SURFACE CHARACTERISTICS 



In order to determine whether seasonal influences were important, 

 the data were divided into two time periods, covering approximately 10 

 days each. Mean hourly sea surface temperatures are plotted in Figure 

 1, which provides a graphic comparison of the mean temperature varia- 

 tions of the periods 2 to 10 September and 11 to 21 September. The 

 curves are similar in shape and have almost identical mean values. Al- 

 though slightly more heating occurs in the afternoon hours during the 

 earlier period, data for the two periods were combined with the subsur- 

 face temperatures for the same period. The curves are nearly identical 

 in value at night. The mean daily range in sea surface temperature was 

 about l.l*' F« 



SUBSURFACE TEMPERATURES 



Subsiurface temperatures were listed according to the standard SERC 

 deck coding procedure used by this Office, This procedure records tem- 

 perat\u:es at 20-foot intervals between the surface and 360 feet and at 

 40-foot intervals between 360 and 880 feet. The influence of the daily 

 temperature cycle was not expected to extend below a depth of 100 feetj 

 therefore the mean hourly temperatures were computed only for the svir- 

 face and for every 20-foot level to this depth. Table 1 lists the 

 hourly means and standard deviations. The means have been plotted in 

 Figure 2, which also shows times of local sunrise, noon, and sunset. 



The temperature apparently fluctuates rather regularly and con- 

 siderably at all levelsi separation of the heating and cooling effects 

 from those due to other influences such as internal waves becomes a 

 problem. This problem was solved by analyzing the thermal structure 

 in layers. Major daily thermal variations resvilt from incoming solar 

 radiation during daylight hours and from loss of heat during night hours. 

 The latter of these effects may result in convection if density insta- 

 bility is produced. 



As an aid to analysis, the temperatvire differences in five layers 

 have been plotted (Figure 3). The resulting curves indicate that con- 

 vection (zero gradient) began at 20 feet at 0200Z, kO feet at O5OOZ, 

 60 feet at lOOOZ, and that it did not extend to 80 feet. 



Figure h, a further exposition of the layer analysis, shows the 

 mean hourly temperature differences between the surface and 60 feet as 

 compared to those in the layer between 60 and 100 feet. Diurnal changes 

 are immediately apparent from the regularity of the curve for the upper 

 layer and lack of regularity of the curve for the lower layer. There- 

 fore, it can be concluded that diurnal effects were confined to depths 

 between the surface and 60 feet at OWS ECHO in September 1959. 



