INTRODUCTION 



This study is the fourth in a series of studies concerned with the analysis 

 of sea-surface temperature observations. The first study dealt with the effect of 

 missing data in long time-series of sea-surface temperature measurements on cer- 

 tain regression and autocorrelation analyses. 1 The second examined the use of re- 

 gression models for time-space interpolation of sea-surface temperature observa- 

 tions. 2 The third presented the results of an autocorrelation, regression, and trend 

 analysis of time-series of sea-surface temperature measurements made at six lo- 

 cations representing different oceanographic conditions and considered the diffi- 

 culties encountered in applying these techniques to oceanographic data samples. 3 



This study considers the oceanographic aspects of the last of the above 

 studies. 3 In particular, it examines the length of time-series necessary to pro- 

 duce reliable long-time estimates of sea-surface temperature. In addition, it con- 

 siders the corollary question of whether or not systematic variations of sea-sur- 

 face temperatures, over periods of several years, are to be expected. 



TIME-SERIES LENGTH 



The length of time-series necessary to produce reliable long-term esti- 

 mates of sea-surface temperatures interests oceanographers concerned with 

 observational programs for obtaining information necessary for establishing aver- 

 age sea-surface temperatures. 



The time-series of data used to obtain insight into this question are 

 listed in table 1. Van Vliet and Anderson 3 concluded from their autocorrelation, 

 regression, and trend analyses of these time-series that the following regression 

 model, with k = 2, provided a good statistical fit to the observed daily sea-sur- 

 face temperatures: 



k 

 T'= 00+ y a t sin [2zrt(D-0,-)/365]+ e (1A) 



t = l 



or expanding, 



ft 

 T'= £„ + V [£„■_! sin (2irt'D/365) + j8.; cos (2^0/365)] + e (IB) 



'Superscript numbers denote references in the list at the end of this report. 



