Geoscience Reference
In-Depth Information
5
Energy Exchanges at the Surface
Overview
As reviewed in
Chapter 3
, the mean annual cycle of energy storage in
the Arctic atmosphere is determined by the interactions between the net
radiation budget at the top of the atmosphere, horizontal energy transport
convergence, and the vertical net surface flux. The vertical net surface flux
was in turn shown to be the key driver of the annual cycle in the energy
content of the underlying Arctic Ocean. In this chapter, we look at surface
energy transfers in more detail. Even today, direct surface measurements
of the various surface energy fluxes, especially in a spatially distributed
sense, are rather sparse. However, a reasonably comprehensive picture can
be assembled by using available surface observations along with satellite-
derived products and model results.
Shortwave radiation exchanges at the surface are strongly influenced
by the high albedo of snow and ice. Both shortwave and longwave
radiation exchanges at the surface are greatly influenced by cloud
cover; the former largely through cloud albedo, and the latter through
impacts on the effective atmospheric emissivity and temperature. During
winter, the surface net radiation budget is almost always directed way
from the surface (upward). Over land, this upward net radiation flux is
typically accompanied by a small downward sensible heat flux from the
atmosphere to the surface, and a small upward conductive flux through
the snow cover. Over the Arctic Ocean, the upward surface net radiation
flux in winter is typically balanced by a small downward sensible heat
flux and upward conductive fluxes through the snow cover, sea ice, and
areas of open water. Away from areas like the Atlantic sector, where there
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