Meteosat-8 IR10.8 Enhanced, Time Sequence: 27 July 2006     

In this chapter some typical phenomena of convection and convective cells will be investigated using the Meteosat-8 IR 10.8 channel with a colour enhancement in the temperature range from -24 to -64°C (see IR Enhanced legend) or klick upon the key symbol (above). This helps us to interpret the information in the IR channel and will show more clearly following structures:

• Cell intensification
• Mesoscale cloud systems (super cells and cell splitting)
• Squall line

At this time step, two small convective cells can be seen over Germany which show cloud top temperatures (CTT) of already -56 to -60°C equivalent to a risk of hail.

During the last 30 minutes the cells intensified and new cells developed. Cloud top temperatures below -64°C reveal over Western and Northwestern Germany. The cell over Western Germany exhibits two spots that indicate the onset of intense convection.

During the last 30 minutes, two convective cells growed rapidly. The (CTT) is partly below -64°C (purple colour). This indicates huge CBs and probably severe thunderstorms with hail or heavy rain. However, no hail was reported (see "surface observations"). This could be due to the relatively coarse observation network's density. This is a typical example that satellite images often give a better overview.

The bigger cell (more to the South) has the typical structure of a super cell with the lowest CTT near its centre indicating the most probable updraft's position. The northern cell (see image above and white rectangle on the left) shows a small second centre of strong convection (low CTTs) at this time step. This gives hint to a possible splitting of this cell, where intensification of its southern part and weakening of its northern part could take place. In the following images the development of this cell will be observed.

Locally, small scale convective phenomena with rapidly increasing vertical height develop like the one near Koblenz (see arrow). In adjacent areas, heavy gusts and thunderstorms occur.

We recognise an further intensification of the cell complexes over Northwest and West to Central Germany. The zoomed image on the right exhibits a developing daughter cell at its southeastern flank. It is very likely that this cell will intensify whereas the older one will decay.

A further remarkable structure can be observed in the zoomed image. We see a chain of convective cells that developed northwest to south of the super cell. This is an example of a outflow boundary. (see "Outflow boundary").

The right part of the northern super cell (secondary cell) intensified during the last 30 minutes in accordance with the rule of "severe right moving". Typically, the right part of this cloud complex (looking downstream) moved slowlier and intensified whereas the left part weakened during its faster displacement.

Looking to the zoomed image we see South of the daughter cell a new development. This is an instructive example of an flanking line. (see "Flanking line").

In the meanwhile, two convective cells moved to the Northeast. The (CTT) is still partly below -64°C (purple colour). However, no hail was reported (see "surface observations"). This could be due to the relatively coarse observation network's density. This is a typical example that satellite images often give a better overview.

Looking to the zoomed image we see that anvil of the northern cell complex growed and that CTT increased slightly. The flanking line can still be recognised at the southern edge. However, it started weakening.

The secondary cell in the northern convective complex dissolved. However, looking further to the South we recognize again two areas of very low CTT (below -64°C). An intensification of the southeastern and a weakening of the northern centre could be expected.

At this time step the cells have formed a squall line with a north-south oriented axis. The cloud configuration shows the classical structure of a squall line:
Rough banded patterns of convection in the parts next to the leading edge and in central areas, and predominantly homogeneous structures between the central and rear parts. While the leading edge is typically a nearly straight line, the rear edge forms deeply frayed structures. In the Enhanced IR-image the typical outline of the squall line can be seen, but the inhomogeneous structures (leading edge) are not as clear as one would expect. This is due to the big cirrus shields yielding a merging of the cloud tops. These properties are better detectable in the radar data. At the warmer leading edge convection is taking place while in the colder central and rear parts intensive rainfall is present. This constellation induces frontogenesis due to direct thermal circulation.

Another case study on squall line describes a typical development of a squall line in several stages.

The structure of the squall line is still to be seen. However, the intensity of the convection decreased (decaying areas of CTT< -64°C).

The weakening of the convection continued.