Geoscience Reference
In-Depth Information
Figure 4.14.
NOAA-9 image for February 27, 1987 of a Polar Low off the coast of
northern Norway. Note the spiral cloud signature and central eye in this example (by
permission of the NERC Satellite Receiving Station, University of Dundee,
http//www.
through continuity, high-level divergence. The low-level convergence provides for
a continued source of moisture and convective latent heat release - a feedback pro-
cess that can lead to rapid development. It seems that cold polar outbreaks over
open water in high latitudes can provide for the deep layer of conditional instability
associated with the CISK process.
The second mechanism is known as WISHE (Wind Induced Surface Heat
Exchange). WISHE is a feedback between the circulation and surface sensible and
latent heat fluxes from the sea surface, with a stronger circulation giving rise to
larger surface fluxes of heat, which are then redistributed aloft by convection, in turn
strengthening the circulation. The feedback arises in that the surface heat fluxes are
proportional to the wind speed - turn on the winds and the heat flux strengthens.
The redistribution by convection results in a pressure drop, further strengthening
the winds and hence the surface heat fluxes. WISHE can explain the growth of both
tropical cyclones (hurricanes) and Polar Lows.
