Climate Of India

India’s Climate

1. The Himalayas:

Because of the Himalayas, the subcontinent acts as a box letting in warm moist tropical air from the south but preventing from spreading further north to central Asia.
The Tibetan Plateau with an average elevation of 5km acts as a high level heat source in the summer
The west-east orientation of the Himalayan cordillera is a major factor in the full-fledged development of the Asiatic monsoon.
The southern slopes to the Himalayan where the summer monsoon current impringes on the slopes experience heavy rainfall.
The highest peak is Shillong Peak (1,916m) in the Khasi Hills.
Cherrapunji located on the southern slopes of the Khasi Hills, gets an average annual rainfall of 1,142cm.
Mawsynram another station located some 16kms to the west has also recorded a slightly higher rainfall amount..

2.The Western Ghats

Oriented north-south, the ranges present a barrier across the Arabian Sea branch of the south-west monsoon current.
Bombay (11m) on the coast experiences annual rainfall of about 190cm and Khandala (539m) nearly 50km to the east but below the crest gets 463 cm, while Pune (559m) about 130km away from Bombay has a rainfall only 50cm during the south-west monsoon season.
The annual rainfall decreases from 400 to 500 cm to about 30 cm all along the Western Ghats, within 80-100 km leeward from the crest.

3.Desertification

Nearly a fifth of the Indian land area is the arid Rajasthan desert, a part of the Great Indian Desert.
The rainfall here is scanty, with less than 15 cm in a year.
Aircraft observations show that the Rajasthan dust layer extends vertically to nearly 9 km.
Indiscriminate defoliation and uncontrolled grazing perhaps increased the dust content, leading to suppression of convection and progressive decrease in rainfall.

4. Tropical Cyclones

Form in Bay of Bengal and the Arabian Sea and move west or north-westwards, sometimes re-curving north or north-east at a later stage.
Re-curvate usually occurs when the cyclones are between latitudes 16° and 18° N.
Cyclones generally form in a lower latitude belt (10° to 14° N) before and after the south-west monsoon season.
They are intense and are responsible for the major portion of the rainfall over the peninsula.
The maximum incidence of cyclones is from April to June and October to December.

5. Western Disturbances

The southward shift of the polar front in winter, the tracks of the middle latitude cyclones now pass across the northern portions of the India subcontinent during the period October to June.
Because of the high terrain, mountain ranges etc. to the west, most of the disturbances are in the mature stage and hence weak or irregular by the time they reach India.
Since these extra-tropical cyclones reach India from the west, they are usually referred as ‘western disturbances’ over the India region.
Reaching Rajasthan, Haryana and Punjab the disturbances slow down and stagnate due to the nearly closed-in nature of the region with high hills to the northwest, north and east, together with open terrain to the south and east.
The tracks of these disturbances come farthest south to latitudes 22° to 23° N in February.

5. Jet Streams

Two types of Jet Streams, the westerly Subtropical Jet Stream (STJ) and the easterly Tropical Jet Stream (TEJ) are seen over the continent.
The STJ appears for about eight months of the year i.e., October to May with mean position at latitude 27° N at an average height of 12 km.
The TEJ appears during the prevalence of the southwest monsoon i.e., June to September, at a height of 14 to 16.5 km with a mean position of 15° N.

7.Precipitation

The mean annual rainfall for the whole of India is 105 cm.
This rainfall is associated mostly with the southwest monsoon.
About 75% of the total rainfall occurs between June and September.
Northern India gets precipitation in January and February due to western disturbances.
In WB, north western storms cause heavy rainfall and hail in April and May.
Monsoon retreats in November and December causes heavy rainfall in Coromondal coast accounting for 44 to 60 per cent of the total annual rainfall.

8. Thunderstorms

They occur when there is instability in the atmosphere under adequate moisture conditions and a mechanism exists to release the instability.
Occur over all parts of the subcontinent and there is no month when some part or the other of the country is not affected by thunderstorms.
The least thunderstorms activity is in December and March.
The highest thunderstorm activity areas are northeast India, Bengal, Orissa and adjoining areas as well as extreme southwest peninsula thunderstorms of Bengal, Bihar plateau and northeast India are locally known as ‘northwesters’ or ‘kalbaisakhis’.
Cause widespread damage to crops and kill cattle and at times people.

9. Hail

The March-May thunderstorms over northern India, particularly in the submonate areas are accompanied by Hail.
Hailstorms occur also in December-February in association with western disturbances.
No region is free from hail.
Hail is rare in southwest monsoon period

10. Fog

India experience mostly radiation fog except in the coastal areas where advection fog also occurs
Fog or mist is possible throughout the year in the valleys and over mountains region, under suitable temperature and moisture conditions.
In the plains fog or mist is confined to the winter months.
Low stratus cloud persists for some time after the fog lifts.