What are Jet streams and how do they affect the climate of India?
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Answer:
Jet streams are relatively narrow bands of strong wind in the upper levels of the atmosphere. The winds blow from west to east in jet streams but the flow often shifts to the north and south. Jet streams are like rivers of wind high above in the atmosphere. These slim strips of strong winds have a huge influence on climate, as they can push air masses around and affect weather patterns.
The jet streams on Earth typically run from west to east, and their width is relatively narrow compared to their length. Jet streams are typically active at 20,000 feet to 50,000 feet, above the surface and travel in what is known as the troposphere of Earth’s multi-layered atmosphere.
It is believed that the southern branch of the jet stream in northern hemisphere exercises an important influence on the winter weather in India.
The western cyclonic disturbances which enter the Indian subcontinent from the west and the northwest during the winter months, originate over the Mediterranean Sea and are brought into India by the westerly jet stream.
The Sub-Tropical Jet stream plays a significant role in both hindering the monsoon winds as well as in quick onset of Indian monsoons.
The burst of monsoons depends upon the upper air circulation which is dominated by Sub Tropical Jet Streams (STJ).
During summer, there is a presence of easterly jet streams. An easterly jet stream flows over the southern part of the Peninsula in June and has a maximum speed of 90 km per. In August, it is confined to 15oN latitude, and in September up to 22o N latitudes. The easterlies normally do not extend to the north of 30o N latitude in the upper atmosphere.
The easterly jet stream steers the tropical depressions into India. These depressions play a significant role in the distribution of monsoon rainfall over the Indian subcontinent. The tracks of these depressions are the areas of highest rainfall in India. The frequency at which these depressions visit India, their direction and intensity, all go a long way in determining the rainfall pattern during the southwest monsoon period.
At times, Jet Streams bring about some moisture to the stratosphere, leading to the formation of Noctilucent clouds (tenuous cloudlike phenomena in the upper atmosphere which are made of ice crystals visible in a deep twilight)
Known to have brought some ozone depleting substances to stratosphere which result in ozone layer depletion.
Conclusion
Jet stream has wide ranging effect on India. The theories explaining and predicting the effects are still evolving.
Jet streams are a narrow belt of high altitude (above 12000 m) westerly winds in the troposphere.
(a) Their speed varies from about 110 km/h in summer to about 184 km/h in winter.
(b) A number of separate jet streams have been identified.
(c) The most constant are the mid latitude and subtropical jet streams.
(d) Jet streams over the Indian peninsula during the summer affect the monsoon.
(e) The subtropical westerly jet stream blow south of the Himalayas and is responsible for the western cyclonic disturbances experienced in the north and north western parts of the country.
(f) An easterly jet stream blows over peninsular India. It affects the coastal regions of the country and is responsible for tropical cyclones during the monsoon as well as during the October to November period.