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ABSTRACT 



As the southwest monsoon develops over the Arabian Sea, a sequence of 

 sea, air, and land interactions occurs that culminates in the production of / 

 a 25 m sec" low level jet at 6OO to 1000 meters blowing off the coast of ^ 

 Somalia. Aircraft and surface observations are presented which describe the 

 jet, the thermal structure of the atmosphere, the sea surface temperatures, 

 and the surface pressures . From these data and climatological data it is 

 shown that the jet results from a sequence of two complete cycles of thermal 

 reactions of the air to sea and land temperatures and kinetic reactions of 

 the water to atmospheric wind stress. These cycles occur on decreasing size 

 scales but with increasing intensities thereby producing an intense local jet. 

 The geographical location of the jet is fixed by the configuration of the land 

 masses and proximity to the equator- The existence, general shape, magnitude, 

 and geographical position of the jet are explained as resulting from (a) a 

 large land mass north of the Indian Ocean, (b) ? land mass to the west of the 

 Ocean, (c) strong heating of the land which intensifies the pressure gradient, 

 (d) a small value of the Coriolis force, and (e) air-sea interactions which 

 produce through upwelling of cold water and cooling of the air thermal winds y 

 and a low frictional drag of the air over the water. 



INTRGDUCTIOW 



As part of the International Indian Ocean Expedition, meteorological 

 studies were carried out over the Arabian Sea using a C-5^Q aircraft. This 

 airplane was equipped with instruments designed to measure temperatures, 

 winds, humidities, clouds, radiation, and turbulence. On August 30, I96U. a 

 flight was made from Aden cutting perpendicularly across the wind blowing from 

 -the SW off the coast of Somalia. The track outbound was flown at 100 to 600 

 meters. A climb was made to il500 m at il-° N, 56° E. The return flight to 

 Aden was made at ii-500 m and 5 radiosondes were released enroute . On 

 September 1, 196^4-, a track was flown from Aden to Bombay cutting the Somali 

 jet again. The portion of the track from Aden to 11 N, 58 E was flown at 

 low levels while the remainder was flown at ^4-500 meters. From these observa- 

 tions it becomes clear that the strong winds take the form of a low- level jet 

 with a maximum speed of about 25 m sec 



DESCRIPTION OF THE JET 



Figures 1 and 2 are presented to show the main characteristics of the 

 wind system as it existed on the 2 days, August 30 and September 1, 196U. 

 The wind speed - height curve. Figure 1, was drafted from the goppler radar 

 winds observed during the aircraft's ascent at about 11 N, 58 E. It is 

 seen that a large wind shear exists in the 500 to 1000 meter region, that a 

 rather broad maximum exists in the 1000 to 15OO meter range, and a steep 

 negative gradient exists above this level. 



