Weather and Climate
(i) Weather is the state atmosphere at any point in time and space, it changes every moment.
(i) Climate refers to the sum total of weather conditions and variations over a large area for a long period of time. it is the sum total of average weather conditions of 30 years.
(ii) Elements of weather are temperature, atmospheric pressure, wind, humidity, and precipitation.
(ii) Elements of climate are the same as those of water.
(iii)Example: Cloudy, dry, windy, wet weather.
(iii) Example: Monsoon, equatorial desert, cold climate etc.
(a) India has Diverse Climatic Conditions:
We can take two important elements-temperature and precipitation, and examine how they vary from place to place and season to season.
(i) In summer, the mercury occasionally touches 50o C in some parts of the Rajasthan desert, whereas it may be around 20o C in Pahalgam in Jammu and Kashmir. On a winter night, the temperature at Drass in Jammu and Kashmir may be as low minus 45o C. Thiruvananthapuram, on the other hand, may have a temperature of 20o C.
(ii) In certain places, there is a wide difference between day and night temperatures. In the Thar Desert, the day temperature may rise to 50o C, and drop down to near 15o C the same night. On the other hand, there is hardly any difference in day and night temperatures in the Andaman and Nicobar islands or in Kerala.
There are variations not only in the form and types of precipitation but also in its amount and the seasonal distribution.
(i) While precipitation is mostly in the form of snowfall in the upper parts of Himalayas, it rains over the rest of the country.
(ii) The annual precipitation varies from over 400 cm in Meghalaya to less than 10 cm in Ladakh and western Rajasthan.
(iii) Most parts of the country receive rainfall from June to September. But some parts like the Tamil Nadu coast get most of its rain during October and November. Coastal areas experience less contrast in temperature conditions, seasonal contrast is more in the interior of the country.
The climate of a place is determined by the interplay of various factors such as location, altitude, distance from the sea, pressure and winds and upper air circulation.
(i) 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.
(ii) As one goes from the surface of the earth to higher to higher altitudes, the atmosphere becomes less dense and temperature decreases. The hills are therefore cooler during summers.
(iii) The pressure and wind system any area depend on the latitude and altitude of the place. Thus it influences the temperature and rainfall pattern.
(iv) The sea exerts moderating influences 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.
(v) Ocean currents along with onshore winds affect the climate of the coastal areas.
(vi) Relief too plays a major role in determining the climate of a place. High mountains act as barriers for cold or not winds; they may also cause precipitation if they are high enough and lie in the path of rain-bearing winds. The leeward side of the mountains remains dry.
Factors Affecting India’s Climate
The Indian Monsoon
The climate of India is strongly influenced by monsoon winds. the Arabs, who had come to India as traders benefited from the reversal of the wind system as they came by sailing ships at the mercy of winds, they named this seasonal reversal of the wind system ‘monsoon’.
The monsoons are experienced in the tropical area roughly between 20o N 20o S. to understand the mechanism of the monsoons, the following facts are important.
The Monet Of The Monsoon And Withdrawal
The Monsoon, unlike the trades, are not steady winds but are pulsating in nature, affected by different atmospheric conditions encountered by it, on its way over the warm tropical seas. The duration of the monsoon is between 100-120 days from early June to mid-September. The monsoon arrives at the southern tip of the Indian peninsula generally by the first week of June. Subsequently, it divides into two – the Arabian Sea branch and the Bay of Bengal branch. The Arabian Sea branch reaches Mumbai about ten days later on approximately the 10th of June. The Bay of Bengal branch arrives is Assam in the first week of June. The lofty mountain s cause the monsoon winds to deflect towards the west over the Ganga Plains. By mid-June, the Arabian Sea branch of the monsoon arrives over Saurashtra-Kachchh and the central part of the country. The Arabian Sea and the Bay of Bengal branches of the monsoon merge over the northwestern part of the Ganga plains. Delhi generally receives the monsoon showers from the Bay of Bengal branch by the end of June. By the first week of July, western Uttar Pradesh, Punjab, Haryana and eastern Rajasthan experience the monsoon. By mid-July, the monsoon reaches Himachal Pradesh and the rest of the country. withdrawal or the retreat of the monsoon is a more gradual process. The withdrawal of the monsoon begins in northwestern states of India by early September. By mid-October, it withdraws completely from the northern half of the peninsula. The withdrawal from the southern half of the peninsula is fairly rapid. By early December, the monsoon has withdrawn from the rest of the country.
Four main reasons can be identified in India –
(A) The Cold Weather Season (Winter):
(b) Hot weather season (Summer):
(c) Advancing Monsoon (The Rainy Season):
The climate of India is described as of monsoon type. Derived from an Arabic word ‘mausim’, monsoons refer to the seasonal reversal in the wind direction through the year.