TRANSFER OF HEAT AND ‘VATER ACROSS THE SEA SURFACE. 
by R,D.M VAAN EAN ans) ice en Taal 
General discussion 
Next to the sea surface there is usually a layer of water 
wha ch is nearly isothermal vertically. The thickness of this.Jayer 
is extremely variables; in winter it may exceed 100 meters, while 
in summer it is often less than a centimeter thick. The temperature 
range vertically in these layers is nct more than a few tenths of 
one degree Fahrenheit, 
A nearly isothermal layer may be produced and deepened by 
stirring due to wind friction, and in shallow water sometimes bot- 
tom friction mixes the water from bottom to top. When a nearly 
\ 
isothermal layer exists it is deevened by horizontal convergence of 
the layer, as happens when the wind blows the surface water against 
mins i i 
the shore. Conversely, horizontal divergence of surface water may 
result in the thinning or destruction of the isothermal layer. M 
The other class of factors which tend to form, deepen or de- 
stroy the nearly isothermal layer is the one including all effects 
which change the density of the water. The only important factors 
of this class are those involving the transfer of water and heat 
across the sea surface. These are solar radfation, nocturnal radi- 
ation, conduction to or from the atmosphere, evanoration, and pre- 
cipitation. 
Of these all but solar radiation affect directly only the very 
surface film, a layer less than a millimeter thick. Their effect 
on the water below is by means of conduction, diffusion and mixing 
in the water. Conduction and diffusion are negligibly effective 
over distances as great as a few centimeters, so mixing is necessary 
for penetration to greater depths, 
