5 
value with respect to the sea water, and the air has the same tem- 
perature as the water. In the air near the surface there is generally 
a vertical gradient of both vapor pressure and temperature. Ina 
region of such gradients any turbulence or mixing which may be present 
transports water vapor vertically from levels of higher vapor pressure 
toward levels of lower vapor pressure, and transports heat from warmer 
levels toward colder levels. This process is easily understood aual- 
itatively, because mixing consists of a rather random vertical motion 
in which of necessity as much air moves uvward as moves downward 
through a large horizontal area. If temperature decreases upward for 
instance, the turbulent parcels moving uo through this area are on 
the average warmer than those m ving down, so the net transfer of 
heat is upward, 
This vertical transport »y mixing brings heat and water vapor 
from or to the sea surface, and thus accounts for heat conduction and 
evaporation oF condensation at the surface. The heat and water vapor 
lost, or gained, by the surface are not to any extent suoplied to, or 
by, the lowest layers of air, but are distributed by mixing through 
a deep layer of air. The vertical transsort is therefore practically 
the same at all levels sufficiently near the surface -- certainly for 
all levels up to any masthead. 
The rate of vertical transport of heat or water vapor is 
proportional, for unit horizontal area, to the product of the gradient 
of temperature Of vapor pressure and of the intensity of mixing. 
Near a boundary such as the sea surface the intensity of mixing in- 
ereases with distance from the boundary. Since the intensity of 
mixing increases upward fron the sca surface, and since the vertical 
transport of heat or vapor is the same at all levels near the surface, 
it follows that the gradients of temperature and water vapor decrease 
