223 



stability conditions in the west central Arabian Sea seem to persist with a 

 minimum of variation throughout the monsoon season. 



As the monsoon current moves northeastward over the sea, flux from the 

 sea surface, mixing enhanced by the relatively strong flow near the surface, 

 and adiabatic ascent imposed by the field of motion act to increase the heat 

 and moisture content of the monsoon air and to increase upward the depth of 

 the moist layer. The flux of heat from the sea to the ocean in this area has 

 been computed as close to 60O-700 cal cm' ^^J~ . At the same time sinking 

 motion in the warm air mass aloft contributes also to vertical mixing with 

 the moist mass below. 



In the western two-thirds of the sea the properties of the monsoon / 

 current appear to be influenced almost exclusively by the process of air-sea 

 property exchange. In the eastern third of the oceanic mass, closer to 

 the Indian coast, the prevailing tendency is for dissolution of the inversion, 

 violent vertical mixing leading to generally unstable conditions with 

 considerable layered cloudiness and convection. The prevalence of unsettled 

 weather in that area throughout the monsoon season is very well supported by 

 the mean weather distribution charts . The destruction of the inversion cannot 

 be ascribed to purely air-sea interaction processes; it is apparently due to 

 developments in the synoptic scale. Conditions in the area to the west of 

 Bombay suffer significant interdiumal variations and periods of relatively 

 good weather alternate with periods of more violent and widespread rain 

 activity. Periods of so-called breaks in the monsoon over the west coastal 

 sector of India seem to be associated with conditions over the Arabian Sea 

 such that the relatively stable conditions over the ocean are extended east- 

 ward into the Indian coast. Our studies in Bombay indicated synoptic develop- 

 ments at 500 mb as being largely responsible for weather variations along 

 the west coast of India; the low level flow showed little evidence of the 

 synoptic systems . 



The conditions of flow and the distribution of the water and land masses 

 are such that the air that penetrates the west coast of India properly has 

 had considerable oceanic influence and has great rain producing potential. 

 On the other hand on account of the decrease of the water mass northward and 

 associated increase in the influence of the Arabian land mass, the air mass 

 moving into west Pakistan and northwest India, even at the height of the 

 monsoon season, has a minimum of oceanic influence. This is an important 

 contributing factor to the heat and dryness that prevails in that area. 



As mentioned at the beginning ,the Arabian Sea during the southwest 

 monsoon season offers many interesting examples of air-sea interactions, and 

 every comer of the ocean exhibits conditions that differ significantly from 

 the others . There is no question that the processes of air-sea interaction 

 play a major role on rain-producing processes over the Indian Subcontinent. 



