Climate

Climate -
Refers to the sum total of weather conditions and variations over a large area for a long period of time.
Weather -
Refers to the state of the atmosphere over an area at any point of time
The climate of India is described as the ‘monsoon’ type. This type of climate is found mainly in the south and the Southeast Asia.
Despite an overall unity in the general pattern there are perceptible regional variations in climatic conditions within the country.
Climatic Controls -
There are six major controls of the climate of any place. They are : latitude, altitude, pressure and wind system, distance from the sea, ocean currents and relief features.
Factors Affecting India’s Climate
(a) Latitude
(b) Altitude
(c) Pressure and Winds
Jet Stream : These are a narrow belt of high altitude westerly winds in the troposphere. Thier sped varies from about 110 km/h in summer to about 184 km/h in winter
(a) Subtropical westerly jet streams
(b) Tropical easterly jet streams
The Indian Monsoon
Facts important for understanding the mechanism of the monsoons -
(a) The differential heating and cooling of land and water
(b) The shift of the position of Inter Tropical Convergence Zone
(c) The presence of the high-presure area, east of Madagascar
(d) Tibetan plateau gets intensely heated
(e) Movement of the westerly jet stream to the north of the Himalayas and the presence of the tropical easterly jet stream over the Indian peninsula.
Southern Oscillation -
Changes in the pressure conditions over the southern oceans also affect the monsoons. 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 Southern Oscillation.
The Onset of the Monsoon and Withdrawal
Onset of the Monsoon
The monsoon arrives at the southern tip of the Indian peninsula generally by the first week of June. Around the time of its arrival, the normal rainfall increases suddenly and continues constantly for several days. This is known as the ‘burst’ of the monsoon.
(a) Arabian Sea Branch
(i) Entering from the Western Ghats
(ii) Entering from the Rann of Kuchchh
(b) Bay of Bengal Branch
(i) Entering into the North-east region
(ii) Entering into the Ganga Valley region.
Withdrawal  of the Monsoon
Begins in the norhtwestern states of India by early September. By mid-October , it withdraws completely from the northern half of the peninsula.
The Seasons
The Cold Weather Season
The cold weather season begins from mid-November in northern India and stays till February. December and January are the coldest months in the northern part of India. The temperature decreases as one moves from south to the north. Days are warm and the nights are cold. Frost is common in the north and the higher slopes of the Himalayas experience snowfall. 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. In the northern part of the country, a feeble high-pressure region develops, with light winds moving outwards from this area. The weather is normally marked by clear sky, low temperatures and low humidity and feeble variable winds.
The Hot Weather Season
Due to the apparent movement of the sun, the global heat belt shifts northward. As such, from March to May, it is hot weather season in India. Temperature increases from south to north. In peninsular India, temperatures remain lower. High temperature between 38º C and 48º C in the plains. Local dust storms accompanied with light rains. Hot dry winds, ‘loo’ is common in May and June. Kerala and Karnataka coast receives pre-monsoon showers (Mango showers). West Bengal and Assam are affected by northwesterly winds. (Kalbaisakhi).
Advancing Monsoon
By early June, the low-pressure condition over the northern plains intensifieswhich attracts the trade winds of the southern hemisphere. These winds cross the equator and blow in a south westerly dirction entering the Indian peninsula as the south-west monsoon.
Monsoon has a tendency to have ‘breaks’ in rainfall. It has wet and dry spells. The monsoon rains take place only for a few days at a time. They are interspersed with rainless intervals. These breaks in monsoon are related to the movement of the monsoon trough.
The monsoon is known for its uncertainties. The alternation of dry and wet spells vary in intensity, frequency and duration.
Retreating Monsoon
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. This is gradually replaced by a high-pressure system. The south west monsoon winds weaken and start withdrawing gradually. By the beginning of October, the monsoon withdraws from the Northern Plains.
Owing to the conditions of high temperature and himidity, the weather becomes rather oppressive during the day. This is commonly known as ‘October heat’.
The low-presure conditions, over north-western India, get transferred to the Bay of Bengal bny early November. This shift is associated with the occurrence of cyclonic depressions, which originate over the Andaman Sea.
Distribution Of Rainfall
The western coast and northeastern India receive over about 400 cm of rainfall annualy. However , it is less than 60 cm in western Rajasthan and adjoining part 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.
Monsoon as a Unifying Bond
There is great diversity in the climatic conditions due to location, extent and relief features. But these diversities are subdued by the monsoons, which prevails over the whole country. These monsoons are active for just three to four months and rest of the year India remains almost thirsty. This water scarcity is felt all over the country. Thus the arrival of the monsoon is most welcome; it changes the Indian landscape, gives impetus to agricultural activities, the total life of the Indian people revolves around the monsoons, including festivals.