The wind and thermal structure of the Asian summer monsoon in the lower and upper troposphere have been examined during different stages of development of the monsoon. It is seen that an upper tropospheric warm ridge overlies the lower monsoon trough and shifts along with it. The activity of the monsoon is affected by the upper ridges as well as perturbations in the upper flow patterns. It is suggested that the summer monsoon circulation represents a Hadley type of meridional cell with its heat source over the monsoon trough near the thermal equator and 'sink' over the cooler oceanic areas near the geographical equator.
Koteswaram et al. (Sun,) studied this question.