Geoscience Reference
In-Depth Information
80°N
8
8
60°
40°
20°
0°
20°
40°
60°S
Ice
160°W
140°
120°
100°
80°
60°
40°
20°
0°
20°
40°
60°
80°
100°
120°
140°
160°
180°E
Figure 3.12
Average annual snow cover duration (months).
Source: Henderson-Sellers and Wilson (1983). Courtesy of the American Geophysical Union.
Figure 3.12
and
Plate 3.3
) causes much of the
incoming radiation in winter to spring to be
reflected. However, the global distribution of
annual average surface albedo (
Figure 3.13A
)
shows mainly the influence of the snow-covered
Arctic sea ice and Antarctic ice sheet (cf.
Figure
3.13B
for planetary albedo).
The global solar radiation absorbed at the
surface is determined from measurements of
radiation incident on the surface and its albedo
(α). It may be expressed as
the turbulent mixing of water masses by the action
of waves and currents.
Figure 3.15
, for example,
illustrates the mean monthly variations with depth
in the upper 100 meters of the waters of the
eastern North Pacific (around 50
W; it
shows the development of the seasonal thermo-
cline under the influences of surface heating,
vertical mixing and surface conduction.
A measure of the difference between the
subsurfaces of land and sea is given in
Figure 3.16
,
which shows ground temperatures at Kaliningrad
(Königsberg) and sea temperature deviations
from the annual mean at various depths in the Bay
of Biscay. Heat transmission in the soil is carried
out almost wholly by conduction, and the degree
of conductivity varies with the moisture content
and porosity of each particular soil.
Air is an extremely poor conductor, and for
this reason a loose, sandy soil surface heats
up rapidly by day, as the heat is not conducted
away. Increased soil moisture tends to raise the
conductivity by filling the soil pores, but too much
moisture increases the soil's heat capacity, thereby
°
N, 145
°
)
where the albedo is a percentage. A snow cover
will absorb only about 15 percent of the incident
radiation, whereas for the sea the figure generally
exceeds 90 percent. The ability of the sea to absorb
the heat received also depends upon its trans-
parency. As much as 20 percent of the radiation
penetrates as far down as 9m (30ft).
Figure 3.14
illustrates how much energy is absorbed by the sea
at different depths. However, the heat absorbed by
the sea is carried down to considerable depths by
S
↓
(100 -
α
