HARMONIC FUNCTIONS FOR SEA-SURFACE TEMPERATURES AND 



SALINITIES, KOKO HEAD, OAHU, 1956-69, AND SEA-SURFACE 



TEMPERATURES, CHRISTMAS ISLAND, 1954-69 



GUNTHER K. SECKEL' AND MARIAN Y. Y. YONG'' 



ABSTRACT 



Harmonic functions have been fitted to time-series, sea-surface temperatures and salinities in order to 

 facilitate studies of the oceanographic climate near Hawaii and Christmas Island. The manner in 

 which Fourier analysis has been adapted to this application has been described. The standard errors 

 of estimate for Koko Head temperatures and salinities are less than 0.26° C and less than 0.05/^», 

 respectively. The standard errors of estimate for Christmas Island temperatures are approximately 

 60 % above those for the Koko Head temperature. The expected values of the Koko Head tem- 

 perature and salinity functions have an uncertainty of ±0.1° C and ±0.015^fr, respectively, when 

 samples are obtained twice weekly. Error terms of the Christmas Island temperatures, with daily 

 sampling, are on average 0.07° C. Harmonic analysis spanning the entire sampling duration shows that 

 long-term variations in the Christmas Island temperature and Koko Head salinity are larger than the 

 seasonal variations. Seasonal variations in the Koko Head temperatures are dominant and longer 

 term variations small. The results of the harmonic analyses are presented in the appendixes: (1) 

 a listing of coefficients that define the Koko Head temperature and salinity functions for each year 

 and the Christmas Island temperature functions for each quarter of each year, (2) graphs of the fitted 

 curves together with the observed values for each year. 



In this paper harmonic functions are presented 

 of sea-surface temperatures and salinities that 

 have been regularly measured near Koko Head, 

 Oahu (lat. 21°16' N., long. 157°41' W.) since 

 1956 and at Christmas Island (lat. 1°51' N., 

 long. 157°23' W.) since 1954 (Fig. 1). 



Sea-surface temperatures and salinities 

 change in response to, and therefore reflect, 

 sea-air interaction processes (heat exchange, 

 evaporation minus precipitation) and ocean- 

 ographic processes (advection, diff'usion). For 

 example, the mean sea-surface temperature for 

 a month at Koko Head provides a measure of 

 the mean heat content of the water near the 

 surface. Thus, if the mean temperature for 

 March is above that for February, then meteor- 

 ological and oceanographic processes must have 

 taken place to raise the mean heat content of 



Figure 1. — Location of Koko Head, Oahu 

 and Christmas Island. 



' National Marine Fisheries Service Environmental 

 and Fishery Forecasting Center, Monterey, Calif. 93940; 

 formerly National Marine Fisheries Service Hawaii Area 

 Fishery Research Center, Honolulu, Hawaii. 



' National Marine Fisheries Service Hawaii Area 

 Fishery Research Center, Honolulu, Hawaii 96812. 



Manuscript received September 1970. 



FISHERY BULLETIN. VOL. 69, NO. I, 1970. 



181 



