mausam, (1989), 40, 2, 137·d2 - metnet · mausam, (1989), 40, 2, 137·d2 551 .577: 551.553.21 :...
TRANSCRIPT
Mausam, (1989), 40, 2, 137·d2
551 .577: 551.553 .21 : 551.509.31
Main features of the westward-moving low pressure systemswhich form over the Ind ian region during the summermonsoon season and their relat ion to the monsoon rainfall
D. A. MOOLEY and J . SHUK LA
Centre for Oceotl·Lonn.Atmosplzere Interaction,University of Marylallll, College Park , U.S .A.
( Received /9 October / 987)
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_ 'IT''I 'T': '""'I.'I ..n .. '"'" "" >;ffrr.mI ~rir "~, Rf"" R"lll"TlR1ii ( LPS) .,;, *"" 'IT''I if '""'1.'1..n if f<irt .,.,if >ia11Pl 'li,r~ ,~ oj; "':;Hf.r<;f"'" """rom ( LPS) oj; ff;ii ~ *""~ '""'1.'1 ..n(s m'R if.mr.:) ,,'\7 _\flV< '""'1.'1 "'; ( IlIf.!>R if 3W) if Wi".,., ii" 'lfu>! ~ 'l'\7l'1 'l#i ii " '81"'14' 31'1<1 "ITfwr f<mf~ ~ I '1['1 i.'\Tr-t ( LPS) f.r<;f "'" ll"TIR1ii "" '!! 'If>'<'IIfor,!," "'l''''~ '"' "". 'l1"1 '"' 'l1
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AHSTRACT. The main features of the transitory monsoon 10" pressure systems I LPS) over the Indianregion during the period I Jo(g~· 19~J. in respect of their formation, life• . mavcm:nl. intensity and ~ issiJl~tion,as well a" thei r in teran nual va riabilltv are examined b)' utilizing the Information and data co ntained In theIndian Daily H't'otlu'r Report s. The relationship- of these feat ures with the monsoon rain fal l over India/northIndiace ntral India-south India are examined.
The paper discusses a variety of statistics about the low pressure systems. e.e., formation, location. li fe,intensity. movement and di ssipation.
T he number of tp.:) formed i.:; 1101 significantly related to the monsoon rainfall over India except (or aweak rela tionship with central India monsoon rainfall. Number of LPS days during the season is significantly and directly related 10 the Indian monsoon rainfall (above 5 ;{) and 10 central India monsoon rainfal l(a bove I %) and these relationships generally show good stability. Total westward longitudina l di splace mentof the LPS during the season and the monsoon rainfall oyer India and central India are directly and sig nificantly (above 1%) related and these relat ionships also generally che w good stability.
I . Introduction
During the summer mon soon sea so n (June throu ghSeptember), the syn opt ic sys tems wh ich a ffect the wcather over Ind ia and neighbourhood are, th e semi-permanent monsoon trough which extends from west Pakistan10 Burma, the closed low pressure systems which frequently move in a westerly direction across the centralpa rts of Ind ia lind the westerly trough s which occasionally move in an eas ter ly direction and affect the northwestern parts of India. The westward-movi ng lowpressure systems either form over the Indian subcont inen t, the Bay of Ben gal an d th e Ara bian Sea (hereafter,
Ind ian region) o r develop from the remnants of depressio ns/s to rms which strike the Viet Nam coast and movewestward into the Bay of Benga l, hereafter. Bay (Sahaet al. 1981), A large majority of the se low pressure systerns (hereafter LPS) form over the Ind ia n region northof 15Q N. As per cri teria of I n d i ~ Meteorological Dcpa,rtment. an LPS ISa depression If the Wind speed associated with the e~'c1on ie circula tion is 17-33 kt, a cyclonicstorm,. If the :--'Ind speed IS ;;' 34 kt, a severe cyclonicstorm if the Wind speed is ;;, 48 kt and a severe cyclo nicsto rm with core of h~rrieane win ds if the wind speed is;;' 64 kt. T hese cntena a rc generally follo wed fo r idcnt ifying the systems over the sea and adjoining coasta l a rea.
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