Class IX
Geography
Unit IV – Climate
Notes
Drainage: It refers to the physical features associated with
the water bodies, rivers and tributaries in an area.
Climate: Sum total of weather conditions and variations over
a large area for a long period of time (more than thirty years)
Weather: State of atmosphere over an area at any point of
time
Monsoon: Seasonal reversal in the wind direction during a
year
Stilts: Pillars or poles that allow a structure to stand at
a height above the ground
Terai: The damp region between the Siwaliks and the Northern
Plains.
Ferrel’s Law: The winds in the northern hemisphere get
deflected to the right and the winds in the southern hemisphere get deflected
to the left.
Coriolis force: An apparent force caused by the earth’s
rotation and is responsible for the deflection of winds to the right in the
northern hemisphere and to the left in the southern hemisphere
Jet streams: Westerly winds blowing at a speed of 110 kmph (in
summer) – 184 kmph (in winter) at an altitude of more than 12,000 m in the
troposphere
ITCZ: Inter Tropical Convergence Zone is where the
north-east trade winds and the south-east trade winds converge.
SO: Southern Oscillation refers to periodic reversal of
pressure conditions between the Pacific Ocean and the Indian Ocean.
ENSO: El Nino Southern Oscillations
The year is divided into seasons on the basis of generalized
monthly conditions of atmosphere.
The climate of India is described as the monsoon
type.
The word ‘monsoon’ is derived from the Arabic word mausim
which means season.
Monsoon climate is found in south Asia and south-east
Asia.
Precipitation in the Himalayas is mostly in the form of snowfall.
Temperature contrasts and seasonal contrasts are high in landlocked
areas and low in coastal areas.
The annual precipitation in India varies from 400cm in Meghalaya
to less than 10 cm in Ladakh and western Rajastan.
Most parts of India receive rainfall between the months June
and September.
The rainfall in the Northern Plains decreases from east
to west.
Tamilnadu coast gets most of its rainfall during the months
of October and November.
Houses in Assam are built on stilts to protect people
from snakes, damp soil and floods.
In the Terai region and in Goa and Mangalore in the Konkan
coast, houses have sloping roofs because the areas experience
heavy rainfall.
Houses in Rajastan have thick walls and flat
roofs because the temperature is harsh and rainfall is scanty.
Air temperature decreases from the equator towards
the poles.
Hills are cooler in summer because temperature decreases
with increase in altitude.
The condition of continentality refers to very hot
summers and very cold winters.
The sea exerts a moderating influence on the climate.
India’s climate has the characteristics of tropical
as well as sub-tropical climates.
The Tropic of Cancer in India runs from the Rann of
Kachch in the west to Mizoram in the east.
The average height of the mountains in the northern part of
India is 6000 m.
The maximum altitude of the coastal part of India is 30
m.
The Himalayas
prevent the cold winds of Central Asia from entering the Indian subcontinent.
India lies in the region of north-easterly winds.
Winds from the high pressure belt of the northern hemisphere
get deflected to the right due to the Coriolis force.
Upper air circulation in India is dominated by a westerly
flow.
Sub-tropical westerly jet streams are located between 270N
and 300N latitudes.
Tropical easterly jet stream is located around 140N
latitude.
Western cyclonic disturbances, experienced in the winter
months, are caused by the influence of westerly winds from the Mediterranean
region.
Western cyclonic disturbances influence the weather of the
north and the north-western regions of India.
Tropical
cyclones, caused by easterlies, affect the coastal parts of India.
Tropical cyclones occur during the monsoon and also during
the months of October and November.
Monsoons are experienced between 200N and 200S
latitudes approximately.
The Ganga Plain is known as the equatorial
trough or the monsoon trough during the monsoon season.
Normally the atmospheric pressure in the south Pacific Ocean
is higher than the atmospheric pressure in the eastern Indian
Ocean.
The intensity of monsoon can be predicted by computing the
pressure difference between Tahiti in the Pacific Ocean and Darwin
in northern Australia.
Negative pressure difference
between Tahiti and Darwin indicate average or late monsoons.
El Nino is a warm
ocean current that flows past the coast of Peru (South America) in place of the
cold Peruvian current every 2-5 years.
El Nino, which starts flowing at Christmas time, is a
Spanish word meaning the child.
The duration of monsoon is 100-120 days from early
June to mid-September.
A sudden increase in rainfall at the time of the monsoon’s
arrival is known as the burst of the monsoon.
The islands of India receive the
very first monsoon.
The islands of India receive the monsoon from the first
week of April to the first week of May.
Monsoon arrives at the southern tip of India generally by the
first week of June.
After reaching Assam, the mountains cause the
monsoons to deflect towards the Ganga Plains.
Delhi receives rain from the Bay of Bengal
branch of the monsoon tentatively by 29 June.
Monsoon reaches Himachal Pradesh by mid-July.
Retreat of monsoon begins in the north-western states
of India by early September.
The monsoon withdraws completely by early December.
The monsoon withdraws from the islands of India from the
first week of December to the first week of January.
Four main seasons
can be identified in India.
The cold weather season begins from mid-November and
extends till February.
December and January
are the coldest months.
Warm days and cold
nights characterize the cold weather season in India.
During the cold weather season, the north-east trade
winds prevail over the country.
The cold weather season in the northern plains
is characterized by cyclonic disturbances from the west.
The winter rainfall in the northern part of India is locally
known as mahawat.
The peninsular region does not have a well-defined
cold season.
The hot weather season in India is from March to May.
Loo refers to
the hot, dry winds that blow over north and north-western India during summer.
Localized thunderstorms in West Bengal are known as Kaal
Baisakhi.
Pre-monsoon showers in Kerala and Karnataka are known as mango
showers.
The windward side of the Western Ghats receives more than
250 cm of annual rainfall.
Monsoons bring the maximum rainfall to the north-eastern
part of the country.
North-east India receives about 400 cm of rainfall
annually.
Mawsynram
in the Khasi Hills receives the highest average rainfall in the world.
Dry spells occur when the axis of the monsoon trough shifts
closer to the Himalayas.
The retreating monsoon season is also known as the
transition season.
Tropical cyclones hit the east coast during the retreating
monsoon season.
The bulk of the rainfall of the Coromandel Coast is
derived from depressions and cyclones.
Elements of climate / weather:
-
Temperature
-
Atmospheric pressure
-
Wind
-
Humidity
-
Precipitation
Climatic variations have given rise to variety in the lives
of people in terms of
-
the food they eat
-
the clothes they wear and
-
the kind of houses they live in
Factors that influence the climate of a place:
-
latitude
-
altitude
-
pressure and wind system
-
distance from the sea
-
ocean currents
-
relief features
Factors that influence the climatic conditions of India:
-
pressure and surface winds
-
upper air circulation
-
western cyclonic disturbances
-
tropical cyclones
Most of the world’s deserts are located in the western
margins of continents because:
-
the winds in the tropics and the
subtropics are easterly, so the precipitation in the west coast is scanty
-
west coasts are washed by cold
currents
Important types of jet streams:
-
mid-latitude jet streams
-
sub-tropical jet streams
Difference between trade winds and monsoons:
-
trade winds are steady
-
monsoons are pulsating
The two branches of monsoon:
-
the Arabian Sea branch and
-
the Bay of Bengal branch
Seasons in India:
-
the cold weather season
-
the hot weather season
-
the advancing monsoon season
-
the retreating monsoon season
Areas of scanty rainfall:
-
Gujarat
-
Western Rajastan
-
The interior of the Deccan
-
The eastern part of the Sahyadris
-
Leh in Jammu and Kashmir
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