DETACHED WARM FRONT - CLOUD STRUCTURE IN SATELLITE IMAGES

by ZAMG


22 March 1995/23.30 UTC - Meteosat IR image; position of vertical cross section indicated
22 March 1995/23.30 UTC - Meteosat WV image
The satellite image at 23.30 UTC shows the cloud band of a Cold Front, from the Azores across Scotland and the northern part of Norway where it changes over to the cloud shield of a Warm Front over Finland and the Baltic Sea. Downstream, from Poland southward as far as Croatia, the satellite image shows a bright cloud field of a Detached Warm Front, which is already separated from the Warm Front Shield mentioned above.

The IR image shows bright grey shades indicative of the initial stage of the life cycle, with the brightest grey shades in the centre and at the leading edge which is nearly in accordance with the description of the ideal situation. The sudden decrease of the pixel values along the leading edge fits to the superimposed jet at approximately 300 hPa. The boundary between white to grey characterizes the jet axis.

The main difference between the IR and the WV image is the anticyclonically curved grey band connecting the classical frontal system with the Detached Warm Front. An interesting and dominant feature in the WV image is the black, dry stripe from the Mediterranean Sea across France and the North Sea nearly up to the west coast of Denmark. It is an indication of the anticyclonic circulation in the upper level ridge.

23 March 1995/06.00 UTC - Meteosat IR image
23 March 1995/06.00 UTC - Meteosat WV image
23 March 1995/12.00 UTC - Meteosat VIS image
The whole system has moved rather south-east and the main differences from the 23.30 UTC image are the much warmer cloud tops. At this point of time a clear separation between a part on the windward side of the Alps (Czech Republic, south-east Germany and the northern parts of Austria) and a part east of the Alps (Poland, Slovakia, Hungary, Croatia and Bosnia) can be recognized. As the Detached Warm Front is influenced by the orography of the Alps, intensified cloudiness on the windward side and high Lee Cloudiness on the lee side (south-east Austria) develops.

The WV image is dominated by the wet air mass from the Baltic to Italy and the anticyclonic spiral from the North Sea to east Germany.

IR and WV images from 6 to 12 UTC (not shown here) show a continuous development of the described features. The VIS image indicates with the white grey shades the intensive cloud layer of the Warm Front. Also in this image the two parts north and south-east of the Alps can be discriminated.


SUB-MENU OF DETACHED WARM FRONT
METEOROLOGICAL PHYSICAL BACKGROUND