climatology and seasons of india

8/8/2019 Climatology and Seasons of India

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PHYSIOGRAPHYPHYSIOGRAPHY TOTO THETHE NORTHNORTH THETHE HIMALAYASHIMALAYAS EXTENDINGEXTENDING FROMFROM PAMIRPAMIR

KNOTKNOT TOWARDSTOWARDS EASTEAST OVEROVER 25002500KMKM (WIDTH(WIDTH 150150--250250KM)KM)

NAMKAINAMKAI--PATKAIPATKAI--NAGANAGA--LUSHAILUSHAI EXTENDSEXTENDS SOUTHWARDSSOUTHWARDSFROMFROM THETHE EASTERNEASTERN ENDEND OFOF HIMALAYASHIMALAYAS GAROGARO--KHASIKHASI--JAAINTIAJAAINTIA HILLSHILLS OFOF ASSAMASSAM RUNRUN EASTEAST--WESTWEST

FROMFROM ITIT SOUTHSOUTH OFOF THETHE HIMALAYASHIMALAYAS LIESLIES THETHE INDOINDO--GANGETICGANGETIC

PLAINPLAIN ABOUTABOUT 30003000KMKM LONGLONG ANDAND 250250--400400 WIDEWIDE

FURTHERFURTHER SOUTHSOUTH VINDHYAVINDHYA ANDAND SATHPURASATHPURA RANGESRANGES RUNRUNEASTEAST--WESTWEST (ABOUT(ABOUT 11 KMKM HIGH)HIGH) FURTHERFURTHER SOUTHSOUTH LIESLIES THETHE PENINSULARPENINSULAR PLATAUPLATAU WESTERNWESTERN GHATGHAT ONON WESTWEST COASTCOAST SLOPESSLOPES TOWARDSTOWARDS THETHE

EASTEAST BROKENBROKEN EASTERNEASTERN GHATGHAT ONON THETHE EASTEAST COASTCOAST

THETHE WESTERNWESTERN GHATGHAT ISIS HIGHERHIGHER THANTHAN THETHE EASTERNEASTERN GHATGHATWITHWITH AVERAGEAVERAGE HEIGHTHEIGHT OFOF 20002000 THETHE ARABIANARABIAN SEASEA ONON THETHE WESTWEST ANDAND THETHE BAYBAY OFOF BENGALBENGAL

ONON THETHE EASTEAST THETHE INDIANINDIAN OCEANOCEAN ONON THETHE SOUTHSOUTH


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SURFACE CLIMATOLOGYSURFACE CLIMATOLOGY

PRESENTSPRESENTS WIDEWIDE CONTRASTCONTRAST ININ CLIMATICCLIMATICCONDITIONSCONDITIONS

RAINFALLRAINFALL VARIESVARIES FROMFROM 1010 CMCM ININ THETHE THARTHARDESERTDESERT TOTO OVEROVER 10001000 CMCM ININ CHERAPUNJICHERAPUNJI //MAWSYNRAMMAWSYNRAM (ANNUAL(ANNUAL AVERAGEAVERAGE ISIS 11401140 CM)CM)

TEMPERATURESTEMPERATURES VARYVARY FROMFROM --4545CC ININ DRASDRAS TOTO4949CC ININ RAJASTHANRAJASTHAN

SWSW MONSOONMONSOON ANDAND NENE MONSOONSMONSOONS AREARE THETHEMAINMAIN SEASONSSEASONS WITHWITH TWOTWO TRANSITIONTRANSITIONSEASONSSEASONS


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MAIN SYNOPTIC FEATURESMAIN SYNOPTIC FEATURES EXTRAEXTRA--TROPICALTROPICAL DISTURBANCESDISTURBANCES (WDs)(WDs)::

AFFECTSAFFECTS NORTHERNNORTHERN PARTSP ARTS OFOF THETHE COUNTRYCOUNTRYDURINGDURING WINTERWINTER SEASONSE ASON AND AND COMESCOMES TOTO ITSITSSOUTHSOUTH MOSTMOST POSITIONPOSITION TOTO 2323NN LATLAT ININFEBRUARYFEBRUARY

TROPICALTROPICAL CYCLONESCYCLONES:: ORIGINATEORIGINATE ININ THETHE BAYBAY

OROR ININ THETHE ARABIAN ARABIAN SEA,SE A, MOVEMOVE ININ W/NWW/NWDIRECTIONDIRECTION (SOME(SOME RECURVERECURVE TOTO N/NE)N/NE).. ININ SWSWMONSOONMONSOON THEYTHEY AREARE OFOF SMALLSMALL INTENSITYINTENSITY ANDANDFORMFORM ININ NWNW BAYBAY.. STORMSSTORMS ININ PREPRE ANDAND POSTPOSTMONSOONMONSOON AREARE OFOF GREATERGREATER INTENSITYINTENSITY

INTERACTIONINTERACTION BETWEENBETWEEN HIGHHIGH AND AND LOWLOW LATLATSYSTEMSSYSTEMS :: THISTHIS INTERACTIONINTERACTION CAUSESCAUSES TROPICALTROPICALSTORMSSTORMS TOTO RECURVERECURVE TOTO N/NE/E,N/NE/E, BREAKBREAKMONSOONMONSOON


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SURFACE FEATURESURFACE FEATURE ININ WINTER,WINTER, THETHE SIBERIANSIBERIAN HIGHHIGH WITHWITH CENTRALCENTRAL

PRESSUREPRESSURE OFOF ABOUTABOUT 10351035 hPahPa ISIS PREDOMINENTPREDOMINENT BYBY MARCHMARCH THISTHIS HIGHHIGH WEAKENSWEAKENS AND AND THETHE

TENDENCYTENDENCY FORFOR LOWLOW FORMATIONFORMATION DEVELOPSDEVELOPS OVEROVERCENTRALCENTRAL INDIAINDIA

ININ MAYMAY THETHE THERMALTHERMAL LOWLOW EXTENDSEXTENDS FROMFROM MPMP TOTORAJRAJ WITHWITH CENTRECENTRE PRESSUREPRESSURE OFOF ABOUTABOUT 10041004 hPahPa

ININ JULYJULY (A(A TYPICALTYPICAL MONSOONMONSOON MONTH)MONTH) THETHE LOWLOWEXTENDSEXTENDS OVEROVER RAJRAJ ANDAND PAKP AK WITHWITH CENTRECENTREPRESSUREPRESSURE OFOF ABOUT ABOUT 998998 hPahPa AND AND A A TROUGHTROUGHEXTENDSEXTENDS FROMFROM THETHE LOWLOW TOTO NN BAYBAY.. THETHE PRESSUREPRESSUREGRADIENTGRADIENT ISIS STRONGESTSTRONGEST OVEROVER WESTWEST COASTCOAST

BYBY SEPTEMBERSEPTEMBER PRESSUREPRESSURE GRADIENTGRADIENT DECREASESDECREASESAND AND SIGNSSIGNS OFOF FORMATIONFORMATION OFOF WINTERWINTER HIGHHIGHDEVELOPDEVELOP

BYBY OCTOBEROCTOBER AA HIGHHIGH FORMSFORMS OVEROVER SINKIANGSINKIANG ANDANDBYBY DECEMBERDECEMBER THETHE WINTERWINTER FEATUREFEATURE ISIS ATTAINEDATTAINED


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TEMPERATURETEMPERATURE ININ WINTERWINTER DRYDRY AND AND COLDCOLD CONTINENTALCONTINENTAL

WINDSWINDS PREVAILPRE VAIL OVEROVER MOSTMOST PARTSP ARTS OFOF THETHE

COUNTRYCOUNTRY MAXMAX TEMPTEMP OVEROVER PLAINSPLAINS OFOF NN INDIAINDIA ISIS ININ THETHE

ORDERORDER OFOF 2020--2525CC AND AND ABOUT ABOUT 3030CC OVEROVERPENINSULAPENINSULA

MINMIN TEMPTEMP OVEROVER PLAINSPLAINS OFOF NN INDIAINDIA ISIS ININ THETHE

ORDERORDER OFOF 55--1010CC ANDAND OVEROVER PENINSULAPENINSULA 2020--2525CC COLDCOLD WAVEWAVE CONDITIONCONDITION PREVAILSPRE VAILS OVEROVER NN

INDIAINDIA WHENWHEN MINMIN TEMPTEMP GOESGOES 55--1010CC BELOWBELOWNORMALNORMAL

ININ SUMMERSUMMER WESTWEST AND AND NWNW PARTSPARTS HAVEHAVE MAXMAXTEMPTEMP ININ ORDERORDER OFOF 3535--4545CC.. ATAT TIMESTIMES HEATHEATWAVEWAVE CONDITIONSCONDITIONS OCCUROCCUR

MEANME AN MINMIN TEMPTEMP ININ ORDERORDER OFOF 2020--2525CC OVEROVERTHETHE COUNTRYCOUNTRY


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RAINFALLRAINFALL

WESTERNWESTERN SLOPESSLOPES OFOF WESTERNWESTERN GHATGHAT RECEIVESRECEIVES

RAINFALLRAINFALL ININ THETHE ORDERORDER OFOF 200200 CMCM A A NARROWNARROW STRIPSTRIP BETWEENBETWEEN 1111--1313NN ANDAND

SOUTHERNSOUTHERN SLOPESLOPE OFOF KHASIKHASI HILLSHILLS RECEIVERECEIVE R/FR/FOVEROVER 400400 CMCM

R/FR/F DECREASESDECREASES TOWARDSTOWARDS EASTEAST FROMFROM WESTERNWESTERN

GAHTGAHT ANDAND TOWARDSTOWARDS WESTWEST FROMFROM NENE STATESSTATESWITHWITH LEASTLEAST R/FR/F OVEROVER RAJANTHANRAJANTHAN DESERTDESERT ABOUT ABOUT 7575%% OFOF ANNUAL ANNUAL R/FR/F ISIS DURINGDURING SWSW

MONSOONMONSOON SEASONSE ASON OTHEROTHER THANTHAN TNTN AND AND NWNWINDIAINDIA

TNTN RECEIVESRECEIVES MAXMAX R/FR/F ININ THETHE NENE MONSOONMONSOONFROMFROM TROPICALTROPICAL CYCLONECYCLONE ANDAND EASTERLYEASTERLY WAVEWAVE NWNW INDIAINDIA RECEIVESRECEIVES MAXMAX R/FR/F DURINGDURING WINTERWINTER

FROMFROM WDsWDs


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9/37

DUSTDUST STORMSSTORMS

DustDust stormsstorms occuroccur overover NWNW IndiaIndia duringduring prepre--monsoonmonsoon seasonseason (mainly(mainly fromfrom MarMar--Jun),Jun), whichwhich

areare locallylocally knownknown asas andhisandhisFOGFOG

FogFog occursoccurs mainlymainly duringduring winterwinter seasonseason

HoweverHowever inin thethe valleysvalleys fogfog isis possiblepossiblethroughoutthroughout thethe yearyear

TheThe fogfog isis mainlymainly radiationradiation fogfog

HoweverHowever advectionadvection isis possiblepossible anywhereanywhere inin thethecoastalcoastal beltbelt

LowLow stratusstratus cloudsclouds persistpersist forfor sometimessometimes whenwhenthethe fogfog isis liftedlifted


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UPPER AIR FEATURESUPPER AIR FEATURES WindsWinds areare easterlyeasterly southsouth ofof 1515NN andand westerlywesterly

northnorth ofof 3434NN.. ZonalZonal westerlieswesterlies (speed)(speed) increaseincrease withwith heightheight

andand attainattain maximummaximum speedspeed ofof 150150--200200 ktkt (mean(mean8080 kt)kt) atat 150150--200200 hPahPa levellevel betweenbetween 2525--3030NN(tropical(tropical jet)jet) inin winterwinter..

ZonalZonal easterlieseasterlies (speed)(speed) alsoalso increaseincrease withwithheightheight andand attainattain maximummaximum speedspeed ofof aruondaruond 120120ktskts (mean(mean 6060--7070 kts)kts) atat 150150//100100 hPahPa levellevel (TEJ)(TEJ)inin summersummer..

InIn SWSW monsoonmonsoon westerlieswesterlies inin westwest coastcoast

strengthenstrengthen fromfrom surfacesurface andand reachreach anan averageaveragespeedspeed ofof 2525--3030 ktskts atat 850850 && 700700 hPahPa levellevel withwithmaxmax speedspeed reachingreaching uptoupto 5050 ktskts (LLJ)(LLJ)..


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12/37

SEASONS OF INDIASEASONS OF INDIA ColdCold SeasonSeason -- DecemberDecember toto MarchMarch

(Winter)(Winter) HotHot SeasonSeason -- AprilApril toto MayMay

(Pre(Pre--monsoon)monsoon) WetWet SeasonSeason -- JuneJune toto SeptemberSeptember

(Southwest(Southwest monsoon)monsoon) CoolCool SeasonSeason -- OctoberOctober andand NovemberNovember

(Post(Post--monsoon)monsoon)

TheThe fourfoldfourfold seasonalseasonal divisiondivision isis basedbased ononlowlow levellevel features,features, mainlymainly winds,winds, temperaturetemperatureandand precipitationprecipitation whichwhich areare oftenoften highlyhighlyvariablevariable..


13/37

WINTER (COLD) SEASONWINTER (COLD) SEASON

ThisThis isis thethe coldestcoldest portionportion ofof thethe yearyear andand hencehencecalledcalled thethe coldcold seasonseason..

InIn winterwinter NortheastNortheast monsoonmonsoon prevailsprevails overover thethesubcontinent,subcontinent, soso itit isis alsoalso calledcalled NENE monsoonmonsoon..

SubsidingSubsiding anticyclonicanticyclonic airair isis prevalentprevalent overover thethemajormajor portionportion ofof thethe country,country, givinggiving riserise totomainlymainly clearclear weatherweather..

InIn thethe north,north, onon anan averageaverage aboutabout 44--55 westernwestern

disturbancesdisturbances traveltravel fromfrom westwest toto east,east, breakingbreakingthethe spellspell ofof clearclear weatherweather.. TheseThese causecause cloudingcloudingandand precipitationprecipitation andand laterlater onon widewide spreadspread fogfog..MaximumMaximum frequencyfrequency ((55--66/month) /month) andand thethesouthernmostsouthernmost tracktrack ((2323N)N) isis inin thethe monthmonth ofof

JanJan--FebFeb..


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.HYD

.MDS

.BMB

.DLH

BASED ON 25/1130H1004

10061008

1002

PRESSURE DISTRIBUTION

10121012

1014

1014

1016

1016

10181018

1020

1020

10221022

1024 1024

MEAN SEA LEVEL PRESSURE (mb)

JANUARY

H

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WEATHERWEATHER::

GenerallyGenerally coldcold drydry northnorth oror northwesterlynorthwesterlycontinentalcontinental airair prevailsprevails overover thethe countrycountry outsideoutside

southeastsoutheast PeninsulaPeninsula.. ClearClear skies,skies, finefine weather,weather,lowlow humidityhumidity andand lowlow temperaturestemperatures withwith largelargediurnaldiurnal rangerange areare normalnormal featuresfeatures.. TheseThese drydryspellsspells areare brokenbroken atat intervalsintervals whenwhen migratorymigratoryextraextra--tropicaltropical disturbancesdisturbances movemove acrossacross northernnorthern

IndiaIndia.. ApproachApproach ofof aa WDWD isis markedmarked byby fallfall ofof pressure,pressure, riserise inin

temperature,temperature, backingbacking ofof winds,winds, cloudsclouds loweringlowering fromfromCi/CsCi/Cs toto Ac/AsAc/As andand thenthen toto StSt withwith rain/drizzlerain/drizzle

WhenWhen thethe systemsystem isis overhead,overhead, Cu/CBCu/CB cloudsclouds developdevelop

associatedassociated withwith ThunderThunder storms/showers,storms/showers, occasionallyoccasionallywithwith squallsquall andand gustgust..

AfterAfter thethe passagepassage ofof thethe system,system, pressurepressure increases,increases,temperaturetemperature falls,falls, windwind veersveers toto itsits northerlynortherly component,component,weatherweather clearsclears upup andand asas aa resultresult widewide spreadspread fogfog occursoccursforfor 22--33 daysdays..


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InIn thethe southsouth aa troughtrough extendsextends fromfromKeralaKerala toto GujratGujrat alongalong westwest coastcoast whichwhich

sometimessometimes extendsextends uptoupto RajasthanRajasthan andand oftenoftenaa cutcut--offoff lowlow formsforms andand movemove towardstowards easteastacrossacross centralcentral IndiaIndia causingcausing rainfallrainfall overover thethecentralcentral partsparts..

InIn SESE PeninsulaPeninsula,, thethe NENE currentcurrent afterafteracquiringacquiring moisturemoisture fromfrom thethe BayBay givegive riserise totofewfew thunderstormsthunderstorms.. WesterlyWesterly movingmoving easterlyeasterly

waveswaves alsoalso causecause cloudinesscloudiness andand rainrain overoverPeninsulaPeninsula.. SometimesSometimes aa cycloniccyclonic stormstorm maymaycausecause heavyheavy rainrain inin extremeextreme SESE TNTN..


18/37

AVIATIONAVIATION WEATHERWEATHER HAZARDSHAZARDS::

(a)(a) VisibilityVisibility:: RadiationRadiation fogfog oror mistmist isis commoncommoninin manymany partsparts ofof thethe countrycountry..

(b)(b) IcingIcing:: FreezingFreezing levelslevels areare thethe lowestlowest ininwinterwinter.. IceIce accretionaccretion onon aircraftaircraft isis experiencedexperienced

atat comparativelycomparatively lowerlower levelslevels inin thethe northnorth ininthisthis seasonseason..

(c)(c) SubSub--tropicaltropical jetjet streamstream:: TheThe corecore ofof thethe subsub--tropicaltropical jetjet streamstream nownow lieslies betweenbetween latitudeslatitudes2525oNoN andand 3030 oNoN atat aa levellevel betweenbetween 300300mbmb andand200200 mbmb.. TheThe averageaverage speedsspeeds areare ofof thethe orderorderofof 8080 kt(maximumkt(maximum speedspeed reachesreaches uptoupto 150150--200200 kts)kts)..


19/37

PREPRE--MONSOON (HOT) SEASONMONSOON (HOT) SEASON

TheThe hothot seasonseason isis aa transitionaltransitional seasonseason whenwhen thethewinterwinter monsoonmonsoon patternpattern ofof pressurepressure andand windswindsgetsgets disrupteddisrupted priorprior toto thethe establishmentestablishment ofof thethesummersummer monsoonmonsoon patternpattern andand isis thusthus referredreferred totoasas thethe prepre--monsoonmonsoon..

WidespreadWidespread dustdust hazehaze andand extremelyextremely highhightemperaturestemperatures areare prevalentprevalent overover northnorth IndiaIndia..

LandLand andand seasea breezebreeze isis prominentprominent overover thethecoastalcoastal areasareas..

AA fewfew tropicaltropical cyclonescyclones formform inin thethe IndianIndian seasseas..


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.HYD

.MDS

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BASED ON 01Sep/1130H1000

1004 1006

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APRIL1010

1010

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22/37

WeatherWeather::RainfallRainfall occuroccur mostlymostly inin easterneastern IndiaIndia withwith 55 toto 2525

cmcm ofof rainrain perper monthmonth.. ThereThere isis largelarge--scalescale thunderstormthunderstorm

activityactivity.. WhenWhen thethe moisturemoisture contentcontent isis less,less, dustdust--stormsstorms occuroccur inin westernwestern IndiaIndia.. FrequencyFrequency isis 33--55 perpermonthmonth.. TheseThese areare locallylocally knownknown asas andhisandhis..

ViolentViolent locallocal thunderthunder squallssqualls accompaniedaccompanied byby hailhailandand rainrain occuroccur inin thethe easterneastern IndiaIndia wherewhere deepdeep humidhumidwindswinds fromfrom thethe seasea meetmeet hothot drydry landland windswinds.. TheseThese arearelocallylocally knownknown asas kalbaisahkiskalbaisahkis..

TheThe frequencyfrequency ofof TropicalTropical cyclonescyclones increasesincreases.. TheThetropicaltropical stormsstorms inin ArabianArabian SeaSea mostlymostly movemove westwardswestwardsandand dodo notnot affectaffect India,India, howeverhowever fewfew ofof themthem recurverecurve totonorthnorth andand affectaffect MaharastraMaharastra andand GujratGujrat..

InIn thethe BayBay stormsstorms developdevelop betweenbetween 1010--1515NN.. SomeSomeofof themthem movemove N/NEN/NE andand affectaffect Bengal,Bengal, BDBD oror MyanmarMyanmarcoastcoast andand somesome movemove toto W/NWW/NW andand affectaffect TN,TN, APAP ororOrissaOrissa.. AA fewfew ofof themthem whichwhich traveltravel toto westwest afteraftercrossingcrossing thethe peninsulapeninsula enterenter thethe ArabianArabian SeaSea andandreviverevive..


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AviationAviation WeatherWeather HazardsHazards::

(a)(a) ThunderstormsThunderstorms:: TheseThese areare mostlymostlyviolentviolent convectionalconvectional typetype ofof thunderstormsthunderstorms

causedcaused byby thethe intenseintense insolationinsolation.. TheThe mostmostdestructivedestructive typetype ofof convectionalconvectional thunderthundersquallssqualls areare thethe norwestersnorwesters ofof easterneastern IndiaIndia..TheyThey occuroccur fromfrom midmid--MarchMarch toto JuneJune duringduring

afternoon/eveningafternoon/evening hourshours(b)(b) DustDust HazeHaze:: WithWith drydry looseloose soilsoil andandstrongstrong winds,winds, mostmost ofof thethe westernwestern IndiaIndia getsgetsenvelopedenveloped inin dustdust.. At At timestimes thethe dustdust beltbelt

extendsextends eastwardseastwards uptoupto UpperUpper AssamAssam.. VisVis isisreducedreduced toto 22 kmkm oror lessless forfor daysdays together,together, atattimestimes reducingreducing toto fewfew metresmetres.. VerticalVertical extentextent isisgenerallygenerally uptoupto 33--55 km,km, butbut atat timestimes extendextenduptoupto 77--88 kmkm..


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(a)(a) DustDust--raisingraising windswinds:: SometimesSometimes strongstrong surfacesurfacewindswinds ofof thethe orderorder ofof 3030 ktkt ss gustinggusting toto 4040--5050kts,kts, raiseraise thethe dustdust whichwhich affectsaffects thethe visibilityvisibility..

ThisThis happenshappens overover thethe dustdust hazehaze affectedaffected areasareasduringduring dayday timetime..

(b)(b) DustDust stormsstorms:: Dust Dust stormsstorms ofof northnorth IndiaIndia arearethethe resultresult ofof dustdust scoopedscooped upup fromfrom thethe earthearth bybythethe squallssqualls fromfrom thunderstormsthunderstorms.. TheThe squallssquallsspeedspeed oftenoften reachreach 4040//5050 ktkt.. occasionallyoccasionally 6060//7070ktkt.. andand thethe visibilityvisibility deterioratesdeteriorates toto aa fewfew

metresmetres.. Cu/CBCu/CB areare prepre--conditioncondition forfor dustdust stormstorm..


25/37

SOUTHWEST MONSOONSOUTHWEST MONSOON(WET) SEASON(WET) SEASON

TheThe countrycountry (out(out sideside westernwestern andand easterneasternHimalayasHimalayas andand southwestsouthwest Peninsula),Peninsula), receivesreceivesnearlynearly 7575%% ofof itsits rainfallrainfall duringduring thisthis periodperiod..

TheThe subsub--tropicaltropical westerlywesterly jetjet streamstream shiftsshifts northnorth ofofthethe HimalayasHimalayas andand thethe tropicaltropical easterlyeasterly jetjet streamstreammakesmakes itsits appearanceappearance overover thethe PeninsulaPeninsula..

TheThe mainmain characteristicscharacteristics ofof thethe seasonsseasons areare

moderatemoderate toto heavyheavy rains,rains, veryvery lowlow clouds,clouds, highhighhumidityhumidity andand sultrysultry weatherweather.. ThisThis isis alsoalso thethe periodperiodwhenwhen devastatingdevastating floodsfloods occuroccur inin manymany partsparts ofof thethecountrycountry..


26/37

SURFACESURFACE::

An An intenseintense lowlow pressurepressure systemsystem developsdevelops

overover thethe northwesternnorthwestern partpart ofof thethe subcontinentsubcontinentandand adjoiningadjoining Afghanistan, Afghanistan, spreadingspreadingeastwards,eastwards, thethe troughtrough ofof lowlow pressurepressure inin thetheIndoIndo--GangeticGangetic plainplain isis usuallyusually referredreferred toto asas thethe

monsoonmonsoon troughtrough.. ThisThis troughtrough isis modifiedmodified whenwhendepressiondepression formsforms overover thethe BayBay..

StrengtheningStrengthening andand breaksbreaks inin thethe monsoonmonsoon

areare associatedassociated withwith thethe formationformation ofof depressiondepressionandand itsits movementmovement.. SomeSome movemove alongalong thethemonsoonmonsoon troughtrough andand finallyfinally mergemerge withwith thetheseasonalseasonal lowlow andand somesome recurverecurve toto N/NEN/NE..


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998

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15 JUL01 JUL

15 JUN

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05 JUN

01 JUN

ONSET OF SW MONSOON


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WITHDRAWL OF SW MONSOON

15 SEP

01 OCT

15 OCTO1 NOV

15 NOV

01 DEC15 DEC


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WeatherWeather::TheThe monsoonmonsoon currentcurrent meetingmeeting thethe WesternghatWesternghatyieldsyields heavyheavy rainfallrainfall onon thethe westwest sideside andand therethere

isis aa rainrain shadowshadow areaarea toto thethe easteast.. TheThe ArabianArabianseasea branchbranch givesgives somesome rainfallrainfall inin GujratGujrat andandRajasthanRajasthan..

TheThe BayBay branchbranch causescauses rainrain overover MyanmarMyanmarcoastcoast andand beltbelt ofof easterneastern HimalayasHimalayas.. FromFrom

BengalBengal thisthis branchbranch movemove towardstowards westwest asaseasterlieseasterlies almostalmost parallelparallel toto thethe HimalayasHimalayas..Along Along thethe troughtrough thethe BayBay branchbranch andand thetheArabianArabian seasea branchbranch meetmeet andand givegive moderatemoderate totoheavyheavy rainfallrainfall.. ThusThus thethe rainrain overover thethe IndoIndo--

gangeticgangetic plainplain isis mainlymainly governedgoverned byby thetheorientationorientation ofof thethe monsoonmonsoon troughtrough..TheThe depressionsdepressions formform inin thethe BayBay movemove

towardstowards westwest alongalong thethe troughtrough andand causecause heavyheavyrainrain overover thethe regionregion (heaviest(heaviest inin thethe SWSW sector)sector)..


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AviationAviation weatherweather hazardshazards:: LowLow cloudsclouds:: stratusstratus cloudsclouds lowerlower toto aboutabout 150150--

200200mm underunder moderatemoderate andand strongstrong monsoonmonsoon

conditioncondition.. HoweverHowever duringduring thethe passagepassage ofof anyanydepressiondepression itit maymay lowerlower downdown toto 3030mm.. StrongStrong surfacesurface windswinds:: UnderUnder strongstrong monsoonmonsoon

conditioncondition surfacesurface windswinds areare inin thethe orderorder ofof 2525--3030kts,kts, butbut duringduring thethe passagepassage ofof anyany depressiondepressionwindwind speedspeed maymay reachreach uptoupto 4040--5050 ktskts..

VisibilityVisibility:: InIn generalgeneral visibilityvisibility isis goodgood.. DuringDuringthisthis seasonseason visibilityvisibility isis reducedreduced onlyonly duedue totorain/showerrain/shower.. InIn heavyheavy rainrain visibilityvisibility maymay reducereduce

toto fewfew hundredhundred metresmetres.. TropicalTropical EasterlyEasterly JetJet StreamStream:: DuringDuring thisthis seasonseason

TEJTEJ lieslies betweenbetween 1010--1515 degdeg NN atat 150150--100100 hPahPalevellevel withwith averageaverage speedspeed ofof 6060--7070 ktskts.. ButButoccasionallyoccasionally speedspeed reachesreaches uptoupto 100100--120120 ktskts..


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POST MONSOONPOST MONSOON TheThe transitionaltransitional periodperiod fromfrom summersummer toto winterwinter..

ByBy firstfirst weekweek ofof OctOct monsoonmonsoon isis withdrawnwithdrawn fromfromnorthernnorthern halfhalf ofof thethe countrycountry..

TemperatureTemperature startsstarts decreasingdecreasing allall overover thethecountrycountry..

DuringDuring thisthis seasonseason TamilnaduTamilnadu getsgets maximummaximumrainfallrainfall..

ZonalZonal westerlieswesterlies shiftsshifts southsouth andand thethe SubSub

TropicalTropical JetJet appearsappears overover thethe extremeextreme northnorth.. TrackTrack ofof WDsWDs alsoalso movemove toto southsouth andand affectaffect NWNW

IndiaIndia..

FrequencyFrequency ofof cycloniccyclonic stormstorm isis maximummaximum andand

alsoalso havehave maximummaximum intensityintensity


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WeatherWeather

Clear weather with mist/haze duringClear weather with mist/haze during

dawn/duskdawn/dusk

11--2 WDs may cause clouding/precipitation2 WDs may cause clouding/precipitationover Kashmir and Punjabover Kashmir and Punjab

To the east weather is generally clear, butTo the east weather is generally clear, butwhen CS hits BD, weather may be badwhen CS hits BD, weather may be bad

Weather is caused over Peninsula mainlyWeather is caused over Peninsula mainly

by Cyclonesby Cyclones


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AviationAviation weatherweather hazardshazards LowLow visibilityvisibility:: MainlyMainly duedue toto stratifiedstratified smokesmoke nearnear

thethe inhabitedinhabited areasareas duringduring dawndawn andand duskdusk..

InIn thethe extremeextreme northnorth mist/fogmist/fog maymay occuroccur afterafterthethe passagepassage ofof WDsWDs andand liftinglifting stratusstratus maymay alsoalsooccuroccur forfor 11--22 daysdays

InIn thethe southsouth poorpoor visibilityvisibility isis causedcaused onlyonly byby

precipitationprecipitation TropicalTropical StormsStorms:: duringduring thisthis seasonseason severesevere

cycloniccyclonic stormsstorms developdevelop overover thethe BayBay andand thetheArabian Arabian SeaSea betweenbetween 1010--1515NN andand affectaffect thethecoastalcoastal beltbelt

SubSub--TropicalTropical JetJet:: STJSTJ isis seenseen onlyonly betweenbetween 3030--3535NN andand graduallygradually shiftsshifts southwardssouthwards atat aboutabout 200200hPahPa withwith averageaverage speedspeed ofof 6060--7070 ktskts (maximum(maximumspeedspeed reachesreaches uptoupto 100100--150150 kts)kts)

climatology and seasons of india

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