132 EIGHTH PACIFIC SCIENCE CONGRESS 



In a paper now in press Cromwell ^ has erected a hypothetical 

 model which postulates the effect of winds from various directions on 

 the ocean circulation and which is consistent with the empirically de- 

 termined hydrographical and biological conditions. He has kindly per- 

 mitted our use here of Figure 3 (Fig. 6 of his paper) and has prepared 

 the following statement on the particular effects of wind which are most 

 significant to the present discussion. 



"Figure 3 shows directions of current transport (solid arrows) that 

 would exist near the equator under various wind conditions were there 

 no pressure gradient force acting.^ For each wind direction the meri- 

 dional components of current transport (dotted arrows) are drawn to 

 emphasize the regions of divergence (Div.) and convergence (Conv.). 

 The magnitude of the current is drawn everywhere constant, and hence 

 the regions of divergence and convergence shown are associated with 

 differences in current direction only. Upwelling can occur in the re- 

 gions of horizontal divergence. 



"The intensity of the horizontal divergence is partially dependent 

 on the current magnitude which increases with increasing wind speed. 

 Thus, during strong trade winds near the equator, horizontal diver- 

 gence and upwelling will be intense and the sea surface temperature 

 will be low. 



"Figure 3 shows further that the position of the convergent and di- 

 vergent currents depend on the wind direction. During a steady east 

 wind horizontal divergence is centered at the equator. When the wind 

 is southeast there is horizontal convergence in the northern part of 

 the equatorial region between the 3° parallels, with the divergent cur- 

 rent now centered somewhat south of the equator." 



As an empirical example for examining the distribution of proper- 

 ties in the meridional plane, for inferring the circulation, and for see- 

 ing the effect of the circulation on plankton and tuna distribution, we 

 shall use Cruise 11 of the Fish and Wildlife Service vessel HUGH M. 

 SMITH (Fig. 4) which occupied the period August 20 to October 6, 

 1951. On this cruise the SMITH proceeded southward along meridian 

 150° W. occupying fishing stations, and returned northward along the 

 same meridian occupying hydrographic stations (Fig. 5). Bathythermo- 

 grams and zooplankton hauls were taken on both transits. The south- 



' Cromwell, Townsend: "Circulation in a meridional plane in the central equatorial Paci- 

 fic." In Press. Journal o/ Marine Research. 



-In Figure 3 the vectors at the 3° parallels are in accordance with Ekman's theory of the 

 pure wind drift current (Ekman 1905), i.e., the current transport is indicated at one right 

 angle cum sole with the generating wind. Ekman's theory is considered to apply 3° from the 

 equator in accordance with a recent paper by Weenink and Groen (on the computation of sur- 

 face current velocities in the equatorial regions from wind data. Proc. of Koninld. Nederl. 

 Akad. van Wetenschappeii, Amsterdam, Ser. B, 55, No. 3, pp. 239-246, 1952) in which they 

 conclude that at ". . .2 or 3 degrees ..." and higher latitudes the internal frictional 

 force is small compai-ed to the Coriolis force. Cromwell has discussed completely the assump- 

 tions involved in eonstructing the figure. 



