- Jet streams are relatively narrow bands of geostrophic wind blowing horizontally through the upper layers of the troposphere.
- The main jet streams on Earth flow from west to east (Westerlies) but the flow often shifts to the north and south.
- Jet streams often follow the boundaries between hot and cold air and greater the temperature gradient, faster is the wind velocity inside the jet stream.
- Hence jet streams are the strongest during winters in the northern and southern hemisphere.
- Aviators use Jet streams if they are flying in the direction of the flow of the jet streams, and avoid them when flying in opposite direction in order to improve fuel efficiency.
- Jupiter and Saturn are known for having noticeable Jetstreams.
Types of Jet Streams
Polar jet stream
- Polar jet stream flows in the 50°-60° N/S region between the polar cell and the Ferrel cell.
- In the winter the polar jet moves southwards and increases in strength since the North Pole gets colder but the equator stays about the same temperature.
Subtropical jet stream
- Subtropical jet stream flows in around 30°N/S region between the Hadley Cell and the Ferrel Cell.
- Subtropical jet stream is nearly continuous in both hemispheres during winter.
- Although exists all year in the southern hemisphere, it is intermittent in the northern hemisphere during summer when it migrates northwards.
How Jet Streams Affect Weather?
- Jet streams have distinct peaks (ridges) and troughs following the contours of low and high pressure areas.
- If a trough is above an area, it will have a very cold and snowy or rainy climate meanwhile, if a ridge is above an area, it will have generally warm and dry climate.
- In other words, formation of the trough region creates cyclonic condition at the surface of earth meanwhile the ridge regions create anticyclonic condition.
Jet Streams and Monsoon
- Subtropical jet stream has significant influence on Indian monsoons meanwhile, Polar Jet stream has none.
- The Subtropical jet stream shifting to the north of Himalayas is often the indicator of the onset of Southwest Monsoon.
- While its return back to the south of Himalayas is often the indicator of withdrawal/retreating of monsoon.
- Subtropical jet stream is also responsible for bringing “Western Disturbances” to the subcontinent.
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