The mean Jet Stream over India in the pre-monsoon and post monsoon season and vertical motions associated with sub-tropical Jet Streams

Abstract

On lines similar  to the authors' work on the jet stream in winter (1953b) the mean jet stream over the Indian sub-continent has been computed for the post monsoon and pre-monsoon seasons. It  is found that the westerly jet stream persists in  these two seasons also, but with diminished velocity, The monthly variation of the position of  the jet in the dry season has been studied and the thermodynamic features of  the mean jet discussed.

               From pibal means, the vertical motion over the country in the dry seasons has been evaluated. An attempt  has been  made to picture the circulation patterns  near the jet stream as well as over the subtr.opical anticyclone. The convergenc and vertical  motion patterns in the vicinity of the jet over Indla give support  to the confluence mechanism for its formation.

              Reports of clear air turbulence over India have been examined in relation to the vertical motion pattern and it is pointed out that the region to the south of the sub-tropical jet is favourable for such turbulence.