jet stream are fast blowing wind in upper atmosphere at the height of 4-14 km mainly from west to east.
types of jet streams :
1) polar jet stream (60degree)
2) sub tropical westerly jet stream (30 degree)
3) tropical easterly jet stream over india in june till september
4) african easterly jet stream (3-5km height in summers)
5) flindlanter jet stream/ somalian jet stream
6) polar night/stratospheric jet stream at the height (30-50km)
causes of jet stream :
meeting of two opposte types of atmospheric cycles or air masses in upper atmosphere produces jet stream as the temperature contrast, pressure gradient is very stong and satisfy two condition :
1) baroclinical curve get stronger from hot areas to cold areas so wind flows from hot areas to cold areas stongely apposite to surface wind. therefore all upper atmospheric wind are jet streams including antitrade winds, antiwesterlies, anti-easterlies, anti-walker wind ,etc.
2) geostophic balance is obatined when pressure gradient force become equal and opposite to coriollis force at some height.therefore at some height these jet stream flows parallel to isobars such wind become geostrophic winds.
role of jet streams :
1) atmospheric circulation system by forming convergence and divergence zones
2) explains the cyclonic and anticyclonic development over ground
3) wet and dry, stable and unstable atmospheric condition
4) indian summer monsoon arrival, withdrawl and breaks, etc
5) western disturbance by westerly jet stream
6) north east monsoon by westerly jet stream
7) ozone depletion in polar areas and it grows in winter season due to polar night jet stream.
8) tropical storm development over warm waterbodies by jet streams as it maintains high pressure from top and descent over the cyclonic lows
9) extreme weather events are increasing due to polar vortex is weakening with more zig-zag flow of polar jet stream.
