The monsoon gathers strength as the land and ocean temperatures contrast with each other. This intensified heat transfer from land to sea develops a low-pressure region over the western part of India’s peninsula.
A low pressure system is not exactly a ‘low’ temperature, but actually an area of cooling air (where air pressure is low). Thus, the heat-zone develops in such a way that it is self perpetuating and steady.
The cold winds develop over the southern Indian Ocean and blow towards India’s landmass — causing monsoonal rains there each summer.
Onset of the Monsoon
The large landmass in the north of Indian ocean gets intensely heated. This causes the formation of an intense low pressure in the north-western part of the subcontinent.
The air flowing from the lower latitudes of the southern hemisphere get compressed, due to which it gains more weight, since it is already more dense, thus making it even hotter.
Since the pressure in the Indian Ocean in the south of the landmass is high as water gets heated slowly, the low pressure cell attracts the southeast trades across the Equator.
These conditions help in the northward shift in the position of the ITCZ. The southwest monsoon may thus, be seen as a continuation of the southeast trades deflected towards the Indian subcontinent after crossing the Equator. These winds cross the Equator between 40°E and 60°E longitudes.
