Table 3. — Mean monihly values of the indices for the 20-yr period, 1948-1967. Units are cu- 

 bic meters per second per 100 m of coastline. 



locution, this set of indices may be admirably 

 suited for describing the spatial variations of 

 timing and duration of upwelling. In Table 3 are 

 listed the long-term monthly mean values of the 

 indices for the 20-yr period, 1948-67. Figure 6 

 displays plots of these values. 



The period of maximum values of the indices is 

 earliest to the south, becoming progressively 

 later in the year with distance to the north. At 

 lat. 21 °N the peak is in April. Off the coast of 

 Baja California the peak is in May. A June peak 

 occurs off southern and central California. North 

 of San Francisco the peak is generally in July, 

 with a slight shift back to June at the northern 

 extremity of the Gulf of Alaska. 



From the southern tip of Baja California north- 

 ward to Monterey Bay the mean values of the 

 indices indicate upwelling throughout the year. 

 Northward from San Francisco the season of 

 indicated upwelling becomes progressively re- 

 stricted, lasting March through October off north- 

 ern California, April through September off Ore- 

 gon, May through August off northern Vancouver 

 Island, finally narrowing at lat. 57 °N to a scarce- 

 ly significant positive value of the index during 

 July. 



Tabulations of the deviations from these long- 

 term mean values accompany the tabulations of 

 the values of the indices in the Appendix. Graph- 

 ical plots of both the anomalies and the values 

 of the indices are included. 



DISCUSSION 



Detailed analysis and interpretation of the 

 time-.series plots contained in the Appendix is 

 beyond the scope of this report. However, it may 

 be useful to point out several examples and to 

 speculate briefly upon possible consequences. 



Accompanying the plots of the monthly indices 

 for each location are tables of quarterly and an- 

 nual averages. The following three examples are 

 each illustrative of phenomena occurring basi- 

 cally on one of these three different time-scales. 

 As it happens, the first two concern negative 

 values of the index. Negative values of the index 

 indicate accumulation of wind-transported sur- 

 face waters at the coast and resulting down- 

 welling. 



Short-Term Intense Convergences in 

 the Northern Gulf of Alaska 



A glance at the first chart in the Appendix 

 reveals an extreme negative spike in the up- 

 welling index at lat. 60 °N, long. 149 °W during 

 February 1950. In this case, the indicated con- 

 vergence is over 4y2 times the 20-yr mean value 

 for February. It is interesting to speculate upon 

 the effect of such an anomaly on the density struc- 

 ture of the northern portion of the Alaskan Gyre. 



If the given numerical value is accepted as an 

 estimate, we find for February 1950 an anomalous 

 onshore flow of nearly 300 m-' /sec along each 



