Some synoptic aspects of the low level inversion over Arabian Sea during MONEX'79

Abstract

Aerological observations over the Arabian Sea during the Summer Monsoon Experiment in 1979 show the presence of low level thermal inversion over the oceanic region prior to the onset, at the time of onset and at the established phase of the southwest monsoon. The thermal and moisture stratifications in the sub-inversion layer have been presented on the basis of thermodynamic chart. The spatial and temporal variations of the inversion layers as found from the dropsonde data coflected from the United States aircraft Convair 990, Electra and P-J, have been presented in the form of charts. The formation of inversion may be attributed mainly to the confluence of the cool moist air of oceanic origin and the dry warm air of continental origin.

When a synoptic disturbance approached the area, a moist tongue was seen to form in the sub-inversion layer. The formation of this sharp moisture gradient may be related to the vertical upward motion below the inversion. The profiles of static stability during this period show that the height of the base of inversion becomes higher with the increase of static stability parameter in the sub-inversion layer.

Vertical p-velocities have been calculated at different locations using the dropsonde data. The impact of the vertical p-velocity on the inversion layer at different phases of monsoon has been discussed.