1. Define Climate and Weather
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 refers to the state of the atmosphere over an area
at any point of time.
2. Describe Monsoon.
The word monsoon is derived from the Arabic word ‘mausim’
which literally means season. • ‘Monsoon’ refers to the seasonal reversal in
the wind direction during a year.
3. Factors which control the climate
There are six major controls of the climate of any place.
They are: latitude, altitude, pressure and wind system, distance from the sea
(continentally), ocean currents and relief features.
Latitude Due to the curvature
of the earth, the amount of solar energy received varies according to latitude.
As a result, air temperature decreases from the equator
towards the poles.
Altitude 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 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 continentality (i.e. very hot
during summers and very cold during winters)
Ocean currents any coastal
area with warm or cold currents flowing past it, will be warmed or cooled.
Factor affecting India
Latitude Almost half of the
country, lying south of the Tropic of Cancer, belongs to the tropical area. All
the remaining area, north of the Tropic, lies in the sub-tropics.
Altitude India has
mountains to the north. The Himalayas prevent the cold winds from Central Asia from entering the subcontinent.
Pressure and Winds Pressure
and surface winds; • Upper air circulation; and • Western cyclonic disturbances
and tropical cyclones.
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’.
Western Cyclonic Disturbances: The
western cyclonic disturbances are weather phenomena of the winter months
brought in by the westerly flow from the Mediterranean region. They usually
influence the weather of the north and north-western regions of India .
The mechanism of the monsoons.: (a) The differential heating and cooling of land and water-
creates low pressure on the landmass of India while the seas around
experience comparatively high pressure.
(b) The shift of the position of
Inter Tropical Convergence Zone (ITCZ)- in summer, over the Ganga plain.
(c) The presence of the
high-pressure area, east of Madagascar-
(d) The Tibetan plateau gets
intensely heated- during summer the formation of high pressure over the
plateau at about 9 km above sea level.
The movement of the westerly jet
stream to the north of the Himalayas and
tropical easterly jet stream over the Indian peninsula.
What is Inter Tropical Convergence
Zone?
The Inter Tropical Convergence Zone (ITCZ,) is a broad
trough of low pressure in equatorial latitudes. This is where the northeast and
the southeast trade winds converge.
Describe Southern Oscillation.
Normally when the tropical eastern south Pacific Ocean
experiences high pressure, the tropical eastern Indian
Ocean experiences low pressure. But in certain years, there is a
reversal in the pressure conditions and the eastern Pacific has lower pressure
in comparison to the eastern Indian Ocean .
This periodic change in pressure conditions is known as the Southern
Oscillation.
From where the intensity of monsoon
is predicted?
The difference in pressure over Tahiti (Pacific Ocean,
18°S/149°W) and Darwin in northern Australia
(Indian Ocean, 12°30’S/131°E) is computed to predict the intensity of the
monsoons. If the pressure differences were negative, it would mean below
average and late monsoons.
El Nino: This is a name given
to the periodic development of a warm ocean current along the coast of Peru
as a temporary replacement of the cold Peruvian current. ‘El Nino’ is a Spanish
word meaning ‘the child’, and refers to the baby Christ, as this current starts
flowing during Christmas. The presence of the El Nino leads to an increase in
sea-surface temperatures and weakening of the trade winds in the region.
What is monsoon burst?
Around the time of
monsoon arrival, the normal rainfall increases suddenly and continues
constantly for several days. This is known as the ‘burst’ of the monsoon.
Four main seasons can be identified
in India
The Cold Weather Season (Winter)-
The cold weather season begins from midNovember in northern India and stays till February.
During this season, the northeast trade winds prevail over the country. They
blow from land to sea and hence, for most part of the country, it is a dry
season.
Over the northern plains is the inflow of cyclonic
disturbances from the west and the northwest. These low-pressure systems
originate over the Mediterranean Sea and western Asia and move into India ,
along with the westerly flow. They cause the much-needed winter rains over the
plains and snowfall in the mountains.
The Hot Weather Season (Summer)
- from March to May, it is hot weather season in India . The summer months experience
rising temperature and falling air pressure in the northern part of the
country.
A striking feature of the hot weather season is the ‘loo’.
These are strong, gusty, hot, dry winds blowing during the day over the north
and northwestern India .
In West Bengal , these
storms are known as the ‘Kaal Baisakhi’ calamity for the month of Baisakh.
mango showers- pre-monsoon
showers are common especially, in Kerala and Karnataka. They help in the early
ripening of mangoes, and are often referred to as ‘mango showers’.
Advancing Monsoon (The Rainy
Season)- Start By early June. The trade winds of the southern hemisphere
entering the Indian peninsula as the south-west monsoon.
The windward side of the Western Ghats
receives very heavy rainfall, more than 250 cm.
Mawsynram in the southern ranges of the Khasi Hills receives
the highest average rainfall in the world.
Monsoon has a ‘breaks’ in rainfall.
When the axis of the monsoon trough lies over the plains,
rainfall is good in these parts. On the other hand, whenever the axis shifts
closer to the Himalayas , there are longer dry
spells in the plains, and widespread rain occur in the mountainous catchment
areas of the Himalayan rivers.
The monsoon is known for its
uncertainties. Justify.
It causes heavy floods one part; it may be responsible for
droughts in the other. It is often irregular in its arrival and its retreat.
Hence, it sometimes disturbs the farming schedule of millions of farmers all
over the country.
Retreating Monsoon (The
Transition Season) During October-November, with the apparent movement of the
sun towards the south, the monsoon trough or the low-pressure trough over the
northern plains becomes weaker. The south-west monsoon winds weaken and start
withdrawing gradually. By the beginning of October, the monsoon withdraws from
the Northern Plains.
The retreat of the monsoon is marked by clear skies and rise
in temperature.
October heat-
Distribution of rainfall- The
western coast and northeastern India
receive over about 400 cm of rainfall annualy. It is less than 60 cm in western
Rajasthan and adjoining parts of Gujarat, Haryana and Punjab .
Rainfall is equally low in the interior of the Deccan plateau, and east of the Sahyadris. A third area
of low precipitation is around Leh in Jammu
and Kashmir . The rest of the country receives
moderate rainfall.
