Climate-9th Geography

This PPt may be useful for the 9th std students. it is based on the 9th Std Geography (CBSE) book. for better understanding, some of the other related PPTs and pictures are also included in this PPT. Let enjoy your studies. yours.. R. Ezhilraman, PGT-Social Science, JNV Lepakshi, Ananthapur Andhra Pradesh

1. 02-03-2015 R. Ezhilraman, PGT-Social Science 1
R. Ezhilraman
PGT-Social Science
JNV Lepakshi
Subject: Geography
For Class: IX

2. What is Climate?
Climateisthecharacteristicconditionofthe
atmosphereneartheearth'ssurfaceatacertain
placeonearth.
Itreferstothesumtotalofweatherconditionsand
variationoveralargeareaforalongperiodoftime.
Itisthelong-termweatherofthatareawhich
remainsatleast30years.
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3. Weatherreferstothestateof
atmosphereoveranareaat
anypointoftime.The
elementsofbothweather
andclimatearesame.Itisthe
combinationoftemperature,
humidity,precipitation,wind,
cloudinessand other
atmosphericconditionsata
specifictime.
What is Weather?
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4. Monsoon
ThewordmonsoonisderivedfromtheArabicword‘mausim’
whichliterallymeansseason.
‘Monsoon’referstotheseasonalreversalinthewind
directionduringayear.
TheWorldisdividedintoanumberofClimaticRegions.The
ClimateofIndiaisdescribedasthe‘monsoon’type.Thistype
ofclimateisfoundinSouthandSoutheastAsia.But,thereare
perceptibleregionalvariationsinclimaticconditionswithin
thecountry.
Twoimportantelementsviz.,temperatureandprecipitation,
oftenvaryfromplacetoplaceandseasontoseason.
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5. Difference in Temperature
Insummer,thetemperatureinpartsofRajasthanDesert
is50°C,anditisaround20°CinPahalgaminJ&K.On
awinternight,temperatureatDrassinJ&Kmayless
than-45°C,andatTiruvananthapuramitmaybeof
22°C.
Insomeplacestemperaturebetweendayand
nighttemperaturediffers.IntheTharDesert,itriseto
50°C,indayanddropdowntonear15°Cinnight.But
intheAndamanandNicobarislandsorinKerala,there
isnomuchdifferenceindayandnighttemperatures.
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6. Precipitation
Precipitationvariesinitsform,typesandamountand
seasonaldistribution.Itisintheformofsnowfallinthe
upperpartsofHimalayas,itrainsovertherestofthe
country.Theannualprecipitationvariesfrom400cmin
Meghalayatolessthan10cminLadakhandwestern
Rajasthan.Mostpartsofthecountryreceiverainfallfrom
JunetoSeptember.ButTamilNaducoastgetsrainduring
OctoberandNovember.
Rainfallgenerallydecreasefromeasttowestinthe
NorthernPlains.Thesevariationshavegivenriseto
varietyinlivesofpeople,theirfood,clothesandhouses.
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7. Vegetation
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Vegetationcanaffectbothtemperatureand
theprecipitationpatternsinanarea.

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9. 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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10. Latitude
Latitudeisthe
distanceaplace
liesnorthor
southofthe
equatorandis
measuredbyan
imaginaryline
calledlinesof
latitude.
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11. EQUATORIAL REGION
LATITUDE
High Temp
Low range
High range
of Temp
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12. Latitude
Aslatitudeincreases,theintensityofsolarenergy
decreases.DuetocurvatureoftheEarth,the
amountofsolarenergyvariesaccordingtolatitude.
InIndia,theTropicofCancerpassesthroughthemiddle
ofthecountryfromtheRannofKuchchhinthewestto
Mizoramintheeast.
Almosthalfofthecountry,lyingsouthoftheTropicof
Cancer,belongstothetropicalarea.Alltheremaining
area,northoftheTropic,liesinthesub-tropics.
Therefore,India’sclimatehascharacteristicsoftropical
aswellassubtropicalclimates.
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13. Tropical, Temperate and Polar Zones
•Thetropicalzoneisbetween23.5
o
north(thetropicof
Cancer)and23.5
o
south(thetropicofCapricorn)ofthe
Equator.TheSun’sraysaremostintenseandthe
temperaturesarealwayswarm.
•Thetemperatezonesarebetween23.5
o
and66.5
o
northandbetween23.5
o
and66.5
o
southofthe
Equator.TheSun’sraysstrikeEarthatasmallerangle
thanneartheEquator.
•Polarzonesarebetween66.5
o
northandsouth
latitudesandthepoles.Thesun’sraysstrikeEarthata
verysmallangleinthepolarzones.
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14. Highland Climates
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In general, highland climates are cooler and wetter than
nearby areas at lower elevations.

15. Earth’s Major Climate Zones
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16. North Frigid Zone
Temperate Zone
Temperate Zone
South Frigid Zone
Torrid Zone
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17. AGRA
16
0
C in Jan
DARJILING
4
0
C in January
ALTITUDE
HIGH ALTITUDE
LOW ALTITUDE
Temperature decreased from low to high altitude
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18. Air Temperature decreases with altitude.
Aselevationincreases,theairgetscoolerbecauseof
theenergydrawnfromthesurroundings.
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19. Factors That Affect Climate
Water Bodies
Largebodiesofwatersuchaslakesandoceanshavean
importanteffectonthetemperatureofanareabecause
thetemperatureofthewaterbodyinfluencesthe
temperatureoftheairaboveit.
Atmospheric Circulation
Globalwindsareanotherfactorthatinfluencesclimate
becausetheydistributeheatandmoisturearoundEarth.
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20. Solar Activity
WhentheSunismostactive,itcontainsdarkblemishes
calledsunspots.Theformationofsunspotsappearsto
correspondwithwarmperiodsinEuropeandNorth
America.
Earth Motions
GeographicchangesinEarth’slandandwaterbodies
causechangesinclimate.Changesintheshapeof
Earth’sorbitandthetiltofEarthonitsaxisareother
Earthmotionsthataffectglobalclimates.
Natural Processes That Change Climates
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21. Human Impact on Climate Changes
The Greenhouse Effect
Thegreenhouseeffectisanaturalwarmingofboth
Earth’sloweratmosphereandEarth’ssurfacefromsolar
radiationbeingabsorbedandemittedbythe
atmosphere.
Global Warming
Asaresultofincreasedlevelsofcarbondioxideand
othergreenhousegases,globaltemperatureshave
increased.Thisincreaseiscalledglobalwarming.
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22. The Pressure and Surface Winds
Thepressureandwindsystemofanyareadependonthelatitude
andaltitudeoftheplace.Itinfluencesthetemperatureandrainfall
pattern.
TheclimateandweatherconditionsinIndiaaregovernedbythe
atmosphericconditionslike:
•Pressure and surface winds;
•Upper air circulation; and
•Western cyclonic disturbances and tropical cyclones.
Indialiesinthenortheasterlywindsregion.Thesewindsoriginate
fromthesubtropicalhigh-pressurebeltofthenorthern
hemisphere.Theyblowsouth,getdeflectedtotherightduetothe
Coriolisforceandmovetowardsequatoriallow-pressurearea.
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23. 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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24. AIR MASSES CIRCULATE GLOBALLY
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•AttheEquator,temperaturesarerelatively
high.Landandwatermassesheatupandasa
resultthesewarmtheairoverthem.
•Airheatedattheequatorialregionrisesto
thetopoftheatmosphere.
•Moreairrisingbeneathitforcestheairmass
tospreadnorthandsouthtowardthepoles.

25. Coriolis Effect
•TherotationoftheEarthcausesallmoving
objectsintheNorthernHemisphere,
includingairmass,todeflecttotherightand
thoseintheSouthernHemispheretomoveto
theleft.
•ThisCorioliseffectisabsentattheEquator.
•CoriolisForce-preventsadirectsimpleflow
fromtheEquatortothePoles.
•Thisisalsoknownas‘Ferrel’sLaw’.
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26

27. The Pressure and Surface Winds in India
ThepressureandwindconditionsinIndiaisunique.Duringwinter,
thereisahigh-pressureinthenorthoftheHimalayas.Colddry
windsblowfromthisregiontothelow-pressureareasoverthe
oceanstothesouth.Insummer,alow-pressureareadevelopsover
interiorAsiaandinnorth-westernIndia.Thiscausesacomplete
reversalofthedirectionofwindsduringsummer.Airmovesfrom
thehigh-pressureareaoverthesouthernIndianOcean,inasouth-
easterlydirection,crossestheequator,andturnsrighttowardsthe
low-pressureareasovertheIndiansubcontinent.Theseareknown
astheSouthwestMonsoonwinds.Thesewindsblowoverthe
warmoceans,gathermoistureandbringwidespreadrainfallover
themainlandofIndia.
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28. ARABIAN
SEA
BAY OF
BENGAL
INDIAN OCEAN
LOW AND HIGH PRESSURE
HIGH PRESSURE
IN WINTER
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29. MUMBAI
CHENNAI
KOLKOTA
DELHI
SIMLA
DISTANCE FROM SEA
Coastal areas have equable climate where
as Interior parts have extreme climate.
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30. Relief
•Relieftooplaysamajorroleindetermining
theclimateofaplace.Highmountainsact
asbarriersforcoldorhotwinds;theymay
alsocauseprecipitationiftheyarehigh
enoughandlieinthepathofrain-bearing
winds.Theleewardsideofmountains
remainsrelativelydry.
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31. Receives high
rainfall
Receives low
rainfall
RELIEF
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32. RELIEF
The Rain Shadow Effect
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34. Jet Stream
•TheupperaircirculationinIndiaisdominated
byawesterlyflow,knownasthejetstream.
•Theseareanarrowbeltofhighaltitude(above
12,000m)westerlywindsinthetroposphere.
Theirspeedvariesfromabout110km/hin
summertoabout184km/hinwinter.
•Manyjetstreamshavebeenidentified.The
mostconstantarethemid-latitudeandthesub
tropicaljetstream.
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35. TIBET
JET STREAM IN WINTER
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36. Jet Stream
Jetstreamsarelocatedat27°-30°northlatitude,are
knownassubtropicalwesterlyjetstreams.OverIndia,
thesejetstreamsblowsouthoftheHimalayas,all
throughtheyearexceptinsummer.Thewesterncyclonic
disturbancesexperiencedinthenorthandnorth-western
partsofthecountryarebroughtinbythiswesterlyflow.
Insummer,thesubtropicalwesterlyjetstreammoves
northoftheHimalayaswiththeapparentmovementof
theSun.Aneasterlyjetstream,calledthetropical
easterlyjetstreamblowsoverpeninsularIndia,
approximatelyover14°Nduringthesummer.
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37. JET STREAM IN SUMMER
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38. Western Disturbances
•Thewesterncyclonicdisturbancesareweather
phenomenaofthewintermonthsbroughtinbythe
westerlyflowfromtheMediterraneanregion.They
usuallyinfluencetheweatherofthenorthandnorth-
westernregionsofIndia.Tropicalcyclonesoccurduring
themonsoonaswellasinOctober-November,andare
partoftheeasterlyflow.Thesedisturbancesaffectthe
coastalregionsofthecountry.
•ThusveryoftenthecoastofOrissaandAndhraPradesh
areaffectedbythosedisasters.
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39. WESTERN DISTURBANCE
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40. OCEAN CURRENTS
Solar energy, wind, and Earth’s rotation creates Ocean currents
Current-thesystematicpattersofwatermovement.
Gyres-twogreatcircularwatermotion.
NorthernHemisphere-theoceancurrentmovesclockwise.
SouthernHemisphere-theoceancurrentmoveanti-clockwise.
Tradewindspushwarmsurfacewaterswestwardattheequator.
Asthewatersencounterthecontinents,theysplitintonorth-
andsouth-flowingcurrentsalongtheeasterncoast,forming
northandsouthgyres.
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41. SurfaceWaterblownbythewindsatpointAwillweirstothe
rightofitsinitialpathandcontinueeastward.Wateratpoint
Bweirstotherightandcontinueswestward.
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44. WindsdrivenbyunevensolarheatingandEarth’sspin,drivethe
movementoftheocean’ssurfacecurrents.Theprimemoversarethe
powerfulwesterliesandthepersistenttradewinds(easterlies)
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45. TheKöppenclimateclassificationsystemuses
meanmonthlyandannualvaluesoftemperatureand
precipitationtoclassifyclimates.
AccordingtotheKöppenclassification,theearthcanbe
dividedintoseveralmajorclimaticzonesandbands:
The KöppenClimate 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 Antarctica
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46. Tropical Climate
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47. Subtropical Climate
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48. Arid Climate
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49. Equatorial Climate
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50. Semiarid Climate
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51. Mediterranean Climate
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52. Temperate Climate
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53. Oceanic Climate
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54. Continental Climate
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55. Subarctic Climate
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56. Polar Climate
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57. Polar Climate
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Polar climates are those in which the mean temperature
of the warmest month is below 10
o
C.

58. Climate of Antarctica
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59. The Indian Monsoon
TheclimateofIndiaisstronglyinfluencedby
monsoonwinds.ThesailorswhocametoIndiain
historictimeswereoneofthefirsttohavenoticed
thephenomenonofthemonsoon.Theybenefited
fromthereversalofthewindsystemastheycame
bysailingshipsatthemercyofwinds.TheArabs,
whohadalsocometoIndiaastradersnamedthis
seasonalreversalofthewindsystem‘monsoon’.
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60. Atmospheric Conditions over the Indian Subcontinent
in the Month of January
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61. Atmospheric Conditions over the Indian Subcontinent
in the Month of June
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62. Facts of Mechanism of the Monsoons
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InIndia,themonsoonsareexperiencedinthetropicalarea
roughlybetween20°Nand20°S.TheFollowingfactsarethe
MechanismoftheMonsoons.
(a)Thedifferentialheatingandcoolingoflandandwater
createslowpressureonthelandmassofIndiawhilethe
seasaroundexperiencecomparativelyhighpressure.
(b)TheshiftofthepositionofInterTropicalConvergenceZone
(ITCZ)insummer,overtheGangaplain(thisistheequatorial
troughnormallypositionedabout5°Noftheequator.Itisalso
knownasthemonsoon-troughduringthemonsoonseason).

63. Inter Tropical Convergence Zone (ITCZ)
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TheInterTropicalConvergenceZone
(ITCZ)isabroadtroughoflowpressure
inequatoriallatitudes.Thisiswherethe
northeastandthesoutheasttradewinds
converge.Thisconvergencezonelies
moreorlessparalleltotheequatorbut
movesnorthorsouthwiththeapparent
movementofthesun.

64. Facts of Mechanism of the Monsoons
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(c)Thepresenceofthehigh-pressurearea,eastof
Madagascar,nearlyat20°SovertheIndianOcean.The
intensityofthishigh-pressureareaaffectstheIndian
Monsoon.
(d)TheTibetanplateaugetsintenselyheatedduring
summer,resultsinstrongverticalaircurrentsandthe
formationoflowpressureovertheplateauatabout9km
abovesealevel.
(e)Themovementofthewesterlyjetstreamtothe
northoftheHimalayasandthepresenceofthetropical
easterlyjetstreamovertheIndianpeninsuladuring
summer.

65. Southern Oscillation
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Thechangesinthepressureconditionsoverthesouthern
oceansalsoaffectthemonsoons.Whenthetropicaleasternsouth
PacificOceanexperienceshighpressure,thetropicaleasternIndian
Oceanexperienceslowpressure.Butsometimes,thereisareversalin
thepressureconditionsandtheeasternPacifichaslowerpressurein
comparisontotheeasternIndianOcean.Thisperiodicchangein
pressureconditionsisknownastheSouthernOscillationorSO.
ThedifferenceinpressureoverTahitiinPacificOceanandDarwinin
northernAustraliaofIndianOceanispredictedtheintensityofthemonsoons.
Ifthepressuredifferenceswerenegative,itwouldmeanbelowaverageand
latemonsoons.AfeatureconnectedwiththeSOistheElNino,awarmocean
currentthatflowspastthePeruvianCoast,inplaceofthecoldPeruvian
current,every2to5years.Thechangesinpressureconditionsareconnected
totheElNino.Hence,thephenomenonisreferredtoasENSO(ElNino
SouthernOscillations).

66. Darwin
Tahiti
SOUTHERN OSCILLATION
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67. Effect of El Niño
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ElNinoisanamegiventothe
periodicdevelopmentofawarm
oceancurrentalongthecoastof
Peruasatemporaryreplacementof
thecoldPeruviancurrent.‘ElNino’
isaSpanishwordmeaning‘the
child’,andreferstothebabyChrist,
asthiscurrentstartsflowingduring
Christmas.ThepresenceoftheEl
Ninoleadstoanincreaseinsea-
surface temperatures and
weakeningofthetradewindsinthe
region.

68. Homboldt Cold
Current
EL-NINO EFFECTS
1990
Delay in
Monsoon
Equatorial Warm
Current
El-Nino
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69. Beginning of the Monsoon
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Thedurationofthemonsoonisbetween100-120daysfrom
earlyJunetomid-September.
Duringitsarrival,thenormalrainfallincreasessuddenlyand
continuesconstantlyforseveraldays.Thisisknownasthe
‘burst’ofthemonsoon,andcanbedistinguishedfromthe
pre-monsoonshowers.
ThemonsoonarrivesatthesoutherntipoftheIndian
peninsulagenerallybythefirstweekofJune.
Subsequently,itproceedsintotwo–
(i)theArabianSeabranchand
(ii)theBayofBengalbranch.

70. Beginning of the Monsoon
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TheArabianSeabranchreachesMumbaiabouttendayslateron
approximatelythe10thofJune.Thisisafairlyrapidadvance.
TheBayofBengalbranchalsoadvancesrapidlyandarrivesinAssam
inthefirstweekofJune.Theloftymountainscausesthemonsoon
windstodeflecttowardsthewestovertheGangaplains.
Bymid-JunetheArabianSeabranchofthemonsoonarrivesover
Saurashtra-Kuchchhandthecentralpartofthecountry.TheArabian
SeaandtheBayofBengalbranchesofthemonsoonmergeoverthe
north-westernpartoftheGangaplains.
DelhigenerallyreceivesthemonsoonshowersfromtheBayofBengal
branchbytheendofJune(tentativedateis29thofJune).BytheJuly
firstweek,westernUttarPradesh,Punjab,Haryanaandeastern
Rajasthanexperiencethemonsoon.Bymid-July,themonsoonreaches
HimachalPradeshandtherestofthecountry.

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72. End of the Monsoon
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Withdrawalortheretreatofthemonsoonisamoregradual
process.Thewithdrawalofthemonsoonbeginsinnorth-western
statesofIndiabyearlySeptember.Bymid-October,itwithdraws
completelyfromthenorthernhalfofthepeninsula.Thenit
quicklywithdrawfromthesouthernhalfofthepeninsula.By
earlyDecember,themonsoonhastotallywithdrawnfromthe
country.
Theislandsreceivetheveryfirstmonsoonshowers,fromsouthto
north,betweenthelastweekofAprilandthefirstweekofMay.
Thenitwithdrawfromnorthtosouthduringthefirstweekof
DecembertothefirstweekofJanuary.Bythistime,theother
partsofthecountryisalreadyinfluencingthewintermonsoon.

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75. RHYTHM OF SEASONS
COLD WEATHER
RETREATING MONSOONHOT WEATHER
SOUTH WEST MONSOON
Let us discuss each of them individually
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76. 02-03-2015
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76
Themonsoontypeofclimateischaracterisedbyadistinct
seasonalpattern.Theweatherconditionsgreatlychangefromone
seasontotheother.Thesechangesareparticularlynoticeablein
theinteriorpartsofthecountry.But,thecoastalareasdonot
experiencemuchvariationintemperaturethoughthereisvariation
inrainfallpattern.
InIndia,Fourmainseasonscanbeidentified:
(i)thecoldweatherseason,
(ii)thehotweatherseason,
(iii)theadvancingmonsoonand
(iv)theretreatingmonsoonwithsomeregionalvariations.

77. COLD WEATHER SEASON
►Itextends from
DecembertoFebruary.
►Verticalsunraysshift
towards southern
hemisphere.
►NorthIndiaexperiences
intensecoldwhereas
thisseasonisnotwell
definedinsouthIndia.
►Lightwindblowmakes
thisseasonpleasantin
southIndia.
►Occasional tropical
cyclonevisiteastern
coastinthisseason.
Tropical Cyclone
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78
Thecoldweatherseasonbeginsfrommid-NovemberinnorthernIndiaand
staystillFebruary.DecemberandJanuaryarethecoldestmonths.The
temperaturedecreasesfromsouthtothenorth.Theaveragetemperatureof
Chennai,ontheeasterncoastisbetween24°-25°Celsius,whileinthenorthern
plains,itrangesbetween10°-15°Celsius.Daysarewarmandnightsarecold.
FrostiscommoninthenorthandthehigherslopesoftheHimalayasexperience
snowfall.
Duringwinter,thenortheasttradewindsblowfromlandtosea.So,mostpartof
thecountryfacesadryseason.SomeamountofrainfalloccursontheTamil
Naducoastfromthesewindsas,tradewindsblowfromseatoland.
Inthenorthernpartofthecountry,afeeblehigh-pressureregiondevelops,with
lightwindsmovingoutwardsfromthisarea.Influencedbytherelief,these
windsblowthroughtheGangavalleyfromthewestandthenorthwest.The
weatherisnormallymarkedbyclearsky,lowtemperaturesandlowhumidity
andfeeble,variablewinds.

79. 25
0
C
25
0
C
20
0
C
20
0
C
20
0
C
15
0
C
20
0
C
10
0
C`
TEMPERATURE -JANUARY
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80. PRESSURE-JANUARY
101
4
HIGH
PRESSURE
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Inthenorthernplains,thereistheinflowofcyclonic
disturbancesfromthewestandthenorthwest.Theselow-
pressuresystems,fromtheMediterraneanSeaandwestern
AsiaandmoveintoIndia,alongwiththewesterlyflow.They
causethewinterrains(locallyknownas‘mahawat’)overthe
plainsandsnowfallinthemountains.Althoughtheamountof
rainfallissmall,itismoreimportanceforcultivatingthe‘rabi’
crops.
But,thepeninsularregiondoesnothaveawell-definedcold
season.Thereisrareseasonalchangeintemperature
patternduringwintersduetothemoderatinginfluenceofthe
sea.

82. WIND DIRECTION-WINTER
Bay of Bengal
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83. WINTER RAINFALL
RAINFALL DUE
TO WESTERN
DISTURBANCES
RAINFALL DUE
TO NORTH EAST
WIND
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84. Winter is cold.
Children dress warmly to
play in the snow.
Animals head to their winter
homes.
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85. HOT WEATHER SEASON
►ItextendsfromMarchto
May.
►Verticalsunraysshift
towards Northern
hemisphere.
►Temperature rises
graduallyfromsouthto
north.
►Highest Temperature
experiencesinKarnataka
inMarch, Madhya
PradeshinApriland
RajasthaninMay.
March 30
0
C
April 38
0
C
May 48
0
C
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86. 02-03-2015
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86
DuetotheapparentnorthwardmovementoftheSun,theglobal
heatbeltshiftsnorthward.So,fromMarchtoMay,itishotweather
seasoninIndia.InMarch,thehighesttemperatureisabout38°C,in
Deccanplateau.InApril,temperaturesinGujaratandMadhya
Pradesharearound42°C.InMay,45°Ctemperatureiscommonin
thenorth-westernpartsofthecountry.InpeninsularIndia,
temperaturesremainlowerduetothemoderatinginfluenceofthe
oceans.
Thesummermonthsexperiencerisingtemperatureandfallingair
pressureinthenorthernpartofthecountry.BytheendofMay,an
elongatedlow-pressureareadevelopsintheregionextendingfrom
theTharDesertinthenorthwesttoPatnaandChotanagpurplateau
intheeastandsoutheast.Circulationofairbeginstosetinaround
thistrough.

87. TEMPERATURE -JULY
25
0
C
30
0
C
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88. PRESSURE-JULY
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89. LOO
KALBAISAKHI
BARDOLI
CHHEERHA
MANGO
SHOWER
BLOSSOM
SHOWER
STORMS IN HOT WEATHER SEASON
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90. 02-03-2015
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90
Animportantfeatureofthesummerseasonisthe‘loo’.Theseare
strong,gusty,hot,drywindsblowingduringtheday,sometimestill
lateeveningoverthenorthandNorth-westernIndia.Direct
exposuretothesewindsmaybeharmful.Duststormsarevery
commonduringMayinnorthernIndia.Thesestormsbring
temporaryreliefastheylowerthetemperatureandmaybringlight
rainandcoolbreeze.Thisisalsotheseasonforlocalised
thunderstorms,associatedwithviolentwinds.InWestBengal,
thesestormsareknownasthe‘KaalBaisakhi’.
Bycloseofthesummerseason,pre-monsoonshowersarecommon
especially,inKeralaandKarnataka.Theyhelpintheearlyripening
ofmangoes,andareoftenreferredtoas‘mangoshowers’.

91. 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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92. Advancing Monsoon (The Rainy Season)
SOUTH WEST MONSOON SEASON
►ItextendsfromJuneto
September.
►Intenseheatinginnorth
westIndiacreateslow
pressureregion.
►Lowpressureattractthe
windfromthesurrounding
region.
►Afterhavingrainsfora
fewdayssometime
monsoonfailstooccurfor
oneormoreweeksis
knownasbreakinthe
monsoon.
HIGH TEMPERATURELOW PRESSURE
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93. INTER TROPICAL CONVERGENCE ZONEEQUATOR
MONSOON WIND
Arabian sea
Branch
Bay of Bengal
Branch
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94. ONSET OF SW MONSOON
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95. 02-03-2015
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95
ByearlyJune,thelow-pressureconditionoverthenorthernplains
attractsthetradewindsofthesouthernhemisphere.Thesesouth-
easttradewindsoriginateoverthewarmsubtropicalareasofthe
southernoceans.Thesewindsarestrongandblowatanaverage
velocityof30kmph.Withtheexceptionoftheextremenorth-west,
themonsoonwindscoverthecountryinaboutamonth.
Thesouth-westmonsoonentirelychangestheweatherinIndia.The
WesternGhatsreceivesheavyrainfall,morethan250cm.Therain
shadowareaslikeDeccanPlateauandpartsofMadhyaPradesh
alsoreceivesrain.Thenorth-easternpartofthecountryreceives
themaximumrainfall.Mawsynraminthesouthernrangesofthe
KhasiHillsreceivesthehighestaveragerainfallintheworld.
RainfallintheGangavalleydecreasesfromtheeasttothewest.
RajasthanandpartsofGujaratgetscantyrainfall.

96. 02-03-2015
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96
Themonsoonrainstakeplaceonlyforafewdaysatatime.They
areinterspersedwithrainlessintervals.Thesebreaksinmonsoon
arerelatedtothemovementofthemonsoontrough.Thetroughand
itsaxiskeeponmovingnorthwardorsouthward,whichdetermines
thespatialdistributionofrainfall.Whenevertheaxisshiftscloser
totheHimalayas,widespreadrainoccurinthemountainous
catchmentareasoftheHimalayanrivers,whichalsocausefloods.
Thefrequencyandintensityoftropicaldepressionsdeterminethe
amountanddurationofmonsoonrains.Thesedepressionsformat
theBayofBengalandcrossovertothemainland.Thedepressions
followtheaxisofthe“monsoontroughoflowpressure”.Itcauses
heavyfloodsinonepart,anddroughtsintheother.Sometimesit
disturbsthefarmingscheduleofmillionsoffarmersalloverthe
country.

97. ►ItextendsfromOctober
toNovember
►Verticalsunraysstart
shiftingtowardsNorthern
hemisphere.
►Lowpressureregionshift
fromnorthernpartsof
Indiatowardssouth.
►Owingtotheconditions
ofhightemperatureand
humidity,theweather
becomes rather
oppressive.Thisis
commonlyknownasthe
‘Octoberheat’
RETREATING MONSOON SEASON
LOW PRESSURE
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98. WITHDRAWAL OF MONSOON
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99. 02-03-2015
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99
Partsofwesterncoastandnorth-easternIndiareceiveoverabout
400cmofrainfallannually.But,inwesternRajasthanand
adjoiningpartsofGujarat,HaryanaandPunjabitislessthan60
cm.RainfallisequallylowintheinterioroftheDeccanplateau,
andeastoftheSahyadris.Becauseoflowprecipitationfound
aroundLehinJammuandKashmir.Therestofthecountry
receivesmoderaterainfall.SnowfallisrestrictedtotheHimalayan
region.
Basedonthenatureofmonsoons,theannualrainfallishighly
variablefromyeartoyear.Variabilityishighintheregionsoflow
rainfallsuchaspartsofRajasthan,Gujaratandtheleewardsideof
theWesternGhats.Similarly,theareasofhighrainfallareoften
affectedbyfloods,areasoflowrainfallaredrought-prone.

100. DISTRIBUTION OF RAINFALL
> 200cm
100-200cm
50-100 cm
< 50cm
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101. 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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102. Leaves change to yellow,
orange, and red.
Picking fruit and
vegetables.
Animals get ready for
winter.
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103. 02-03-2015
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103
TheHimalayasprotectthesubcontinentfromextremelycoldwinds
fromcentralAsia.ThisenablesnorthernIndiatohaveuniformly
highertemperatureswhencomparedtootherareasonthesame
latitudes.
Similarly,thepeninsularplateau,undertheinfluenceofthesea
fromthreesides,hasmoderatetemperatures.
TheunifyinginfluenceofthemonsoonontheIndiansubcontinent
isquiteperceptible.Theseasonalalterationofthewindsystems
andtheassociatedweatherconditionsprovidearhythmiccycleof
seasons.
TheIndianlandscape,itsanimalandplantlife,itsentire
agriculturalcalendarandthelifeofthepeople,includingtheir
festivities,revolvearoundthisphenomenon.

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