The climate of India is strongly influenced by monsoon
winds.
 The monsoons are experienced in the tropical area
between 20º N to 20º S.
 Let us understand the following facts:
1. The differential heating and cooling of land and water.
2. The shift of the position of Inter Tropical Convergence
Zone. (ITCZ)- The equatorial trough (monsoon trough)
from 5º N shifts to Ganga Plain in summer.
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3. The presence of the high pressure area, east of
Madagascar. (approx. at 20º over the Indian
ocean.) The intensity and position of the this
high pressure effects the IM
4.The Tibetan plateau gets intensely heated during
summer and which results in strong vertical air
currents and low pressure at 8 km above the
sea level.
5. The movement of westerly jet stream to the
north of Himalayas and the presence of tropical
easterly jet stream over the Indian Peninsula.
Deserts & winds
1) Deserts: where & why
Middle-latitude deserts
u exist in rain shadows.
Deserts & winds
1) Deserts: where & why
SOUTHERN OSCILLATION
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Changes in the pressure conditions over the
southern ocean also affect the monsoon.
Normal condition- The tropical eastern south
Pacific ocean experiences high pressure and the
tropical eastern Indian ocean experience low
pressure.
But in certain years there is a reversal in the
above condition. This periodic change is known
as SO.
EL NINO
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EL NINO EVENT connected to SO- During
which a warm ocean current that flows
past the Peruvian Coast, in place of the
cold Peruvian current, every 2 to 5 years.
The changes in pressure conditions are
connected to the El Nino.
HOW TO PREDICT THE INTENSITY
OF MONSOON
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The difference in pressure over Tahiti and
Darwin in north Australia (Pacific ocean,
18º S/149º W and Indian Ocean
12º30’S/131ºE) is computed.
If the pressure difference were negative, it
would mean below average and late
monsoon.
The onset of monsoon
Monsoon winds are affected by different
atmospheric conditions.
In May- summer month, the temperature riseslow pressure trough is developed. In June this
trough attracts south-east trade winds from the
south of equator. These moisture carrying winds
deflect right in lands and known as southwesterly winds.
These strong winds overrun the whole country in a
months time.
DIVISION OF MONSOON WINDS
BY PENINSULA
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THE ARABIAN SEA BRANCH
It enters Kerela till 1st June.
It reaches Mumbai till 10th June.
It arrives over Saurashtra-Kuchchh and central India till
Mid June
THE BAY OF BENGAL BRACH
It advances rapidly and reaches in Assam in the 1st week
of June.
It turns to Ganga Plain because of Mountain range
It causes rain in Delhi till 29th June and in Punjab till 5th
July.
Merging of branches
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Both the branches merge over northwestern part of Ganga Plain.
In the western Himalayas ( Himachal
Pradesh) They cause heavy rainfall.
The islands receive the very first monsoon
from south to north from the 1st week of
April to 1st week of May.
WITHDRAWAL OF MONSOON
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It begins in north-western states by early
sep.
It withdraws completely from the northern
half of peninsula till mid oct. in slow pace.
It withdraws from southern part rapidly.
By early Dec. Withdrawal is completed.
From the islands withdrawal takes place
from 1st week of Dec. to 1st week of Jan
from north to south direction.
THE SEASONS
THE COLD WINTER SEASON
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Northern India ( Mid Nov. to Feb.)
Dec. and Jan. coldest months
Normal tem. 10º to 15ºC
Days are warmer than nights
Frost in common in north and snowfall in
Himalayas
The northern trade winds prevail over
country. They do not cause rain in north
india.(Land to sea)
NORTHERN INDIA
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In northern india high pressure regions
develops and with light winds moving outwards
from this area.
Because of relief these winds blow through
Ganga valley from west to the northwest.
Clear sky, low temp., and variable winds.
Rain fall- The two parts of india get rainfall.
1. North-west part of india- from the
Mediterranean cyclones.
2.Tamil Nadu- north-east winds which blow over
the Bay of Begal.
SOUTHERN INDIA
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Average Tem- 24º-25
Temperature decrease from south to
north.
The peninsula region does not have well
defined cold season due to moderating
influence of the sea.
THE HOT WEATHER SEASON
march to may
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Heat belt shifts from south to north- due to the
apparent movement of sun.
In March, April and May the highest temp. occur
in The Deccan (38ºC), Gujarat (42ºC) and
North-west of India(45ºC).
In may rising temp. leads to a low pressure in a
wider area from Thar Desert to Chhota Nagpur.
Due to low pressure, the moisture-laden winds
from the Arabian Sea are attracted towards this
area.
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Consequently there is (about 158cm) rainfall in
the Raj Mahal and Chhota Nagpur hills lying
between the Satpuras and the Vindhyas.
Kerala and Karnataka also experience the premonsoon showers. They help in early ripening of
mangoes- so also known as Mango showers
In Peninsula temp. remains lower due to the
moderating influence of oceans.
Other Climatic Features
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1. Loo- Strong, gusty, hot and dry winds blowing
over north and north-west during the day
(Sometimes until late in the evening).
2. Dust storms-In may in north.
They bring temporary relief rain and cool
breeze.
Thunderstorms-with violent winds, torrential
downpour with hails.-In west Bengal these are
known as Kaal Baisakhi.
ADVANCING MONSOON
RAINY SEASON
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In June the low pressure in north intensifies. It
attracts the south-west trade winds from
subtropical areas of southern oceans(Southern
hemisphere). They cross the equator and blow
in a south-west and enter in Indian Peninsula.
They move from sea to land so bring abundant
moisture.
Speed- 30km/h
Break or Burst
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Early in the season, the windward side of
western Ghats receives more than 250cm rainfall
but decrease when it goes further.
The Deccan Plateau and MP get less rainfall
because they are in the rain shadow area.
Other branch cause rainfall in north-east
(Mawsynram) in Khasi range get heighest
rainfall.
Rainfall in Ganga valley decreases from east to
west. So Gujarat and Rajasthan get scanty
rainfall.
DRY SPELL OR BREAKS
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Monsoon has wet and dry spells.
Monsoon rains take place only few days at a
time.
These breaks in monsoon are related to the
movement of monsoon trough and its axis keep
on moving northward or southward. It
determines the spatial distribution of rainfall.
DIFFERENTIAL RAINFALL
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Whenever the axis moves to Himalaya, It gets
heavy rainfall and the plains are dry and visa
versa.
Heavy rainfall brings devastating flood.
The frequency and intensity of tropical
depressions form at the head of Bay of Bengal
and cross over to mainland.
The depression follow the axis of the monsoon
trough of low pressure.
(Effects of rainfall)
RETREATING MONSOONS
(Transition or Autumn Season)
From hot rainy to dry winter
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During Oct.-Nov. with the apparent
movement of the sun towards the south,
the low pressure trough become weaker.
This is gradually replaced by high
pressure.
The south-west monsoon winds weaken
and start withdrawing gradually.
Weather phenomena
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Clear sky and rise in temp.
Days are warm, nights are cool and pleasant.
Land is still moist.
Oct. heat is present because of rise in temp. and
humidity.
In northern india temp. starts falling in mid oct.
Low pressure over north-west part starts shifting
towards Bay of Bengal and create cyclonic
disturbances over the Andaman sea.
Rain fall
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These cyclones cross the eastern coast
and cause heavy and widespread rainfall.
They are often destructive. They struck
the deltas of krishna, Godavari and Kaveri.
Sometime in Orissa, West Bengal and
Bangladesh.
The Coromonadel coast is derived from
depression and cyclones.
DISTRIBUTION OF RAINFALL
Regions of heavy rainfall(Over 200 cm rianfall Western slopes of Western Ghats, West Coastal
Plain, hills of Meghalaya. Highest rainfall in
Mawsynram above 1000cm.
 Regions of Moderate Rainfall-(100-200cm)
Area adjoining to western ghats, Brahmaputra
valley, Orissa, Bihar, Jharkhand, Chhatisgarh,
MP, some parts of UP, HP, J & K, etc.
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DISTRIBUTION OF RAINFALL
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Regions of Low rainfall (50-100cm) Upper
ganga valley, parts of Punjab, Haryana, J
& K, Andhara Pradesh and Tamil Nadu.
Regions of Scanty rainfall (less than 50cm
annual rainfall)-Kutch, Leh in Kashmir,
Western Rajasthan. Some parts of punjab
and Haryana.
CAUSES OF UNEVEN
DISTRIBUTION
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1. Hilly and forest area get heavy rainfall because of
high altitude and abundance of trees.
2. The areas without mountains to check rain bearing
winds get scanty rainfall. As in Rajasthan, the Aravalli
Hills standing parallel to the monsoon.
3. Areas which come in the rain shadow like western
side of western ghats or Ladakh.
4. The areas which come first in the way of rain bearing
winds get more as compared to areas which come last of
all. As Kolkata gets more rain than Delhi.