Paper 6 



indicate onshore surface transport and downwelling at the coast. 

 Monthly mean upwelling index values for the period 1946-71 were 

 presented for the 15 locations shown in Figure 6.1. These time 

 series have been updated for 1972-74 and 1975 (Bakun 1976* 1978). 



Monthly upwelLing indices for 1976 are given in Table 6.1. 

 Anomalies from the 20-yr (1946-67) mean monthly values are 

 presented in Table 0.2. Upwelling indices are displayed in 

 percentiles in Figure 6.2. Percentile values were based on the 

 rank of the upwelling index for each month and Location within 

 the 31-yr (1946-76) time series. 



THE GULF OF ALASKA 



wind driven surface transport in the Gulf of Alaska (60N* 149W to 

 5 1 N * 171w) tends to be divergent in the interior and convergent 

 at the coast.' The annual cycle of coastal convergence is 

 dominated by vigorous downwelling during the winter season/^ when 

 intense cyclonic storm activity characterizes the atmospheric 

 circulation in the region. During 1976 monthly upwelling indices 

 were negative along both northern and eastern boundaries* except 

 in June and July when small positive values were evident. 



In January more intense than normal downwelling was indicated 

 alono the eastern boundary* while positive anomalies occurred in 

 the northern GuLf of Alaska. This pattern of anomalies reversed 

 the trends for these two areas begun during the last quarter of 

 1975 (bakun 1978). The remainder of the first quarter of 1976 

 was marked i? y less intense than normal winter downwelling. 

 Reduced levels of coastal convergence may be associated with less 

 intense than normal surface divergence offshore. A decrease in 

 the strength of the coupled "punping" between the central Gulf of 

 Alaska and the coast would tend to reduce the baroc I in i c i t y 

 established during the previous three months. 



More intense than normal coastal convergence was evident during 

 the remaining months of 1976. A general pattern of upwelLing 

 indices below the median (Fig. 6.2) was interrupted in June* when 

 small positive, values occurred* and in October* when an irregular 

 transition to vigorous winter downwelling was apparent. 

 Anomalies from the long-term monthly means (Table 6.2) were 

 negative from April through September* except during June* at 



Ingraham* W. J.* Jr.* A. Bakun* and F. Favorite. 1976. 

 Physical Oceanography of the GuLf of Alaska. U.S. Dep. Commer.* 

 MOAA*Ni*iFS, Northwest Fish. Cen.* Processed Rep.* 132 p. 



66 



