Question

what are subtropical westerly jet stream

Answer 1

It is belt of strong upper-level winds lying above region of subtropical high- pressure. It mainly travel in lower latitudes and at slight higher elevation. It is one the reason for more height of troposphere in equator than in pole region. ... And it's direction is West to East, so called subtropical westerly jet stream

Answer 2

Jet stream theory. According to this theory, the onset of the southwest monsoon is driven by the shift of the subtropical westerly jet north from over the plains of India toward the Tibetan Plateau. This shift is due to the intense heating of the plateau during the summer months.