The Tropospheric Circulation 



645 



analysis of the thermal conditions in this oceanic region has been carried out by 

 Thorade (1909) and McEwen (1912, 1934). The onset of upwelling phenomena usually 

 occurs in March and reaches its maximum during the summer months (July to August). 

 The culmination coincides with the maximum frequency of the north-west winds. It is 

 absent during the autumn and winter although off-shore south-easterly winds are not 



40° 35" 30 25° 20" 15 10" 5° 0° 5° 



Fig. 301. Mean anomaly of the sea surface temperature off the north-west coast of Africa 

 for April (drawn from means of two degree squares of the Atlantic Ocean). 



uncommon. The cold upwelHng water off the South American coast has been dealt 

 with by GuNTHER (1936) (see p. 571). The west coast of Austraha is not entirely free 

 of cold coastal water as has been shown by Schott (1933) and rising water sometimes 

 occurs off the north-western coast. Occasional observations of cold upwelling water 

 have also been made along many other coasts, for instance, off the Somali coast 

 during the summer months during off-shore winds and at the southern tip of Ceylon 

 and others. 



In considering the dynamics of the phenomenon it should particularly be remem- 

 bered that for a current in stratified water the mass field adjusts baroclinic, so that 



