Geoscience Reference
In-Depth Information
Figure 3.7.
Mean annual cycle
of 300 hPa geopotential height for
the region 70-90°N. Results are
based on NCEP/NCAR reanalysis
data over the 1970-1999 period
(by the authors).
Figure 3.8.
Mean annual cycle of
precipitable water averaged for the
region 70-90°N. Results are based
on NCEP/NCAR reanalysis data
over the 1979-2000 period (by the
authors).
Consider, in this simple model, the effects of the solar radiation flux on the atmo-
spheric energy content. Solar radiation is the external energy source to the system.
Remember that the atmosphere is approximately transparent to shortwave radia-
tion but absorbs longwave radiation strongly outside the “atmospheric windows”
(3-5 and 8-12 µm regions). Solar radiation heats the surface. The atmosphere is
then heated from the bottom up by sensible and latent heat fluxes and the absorp-
tion of longwave radiation emitted by the surface. The system radiates longwave
radiation into space. In radiative balance, the net solar radiation at the top of the
atmosphere must equal the longwave loss to space. With the assumption of radia-
tive balance, the energy content of the atmosphere would follow the annual cycle of
the solar radiation flux. The energy content would be largest in summer when the
solar flux is strongest, and smallest in winter, with intermediate values during the
shoulder seasons. The change in energy storage would be positive as the solar flux
increases and negative as the solar flux decreases.
The observed annual cycle of the change in atmospheric energy storage bears
qualitative resemblance to that expected from this simple model. The observed val-
ues are most positive in spring when the solar flux is increasing rapidly, and are
