circulation parameters under consideration. 

 Seasonal averages within each decade were 

 computed for the California, Alaska, Wester- 

 ly, Trade, Kuroshio and Oyashio indices and 

 are shown as vector components in figure 8 

 (pages 11 and 12). The length of each arrow 

 is proportional to the magnitude of the mean 

 geostrophic wind component for the indicated 

 region, decade and season. 



The most striking case of a widespread 

 change in average circulation intensity 

 occurred during the winter months of the 

 1946-55 period (fig. 8a, page 11). The lower 

 values of the Oyashio and Alaska indices and 

 higher values for the California index for 

 this period, compared with the two earlier 

 decades, reflect a weaker average intensity 

 of the Aleutian Low and a higher average 

 intensity and more northerly mecin position 

 of the eastern North Pacific High. 



The California index also shows greater 

 average intensity in the spring months of 

 1946-55 compared with earlier years (fig. 8b, 

 pa^e 11). For the same season, the Alaska 

 and Oyashio indices show decreasing values 

 (in the algebraic sense) with time, possibly 

 indicating a trend toward earlier transition 

 from winter to summer circulation regimes, 



A recommendation that the ten year period 

 1949-58 be used as a common base reference 

 period for marine biological and oceanograph- 

 ic data was made by a committee of the East- 

 ern Pacific Oceanic Conference at its October 

 1958 meeting at Lake Arrowhead, California. 

 With the recent availability of sea level 

 pressure charts through 1958 it has been pos- 

 sible to compute, for this reference 

 period, averages by month of the re- 

 gional indices and geostrophic com- 

 ponents at the individual locations 

 used in this report. Monthly means ^ e 



for the base reference period 1949-58 5 



are given in table 7 (page 106) for ^ 4 



individual locations and in table 8 ^ 



(page 108) for regional indices. "> z 



TIME SERIES 



When the monthly anomalies of tlie 

 various indices are plotted against 

 time, it is apparent that the ampli- 

 tudes of the short period fluctua- 

 tions (two to four months) are very 

 large and make it difficult to dis- 

 cern fluctuations of longer periods. 



In order to follow the tendencies of the 

 longer period fluctuations over several 

 years it is helpful to eliminate the short 

 periodicities by smoothing. 



The time series of anomalies for the 

 Kuroshio, Westerly, Trade, California, Oya- 

 shio and Alaska indices were each smoothed 

 by taking weighted running averages of eleven 

 successive monthly values. The weighting 

 factors were based on binomial coefficients 

 and applied as follows: 



»i = TO!7 f» 





where ai_5, ai_4. 



etc. refer to successive 

 monthly anomalies and "Sj is the weighted 



mean plotted for the i^^ month. In applying 

 this smoothing the very small first and last 

 terms of the above expression were omitted 

 and the denominator v.'as rounded to 1020, 



This method of smoothing, known as the 

 binomial smoothing function, has been dis- 

 cussed by Brooks and Carruthers (1953). As 

 here applied the effect is to eliminate al- 

 most completely periodicities of four nwnths 

 or less. Periodicities of six to eight 

 months are damped to less than half their 

 original amplitudes while periodicities ex- 

 ceeding one year are relatively unaffected. 



Figure 9 shows examples of smoothed and 

 unsmoothed time series graphs representing 

 a portion of the California index anomalies. 



CALIFORNIA INDEX 



J L 



46 47 48 49 50 51 52 53 54 55 66 57 

 YEAR 



Figure 9. --Smoothed and unsmoothed time series graphs of 

 California index for period 1946-57. 



13 



