A considerable portion of the Indian subcontinent belongs to the subtropical zone. However, the region as a whole shares the characteristics of a tropical climate. Literally, the word ‘monsoon‘ means a wind system which undergoes a seasonal 180 degree reversal of direction. Many regions of the world experience the monsoon. In India, however, two factors make it unique. One is the continuous & high mountain mass in the north which forms an effective barrier to the air movement across them. The second is the peninsular shape of the subcontinent with its land in close proximity to the ocean, thereby providing a rich source of moisture.
The in the country is primarily orographic, associated with tropical depressions originating in the Bay of Bengal & the Arabian sea. The moisture-laden summer monsoon, accounting for the bulk of rainfall in the country, originates from the vast expanse of the Indian Ocean & enters the Indian subcontinent from the south-west as south-westerly current. The physiographic features of the Indian peninsula & the Western Ghats divert the monsoon into two branches, namely, the Arabian Sea branch & the Bay of Bengal branch. The Arabian Sea branch strikes the Western Ghat & precipitates heavily along the Western Ghat from Kerala to Gujarat between the last week of May & the first week of June. After surmounting the Ghats the southern part of the current blows across the Peninsula as a westerly or in places, as a north-westerly wind.The northern portion of the current which crosses the Saurashtra coast blows across Rajasthan as a south-westerly wind & gives rain mostly in the coastal districts near the Aravalli hills & the Punjab Kumaon Hills, but very little in the plains of Rajasthan.