The Jet Stream Theory
Monsoon is driven by the atmospheric circulation phenomenon which produced by unequal and differential heating of continental and oceanic areas. Jet Stream play an important role in the possible formation, streering or intensifying weather phenomena such as monsoons, cyclones, anti-cyclones and other weather conditions.
What is Jet Stream Theory?
The Jet Stream Theory is a study of a narrow belt of high altitude westerly winds in the troposphere. It's speed varies from 110 km/h in summer to 184 km/h in winter. This system works as a cover over the Earth which affects the weather of the lower atmosphere. This theory was propunded by the Yest.
It is driven by air pressure, temperature and moisture differences between one place and another. The greater the difference in temperature, the faster the wind velocity inside the jet stream. The path of the stream have a meandering shape which may start, stop, split into two or more parts, combine into one stream, or flow in various directions including opposite to the direction of the remainder of the jet. The main types are the polar jets, the subtropical westerly jets and the less common tropical easterly jets.
How does Jet Stream affect Indian Monsoon?
The Sub-Tropical Jet stream plays a significant role in both hindering the monsoon winds as well as in quick onset of Indian monsoons.
During winter season the upper air westerly jet streams are positioned in Asia. These are bifurcated in two branches due to Tibet Himalayan obstruction. North branch blows north of Himalayas and the Tibetan Plateau. Southern branch blows south of the mighty mountains.
During summer season as sun falls vertically over the Tropic of Cancer the polar surface high pressure is weakened and upper air circum polar whirl shift northward as a result of which the upper air westerly jet are also withdrawn from southern slopes of the Himalayas. The removal of jet stream to north of the Tibetan plateau results in reversal of the curvature of How of free air to the north and north-west of the subcontinent. This event may well be the trigger that sets off the ‘burst’ of the monsoon. Origin of the Easterly Jet Stream because of the Plateau of Tibet becoming Hot in summer.
Hence, we can say that the theory does not explain why easterly jet stream is so much indefinite. A general interpretation is given that it is the result of the variation in insolation. However, this kind of variation needs a proper analysis.