Explanation:

Jet Streams:Jet streams are high speed winds that occur in narrow bands of upper air westerlies. The width of this air band can be 160-480km wide and 900-2150m thick, with core speed exceeding 300km/hr. such is their strength that aircraft routes which run counter to jet movements are generally avoided. Jets are coincident with major breaks in the tropopause.
Jet streams can be classified as follows:
1) Polar front jet stream: this is a thermally induced jet stream and it flows parallel to surface fronts. They flows west to east in a sinusoidal fashion. It is strongest at 200-300mb level and swings between 40o-60o latitude. It is found in both the hemispheres. Its band is non continuous but flows all round the year. It can reach up to 160-200 km/hr.
2) Tropical westerly jet streams: they also flow all round the year. They flow to conserve the angular momentum in upper atmosphere. They are found at the poleward limit of Hadley cell around 30oN and S latitude. It follows a more fixed pattern than polar jet stream. It is strongest on Indian sub continent. The maximum speed can reach upto 300km/hr. the subtropical westerly jet do not seem to affect surface weather as much as the polar fronts jets do.
3) Tropical easterly jet: they are seasonal jet streams flowing east to west. These are only found in northern hemisphere and generates only in summer season. These are also thermally induced.