An interchange of air between the land and oceans due to unequal heating and cooling of continents and oceans is known as monsoon winds.
It has an annual period of occurrence. During summer, the land is heated Very much as compared to the oceans which cause which oceans low pressure Over the land and the winds blow from the oceans to the continents. During winter, land cools down faster than the oceans causing high Pressure over continents and low pressure over the oceans and the wind Blows from continents to oceans. The Indian monsoon is the best known Example of this alternating circulation system. There are two types of Monsoons over India i.e. south – west monsoon and North- East monsoon.
1.South – West Monsoon:
India is positional situated in North – East trade winds and should have N- E winds throughout the year, but a low pressure through lies along the Ganges and upper India, due to which S.- W winds predominate. During April to September a low pressure center is formed over N – W India. The s-W trade winds of the Indian ocean blow to the equator and then turning to the right under carioles force and move on a S – W winds Around the low pressure center over India. [This monsoon blows from the African coast (150E)]. The moisture laden air while rising the mountain of Asia cools, condense and precipitate. As a result the pressure is lowered to increase the pressure gradient.
2. North – East Monsoon:
Complete reversal of the S – W monsoon winds takes place as the high pressure centre is located in eastern Asian (1035 mb) and low in about 1010 mb. During this time from North to South the cold season is established. This monsoon is active during October and November. The winds flow in North- East direction. This wind is generally dry but gives rains to AP, TN states. Monsoon winds also exist over west Africa, Brazil, eastern USA, Australia. Philippines etc.