The Tropospheric Circulation 



601 



The equatorial currents are particularly well developed in the Pacific. As in the 

 Atlantic the counter current lies in the Northern Hemisphere throughout the whole 

 year and especially far from the equator during the northern summer. The surface 

 velocities reach values of more than 2 knots. The structure of the water masses was 

 first pictured in a "Carnegie" section (at about 140° W.) in October 1929 (Sverdrup 

 et al. 1 942., p. 709). Figure 276 shows the temperature and salinity distributions between 



Stot 159 

 Lcrti O"! S 



300 



Horizontal velocity, cm/sec 



Fig. 276. Temperature, salinity and computed velocity in a vertical section in the Pacific 



Ocean between 10° S. and 20° N. (according to the "Carnegie" observations; arrows 



indicate direction of the north-south flow; E. and W. indicate flow towards east and west 



respectively) (according to Sverdrup, 1942). 



the sea surface and 300 m as well as the velocity distribution calculated on the assump- 

 tion of no motion at the 700-decibar surface. The equatorial counter current hes 

 between 5° and 10° N., and in correspondence with the sea surface slope flows 

 downwards in the calm belt between the trade winds. The maximum velocity at 

 the surface is a little over 50 cm sec-^ in good agreement with observed values. The 

 "Carnegie" section gives an eastward transport by the equatorial counter current of 

 approximately 25 million m^ sec-^. The character of the transverse circulation is 

 evident from the distribution of salinity, oxygen, phosphate and also silicate and is 

 quite similar to that shown in Fig. 269 derived from observations in the Atlantic. 



A detailed theoretical treatment of the circulation in the top layer of the equatorial 

 parts of the oceans has been given by Yoshida, Mao and Hoover (1953). They start 

 out with the steady-state equations involving the Coriolis force, the pressure gradient 

 and horizontal as well as vertical mixing. For the mean wind-stress distribution and 



