Water vapour vortices over Western Europe

By Jochen Kerkmann (EUMETSAT)

The Meteosat-8 image below shows an interesting case of water vapour eddies or 'eyes' over Western Europe. This kind of water vapour feature is discussed in the Manual of Synoptic Satellite Meteorology, under the conceptual model of Water Vapour Vortices.

However, this manual does not give a complete scientific reason for the development of these eddies. In the case shown below, the eddies developed along a decaying frontal system that became blocked by a stable high pressure system over Eastern Europe (see Interpretation). In this blocking situation, the wavelength of the upper-level trough approaching from the west (the one related to the frontal system in question) decreased significantly, because another trough was moving in from the west.

One explanation for the formation of the eddies could be that in the end, when the trough became very narrow and when the shear vorticity increased, the flow became unstable and the trough broke up into small vortices. In this respect, this case could be regarded as an example of energy cascade/dissipation from large scales to small scales. It would be interesting to find out if similar cases have been observed in other blocking situations.

One case that shows a very similar water vapour feature has been observed on 11 May 1998 over Eastern Europe (see Met-7 WV images, source: ZAMG), but the synoptic situation of this case is not known.