Friday, 5 February 2016

CLIMATE part 2


There are four main seasons in India, viz. the cold weather season, the hot weather season, the advancing monsoon and the retreating monsoon.

The Cold Weather Season (Winter):

• The winter season begins from mid-November and stays till February;
• in northern India. December and January are the coldest months in the northern part of India. 
• The temperature ranges between 10°-15°C in the northern plains, while it ranges between 24°-25°C in Chennai.
• The northeast trade winds prevail over the country in this season.
•  As these winds blow from land to sea, most parts of the country experience a dry season.
• The weather is usually marked by clear sky, low temperatures and low humidity and feeble variable winds.

• Western disturbance:

• The inflow of the cyclonic disturbances from the west and the northwest is a characteristic feature of the cold weather over the northern plains.
• These low-pressure systems originate over the Mediterranean Sea and Western Asia and move into India. • They cause winter rains over the plains and snowfall in the mountains.
•The winter rainfall is in small amount but is very important for the rabi crop.
• This rainfall is locally known as mahawat.
• The peninsular region does not get a well-defined winter because of the moderating influence of the sea.

The Hot Weather Season (Summer)  ;


• The summer season is from March to May.
• During this period, the global heat belt shifts towards north because of the apparent northward movement of the sun.
• During summer, the temperatures rise and air pressure falls in the northern part of the country.
• Towards the end of May, an elongated low-pressure area develops in the region which extends from the Thar Desert in the northwest to Patna and Chhotanagpur in the east and southeast.
• A characteristic feature of the hot weather season is the ‘loo’. These are strong, gusty, hot and dry winds which blow during the day over the north and northwestern India.
• Dust storms are very common in northern India during the month of May.
• This is also the season of localized thunderstorms; accompanied by violent winds, torrential downpours, and hail.
• Pre-monsoon showers are common towards the end of the summer season; especially in Kerala and Karnataka. • • They are often called ‘mango showers’ as they help in the early ripening of mangoes.
• The rainy season begins from early June.      
• The low-pressure condition over the northern plains intensifies at this time.
• It attracts the trade winds from the southern hemisphere. 
• These south-east trade winds cross the equator and blow in a south-westerly direction to enter the Indian peninsula as the south-west monsoon.
•These winds bring abundant moisture to the subcontinent.
• These winds blow at an average velocity of 30 km/h. 
• The monsoon winds cover the country in about a month; barring the extreme north-west.
• The windward side of the Western Ghats receives very heavy rainfall, early in the rainy season. 
• The Deccan Plateau and parts of Madhya Pradesh also receive some rain, in spite of lying in the rain shadow area.
• The north-eastern part of the country receives the maximum rainfall of this season. 
• Mawsynram (Meghalaya) receives the highest average rainfall in the world.
• Rainfall in the Ganga valley decreases from east to west. Rajasthan and parts of Gujarat get scanty rainfall.
• Monsoon tends to have ‘breaks’ in rainfall; which means that there are wet and dry spells in between. 
• The monsoon rains take place only for a few days at a time and then come the rainless intervals. 
• These breaks in the monsoon are because of the movement of the monsoon trough.
• The trough and its axis keep on moving northwards or southward due to various reasons. 
• The movement of the monsoon trough determines the spatial distribution of rainfall.
• The monsoon is famous for its uncertainties.
• It may cause heavy floods in one part of the country, and may be responsible for droughts in other part. Because of its uncertain behaviour,
• it sometimes disturbs the farming schedule in India. This affects millions of farmers all over the country.

Retreating Monsoon (The Transition Season) :

• During October-November, the sun apparently moves towards the south.
• During this period, the monsoon trough over the northern plains becomes weaker. 
• The south-west monsoon winds weaken and start withdrawing gradually.
• The monsoon withdraws from the northern plains by the beginning of October.
• The retreat of the monsoon is marked by clear skies and rise in temperature. While day temperatures are high, nights are cool and pleasant. 
• Humidity is still present.
• High temperature and humidity, makes the weather quite uncomfortable during the day.
• This is commonly known as “October Heat”.
• The temperature begins to fall rapidly in northern India by the second half of October. 
• The low-pressure conditions over northwestern India move to the Bay of Bengal by early November. 
• This shift leads to cyclonic depressions over the Andaman Sea.
• These cyclones usually cross the eastern coasts of India and cause heavy and widespread rain.
• These cyclones may also arrive at the Coasts of Orissa, West Bengal and Bangladesh. 
• These cyclones contribute to the bulk of the rainfall of the Coromandel Coast.

DISTRIBUTION OF RAINFALL:


• The western coast and northeastern India receive over 400 cm of rainfall annually.
• The annual rainfall is less than 60 cm in western Rajasthan and adjoining parts of Gujarat, Haryana and Punjab.
• Rainfall is also low in the interior of the Deccan Plateau and easth of the Sahyadris.
•The area around Leh also gets low rainfall.
• The rest of the country gets moderate rainfall.
• Snowfall is restricted to the Himalayan region.


























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