FISHERY BULLETIN: VOL. 70, NO. 3 



Table 1. Departures of normal monthly sea level, h, from the long-term mean at each tide station ; normal monthly 



sea level difference, d; and standard deviations, s, of monthly values for total years of record, in centimeters. 

 Honolulu and San Francisco, 1905-69; Hilo and Avila, 1947-59 and 1961-67. 



Month 



Honolulu 



\ 



Son Francisco 



'h 



Honolulu- 

 San Francisco 



Avila 



Hilo-Avila 



Jan. 



Feb. 



Mar. 



Apr. 



May 



June 



July 



Aug. 



Sept. 



Oct. 



Nov. 



Dec. 



-1.9 



-1.7 



-1.7 



-2.8 



-2.6 



-2.0 



0.3 



2.6 



3.7 



3.7 



2.1 



0.1 



4.4 

 4.4 

 5.1 

 5.3 

 5.1 

 5.6 

 5.8 

 5.5 

 4.7 

 4.7 

 3.9 

 4.5 



5.4 



4.4 



-1.1 



-5.1 



-6.3 



-4.6 



-1.3 



-0.5 



1.0 



1.0 



2.3 



4.6 



5.3 

 6.3 

 6.0 

 4.6 

 3.4 

 2.6 

 2.8 

 2.8 

 3.2 

 3.7 

 4.4 

 4.9 



50.6 

 51.9 

 57.4 

 60.3 

 61.7 

 60.6 

 59.6 

 61.1 

 60.8 

 60.7 

 57.8 

 53.5 



6.9 

 6.8 

 7.6 

 7.2 

 5.8 

 6.3 

 6.4 

 5.8 

 5.7 

 6.1 

 5.8 

 6.3 



-2.0 



-3.1 



-2.9 



-2.2 



-3.3 



-2.5 



0.9 



4.0 



4.4 



4.1 



2.8 



0.0 



4.2 

 3.7 

 5.1 

 4.2 

 5.3 

 5.9 

 5.0 

 4.6 

 4.7 

 3.5 

 4.3 

 5.1 



4.6 



1.1 



-4.6 



-6.9 



-66 



-4.3 



0.0 



2.2 



3.2 



3.2 



3.8 



4.4 



4.4 

 4.3 

 3.8 

 3.5 

 3.6 

 2.9 

 3.6 

 3.6 

 3.7 

 4.4 

 3.7 

 5.1 



46.0 

 47.6 

 53.3 

 56.6 

 55.7 

 53.9 

 53.3 

 53.9 

 53.1 

 52.9 

 50.6 

 47.0 



4.2 

 4.4 

 6.3 

 6.C 

 5.6 

 6.0 

 5.2 

 4.7 

 6.4 

 4.5 

 4.8 

 5.5 



Note: Long-term mean differences, Honolulu-minus-San Francisco and Hilo-minus-Av 

 reference to 0/1,000 db dynamic heights, as described in text. 



ila, 



K Ive been adjusted to 58 cm and 52 cm, respectively, by 



Hilo and Avila have been estimated from 0/1,000 

 db dynamic height anomalies. Reed (1970) has 

 shown that the real topography of the 1,000 db 

 surface between Honolulu and San Francisco is 

 probably 1 cm or less. 



The dynamic height anomalies were obtained 

 from listings of hydrographic station data sup- 

 plied by the National Oceanographic Data Center 

 and data reports of the Trade Wind Zone Ocean- 

 ography (TWZO) Program (Charnell, Au, and 

 Seckel, 1967a, b, c, d, e, f). 



Information on the number of stations, loca- 

 tion, and average dynamic height anomalies is 

 given in Table 2. The locations of the hydro- 

 graphic stations relative to the tide stations are 

 shown in Figure 3. Frequent observations made 

 since 1949 by the California Cooperative Oceanic 

 Fisheries Investigations (CalCOFI) made it pos- 

 sible to get a good sampling of stations very near 

 the two California tide stations. The density 

 of sampling was much lower near the Hawaiian 

 Islands, so observations over broader geographic 

 regions were used. The mean dynamic height 

 anomalies were computed for several indepen- 

 dent sets of observations in the vicinity of Hono- 

 lulu and Hilo to reveal the extent of island effects, 

 but no large differences were found in the av- 

 erages. 



All oceanographic stations were taken since 

 1947. Sampling of different months throughout 

 the year was good. Long-term mean Honolulu- 

 minus-San Francisco sea level difference was 



found to be 58 cm and the Hilo-minus-Avila 

 difference was 52 cm. The normal monthly sea 

 level differences in Table 1 reflect the adjust- 

 ment of long-term mean sea level differences to 

 these values. 



HONOLULU-MINUS-SAN FRANCISCO 



The seasonal variation of the normal monthly 

 sea level difference for Honolulu-minus-San 

 Francisco sea level difference is shown in the 

 upper part of Figure 4. The cycle is asymmetric 

 about the mean level. The monthly difference 

 is high, forming a plateau, in the months from 

 April through October, and a sharp minimum 

 occurs from December through February. 

 March and November are transitional months. 

 The range of the normal seasonal cycle is 11 cm 

 or 19 "^.^ of the long-term mean difference of 

 58 cm. 



The lower part of Figure 4 shows how the 

 normal seasonal cycles at each station contribute 

 to the seasonal cycle of the difference. The 

 monthly normal at San Francisco is lowest in 

 May, early in the upwelling season. The Hono- 

 lulu sea level is also at its minimum, but the 

 magnitude of the negative dejxirture at San 

 Francisco is more than double that at Honolulu 

 and the normal cycle of sea level difference is at 

 its maximum. Both station curves rise at nearly 

 the same rate from June to October. A some- 

 what more rapid rise in July at San Francisco, 



624 



