Coastal MC in the Weddell Sea 19 January 1990

In the coastal area of the eastern Weddell Sea, a frequency maximum for summertime MC developments was observed in the climatological study of Heinemann (1990) which was based on NOAA- and METEOR-APT (Automatic Picture Transmission) images (resolution about 4 km and 2 km respectively) for January and February of the summer periods 1983-1988. This study was extended to include the summer periods 1989-1990 by Heinemann (1996). In total, 286 vortices were observed in 346 days during the summer periods 1989-1990. With the exception of February 1985, the short-lived vortices with a lifetime less than 12 h represent the largest class for all years and were found account for 72 % of the smaller-scale types (100-400 km).

The MC on 19 January 1990 represents a typical example of summertime coastal MCs. It developed close to Halley Station (75.60S/26.78W), and had scales of about 200-300 km and their lifetime was about 12 h. Cloud top temperatures from satellite data indicated a shallow vertical extent being confined to the lowest 2 km. For this case the German research vessel Polarstern operated close to the MC and wind observations at Halley and Polarstern indicated a cyclonic circulation with a wind speed of up to about 10 m/s. During the afternoon and evening of 19 January, Polarstern lay at a distance of only 100-150 km from the vortex centre. This MC was investigated using aircraft measurements during the AMES experiment. A detailed description of this case is given in Heinemann (1996).

References:
Heinemann, G., 1990: Meso-scale vortices in the Weddell Sea region. Mon. Wea. Rev. 118, 779-793
Heinemann, G., 1996: Three-dimensional structures of summertime Antarctic meso-scale cyclones: Part I: Observational studies with aircraft, satellite and conventional data. Global Atmosphere-Ocean System 4, 149-180.
Engels, R., Heinemann, G., 1996: Three-dimensional structures of summertime Antarctic meso-scale cyclones: Part II: Numerical simulations with a limited area model. Global Atmosphere-Ocean System 4, 181-208.

Please click on the images for full resolution or animation.

Copyright by Günther Heinemann.

 

Infrared AVHRR (channel 4) image for 19 January 1990 at 1710 UTC (Polarstern (PS) and Halley are marked). Brightness temperature scale is in K, coast-line and grounding-line are indicated.
Animation 19 January 1990. Infrared images 1530, 1710, 2030, 2105, 2210, 2250 and 2350 UTC. An indication of the night-time intensification of the katabatic wind system extending over the Brunt Ice Shelf can be seen at 2350 UTC. Near the continental slope at the western part of the Brunt Ice Shelf the dark (warm) signature of a narrow zone of katabatic outflow is present. This warm signature, which is not connected with clouds, can be followed more than 50 km over the ice shelf and merges with the field of low stratus over the ice shelf extending to the cloud band of the vortex.