Brief Notes on Dynamic Concept of monsoon

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This concept was proposed by Flown in 1951 which is based on the dynamic origin of monsoons. According him monsoon is only the seasonal migra­tion of planetary winds and pressure belts following the sun. During summer solstice sun’s noon rays fall vertically over the Tropic of Cancer.

Consequently all wind and pressure belts of the globe shift towards the north. In these days the zone of inter tropical convergence (ITC or Doldrum) moves northward and its northern boundary (NITC) is extended upon 30° N. Latitude in South and South-East Asia. This is because over the land the annual tempera­ture changes are relatively larger because of which the seasonal shifting of temperature and pressure belts amount to many degrees.

Due to this shifting the major part of the Indian subcontinent comes under the impact of equatorial westerly’s (blowing in dol­drums which are called south-west monsoon. Since NITC is associated with tropical disturbances these also dominate the surface weather. During winter season due to southward shifting of pressure and wind belts the planetary system of north-east trade winds is reestablished over this region.

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These are called north-east winter monsoons which are gener­ally dry and devoid of rains. Hence according to Flown the existence of Asian monsoon is not due to the temperature contrasts between land and sea, but mainly due to the annual migration of thermally produced planetary winds and pressure belts under continental influences.

Thus Flown ascribes the origin of monsoon to the thermal response of the tropical continental at­mosphere to the annual variation of solar radiation. However, he seems to have ignored the upper atmos­pheric circulation which makes the Asiatic monsoon a fairly complex system (Lai, D.S., 1986, pp. 119- 120).

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