Seasonal Rhythm
The climatic conditions of India can best be described in terms of an annual cycle of seasons. The meteorologists recognize the following four seasons:
THE COLD WEATHER SEASON:
- The ITCZ shifts south of the equator resulting in the development of high pressure over north and north-western India. As a result, winds start blowing from northwestern high pressure zone to the low air pressure zone over the Indian Ocean in the south.
- Since the winds move from land to sea, they do not cause any rainfall except in north India where rainfall occurs due to western disturbances.
- An increase in the prevailing night temperature generally indicates an advance in the arrival of these cyclone disturbances.
THE HOT WEATHER SEASON:
- The summer months are a period of excessive heat and falling air pressure in the northern half of the country. Because of the heating of the subcontinent, the ITCZ moves northwards occupying a position centered at 25°N in July.
- This season is associated with some local storms like loo, nor westers, mango showers etc.
THE SOUTHWEST MONSOON SEASON:
- These southeast trade winds cross the equator and enter the Bay of Bengal and the Arabian Sea.
- As these winds approach the land, their southwesterly direction is modified by the relief and thermal low pressure over the northwest India and thus approach the landmass in 2 branches:
o The Arabian Sea branch causes rainfall along the windward side of Western Ghats, in Kutch and Saurashtra region and in Punjab, Haryana after crossing west Rajasthan along the Aravalis.
o After deflection from Arakan Hills in Myanmar, the Bay of Bengal Brach enters West Bengal and Bangladesh from south and southeast instead of from the south-westerly direction. It further bifurcates into 2 under the influence of Himalayas causing rains in North and North-East India.
SEASON OF RETREATING MONSOON:
-
The months of October and November are known for retreating monsoons since the south west monsoon has become weak due to southward shift in ITCZ.
-
The retreating southwest monsoon season is marked by clear skies and rise in temperature. The land is still moist. Owing to the conditions of high temperature and humidity, the weather becomes rather oppressive. This is commonly known as the ‘October heat’.
-
This season is associated with rainfall on the Coromandel coast due to cyclonic depressions which develop over Andaman Sea.