CLIMATE
·
Refers to the sum total of
weather conditions and variations over a large area for a long period of time
(more than thirty years).
Weather
1.
Refers to the state of the
atmosphere over an area at any point of time.
2.
The elements of weather and
climate are the same, i.e. temperature, atmospheric pressure, wind, humidity
and precipitation.
3.
The word monsoon
is derived from the Arabic word ‘mausim’ which
literally means season.
4.
Monsoon’ refers to the seasonal
reversal in the wind direction during a year.
5.
The climate of India is
described as the ‘monsoon’ type
6.
This type of climate is found
mainly in the south and the Southeast Asia
7.
In the Thar Desert the day
temperature may rise to 50°C, and drop down to near 15°C the same night.
8.
There is hardly any difference
in day and night temperatures in the Andaman and Nicobar islands or in Kerala.
CLIMATIC
CONTROLS
1. There are six major
controls of the climate of any place
·
Latitude
·
Altitude
·
Pressure
·
Wind system
·
Distance from the sea
·
Ocean currents and relief
features.
Latitude
·
Due to the curvature of the
earth, the amount of solar energy received varies according to latitude
Altitudes
·
As one goes from the surface of
the earth to higher altitudes, the atmosphere becomes less dense and
temperature decreases. The hills are therefore cooler during summers.
Pressure and wind
·
The pressure and wind system of
any area depend on the latitude and altitude of the place. Thus it influences
the temperature and rainfall pattern.
Distance
from the sea
·
The sea exerts a moderating
influence on climate: As the distance from the sea increases, its moderating
influence decreases and the people experience extreme weather conditions. This
condition is known as continentally (i.e. very hot during summers and very cold
during winters).
Ocean currents
·
Ocean currents along with
onshore winds affect the climate of the coastal areas, For example, any coastal
area with warm or cold currents flowing past it, will be warmed or cooled if
the winds are onshore.
Relief
·
Plays a major role in
determining the climate of a place. High mountains act as barriers for cold or
hot winds; they may also cause precipitation if they are high enough and lie in
the path of rain-bearing winds. The leeward side of mountains remains dry.
FACTORS AFFECTING
INDIA’S CLIMATE
Latitude
1.
The Tropic of Cancer passes
through the middle of the country from the Rann of Kuchchh in the west to
Mizoram in the east
2.
Almost half of the country,
lying south of the Tropic of Cancer, belongs to the tropical area
3.
All the remaining area, north
of the Tropic, lies in the sub-tropics.
4.
Therefore, India’s climate has
characteristics of tropical as well as subtropical climates.
Altitude
1.
India has mountains to the
north, which have an average height of about 6,000 metres.
2.
India also has a vast coastal
area where the maximum elevation is about 30 metres.
3.
The Himalayas prevent the cold
winds from Central Asia from entering the subcontinent.
4.
It is because of these
mountains that this subcontinent experiences comparatively milder winters as
compared to central Asia.
Pressure
and Winds
1.
The climate and associated
weather conditions in India are governed by the following atmospheric
conditions:
•
Pressure and surface winds;
•
Upper air circulation;
•
Western cyclonic disturbances
and tropical cyclones.
2.
India lies in the region of
north easterly winds.
3.
These winds originate from the
subtropical high-pressure belt of the northern hemisphere.
4.
They blow south, get deflected
to the right due to the Coriolis force, and move on towards the equatorial
low-pressure area.
5.
Generally, these winds carry
very little moisture as they originate and blow over land.
6.
Therefore, they bring little or
no rain. Hence, India should have been an arid land, but, it is not so
Coriolis force
An apparent force caused by the earth’s rotation. The Coriolis force
is responsible for deflecting winds towards the right in the northern
hemisphere and towards the left in the southern hemisphere. This is also known
as ‘Ferrel’s Law’.
7.
During winter, there is a
high-pressure area north of the Himalayas.
8.
Cold dry winds blow from this
region to the low-pressure areas over the oceans to the south.
9.
In summer, a low-pressure area
develops over interior Asia as well as over north-western India.
10.
This causes a complete reversal
of the direction of winds during summer.
11.
Air moves from the
high-pressure area over the southern Indian Ocean, in a south-easterly
direction, crosses the equator,
12.
Turns right towards the
low-pressure areas over the Indian subcontinent.
13.
These are known as the
Southwest Monsoon winds.
14.
These winds blow over the warm
oceans, gather moisture and bring widespread rainfall over the mainland of
India.
Jet stream
1.
The upper air circulation in
this region is dominated by a westerly flow. An important component of this
flow is the jet stream
2.
These jet streams are located
approximately over 27°-30° north latitude, therefore, they are known as
subtropical westerly jet streams
3.
Over India, these jet streams
blow south of the Himalayas, all through the year except in summer.
4.
The western cyclonic
disturbances experienced in the north and north-western parts of the country
are brought in by this westerly flow.
5.
In summer, the subtropical
westerly jet stream moves north of the Himalayas with the apparent movement of
the sun.
Tropical easterly
An easterly jet
stream, called the tropical easterly Jetstream blows over peninsular India,
approximately over 14°N during the summer months.
Jet stream
These are a narrow belt of high altitude (above 12,000 m) westerly
winds in the troposphere. Their speed varies from about 110 km/h in summer to about
184 km/h in winter. A number of separate jet streams have been identified. The
most constant are the mid-latitude and the sub-tropical jet stream.
Western
Cyclonic Disturbances
1.
The western cyclonic
disturbances are weather phenomena of the winter months brought in by the
westerly flow from the Mediterranean region.
2.
They usually influence the
weather of the north and north-western regions of India
3.
Tropical cyclones occur during
the monsoon as well as in October -November, and are part of the easterly flow.
4.
These disturbances affect the
coastal regions of the country.
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