CLIMATE

Climate is the weather conditions and variations over a large area for a longer period. Weather is the state of the atmosphere over an area at any point in time. Elements of the weather and climate are the same, i.e. temperature, atmospheric pressure, wind, humidity, and precipitation. The word monsoon is derived from the Arabic word ‘Muslim ‘which means season. It refers to the direction of the wind during the year.

Climatic controls: Six major controls of the climate of any place. Latitude, altitude, pressure and wind system, distance from the sea, ocean currents and relief features.

1. Factors Affecting India’s Climate

Latitude: The tropic of cancer passes through the middle of the country from Rann of Kutch west to Mizoram in the east. South is the tropic of cancer and north is the subtropic.

Altitude: The Himalayas on the north side prevents the cold wind from central Asia resulting in India experiencing milder winters compared to central Asia.

Distribution of land and water: India is surrounded by water on three sides and the continuous Himalayas on the other side. As compared to the landmasses, water heats up or cools down slowly; it creates different air pressure zones and seasons.

Pressure and winds

Pressure and surface winds: India lies in the region of northeasterly winds. These winds cause less rain or no rain due to Coriolis force, [an apparent force caused by the earth’s rotation].

•  Hot dust-laden strong winds known as ‘loo’ blow.
• These strong dust storms are short-lived thunderstorms, which carry solid walls of sand and dust. These are locally known as And his.
• These bring little rainfall and give much-needed relief from the heat.
•  Dust storms in the evening are very common during May in Punjab, Haryana, 
• Eastern Rajasthan and Uttar Pradesh

Upper air circulation

• The upper air circulation in this region is dominated by a westerly flow. 
• The jet stream is a narrow belt of high altitude [above 12,000m] westerly winds in the troposphere.
• The jet streams are located approximately over 27-30 degrees north latitude; hence it is called subtropical westerly jet streams. 

Tropical cyclones occur during October and November due to the weather influence in the north and northwestern. Andhra Pradesh and Orissa coasts were badly affected.

2. The Indian monsoon 

Indian climate is based on the monsoon winds between 20 degrees north and 20 degrees south.

 The monsoon approaches the Indian landmass in two branches: The Arabian Sea branch and The Bay of Bengal branch. 

The Arabian Sea branch

The Arabian Sea branch is split into three.

1. Strikes the Western Ghats causing 250-400 cm of rainfall.
2. Strikes till the coast of Mumbai, the Narmada and Tapi river valleys causing heavy rainfall in central India and
3. Strikes the Saurashtra Peninsula and the Kachchh. It then passes over west Rajasthan and along the Aravallis, causing only a scanty rainfall. 

The Bay of Bengal branch: This branch splits into two under the influence of the Himalayas and the thermal low in northwest India. One branch moves westward along the Ganga plains and Punjab plains. The other branch moves up to the Brahmaputra valley, causing widespread rains.

3. The seasons 

Indians experience four seasons.

• The cold weather season [winter] Mid-November – February: 22nd December, the sun shines vertically over the Tropic of Capricorn in the southern hemisphere. Snowfall in the Himalayan ranges. Small amounts of rainfall in the winter season occur due to the western and northwestern cyclonic disturbances.
• The hot weather season [summer] March-May: As the sun comes from the north towards the Tropic of Cancer, after the Vernal Equinox, the entire country the temperature increases. Pre-monsoon showers in Kerala and Karnataka help mango ripening, referred to as Mango showers. Tea showers in Assam, [they are good for tea, jute and rice].
• Advancing monsoon [the Rainy season] June-mid October: The rain in the southwest monsoon season begins rather abruptly.
• Retreating monsoon [the Transition season] mid-October- November:  Southwest monsoon starts withdrawing gradually. Low-pressure conditions create depression and form cyclones in the Arabian Sea and Bay of Bengal.  The cyclones which form in the Bay of Bengal create massive destruction of life and property in the states of Tamilnadu, Andhra Pradesh, Orissa and West Bengal.