1 - radiation (water, water vapor, CO , clouds) 



2 - sensible heat transfer (water, air) 



3 - latent heat transfer (air) 



4 - precipitation 



5 - wind mixing 



Radiation 



Gains by the surface are received from atmospheric constituents including clouds. 

 Emissions from these sources depend on their temperatures, amounts, and their effective 

 emissivities. Losses from the surface similarly depend on the surface temperature and 

 emissivity. Ordinarily, natural surfaces have emissivities near unity in the infrared portion 

 of the spectrum. However, the value for water (and most natural bodies) appears to lie be- 

 tween 0.96 and 0.98. (Consideration should be given to this factor especially if one employs 

 an IRT which has been calibrated with a blackbody reference). Consequently, to assess 

 radiation exchanges, values of surface temperature, air temperature and humidity, cloud 

 amount and temperatures, and emissivities of radiating bodies must be known. These fluxes 

 may be measured, of course. 



Sensible Heat Transfer 



The transfer of sensible heat to and from the surface film may occur across either 

 boundary. The process, usually called conduction or convection (eddy thermal conduction), 

 results as a consequence of a temperature gradient, and is enhanced by motion or mixing of 

 the fluids. Consequently, the exchange between sea and air is related to the air and surface 

 temperature difference as well as wind speed. Transfers across the bottom boundary of the 

 surface film similarly depend on the temperature difference between surface and sub-surface 

 water as well as water motion. Usually the latter is related to wind speed. Hence a knowledge 

 of the distribution of these parameters is needed for estimating the associated transfers. 

 Unfortunately, the transfer coefficients are not simple constants and the problem is not com- 

 pletely solved. Inherent in the transfer within the fluid is the process of radiation. Presum- 

 ably the coefficient of thermal transfer includes this effect, but the problem needs further study. 



Latent Heat Transfer 



This process, which involves the change of phase of water, is related primarily to the 

 gradient of water vapor above the surface. As with sensible heat transfer, it is enhanced by 

 mixing and the increase of water surface, and consequently is related to wind speed as well 

 as thermal instability. Here, again, the transfer coefficients are not well established, but an 

 understanding of the process at sea may be improved if the involved parameters are known. 

 Since the vapor pressure of the water surface is involved, and since this parameter depends 

 on the surface -skin temperature, the mutual dependence of process and surface temperature 



-95- 



