230 



Figure 2 presents the horizontal distribution of the observed wind 

 vectors on the same 2 days. On August 30, the aircraft crossed the axis of 

 the jet at 10 N, 53 E at 550 meters. At this point the velocity was about 

 25 m sec" . One hundred km either side of the axis the velocity drops to 

 about 15 m sec" indicating a rather sharp narrow jet. 



On September 1, 196^, a track about ^4-5° to the wind was^flown. The plot 



of this flight shows that a strong narrow jet with 27 m sec" winds was 



o o 

 encountered in the vicinity of 12 N, 53 E. Beyond this area the wind dropped 



off to speeds of about l6 m sec" . As the ascent was made at 11 N, 58 E. 



the aircraft passed through a jet at 1000 meters, with 25 m sec speeds. One 



would like to know whether this is the same jet that was encountered at 12° N 



53° E at a height of 56O m. It is possible that it is a broad jet extending 



from 12° N, 53 E to 11° N 53 E with a level of the maximum wind that rises 



in the southeasterly direction. High values of the turbulence encountered 



along this track suggest that the aircraft probably was flying underneath a 



wind maximum. This point will be discussed later after the presentation of 



the turbulence data. 



It should be stated at this point that the jet is not a transient 

 phenomenon that happened to exist in the area on the days that the flights 

 were made. Rather, the intense winds in this area are a persistent feature 

 of the southwest monsoon, as a casual inspection of weather charts of the area 

 will reveal. Ship reports show relatively minor variations in strength and 

 position from day to day. 



THE SEQUENCE OF INTERACTIONS BETWEEN AIR, SEA, AND LAND 

 AND THE DEVELOPMENT OF THE SOMALI JET 



V 



(1) Global-Scale interactions . The first phase in the development of 

 the wind system occurs in the northern hemisphere in the spring on a scale 

 involving the entire continent of Asia and the Indian Ocean. With the return 

 of the sun to the hemisphere the land masses of Asia and North Africa are 

 warmed. The land in turn warms the atmosphere and gradually changes the cold 

 highs to warm lows. During this same time interval the temperature of the 

 Indian Ocean south of the equator remains about the same or cools a small 

 amount. The maintenance of the waiter temperature keeps the air temperature 

 about the same and hence the surface pressure remains the same or increases a 

 bit. By May the pressure in the north has been reduced to about IOO5 millibars 

 while the pressures in the south have increased to about 1022 mb: This pres- 

 sure gradient accelerates the air mass northward across the equator and north- 

 easterly across the Arabian Sea. 



(2) Oceanic-Scale interactions . The reaction of the sea water to this 

 moderate air flow from fhe south is the movement of the surface water to the 

 east away from the coast of Africa. The presence of the African Continent 

 prevents replacement of the water except by upwelling of deeper cool water. 

 As a result of this replacement, the waters from the Mozambique Channel to 

 north of the equator become a few degrees cooler than the water 2000 kilometers 



