Synoptic Situation: Satellite Images
In the set of satellite images below several areas with convection can be seen emerging over France, Germany, Switzerland and Austria. In this case study however we will concentrate on the convection that was triggered over the Southern Alpine ridge in Austria. The origin on why these cells trigger on that location is interesting and extra weight is put to it in this chapter to retrieve an answer to it using plain satellite imagery and a combination of artificial RGBs. In the satellite images below an approaching frontal system can be observed which is slowly moving over Northwestern Europe. Further east over Bulgaria clear cyclonic rotation can be seen of an almost stationary upper level low. In between the warm sector is found that favours the onset of convection as the insolation increases that day. Around noon explosive development of convection is observed over a large part of Central Europe.
Meteosat 8 IR10.8μm: time sequence
The first chapter dealing with the synoptic situation describes the convective developments seen over Central Europe using plain Meteosat infrared 10.8 μm. The channel is appropiate as it pictures the ice particles from high clouds quite clearly. In a sequence of 15 minutes the relevant satellite image is presented and described.
Meteosat 8 Enhanced IR10.8μm: time sequence
In this chapter again Meteosat 8 infrared 10.8 μm is shown, but the images have been artificially colour enhanced. This will improve the discrimination of where most ice particles form during the several convective stages. In a sequence of 15 minutes the satellite images are presented and described.
Meteosat 8 WV6.2μm: time sequence
The chapter presents the several convective developments over Central Europe using Meteosat 8 WV6.2 channel. The channel is suitable as it gives an idea of the upper tropospheric humidity (UTH) and gives a view of the upper air dynamics. 15 minutes sequence of images are presented.
Meteosat 8 RGBs: time sequence
In the following animation three most often used Meteosat Second Generation RGBs are used and presnted to monitor the onset and development of convection, namely the Airmass RGB, the Dust RGB and the Severe Convection RGB. All loops of all three RGBs are presented and beside a detailed description on the difference between these RGBs is given to show the benefit the one RGB has to the other.
Summary of the investigations in this chapter
These basic satellite images as well as artificial RGB composite show that in the warm sector of former Tropical Storm Alberto rapidly several large CBs emerge over Central Europe; the most striking features are the cold cloudtops, over Germany and Austria. In Germany the development of a squall line can even be seen. From WV6.2 it is observed that most of the cells develop at the boundaries of moist to dry air.
In the artificial RGBs a comparison is made between the Airmass, Dust and Severe Convection RGB. The latter RGB is very useful as it is able to discriminate between large and smaller ice particles. With this in mind it is possible to diagnose which cells further develop and which not. The disadvantage is however that this RGB makes use of visible channels and therefor no monitoring in the evening or early morning hours is possible. The clouds all turn lila at this stage. The Dust RGB shows the convection as thick red ice clouds. The anvils of the cells which consist of thin highreaching cirrus clouds are pictured in black. The airmass RGB combines the information of the WV channels with the IR channels. The convection is well monitored. Next to that the WV boundaries discussed in the WV6.2 set of images are pictured in red in this RGB.
The next chapter deals in more detail the meteorological parameters to help analysing the event.