551·58: 551'508,99(545'5)

Radar-Climatoloi:Y of Delhi and neighbourhood: Occurrenceof severe weather

S.)I. KlTLSHRESTHA and P. S. JAIN

M eUorologiool Office, New n elhi

(Receit'ed 25 February 1966)

ABSTRACT. Occurrence ofee vere weather, observed within a range of 200miles around Delhi, has been iDT&.lltigll.ted with reference to the maximum beigbteof echo topereportedtn the area. While the numbercfeevere weather repcrtaIncreases with the increase in maximum beighte of echo tOIN in the eeea, no significa.nt increase in severe weatheractivi ty is observed when the echo tope reecb or penetrate the tropopause. The m~Dthly di.5trib~tion of the Dumberof hail occurrences M well &8 their preferred hours of occurrence have also been et udled for the region.

3 .5. The instances of occurrences ot severeweather phenomena were picked out from theMonthly Meteorological Registers pDlRs) ofthese observa tories. These observations wereplotted on polar diagrams of th e area for eachday selected for the study ,

Weather Radar Unit which has a high power Xband (3 em) radar CPS-9.

3 .2. The date relates to the period December1957 to June 1960. This is the period for whichrada r observational data is ava ilable almostwithout any interruption due to radar break­down etc. The earlier radar-climatological studiesfor the area (Kulshrestha 1962, Kulshresthaand J ain 1964, 1965) also pertained to this periodonly.

3.3. Duri ng the 31-month period, 289 daysof extensive radar echo act ivity were selected.For each of these daya the maximum height ofecho tops, attained in the area on that day, wasnoted from the weather radar records.

3.4. The evidence of severe weather act ivityin the area was collected from the records of the27 surface observatories scattered almost evenlywithin a range of 200 miles around Delhi. Thesurface observatories, whose records were usedfor this purpose, are -

1. Introduction

1. 1. Kulshrestha and J ain (1964), stressingthe need for rad ar-clim atological st udies in d iffc­rent regions where records of radar-ob servationsarc ava ilable for the last few years, mentionedvarious aspects of radar-climatological informs­tion that can be usefully derived from the accu­mulat ed radar-weather data . Two such studieshave already been published by the presentauthors (Kulsh rcstha and J ain 196·1, 1965).

1. 2. The present paper constitutes the thi rdcontribution in the authors' continuing seriesof st udies on rad ar-climatology of Delhi andneighbourhood and deals with th e occurrence ofsever. weather phenomena within a range of200 miles around Delhi.

2. Seope 01 the present study

2.1. The present study deals with th e observa­tions of severe weather within a range of 200 milesaround Delhi observed between December 1957and June 1960. The following have been assumedto consti tute severe weather - thunderstorm(wit h or without ra in), duststorm, squall, hail.

2·2. Occurrence of severe weather observedin th e area has been investigated with referen ceto th e maximum heights of echo tops reportedfrom the area. The association of severe weatheractivity with the penetration of tropopause byecho tops has been investigated.

2 .3. Occurrence of hail has been speciallystudied. The monthly distribution of the numberof hail occurrences reported in the area has beeninvestigated. An attempt has alan been made tofind out the preferred hours of occurrence ofhail in the region around Delhi.

3. Data and the melhodor analysIs

3. 1. The radar data for this study was ob­ined from the routine records of the New Delhi

1. Agra2. .Aligarh3. Alwar4. Ambala5. Bareilly6. Bhatinda7. Chandigarh8. Churu9. Debra Dun

10. Dholpur 19. Nainital11. Hissa r 20. Najibabad12. J aipur 21. New Delhi13. Kama l 22. Pat iala14. Ludhiana 23. Roorkee15. Mainpuri 24. Simla16. )leerut 25. SikarIi. Muktcswar 26. Sriganganagar18. Mll880rie 27. Tonk