During the period of maximum strength of the northeast monsoon in January, 

 the values of curl are substantially less than those of July. Over much of 

 the Somali Basin the curl becomes positive (figure 20) up to >1 x 10"° dynes_ 

 cm-3 with a small area about lO^N just off the Somali coast which is >2 x 10 " 

 dynes cm"-^. In the region to the north of the contour of zero curl between 

 the Somali east coast and the Indian west coast (which has positive curl 

 during the southwest monsoon), the curl during the northeast monsoon becomes 

 negative. A similar reversal of sign occurs to the south of the zero contour. 

 Although in general there is a change of sigh of the curl between monsoons, 

 the magnitude of the values in most regions is considerably less during the 

 northeast monsoon. 



7. TOTAL MERIDIONAL TRANSPORT 



From the July and January values of curl (representing the maximum values 

 for each monsoon) the meridional mass transport (Sverdrup transport), M = B 

 curl T can be determined (Stommel, 1965). My is the sum of the geostrophic 

 and Ekman transports. Values were summed over areas of 2° latitude and longi- 

 tude (figures 21 and 22) from the eastern boundary (transport function consi- 

 dered zero here), i.e., the west coast of India and Sri Lanka and from 80°E 

 for the region south of Sri Lanka down to 2°N, toward the west approaching the 

 Somali and Arabian Coasts. 



In the Somali Basin during July the transport is greater than 30 x 10' ^ g 

 sec"^ and in two regions near G^N and 120N greater than 40 x 10^2 g sec"' to 

 the south. For continuity this would require a northward current of equal 

 magnitude along the Somali coast and off the island of Socotra (12°N, 54°E). 

 The transport around 60N is in agreement with direct measurements here which 

 amount to 40 to 50 x 10^2 g sec"' (Swallow and Bruce, 1966) (figure 22), 

 however, a more northerly section (up to 8° 40' N) of direct measurements where 

 the current turns offshore during the same cruise had a transport over 50 x 

 10'2 g sec"^. It was also found that in the North Atlantic the computations 

 of transport failed to account for the large observed transports in the Gulf 

 Stream after it leaves the coast (Leetmaa and Bunker, 1978). The Somali 

 Basin, as in this area of the Atlantic, has a strong eddy field which in part 

 might account for the greater transport. The northwestern Indian Ocean is 

 subjected to large seasonal changes in wind stress, particularly with the 

 onset and build-up of the southwest monsoon, and it is not clear whether the 

 mean stress curl for a period as short as a month would account for the trans- 

 port which is a function of both barotropic and baroclinic processes (Hantel , 

 1971). However, once the onset of the monsoons has occurred, the wind direc- 

 tion tends to be relatively steady compared to most ocean regions, thus 

 conceivably a shorter response time would be required in this part of the 

 Indian Ocean as suggested by the agreement with direct current observations. 

 A lag of the order of magnitude of a month between the build-up in the wind 

 stress field (greatest in July) and the oceanic response is indicated in 

 figures 6 and 7 where the greatest monthly mean depths of the top of the 

 thermocline are attained during August (Robinson et_ al_. , 1979). 



The fact that there are two areas in figure 21 with transports greater than 

 40 X 10^2 g sec-1 suggests the formation of two eddies. Such a circulation has 

 been observed each southwest monsoon during the period 1975-1979 (Bruce, 1979): 

 a large eddy off the Somali coast and a somewhat smaller one to the east of 



