Meteosat-8 WV6.2 time sequence: 27 July 2006

27 July 2006, 09 UTC

The Meteosat-8 WV6.2 channel is suitable for studying dynamics of upper air processes and upper tropospheric humidity (UTH).

During morning hours a band of high humidity extends from Western France over the Low Countries up to the North Sea. Above eastern Austria and the Czech Republic another region of high water vapour contents can be observed. The grey and dark regions contain less water vapour.

A dark stripe in the WV image can be observed over central Germany. This is due to descending stratospheric air (equivalent to higher values of PV). West of this area (in the transition zone between the dry air and moist air, Central Germany) we should expect convection due to insolation. Further to the East convection is likely because the approaching PV maximum (equivalent to positive vorticity advection in its forefield) leads to upward motion and probably convection.

27 July 2006, 10 UTC

All patterns moved eastward without changing significantly.

27 July 2006, 11 UTC

Convective cells are expected to develop at the boundaries of the dark stripe where stratospheric air is deepening which leads to a potential instable stratification of the atmosphere.

Some convective cells develop at the leading boundary of the dark area. The two convective cells further to the North developed mainly due to orographic effects in connection with irradiation.

27 July 2006, 12 UTC

At this time step the initial growth of the main convective cells takes place. According to the concetptual model "Enhancement of convection by PV" first convective cells developed at the leading edge of the dark stripes. The cells marked by a green oval are in accordance with the conceptual model "Convective cloud features at the leading edge of frontal cloud bands".

27 July 2006, 13 UTC

Due to intensive solar radiation convection intensified at the leading edge of the frontal cloud band (Central and West Germany). East of the dark zone we recognise also convection which is caused by the eastward movinng PV-anomaly. However, the separation between these two areas became less clear during the last hour.

27 July 2006, 14 UTC

In the meanwhile the cirrus shields of the cells began to merge. As we already saw from IR10.8 channel (14 UTC, enhanced) the cells near Hamburg and over central Germany exhibited higher tops.
At the western edge of the frontal cloud complex (over eastern England) we recognize a relative dark structure in the WV. Again, the conceptual model can be applied: "Enhancement of convection by PV" (see also chapter IPV 310 K).
From eastern France to southwestern Germany we observe the onset of convection.

27 July 2006, 15 UTC

The cloud systems have merged in the upper troposphere. The cell intensification over England (PV-triggering) and eastern France (at the leading edge of a frontal cloud band) The merging of the two convective complexes over Germany (West "Leading edge of a frontal cloud band", East "PV-triggering") continued. A squall line developed covering many parts of Germany (better to be seen from the IR-enhanced).

27 July 2006, 16 UTC

Single structures and sharp contours become less in the main cloud complex. Some single cells are detectable in southwestern areas of the Czech Republic.
The cell intensification in the dark area over France, Switzerland and southwestern Germany continued.

27 July 2006, 17 UTC

The cells over eastern England, eastern France and Switzerland kept on intensifying. Over Germany only a huge cirrus shield can be seen.
Cell decaying started over the Czech Republic and strong West winds in the upper troposphere blew out clouds over Austria and Slovenia.

27 July 2006, 18 UTC

The cells' area over East England, France and the Alpine region continued growing. Only a huge Cirrus anvil without clear structures can be found over Germany.