both of the Somali current and equatorial dynamics in the western and central 

 Indian Ocean. As part of the oceanographic participation (INDEX, Indian Ocean 

 Experiment) during FGGE, the eddy structure and current system off the Somali 

 coast was studied during the 1979 southwest monsoon (May-September) with 

 particular emphasis on the commencing stage of the monsoon. Since consider- 

 able data have been made available from the National Climatic Center (NCC) on 

 past wind measurements throughout this region, it is felt that some discussion 

 of these observations would be worthwhile. 



4. WIND DATA 



Using the NCC ship observations from the TDF-11 tapes. Bunker (1976) 

 prepared a program for calculating sea surface energy fluxes. From these 

 determinations the values of wind stress over the western Indian Ocean kindly 

 were made available by him. Using these values, maps of monthly averages of 

 Tx and Ty were contoured in order to observe the patterns occurring during the 

 southwest (May through September) and northeast (December through February) 

 monsoons . 



The values of Cq in the equation t = pC^ U]g (p is air density, U-jq is 

 average wind speed at 10 m or ship's anemometer level) were selected by Bunker 

 (1979, table 2) using various classes of air-sea temperature differences and 

 wind speed ranges from the work of several investigators. Monthly averages 

 for the period 1922-1972 were obtained for subdivisions of the Marsden squares 

 as shown in figure 13 which gives the center of gravity of the observation 

 positions. The total number of observations for each subdivision is given in 

 table 1. The remoteness of some regions of the Indian Ocean results in a 

 number of lesser traveled sea lanes as may be seen by comparing the volume of 

 observations in table 1 with that of the North Atlantic in Bunker (1975, 

 figure 3). The subdivisions of the Marsden squares have been adjusted in an 

 attempt to include sufficient monthly observations to be significant. Averages 

 for periods greater than a month would be of considerably less value in depict- 

 ing the relatively rapid seasonal changes occurring during the monsoons. 



5. WESTERN INDIAN OCEAN WIND STRESS FIELD 



The maps of wind stress (figure 14) have been contoured with the same 

 interval, 0.2 dynes cm~2, for all months with x^ and ly positive to the east 

 and north respectively. Perhaps the most outstanding characteristic of the 

 monthly maps is the large difference in magnitude of the wind stress field 

 between the two monsoons. The southwest monsoon reaches its greatest strength 

 during July and the northeast monsoon during January. In the early stage of 

 the southwest monsoon the components become positive by May off the Somali 

 coast around S^N to 10°N with the largest values (> 1 dyne cm"2) near 8°N. 

 This region is where the first evidence of upwelling at the sea surface is 

 observed from the maps of Wyrtki (1971) with near coastal temperatures falling 

 below 270C. The June and July averages indicate the rapid development of the 

 areas of high positive stress values, particularly off northeast Somali at 

 about 10°N to 120N. June averages greater than 2 dynes cm"2 extend over half 

 the distance to the Indian coast and meridional ly between 50N to IS^N. During 

 July areas with over 4 dynes cm"2 occur, and the band encompassing the strong 



