Section 4, shown in figure 9, is 500 nini long and was taken between 23 

 and 26 August. It is a recrossing of the Great Whirl close to its northern 

 boundary in order to assess the area of maximum upwelling. From the end of 

 the section until about 460 nmi from the coast the warmer isotherms (T>15°C) 

 slope sharply upward. The 25°C and 24°C isotherms break the surface between 

 460 and 480 nmi from the coast, and the 23°C isotherm rises by about 70 m in 

 less than 20 nmi. Between 460 and about 310 nmi from the coast all isotherms 

 slope downward with the warmer (T>20°C) isotherms showing the strongest down- 

 ward slope. A weak near-surface front is evident 300 nmi from the coast. 

 Again, this weak near-surface front is coincident with a strong sea surface 

 salinity gradient (figure 19) marking a zone of transition between relatively 

 fresh (S<35.0 °/oo) coastal and equatorial water and more saline (S>35.6 °/oo) 

 oceanic water of Arabian Sea origin to the east. Within 300 nmi of the coast 

 there is a general shoaling of all isotherms with the most pronounced shoaling 

 occurring within 100 nmi of the coast. The rise of the 14°C isotherm from 

 250 m at 180 nmi to 35 m at 10 nmi is an indication of the intense barocl inicity 

 of the coastal current in the area. Close to the Somali Coast at the end of 

 the section the sea surface temperature dropped from 22°C to less than 15°C in 

 seven miles. The maximum currents were estimated from ship set and drift 

 measurements to be in excess of 5 knots. 



Sections 5 and 6, taken between 26 and 29 August and shown in figures 

 10 and 11, respectively, cross the complex boundaries between the relatively 

 cold water off Ras Mabber at about 9°N, the northern boundary of the Great 

 Whirl, and the southwestern edge of the Socotra Eddy. Along section 5 the 

 15°C isotherm rises 170 m in less than 180 nmi, and the 16°C isotherm breaks 

 the surface just off the coast. The 20OC isotherm breaks the surface at 

 locations 60 and 80 nmi from the coast. This patch of cold (T<20°C) surface 

 water is located about 60 nmi southeast of Ras Hafun and is collocated with a 

 strong gradient in sea surface salinity (figure 19). The cold water in this 

 region is also evident in the NOAA TIROS-N satellite infrared imagery of 

 27 August (figure 3). From both satellite imagery and XBT observations it is 

 evident that this region was undergoing rapid and complex changes at the time 

 of the observations. 



Section 6, taken between 27 and 29 August, was made to study the circula- 

 tion immediately to the south of Socotra Island. The slope of isotherms is 

 somewhat gradual for the first 200 nmi of the section. This gradual downslope 

 is followed by a sharper upslope between 200 nmi and the end of the section. 

 In 80 nmi the 20°C isotherm rises over 100 m. This sharp upslope of isotherms 

 is coincident with a very complex and irregular surface salinity field 

 (figure 19) and is associated with the zone of transition between coastal 

 Somali Current water and water of Arabian Sea origin. 



Section 7 (figure 12) crosses the approximate center of the Socotra Eddy 

 from 29 to 30 August. There is a general downslope of isotherms out to about 

 180 nmi with the 20°C isotherm deepening by about 180 m. This deepening of 

 isotherms is coincident with maximum sea surface salinities (S>35.9 °/oo) 

 (figure 19). Between 180 nmi and the end of the section there is a pronounced 

 and general upslope of the isotherms. The 20°C isotherm rises from 210 m at 

 180 nmi to 105 m at the end of the section. Breaks in the isotherms are 

 indications of repeated XBT failures. The general bowl -shaped structure of 

 the isotherms in this section indicates the presence of an anticyclonic eddy 



