Basic Principles of the General Oceanic Circulation 567 



drift current towards west-south-west or west. Thereby a current boundary is formed 

 beginning north-west of Cape Comorin and can be followed along about 10° N. 

 westwards until 60° E. It carries the character of a convergence line between water 

 from the Arabian Sea and water masses of the main current flowing from the east. 

 ScHOTT (1928fl) has mentioned the great contracts in surface salinity here. Part of this 

 water transport into this region enters as a very strong current into the Gulf of Aden 

 and continues through the Strait of Bab el Mandeb into the Red Sea. The other part 

 forms a strong south-west current flowing along the Somali coast to about 7° S., where 

 the Equatorial Counter Current starts rather abruptly having a direction towards east. 



South of the counter current flows the broad South Equatorial Current and shows 

 large seasonal variations in velocity and constancy caused by the annual variation of 

 the south-east trade winds. The current core lies near the northern boundary of the 

 current at about 10° S. to 15° S. in both summer and winter (Michaelis, 1923). The 

 irregularities in the South Equatorial Current due to Madagascar have been investi- 

 gated by Paech (1926). In the Southern Hemisphere summer a "Stau" current flows as 

 a southward current along the African coast starting at 10° S., the Mozambique 

 Current, with a tributary current from the east coast of Madagascar. Both form the 

 source for the Agulhas Current at about 30° S., which continues closely to the conti- 

 nental shelf until it swings out from the shelf around the Agulhas Bank at the southern 

 tip of Africa. The northern part of the core, however, still keeps to a very large extent 

 over the contmental shelf. From the southern end of the Agulhas Bank part of the 

 current then flows north-west as the Benguela Current and part turns back into the 

 Indian Ocean forming a series of large vortices. The complicated nature of the 

 currents in this part of the convergence zone between the Agulhas Current and the 

 west wind drift is clearly shown in an analysis of the current field which has been 

 prepared by Merz (1925). 



The atmospheric pressure and wind distribution over the Indian Ocean north of the 

 equator changes drastically during April. Almost immediately the sea surface currents 

 react to this change in the wind direction and at the same time there is a redistribution 

 of the water piled up at the coasts. The South Equatorial Current still remains in the 

 Southern Hemisphere (south of 5° S.) but is considerably intensified. The counter 

 current disappears and over the entire northern part of the ocean except the coastal 

 zones a fairly constant eastward current appears, the South-west Monsoon Current. 

 The convergence line between the South Equatorial Current and this monsoon current 

 is well developed along the total width of the ocean and broken only in the extreme 

 west where a strong branch turns northwards from the South Equatorial Current 

 between 5° S. and 0° and flows along the coast into the Arabian Gulf as the Somali 

 Current. It follows closely the steep pressure gradient off" the coast between the region 

 of piled up water ("Anstau"-Gebiet) between 5° and 10° S. and the area from which 

 water has been removed by the monsoon current between 5° N. and 10° N. This is 

 accompanied by upwelling just off" the African and Arabian coasts (Puff, 1890). The 

 Somali Current possesses mostly an extreme intensity, so that speeds here are greater 

 than in the Florida Current (often more than 100 nautical miles in 24 h) (Fig. 259). 

 The formation of anticyclonic vortices to the south-east of Ras Hafun and the marked 

 concentration of the current core into a narrow coastal belt is characteristic and 

 accords with the increase of the Coriohs force towards north. 



