Polar low development at the sea ice edge near the coast 27-28 April 1989

The baroclinic development of an intense MC over the Weddell Sea near the Antarctic coast close to the German Georg-von-Neumayer Station (GvN) took place during the period 26-28 April 1989. This case was studied by Heinemann (1996a/b) by means of satellite and conventional data, ECMWF analyses, radiosonde data, and surface observations. The MC had a diameter of about 500 kms, a lifetime of about 40 hours and reached the intensity of a polar low. Wind speeds up to 19 m/s (with gusts up to 24 m/s) were recorded at GvN as the MC approached on 27 April and remained quasi-stationary for about 24 hours. Its development took place in baroclinic conditions of strong low-level cold air advection close to the sea ice front. The genesis of the MC seemed to be triggered by a 500 hPa short-wave trough and a resemblance to a baroclinic development at a boundary layer front was noticed. Low-level thickness fields from TOVS data reflected the baroclinic structure of the MC, but gradients were relatively weak. Wind speed retrievals from SSM/I data did not allow a full analysis of the wind field structure for this case as they were limited to ice-free ocean. They showed the incipient MC lying in an area with increased wind speed and high surface fluxes of sensible heat. In the mature stage, a maximum in the SSM/I wind speed field was found in the northwestern part of the MC. A meso-scale analysis with a limited area assimilation system for the mature stage showed only weak support of the low-level MC by upper level cyclonic vorticity advection.

References:
Heinemann, G., 1996a: On the development of wintertime meso-scale cyclones near the sea ice front in the Arctic and Antarctic. Global Atmosphere-Ocean System 4, 89-123.
Heinemann, G., 1996b: A wintertime polar low over the eastern Weddell Sea (Antarctica): A study with AVHRR, TOVS, SSM/I and conventional data. Meteor. Atmosph. Phys. 58, 83-102.

Please click on the images for full resolution or animation.

Copyright by Günther Heinemann.

AVHRR channel 4 image (brightness temperature scale in K) for 0110 UTC 27 April. The SSM/I-derived ice edge is shown as a double line (50% isoline). The centre of the MC genesis area on 1650 UTC 26 April is indicated by a star. Wind and temperature observations at GvN and Sanae are shown.
Blow-up for 27 April 0110 UTC with superposition of TOVS retrievals of the geopotential thickness 850/1000 hPa (thin lines, isolines every 0.5 dam).
AVHRR channel 4 image for 27 April 0700 UTC with superposition of the retrievals of the SSM/I wind speed (0850 UTC, numbers in m/s). Winds relative to the centre from cloudmotions are also superimposed (largest arrow corresponds to 9 m/s).
AVHRR channel 4 image (brightness temperature scale in K) for 0100 UTC 28 April. Wind and temperature observations at GvN and Sanae are shown.
Animation 27 April 1989. Infrared images 0110 and 0700 on 27 April and 0100 on 28 April.