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 mausimwhich
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 inlandlocked areas and low in coastal areas.
The
annual precipitation in India varies from 400cm in Meghalayato less than 10
cm in Ladakh and western Rajastan.
Most
parts of India receive rainfall between the months June andSeptember.
The
rainfall in the Northern Plains decreases from east to west.
Tamilnadu
coast gets most of its rainfall during the months ofOctober 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 and300N latitudes.
Tropical
easterly jet stream is located around 140N latitude.
Western
cyclonic disturbances, experienced in the wintermonths, are caused by the influence of westerly winds from theMediterranean 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 ishigher 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 andDarwin 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 asmango 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 monsoonseason.
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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