OQ 7H, AND 9H IN NATURAL WATERS
677
The main sources of water vapor over ocean areas are the sub-
tropics and the trade-wind belts between latitudes 10 and 25°N and
10 and 25°S. Except for a belt around the equator, evaporation exceeds
precipitation between 40°N and 40°S. Polewards of latitude 40°, the
evaporation is less than precipitation. The net evaporationfrom the sea
can be estimated approximately from the distribution of salinity in the
surface layers of the ocean.‘ It can also be computed from the water
transfer in the atmosphere computed from meteorological observa-
tions.! On the whole, these two methodsyield results that are in satisfactory agreement with each other. Figure 1 shows the meridional
distribution of the total water transport in the atmosphere acrosslati-
tude circles for summer, winter, and year. In Fig. 2 the corresponding
ee
MERIDIONAL DISTRIBUTION, 10'' G/SEC
10
-10
-12-—
a
“4b
\
‘
es
Bee
LATITUDE
—
or
Fig. 1—Meridional moisture transfer. The dotted curve denotes the
part of the total yearly transfer due to a mean meridional circula-
tion. [From V. Starry and J. P. Peixoto, Arch. Meteorol. Geophys. u
Bioklimatol., Ser. A, 14: 111-130 (1964). ]