204 WATER MASSES AND CURRENTS OF THE OCEANS 



been examined. According to McEwen the rate of upwelling is about 

 20 m a month, and on an average the process is therefore a very slow one. 



During the entire season of upweUing a countercurrent that contains 

 considerable quantities of Equatorial Water flows close to the coast at 

 depths below 200 m. This subsurface countercurrent appears to be 

 analogous to a subsurface countercurrent off the coast of Peru. In spring 

 and early summer the currents off the coast of California are therefore 

 nearly a mirror image of those off the coast of Peru, but the similarity is 

 found in this season only because the character of the prevailing winds 

 off California changes in summer, whereas off Peru the winds blow from 

 nearly the same direction throughout the year. 



Toward the end of the summer the upwelling gradually ceases, and 

 the more or less regular pattern of currents flowing away from and toward 

 the coast breaks down into a number of irregular eddies, some of which 

 carry coastal waters far out into the ocean. Other eddies carry oceanic 

 waters in toward the coast, particularly in the regions between the centers 

 of upwelling, as shown by Skogsberg in his discussion of the waters of 

 Monterey Bay. 



In the fall, upwelling ceases, and in the surface layers a countercurrent 

 develops, the Davidson Current, which in November, December, and 

 January runs north along the coast to at least lat. 48°N. In this season 

 the subsurface countercurrent still exists, and the main difference between 

 the seasons without and with upwelling is therefore that in the former a 

 countercurrent is present at all depths on the coastal side of the California 

 Current, whereas, when upwelling takes place, the countercurrent has 

 disappeared in the surface layer, where, instead, a number of long- 

 stretched swirls have developed. This suggests that in the absence of the 

 prevailing winds that cause upwelling, a countercurrent would appear on 

 the coastal side, as is the case in other localities. 



Transport. On the basis of the values of the volume transport 

 of the different branches of the current system that have been mentioned 

 and others that have been computed, the schematic picture in fig. 56 has 

 been prepared. The lines with arrows give the approximate direction 

 of the transport, and the numbers give the volume transport in millions 

 of cubic meters per second. In this case the transport numbers include 

 the motion of the Upper and the Intermediate Water, because the Inter- 

 mediate Water of the Pacific appears to flow in general in the same 

 direction as the Upper Water. The lines showing the direction of trans- 

 port are full-drawn where the Upper Water masses are warm and dashed 

 where they are cold. 



The figure shows that in the North Pacific Ocean the Equatorial 

 Countercurrent and the Kuroshio are the two outstanding, well-defined 

 currents. Over the greater part of the Pacific Ocean, weak or changing 

 currents are present, and the transport numbers that are entered refer 



