The temperatiire equivalents are derived by considering the temperature 

 of the layer between the surface and 20 feet to be affected by the 

 evaporative heat change at the surface; but, since an temperature 

 changes associated vith heat exchange are concentrated at the surface, 

 the temperature change is doubled there. If the above temperature 

 eq^uivalents are added to or subtracted from the siirface temperatures 

 in figure 7 or if the hourly evaporative plus sensible heat exchange 

 values are corrected for the Bowen ratios, the resultant corrected sea 

 surface temperature would demonstrate the great amount of heating which 

 occurs under clear sky conditions. 



The effects of evaporation in the 0- to 20-foot layer are graphi- 

 csilly shown in figure 10. This figure shows the diurnal changes in 

 the temperatvtre gradients in the layers to 20 feet and 20 to ko 

 feet. Although temperature gradients in the layer to 20 feet are 

 correlated with cloud amount, the large amount of evaporation vmder 

 clear skies makes the gradients in the layer 20 to i<-0 feet even more 

 striking. 



Temperature gradients in the layers to to 6o feet and 6o to 80 

 feet, shown in figure 11, indicate decreased diiornal heating effects 

 with depth. They also show the pattern of stationary internal waves 

 shown in reference k. 



Figure 12 illustrates average BT traces for each of the varying 

 amounts of cloud cover. These traces differ greatly in gradient, with 

 very stable conditions prevailing vinder clear skies and moderate insta- 

 bility under cloudy skies. Sound transmission loss owing to the "after- 

 noon" or "surface" effect is related to these differences in gradients. 

 Under clear skies, the "surface" effect may have lasted as long as 13 

 hours while under cloudy skies a weak surface effect may have developed 

 for three hours (based on gradients in the layer 20 to kO feet, where 

 sonar transducers are located) . 



SUMMARY AW DISCUSSION 



Availability of solar radiation data and voluminous BT data at 

 OWS ECHO in September 1959 allowed estimation of the amounts of heat 

 absorption, evaporative-sensible heat exchange, and horizontal heat 

 movement into the water colimin. Theoretical absorption values permit 

 evaluation of reasonable values of evaporative, sensible, and hori- 

 zontal heat exchange. 



Evaporation was calculated to be 0.55 cm/day. This figure seems 

 reasonable by comparison with results of other investigators. Evap- 

 oration lowers the mean sea surface temperature by about 0.1°F. Evap- 

 orative heat loss reduces temperature gradients in the layer to 20 

 feet as much as 0.5°e/100 feet during daylight hours. Thus, the diur- 

 nal temperature range at the 20-foot level is more representative of 

 diurnal changes than are surface temperature changes. 



19 



