MAUSAM. '9,4 (October 1998). 45J.460 55 1.5 15. 1: 551.553.2 1: 551.5 13.7 Effect of monsoon depression of east coast at some distant region in west ASOI LAL and R.S. SU I' DAR Meteorological Office. Punr . oJ // 005. India (Received /7 March 1997. Modified 22 January 1998) mt - 'IWfI in 'ftRj 'i <ftrri ahit q \ft ll'fi1<il31ll<lT 11; 'liT il:l lIT in ?R€I t, qfjwfT <R qT 'TIf1 'l'l! 1fufT t I 'TIf1 qqj <tl lim: !IT'IRI qqj i't inft I 3IUl1<-l q 'N% i't IITff I'il·'",lf<l,«i <tl lm'ffiT il 'IR'fl in 'ItRi 'i 'fll oM Iml <i?t 'liT 111m! 'IlIT I '"' ahit <i?t oM <tl ffimT it<Rr qffifJ it iii 'lUI omm 3fR TfU'l q 'TIf1 3fR ilIfq'ifi qqj ir.\ <tl 1fufT % fin oM 3ft>: 1ffiR <i?t oM in 3lR it<Rr il 'mlllT 'IlIT I ABSTRACT. wbe never a vortex or system of low or depression forms ove r head hay dunng Monsoon months. the west coast experiences heavy rainfall.These heavy rainfall oc currences areusually higherthan rhe normal rainfall. An attempt h," been made in thi ...... tudy (0 vi.\uahsc: the easterly wave mode l dunng monsoon months w ith the helpof satellite imageries. The rain is expectedheavy andwrdc spread over Madhya Maharasfura andSouthGujarat wben thirdsector of the wavecovers these arear .., as visualised in satellite wave and depression or vortex lies in 51h or 61h sector of the weve. Key words -c-Easterly wave, Satellite imagerie s, Sinusoidal curve. Migratory . Precursor. J. Introduction Much have been disc ussed about the waves in the easterlies . and separately on the depressions or lows across the country from the Bay of Bengal. Whenever a vorte x or system of low or depression fonns over head bay during the monsoon months, the west coast experiences heavy rainfall. Especially, the western Maharashtra and Konkan regions receive about 15 ems of rainfall per day . Such heav y rain fall occurren ces are quan titatively higher than the usuall y expe - rienced heavy rainfall amountsduring monsoon. This seems 10 be a sequel 10 the effect the synoptic system in the head bay causes on the other side of the western ghats of the pe ninsula. However, on such effects these systems produce over areas this far away . much less has been explored. Sen and Sundar (1994) have derived an explanation for heavy rainfall over Pune, from the combined effect of the system from head bay moving over the central peninsula and the N-S trough off the west coast during the monsoo n month s. In the recent past Mukherjee and Shyamala (1985) have tried 10 explain the rainfal l activity along the west coast during the formation stage of depressions over bay of Ben- gal. Accordiog 10 them. a monsoon depression over north- west bay is associated with increased rainfall activity over Konkan-Kerala coasts, along with an active trough line at 850-700 hPa level. This accompanies a cyclonic circulation over north-east Arabian sea between 1.5 and 3.0 kms asl. The circulation pattern and rainfall over west Rajasthan gets inhibited as a ridge develops over NE Arabian sea and neighbourhood and depre ssion moves inlan d according to Mukherjee (1978). Saxena (1988) while indexing the sys- tems strengthening the monsoon activity o ver Madhya Ma- harashtra and Marathwada lists the monsoon depressions over bay and North -South troughs in the monsoon wester- lies. The waves in the ea. sterlies have a sinusoidal appear- ance throughout their depth in some regions. Th ese migra- torywaves give rise to close lows and depressions in lower levels which move as different entities. while the migra tory easterly waves in mid and upper tropo sphere move away indepen den tly. Reed et al. (1977) postulated Chat the waves over west Africa and eas tern Atlantic have a general wave- length of about 2500 kms - or roughly 25 longitude degrees. with a mea n period of 3 to 4 days. The cloud s and rain were maximum in the southwest sector of the wave near the centre. Propert ies of the waves as env isaged by Riehl ( 1954) indicate downward movement of air ahead of trough. with cumulusof above average development andscattered show- ers close to trough line but ahead of it. whereas over the trough and to the rear of it the cloud development is marked yieldin g heavier rainfall and decrea sing fanher to the east. The picture gels modified with orography and diffemtial
