FISHERY BULLETIN: VOL. 70, NO. 3 



wind systems move through the region, the cor- 

 relations are somewhat lower, but still signifi- 

 cant at the 5'"f level. 



For the entire 20 years of concurrent records 

 for Hilo-minus-Avila and Honolulu-minus-San 

 Francisco, the correlation of unsmoothed anom- 

 alies is 0.49 and for smoothed anomalies it is 

 0.55. The l'"r level of significance for the cor- 

 relation coefficient of a sample of 240 months is 

 0.17, so these values are highly significant. 



A visual comparison of the data in Figures 

 6 and 7 reveals the agreement evidenced by the 

 correlation coefficients. Smoothed anomalies of 

 the same sign tend to occur at the same time. 

 For the most part the oscillations of the smoothed 

 anomalies of sea level diff"erence are in phase. 

 Oscillations are noticeably out of phase in the 

 periods October 1950-February 1951, March 

 1952-January 1953, September 1955-June 1956, 

 and January-July 1958. In the last 18 months 

 of the Hilo-minus-Avila record (July 1966-De- 

 cember 1967) the changes are similar to those for 

 Honolulu-minus-San Francisco, but the smoothed 

 anomaly of the diff"erence is positive rather than 

 strongly negative. Except for the 1955 periods, 

 the nonagreement of the anomalies during these 

 periods results mainly from a rise in sea level at 

 San Francisco as opposed to a drop at Avila. 

 These periods comprise only 209^ of the total 

 20-year coincident records. In the remaining 

 80 Sr the correlation coefficient for unsmoothed 

 anomalies is 0.65 and for the smoothed anomalies 

 it is 0.76. Both are significant well beyond the 

 1% level of 0.186 for a sample of 190. 



CURRENT CHANGES INFERRED FROM 

 SEA LEVEL DIFFERENCES 



In this section some characteristics of the 65- 

 year record of anomalies of sea level difi'erences, 

 Honolulu-minus-San Francisco are described 

 with emphasis on their implications regarding 

 changes in surface currents. Because the 

 smoothed anomalies minimize local effects near 

 the station, such as the set-up by wind and 

 eddy systems passing near the Hawaiian Islands, 

 they will be used as more realistic estimates of 

 the larger scale and longer term changes in cir- 



culation. The term current index will be applied 

 to this usage. 



The discussion will follow the basic premise 

 in this paper, that the currents are geostrophic- 

 ally related to the sea level diff"erence so that a 

 positive current index indicates above normal 

 current, i.e., stronger flow to the south around 

 the eastern limb of the anticyclonic gyre of the 

 North Pacific Ocean. Conversely, negative cur- 

 rent indexes indicate a below-average slope of 

 the sea surface and proportionally weaker circu- 

 lation. 



Three tables have been compiled to show the 

 characteristics of the current indexes. Table 4 

 gives statistical data regarding the current in- 

 dexes by month. The data describe the year-to- 

 year variations that occur. The normal monthly 

 sea level difi'erences, d, (of unsmoothed data) 

 are repeated from Table 1 as a reference against 

 which to measure the ranges and standard de- 

 viations of the current indexes. 



Visual inspection of the time series (Figure 6) 

 indicates that there are a number of different 

 "climatic periods" in the record, i.e., periods 

 characterized by the variability and the mean 

 level of the current index during the period. 

 Table 5 identifies seven such periods, into which 

 I have subjectively divided the time series, and 

 gives the mean and the standard deviation about 

 that mean for each period. Obviously, other in- 

 vestigators might well select different climatic 

 periods based upon other criteria related to their 

 work. 



In Table 6, highly anomalous periods have 

 been identified on the basis of a criterion that 

 the magnitude of the current index exceeded 

 10 cm for two or more consecutive months. As 

 well as information on the dates, sign, magni- 

 tude, and duration of the current index, data are 

 also given on the sign, magnitude, and date of the 

 largest monthly sea level index at Honolulu and 

 San Francisco which coincided with the current 

 index greater than 10 cm. 



Some observations which may be made about 

 the Honolulu-minus-San Francisco differences 

 and the information in these tables are given 

 below. 



1. The standard deviations of year-to-year 

 changes for a given month (Table 4) vary from 



630 



