Question

what is easterly jet stream

Answer 1

The Indian Monsoon is a giant weather system which influences not only the surface winds but also upper winds like jet stream. Before the monsoon onset, the upper air jet stream is westerly over India but as the monsoon onsets, it changes its direction due to the seasonal migration of an anticyclone (high pressure region with clockwise winds) over Tibet region. So over most of India such as central India, we have upper air jet stream from the eastern direction (known as tropical easterly jet). Atmospheric disturbances keep on forming in regions like Western Pacific, South China Sea which travel westwards towards Bay of Bengal due to the upper air winds from the east. These disturbances (known as monsoon low pressures/depressions) intensify over the Bay of Bengal or East India and move towards other parts of India bringing the monsoon rainfall. As the monsoon season concludes, the direction of the jet stream gets ‘restored’. I hope this answers your question.