MIDNIGHT 



MIDNIGHT 



FIGURE 9 AVERAGE TEMPERATURE AT 20 FEET 



Figtire 9 shows the diurnal changes in temperature at 20 feet for 

 varying cloud amounts. In comparing figure 9 with figure T , the excess 

 temperatiore under clear skies is eliminated, and the highest tempera- 

 ture is recorded for cloudy skies after sunset. This figure is pre- 

 sented, because the 20-foot level is removed from the evaporative layer 

 and thus shows radiative effects that are not apparent at the surface. 

 The author has presented elsewhere (reference 9) other reasons for 

 using the 20-foot level as a reference level for surface water tempera- 

 ture, in addition to the fact that the effects of evaporation have been 

 eliminated at the lower level. Referring to the data presented above, 

 the estimated evaporative heat exchange was estimated (from tables k, 

 6f and 7) as follows: 



Estimated Hourly Surface 



Cloud Evaporative Plus Sensible Temperature 



Coverage Heat Exchange Equivalent (°F) 

 (gm cal/cm2/hour) 



0-2 



-20.7^ 



0.13 



3-5 



-15.81 

 1.18 



0.10 

 -0,01 



16 



