FISHERY BULLETIN: VOL. 70. NO. 3 



CO 



ca 



-20^ 



YEAR 



Figure 6. — Monthly sea levels (trend removed and ad- 

 justed to normal atmospheric pressure). Honolulu and 

 San Francisco, 1905-69. A. Unsmoothed anomalies 

 (circles) and smoothed anomalies (solid curve) for dif- 

 ference, Honolulu-minus-San Francisco. B. Smoothed 

 anomalies for Honolulu (solid curve) and San Francisco 

 (dashed curve). Shaded areas show periods when anom- 

 aly of difference is negative. 



YEAR 



stations, two of which were Honolulu and San 

 Francisco. Standard deviations in the former 

 study were slightly larger because trends were 

 not eliminated. At San Francisco, a coastal sta- 

 tion at mid-latitude, the standard deviations 

 show a seasonal change, attaining values near 

 6 cm in the late winter but decreasing to less 

 than 3 cm in summer. At the other stations they 

 vary less with season and those at the island 

 stations generally lie in the range between 4.0 

 and 5.5 cm. 



The standard deviations of the monthly sea 

 level differences (Table 1) do not vary greatly 

 throughout the year. The Honolulu-minus-San 

 Francisco values are slightly larger than those 

 for Hilo-minus-Avila because "climatic" changes, 



to be discussed later, appear in the longer Hono- 

 lulu-San Francisco records. 



The time series of the anomalies of monthly 

 sea level difference are shown by open circles 

 in Figure 6 for Honolulu-minus-San Francisco 

 and in Figure 7 for Hilo-minus-Avila. The vari- 

 ability indicated by the standard deviations is 

 evident. To suppress the shorter period varia- 

 bility and aid in detecting underlying longer pe- 

 riod changes the time series have been smoothed, 

 as indicated by the solid curves. 



A simple 5-point smoothing operator with 

 weights of —1/16, V4., %, 14., —1/16 was se- 

 lected for the smoothing. This is a particular 

 case of one-dimensional, two-element smoothers 

 described by Shapiro (1970). It is a low-pass 

 filter with a response function: 



628 



