICAL CONVERGENCE ZONEEQUATOR
MONSOON WIND
Arabian sea
BranchBay of Bengal
Branch
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ONSET OF SW MONSOON
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By early June, the low-pressure condition over the northern plains
attracts the trade winds of the southern hemisphere. These south-
east trade winds originate over the warm subtropical areas of the
southern oceans. These winds are strong and blow at an average
velocity of 30 kmph. With the exception of the extreme north-west,
the monsoon winds cover the country in about a month.
The south-west monsoon entirely changes the weather in India. The
Western Ghats receives heavy rainfall, more than 250 cm. The rain
shadow areas like Deccan Plateau and parts of Madhya Pradesh
also receives rain. The north-eastern part of the country receives
the maximum rainfall. Mawsynram in the southern ranges of the
Khasi Hills receives the highest average rainfall in the world.
Rainfall in the Ganga valley decreases from the east to the west.
Rajasthan and parts of Gujarat get scanty rainfall.
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The monsoon rains take place only for a few days at a time. They
are interspersed with rainless intervals. These breaks in monsoon
are related to the movement of the monsoon trough. The trough and
its axis keep on moving northward or southward, which determines
the spatial distribution of rainfall. Whenever the axis shifts closer
to the Himalayas, widespread rain occur in the mountainous
catchment areas of the Himalayan rivers, which also cause floods.
The frequency and intensity of tropical depressions determine the
amount and duration of monsoon rains. These depressions form at
the Bay of Bengal and cross over to the mainland. The depressions
follow the axis of the “monsoon trough of low pressure”. It causes
heavy floods in one part, and droughts in the other. Sometimes it
disturbs the farming schedule of millions of farmers all over the
country.
► It extends from October
to November
►Vertical sun rays start
shifting towards Northern
hemisphere.
►Low pressure region shift
from northern parts of
India towards south.
►Owing to the conditions
of high temperature and
humidity, the weather
becomes rather
oppressive. This is
commonly known as the
‘October heat’
RETREATING MONSOON SEASON
LOW PRESSURE
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WITHDRAWAL OF MONSOON
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Parts of western coast and north-eastern India receive over about
400 cm of rainfall annually. But, in western Rajasthan and
adjoining parts of Gujarat, Haryana and Punjab it is less than 60
cm. Rainfall is equally low in the interior of the Deccan plateau,
and east of the Sahyadris. Because of low precipitation found
around Leh in Jammu and Kashmir. The rest of the country
receives moderate rainfall. Snowfall is restricted to the Himalayan
region.
Based on the nature of monsoons, the annual rainfall is highly
variable from year to year. Variability is high in the regions of low
rainfall such as parts of Rajasthan, Gujarat and the leeward side of
the Western Ghats. Similarly, the areas of high rainfall are often
affected by floods, areas of low rainfall are drought-prone.
DISTRIBUTION OF RAINFALL
> 200cm
100-200cm
50-100 cm
< 50cm
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The sun shines more and the days begin to get warmer.
Spring is a time when baby animals are born.
Spring is a time when plants and trees wake up after a long winters nap.
Spring showers help to warm the earth, moisten the soil, helping new plants to grow.
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Leaves change to yellow, orange, and red.
Picking fruit and vegetables.
Animals get ready for winter.
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The Himalayas protect the subcontinent from extremely cold winds
from central Asia. This enables northern India to have uniformly
higher temperatures when compared to other areas on the same
latitudes.
Similarly, the peninsular plateau, under the influence of the sea
from three sides, has moderate temperatures.
The unifying influence of the monsoon on the Indian subcontinent
is quite perceptible. The seasonal alteration of the wind systems
and the associated weather conditions provide a rhythmic cycle of
seasons.
The Indian landscape, its animal and plant life, its entire
agricultural calendar and the life of the people, including their
festivities, revolve around this phenomenon.
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