SECKEL and YONG; HARMONIC FUNCTIONS 



In each year excepting 1957, 1964, and 1966, 

 highest variability occurred during the first 7 

 months of the year. In 1957 a seasonal pattern 

 was not clearly apparent and in 1964 and 1966 

 highest variability occurred during the last 5 

 months of the year. Although the seasonal pat- 

 tern of variability has not been examined in de- 

 tail, it is consistent with the results of previous 

 studies (Seckel, 1962, 1969). First, Hawaii is 

 located in the vicinity of a relatively high sa- 

 linity gradient that delineates the boundary of 

 the North Pacific Central Water. Thus, the 

 salinity measured at the Koko Head sampling 

 station is sensitive to variations in the location 

 of this water type boundary. Secondly, north- 

 ward displacement of water (warm advection) 

 tends to occur during the first 7 months of the 

 year. In consequence the water tyi^e boundary 

 that generally lies south of the Koko Head 

 sampling station during autumn and winter is 

 brought to within the vicinity of the sampling 

 station. The months with higher variability 

 tend to be associated with declines in the Koko 

 Head salinity. 



Insight into the nature of the distributions is 

 also obtained by examining the spectra of the 

 harmonic functions. It is evident from the fig- 

 ures in appendix B, that considei-able temper- 

 ature and salinity variability at Koko Head 

 occurs with timespans of 35 to 60 days. Rather 

 than showing the amplitudes for each harmonic 

 of every function, the 13-year mean of the ab- 

 solute magnitude of amplitudes for each har- 

 monic of the Koko Head temperature and sa- 

 linity functions is presented in Figure 2. 



For both the temperature and the salinity, the 

 amplitude of the annual cycle (n = 1) is largest. 

 The am]ilitudes then decline rapidly with in- 

 creasing harmonics ton =5. In the case of the 

 temperature, a slight increase in amplitude oc- 

 curs at M = 6 and )i = 9. Similar small in- 

 creases in amplitudes occur in the case of the 

 salinity at w = 7 and n = 9. The increased 

 amplitudes at « = 6 and w = 7, resolving 60- 

 and 52-day periods, reflect the climatic signals 

 described by Seckel (1962, 1969). The in- 

 creased amplitude at w = 9, resolving a 41-day 

 period, reflects shorter term variability that may 

 be due to large geostrophic eddies with dimen- 



I 2 3 4 5 6 7 8 9 10 II 12 13 

 365 182 122 91 73 61 52 46 40 36 33 30 28 



PERIOD IN DAYS 



Figure 2. — Mean magnitude of amplitudes for each 

 harmonic of the Koko Head temperature and salinity 

 functions, 1956-69. 



sions near 200 km (Wyrtki, 1967) or eddying 

 flow near the Hawaiian Islands. 



LONG-TERM HARMONIC FUNCTIONS 



Long-term harmonic functions with the fun- 

 damental period spanning the entire duration of 

 observations, can be obtained by the method 

 described before in this paper. Temperatures 

 and salinities were used as computed for the 



191 



