2li; 



The distribution of water temperatures is shown in Figure 2. The 

 isotherms are oriented in a general southwest-northeast direction with very 

 cold temperatures of 22-23 C in the western coastal areas in the regions of 

 upwelling and warm centers of 27-28 C in the east side- The influence of the 

 atmospheric circulation on the distribution of temperatures can be easily 

 visualized. We can note with interest the extremely warm temperatures in 

 the Gulf of .Aden and the thermal gradient between the Gulf and the Arabian 

 Sea. The track of the ATLANTIS II is also reproduced in Figure 2 to show the 

 distribution of data with respect to the water temperature field. 



THERMAL STRATIFICATION - THE MONSOON INVERSION 



Two soundings obtained by the ATLANTIS II in the central Arabian Sea, 

 reproduced in Figure 3> illustrate the essential characteristic of the thermal 

 stratification of the monsoon air over the ocean. One was obtained on 

 August 11, lg63, near 15°N, and 58°E, and the other on August lU, I963, near 

 16 N, and 63 E. Only the dew-point curve for August 1^ is illustrated. 



Figure 3 indicates a well-mixed, humid layer of air near the surface, a 

 pronounced inversion immediately above in the levels from about 900 to 8OO mb;, , 

 and a relatively warm, dry-air mass aloft. The lapse rate is close to dry 

 adiabatic in the surface layer, stable in the inversion, relatively unstable 

 from the top of the inversion to the 500-mb level and close to the moist adia- 

 batic in the high troposphere . The humidity is large in the surface layer and 

 drops off significantly at the base of the inversion. These data illustrate a 

 moist air mass below, evidently dominated by oceanic influences and a dry hot- 

 air mass aloft, presumably of continental origin. Figure 3 shows a larger 

 depth of the moist layer, or higher base of the inversion, in the position 

 farther east. 



The presence of such a pronounced inversion so close upstream from the 

 coast of India was detected quite early in our studies of the monsoon air over 

 the ocean and presented some interesting questions concerning the mechanisms 

 for development of monsoon rains . 



The soundings were analyzed in the form of five cross sections; four of 

 them along latitudinal directions and one along a direction parallel to the 

 flow. They all presented a consistent picture of a low inversion in the 

 western edge of the sea, which rose eastward toward India and showed a 

 pronounced tendency for dissolution near the Indian coast. The cross section 

 along latitude 15N showed a rather deep stable layer in the western end with 

 a warm center of over 20°C temperatures at the 825 mti level, which was about 

 8°C warmer than at the same level in the east side of the ocean. The top 

 of the moist layer or base of the inversion rose fgom the 96O mb level at 

 longitude 50 E to the 850 mb level at longitude 68 E. A sounding obtained 

 near the Indian coast on August 15 showed no presence of the inversion. The 

 other E-¥ cross sections along latitudes 10 N and 5*^^ showed more or less 

 similar characteristics . 



