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ABSTRACT 



During the period August 7 to September 28, I963 the research vessel 

 r/V ATLANTIS II, while participating in the program of the International 

 Indian Ocean Expedition, made several E-W cross sections across the Arabian 

 Sea carrying out a program of meteorological and oceanographic observations 

 which included daily radiosondes . This collection of raob data was analyzed 

 in the form of time and space atmospheric cross sections in order to study 

 the general properties of the monsoon air. 



The southwest monsoon regime is generally established over the Arabian 

 Sea around the latter part of May and is maintained as a fairly steady and 

 persistent current until the latter part of September. Therefore, the data 

 collected by the ATLANTIS II showed characteristic properties of the monsoon 

 current at the height of the season. 



The thermal structure consisted essentially of two layers of air: a 

 shallow layer of humid air near the surface and a dry, relatively unstable 

 air mass on top, separated by a pronounced thermal inversion. The nature 

 of the monsoon inversion and of its distribution over the Arabian Sea was 

 investigated. 



The properties of the surface moist layer and the modifications during 

 its path downstream will be discussed also in relation to the water tempera- 

 ture field and the weather-producing processes responsible for monsoon rains. 



