400 kilometers (250 mi) off Washington to 720 kilometers (450 mi) off southern California 

 (Fig. 5). The California Current turns westerly between 20° and 25°N and becomes the 

 North Equatorial Current with mean speeds between 1 5 and 30 cm/sec to the longitude of 

 Hawaii. 



Overall, the California Current averages about 15 to 30 cm/sec (Figs. 3 and 4). The 

 southward flow, particularly near the coasts (areas C and D in Fig. 5), predominates from 

 March through September. During the months October to February the weak northward 

 moving Davidson Current predominates near the coast. Even during the summer months, 

 when the current is most stable, it tends to be variable. In region A the current sets directly 

 south 23 percent of the time; all other directions average about 10 percent (Ref. 28). In 

 region B the current becomes more consistent, setting between the southwest and southeast 

 48 percent of the time with little or no secondary flow. The speeds in sections A and B, as 

 listed in Fig. 5, vary from 0.15 to 1.1 m/sec. The maximum speeds (above 0.6 m/sec) are 

 probably somewhat high because they are mostly based on ship drift measurements on 

 which prevailing winds can have a highly significant effect. In region C the nearshore cur- 

 rents are higher in velocity and more consistent than in region D. 



During the winter months (November to February) the prevailing current direction 

 in regions C and D in the California Current region (Fig. 5) shifts northward and is called the 

 Davidson Current (Fig. 6), which can be termed more accurately the Winter Coastal Coun- 

 tercurrent (Ref. 28). It has a rather poorly defined variable flow dependent mainly on the 

 influence of the wind. Figure 6 shows the boundary within which the prevailing northward 

 flow generally occurs. 



The table with Fig. 6 indicates the variability of flow by showing monthly percent 

 frequency of observations of speed and direction. The Davidson Current is interrupted by 

 the prevailing southerly flow of the California Current from March through the first half of 

 October. The southern portion of the current (Fig. 6, region B) is more variable than the 

 northern part, with sets occurring in the opposite direction (south) frequently in January 

 and February. There is evidence that there is a permanent northward flow below 200 me- 

 ters of depth running about 64 kilometers wide at speeds of about 25 cm/sec. It is probable 

 that when northerly winds become weak or negligible in late autumn and winter, a north- 

 setting countercurrent forms at the surface inshore of the main California Current. During 

 this period coastal upwelling lessens (upwelling is strongest in the spring and early summer 

 months), and numerous irregular eddies occur along the coast (Refs. 28 and 29). Nearshore 

 currents may be influenced by coastal tidal currents (which are rotary and thus will set in all 

 directions) and by the local winds, hence will tend to have a highly variable nature. In 

 summary, the Davidson Current begins at about 32°N, is variable and weak in the southern 

 section (10 to 25 cm/sec), but becomes more constant as it moves northward. In the north- 

 ern section it averages slightly higher speeds (20 to 35 cm/sec) and meets the more swiftly 

 northern-moving Alaska Current (25 to 50 cm/sec) at about 48°N. 



Current profile (velocity with depth) measurements are relatively sparse. However, 

 this type of information is extremely important to the planning and development of the 

 ocean fann because of the need to design substrate and mooring systems to withstand cur- 

 rent and current shear. Figure 7 gives several current profiles for the northeast Pacific 



14 



