Periodic winds blow at regular intervals in regular cycles. These winds cause differences in temperature and pressure in the region over which they blow.
Periodic Winds
Land and Sea Breeze
The land is a bad conductor and a good radiator of heat. Therefore, it quickly gets heated during the day. This results in building a low-pressure area over the land and a high-pressure area over the sea. Because winds blow from the high-pressure area to the low-pressure area, winds from the sea blow towards the land. They are known as the sea breeze. During the nights, the land cools down rapidly creating high-pressure conditions. Thus, the land breeze blows from the land to the oceans.
Summer Monsoons
- During summers, the land gets more heated than the sea. Because of high temperature, a low-pressure area is created over the land.
- The reverse conditions exist in the oceans. During summers, the air is cool, and hence, a high-pressure area develops. Because winds move from high pressure to low-pressure areas, winds blow from the sea to the land (from the Indian Ocean to the Indian mainland) known as the summer monsoon.
- In the summer months, the landmasses of the Indian subcontinents are heated by the vertical rays of the Sun. This creates a low-pressure area on the land. In the oceans, the high-pressure area develops as the air is cooled. So, the winds blow from the Indian Ocean northwards and in the northwestward direction bringing heavy rainfall to Southeast Asia.
Winter Monsoons
- During winters, the conditions are reverse of summer. A high-pressure area develops over the landmass and a low-pressure area is developed over the seas.
- Because the winds blow from the land to the sea (winds move from high pressure to low-pressure areas), they result in cold dry weather and hardly produce any rainfall.
- These winds can bring rainfall only when they blow over the seas to the adjoining lands. The Coromandel Coast in Tamil Nadu and the Vietnamese Coast get winter monsoon. Because these winter monsoon winds blow to the northeast, they are also known as Northeast Winter Monsoons.
Also, Read Pressure belts and types of winds