KABEG experiment
(Günther Heinemann, MIUB)
The aircraft-based experiment KABEG'97 (Katabatic wind and boundary layer front experiment around Greenland) was performed in April/May 1997 in the area of southern Greenland. The experimental investigations comprised the katabatic wind system over Greenland and measurements of boundary layer fronts (BLFs) over the Davis Strait. Both phenomena are important for the understanding of the climate of the Arctic and the Antarctic. Although no mesocyclone developments at BLFs were observed during KABEG, the results of this experiment can yield some useful data also for polar low investigations.
For further information see the KABEG home page: "http://www.meteo.uni-bonn.de/kabeg/kabeg.html".
Numerical simulations around Greenland
(Thomas Klein, MIUB)
Several realistic simulations of the katabatic wind system over the Greenland ice shield have been performed with the mesoscale limited area model NORLAM using ECMWF analyses as boundary conditions. In one of the model runs with a horizontal resolution of 50 km for the period of 23 to 26 March 1986 a mesocyclonic vortex developed in the valley area near Angmagssalik (38øW, 66øN) at the eastern coast of Greenland (Figure 1) after 30 h of integration. The evolution of the mesocyclone is a result of synoptic-scale forcing in connection with an intense increase in the local katabatic wind in that area due to a short period of cloudless skies. The topographic structure near Angmagssalik gave rise to an additional acceleration of the katabatic downflow by channelling effects and thereby caused near-surface winds of gale force in the valley area. The simulated mesocyclonic circulation had a livetime of about 12 h and was accompanied by a weak signal in the surface pressure field.
Satellite studies for FROST
(Michael Lieder, MIUB)
Michael Lieder and Günther Heinemann further examined the mesocyclone (MC) event over the northern Amundsen and Bellingshausen Seas occuring on 11 and 12 January 1995. First results using satellite data for this case study were presented at the EPLWG meeting in St.Petersburg in 1996. The development of the group of three MCs at about 60øS was studied (Fig.1). Satellite data from AVHRR, ERS scatterometer and SSM/I, and the sparse data of the two buoys in this area were used. Numerical simulations were performed using NORLAM. A distinct signal of the MCs in the infrared imagery and the SSM/I retrievals (near surface wind speed, integrated water vapour (IWV), cloud liquid water) can be found. The numerical model results showing two of the MCs as shortwave baroclinic developments triggered by an upper-level trough are compared to satellite retrievals and buoy measurements in order to assess the quality of the simulation results. Especially the parameters near-surface wind and IWV show good agreement allowing to use the model results with confidence for the study of processes not retrievable from satellite data. The detailed results of this study can be found in Lieder and Heinemann (1998) in a special issue of Weather and Forecasting on FROST.
