Geoscience Reference
In-Depth Information
Figure 4.15.
NOAA-12 image for January 19, 1998 of a Polar Low. Norway is on the
right side of the image, with Iceland to the left side. Note the comma-shaped cloud band
in this example (by permission of the NERC Satellite Receiving Station, University of
Dundee,
http//www.sat.dundee.ac.uk/
).
In WISHE, the emphasis is placed on the surface fluxes as the primary growth-
limiting process - the convection only serves to redistribute the heat. This contrasts
with CISK, which emphasizes that the circulations amplify through their interaction
with the convection itself. In the real world, however, the two mechanisms can be
difficult to distinguish from each other. The common feature of both processes in
Polar Low development, however, is that one needs an initial disturbance. The pres-
ence of some sort of baroclinic disturbance provides the key. Off East Greenland,
mesocyclone development also appears to be forced by the effects of the ice sheet
topography and low-level katabatic winds (
Chapter 8
). T. Klein and G. Heinemann
(
2002
) show from simulations with a mesoscale model that channeling of the flow in
the large valleys of east Greenland around Angmagssalik leads to convergence and
cyclonic vorticity generation. This can be enhanced during strong katabatic events
that supply cold air, augmenting low-level baroclinicity. These katabatic winds are
themselves favored by the presence of a synoptic scale low in the Greenland Sea.
