SAUR: SEA LEVEL DIFFERENCES 



Table 4. — Variability of current index (smoothed anomaly of sea level difference), Honolulu-minus-San Francisco, 

 by months. N ^ 65 years. Standard deviation (s) ; largest positive and negative departures (Max and Min) 

 and year of occurrence; Range (R) in centimeters and in percent of normal monthly sea level difference, d (from 

 Table 1). 



5.1 cm in September to 6.2 cm in March. The 

 seasonal change is due to greater winter-time 

 variability at San Francisco (Saur, 1962) prob- 

 ably caused by year-to-year differences in weath- 

 er conditions. A range of two standard devia- 

 tions is nearly the same as the 11 cm range of 

 the normal seasonal cycle. Long-term non-sea- 

 sonal changes exceed ± 10 9r of the normal over 

 one-third of the time. 



2. The range between extremes (Table 4) in 

 any given month varies from 23.2 cm for No- 

 vember to 33.7 cm in June. These are 39% and 

 54%, respectively, of the normal sea level dif- 

 ferences for these months. 



3. The minimum current index was — 16.1 cm 

 in May 1967 and the maximum was + 17.7 cm 

 in July 1920. The range between the extremes 

 of the current index is 58% of the long-term 

 mean sea level difference of 58 cm for Honolulu- 

 minus-San Francisco, and it is three times as 

 large as the range of the normal seasonal cycle. 



4. The periods 1905-15, 1939-41, and 1955-69 

 were characterized by large changes between 

 positive and negative values of current index 

 over periods up to a few years, but on the aver- 

 age the indicated current is weaker than normal 

 (Table 5). 



5. During the periods 1915-25 and 1942-49, the 

 current index implies moderate to large changes 

 in current over periods of several years but in- 

 dicates on the average a current stronger than 

 normal. Except for large negative values in 

 1918, the current index indicates almost contin- 

 uously stronger-than-normal circulation from 

 mid-1915 through 1925. 



6. The current changes during the periods 

 1926-38 and 1950-54 were relatively small as 

 compared to the rest of the records. The cur- 

 rent index did not exceed 8.5 cm and was nearly 

 evenly distributed between negative and positive 

 values. 



7. The sea level records imply that unusually 

 weak currents (negative anomalies in Table 6) 

 occurred in 1911, 1918, 1941, 1957-58, and 1967, 

 and that the periods of unusually strong currents 

 occurred in 1915, 1920-21, 1943-44, 1948-49, and 

 1959. 



8. During 7 of the 10 highly anomalous pe- 

 riods in Table 6, the absolute value of the month- 

 ly sea level anomaly at Honolulu is much larger 

 than that at San Francisco. This indicates that 

 significant changes in physical conditions which 

 affect circulation occur in the central water of 

 the current gyre as well as in the boundary cur- 

 rent itself. 



CONCLUDING REMARKS 



For the investigation of historical changes in 

 the ocean environment two notable observational 

 deficiencies are apparent: the paucity of time- 

 series subsurface data and the lack of informa- 

 tion on changes in current of periods from a few 

 months to several years. This study has at- 

 tempted to develop some information on the nor- 

 mal seasonal cycle and the nonseasonal change 

 of ocean currents in that part of the eastern 



631 



