Figure 1. — A conceptual diagram of the coastal upwelliriK process. The coast of the 

 continent is represented in cutaway view with the ocean to the left of the figure. Off- 

 shore transport in the surface Ekman layer due to stress of the wind parallel to the 

 coast on the sea surface is replaced by upwelling from depth. 



where Vg and Uy are the respective northward 

 and eastward components of geostrophic wind 

 velocity, / is the Coriolis parameter, p„ is the 

 density of air and R is the mean radius of the 

 earth. The density p„ was considered constant at 

 0.00122 g cm ' . An estimate of the wind near the 

 sea surface was formed by rotating the geo- 

 strophic wind vector 15 degrees to the left and 

 reducing it by 30% as in Figure 3(b) to approxi- 

 mate frictional effects. 



The sea-surface stress was then computed ac- 

 cording to the classical square-law formula 







(4) 



where t is the stress vector, p,; is the density of 

 air, Cfi is an empirical drag coefficient, v is the 

 estimated wind vector near the sea surface with 

 magnitude \r\. A relatively high value, 0.0026, 

 of the drag coefficient was used to partially off- 

 set the effect of using mean data. Finally, the 

 Ekman transport was computed according to 

 Equation (1). Except for the estimates of the 

 pressure derivatives which necessarily differ 

 because of the different grid format, this calcu- 

 lation procedure is the same as that used by 

 Fofonoff (I960).- The offshore transport is de- 

 termined by resolving the component perpendic- 



ular to a line drawn by visual estimation on a 

 bathymetric chart along the dominant trend of a 

 200-mile segment of coastline centered near the 

 grid point in question. 



The indices generated by this method must be 

 considered as indicative of rather large-scale 

 coastal upwelling. The 6-degree gap across which 

 the derivatives are measured as well as the scale 

 of coastline resolution indicates a 100- to 200-mile 

 scale as being appropriate for interpretation of 

 the indices. Certainly, smaller scale upwellings 

 could occur within a larger scale downwelling 

 just as short-term upwellings might occur during 

 a monthly period of average downwelling. 



Pressure Data 



The number of synoptic surface atmospheric 

 pressure fields available at FNWC for each 

 month during the period 1946-71 is variable. 

 Because of the nonlinear dependence of stress on 

 wind velocity (Equation 4), use of a variable sam- 

 pling interval destroys the internal consistency 

 of the time-series. For this reason monthly mean 



- Fofonoff. N. P. 1960. Transport computations for the 

 North Pacific Ocean-1958. Fish Res. Board Can., Manuscr. 

 Rep. Ser. (Oceanogr. Limnol.) 80, 81 p. (Processed.) 



