RGB (HRV-HRV-10.8) Time Sequence: 30min, 01 March 2008

This chapter presents a sequence of day composites (HRV/HRV/IR10.8). This composite enables us to monitor small structures (HRV with a horizontal resolution of about 2 km in Middle Europe) in combination with cloud top temperatures (however, horizontal resolution about 5 km in Middle Europe).

The colours of the clouds in the HRV-HRV-10.8 RGB can be interpreted as:

• blueish white: high thick clouds (e.g. Cbs)
• blueish transparent: thin cirrus clouds
• yellowish: low-level clouds

This image reveals very clearly the cold front over Middle Europe (blueish, shadow), separated by a stripe with only a few low clouds (due to cold air advection). Northwest of it the positive vorticity near the trough's axis exceeded the effects by the cold air advection: We find the convective line extending from the Baltic Sea to West Germany.

All systems moved fast to the Southeast. In the forefield of the convective line (near the trough's axis) some convective clouds can be found.

All systems continued moving fast to the Southeast. From Central to West Germany an area of low clouds developed. This was caused by the change of positive to negative vorticity advection and lee effects in the rear of the low mountains.

All systems continued moving to the Southeast without significant changes.

The cold front and the succeeding convective line moved to the Southeast. We still see very clearly the zones of low clouds in the rear of the cold front and the convective line, respectively. The first one is induced by cold air advection which can be derived from the surface pressure and the temperature in 850 hPa. The second one occured in the rear of the sharp trough's axis.

Besides the processes over Middle Europe, we find some lee waves over Wales and England. The jet axis fits very well with the western edge of the convective clouds extending from Scotland to the Netherlands coast (corresponding wind in 300 hPa).

The cold front arrived at the Alps and the succeeding convective line extended in the meanwhile from East Sweden to Southwest Germany. Lee waves revealed from Ireland to South England.

All structures over Middle Europe continued moving fast to the Southeast.

The cold front crossed the Alps. Over North Italy we see a small area with almost no cloudiness. This is probably due to "Foehn-effects". Further to the south and to the West the image reveals cirrus clouds, so-called lee clouds.

The convective line arrived at the Alps. In its rear we still see an almost cloud free zone near the Danube. Foehn can be now more clearly recognised over East Austria and North Italy.

No significant changes occured.

This image reveals very clearly "Stau-clouds" at the north edge of the Alps almost cloudless areas due to Foehn (from Northwest Hungary to North Italy and lee clouds over Northwest Italy).

A further lee effect can be recognised near the Chech-Germany border (Erzgebirge or Ore Mountains).

The convective line was passing the Alps. An interesting detail can be found near the Swiss-Italian border: Lee waves in upper levels (blueish colour).

The convective line crossed the Alps. Foehn-effects can be still recognised over North Italy. The comparison of the succeeding images 12:30 to 14:30 reveals that the lee waves near the Swiss-Italian border and the lee cirrus clouds did not move significantly although the wind speed in 300 hPa was about 200 km/h.

For more background about the onset of the Foehn klick upon the meteograms Magadino (Switzerland) and/or Torino (Northwest Italy).

No significant changes happened.

This image reveals very clearly the Foehn-effect over South and Southeast Austria and over North Italy. Stau-clouds extended from the West to the East Alps.

For more background klick upon the meteograms Magadino (Switzerland) and/or Torino (Northwest Italy).

No significant changes happened.

Long lasting lee waves over Ireland, Wales and South Scotland can be seen. Foehn effects are still apparent south of the Alps (clear sky, lee clouds, stau clouds north of the main Alpine crest).

The lee clouds near the Swiss-Italian border did not move. However, they started weakening.

For more background klick upon Meteogram Magadino (Switzerland) and/or Torino (Northwest Italy).

No significant changes occured. Many areas of lee waves can be recognised: Irland, Wales, England, North east to East France.

This images reveals also cirrus fibres in relation to the jet extending from Scotland over the Northsea, Germany to Northeast Italy. Over the Northsea it fits well with the west edge of open cells' field.

This image reveals over Germany, Austria and Northeast Italy the shadow due to the cirrus fibres (connected to the jet). Over the North Sea the west edge of the open convective cells fits very well to the jet axis.