Small scale convective Convergence Lines can very often be found in satellite images.

• The best channel to detect small scale convective Convergence Lines is the visible image where the lines are bright.
• In the IR images they can be either white or grey. Because of the more coarse resolution of the Meteosat IR channel, often it is not possible to discriminate between high cloud fibres and convective cloudiness. Consequently, this can lead to an overestimating of convective cloudiness. On the other hand, IR images can be a useful tool to recognize the overall shape of a line which, in fact, might be broken into several pieces in VIS images.
• In the WV image, small scale convective Convergence Lines cannot be detected easily. Only if there are parts with large convective cells can one see white spots in a dark or grey background. If the convective activity is very strong, these spots can merge into one continuous line. But the duration of the presence of such a line in WV images is much shorter than in the IR or VIS image.

Cloud tops can reach heights with temperatures as low as -50°C, whereas in other parts of the convective Convergence Line there are warmer cloud tops of 0 to -10°C.

In Western and Central Europe, such lines can often be found over the Central Mountains in France, over the Alps, the Carpathian Mountains, in Italy, starting at Gargano and extending to the SW, the Jura Mountains, the mountains on the Peloponnes and Pindos with continuation to Macedonia.

Convective Convergence Lines show a typical life cycle of several hours depending on the time of day.

Convective Convergence Lines in four typical regions are described in more detail below.

1. Greek convective Convergence Lines

Often lines can be found over the Pelloponnese (Parnos) Pintos and Grammos mountains. Sometimes there are smaller lines in the East over neighbouring mountain chains, namely, the mountain ridge between Trickle and Florin and the line Pelion to Olympus and its continuation to Macedonia. In several cases convective activity can be seen in all three channels in the afternoon. The convective Convergence Line under consideration extends from the SE Peloponnes across N. Greece to about 40N/21E.

There is a distinct life cycle of the cloud lines during daytime similar to the one described below for the Carpathian mountains. The image above shows the maximum of the development close to noon.

2. Carpathian convective Convergence Lines

Cloudiness situated over the Carpathian and Transylvanian mountains is a regular phenomenon. A typical life cycle shows high relationship with the time of the day.

Clouds begin to develop in the morning hours. The VIS image shows the Carpathian mountains very dark (darker than the cloudfree surroundings) with some few white dots already appearing. In the IR image the mountainous area is grey. In the WV image the greyshades can range from light grey to very dark grey depending on the humidity of the middle atmosphere.

During the next hours the clouds indicate the formation of a convective Convergence Line seen as a white stripe in the VIS image, a light grey stripe in the IR image but still not identifiable in the WV image. Such lines often end at the Romanian - Ukrainian border in the North. If there is a continuation of the line into the Northern Carpathians mountian region, the development can be as strong as in the other parts.

Around noon, convective activity is reaching a peak. This is characterised by bright cloud cells and lines in all three channels. The intensity varies a lot. There can be huge Mesoscale Convective Systems (MCSs) (see Cb and MCS ) or only small convective cells. This is also the only time when the WV image shows a continuous white stripe. If the area of convective activity is large the typical line structure begins to dissipate.
The maximum of this phenomenon can be observed by early afternoon. Sometimes, some clouds may be weakening, whereas at the same time other clouds are still growing. There can be a difference especially between the Eastern Carpathian and the Southern Carpathians which sometimes seem to develop independently. At the "corner", where there is the transition between the Eastern and the Southern Carpathians, the cloudiness is often interrupted (this is also reflected in the Local Area Model (LAM), see Meteorological/physical background and Key parameters ).

During the dissipation stage, the changes are first seen in the VIS image whereas in the IR channel the cloudiness disappears later.

Sometimes a substructure within the Convergence Line can be observed: the line following the main mountain chain contains several lines perpendicular to it. This can be observed both in the Eastern and Southern Carpathian mountains.

3. Convergence Lines in the French Mountains

In southern France, convective Convergence Lines can be observed associated with the mistral, a regional northerly cold low level wind. This phenomenon is much less frequent than the two convective Convergence Lines mentioned above.
This situation is characterised by a lot of roughly parallel lines with a north to south orientation. These lines are evolving from unstructured convective clouds near the Central Mountains as a consequence of convergence at low levels parallel to the mountain ridges (see Meteorological/physical background and Key parameters ). The conditions at higher levels are quite different showing divergence, westerly flow and low humidity so that convective activity does not reach high levels. That is the reason why a line structure cannot be seen in the WV image but only a grey tongue over France which indicates a region of humidity. The case of 11 June 1999/12.00 UTC shows the maximum of development. The convective lines are clearly N. - S. oriented and typically fan-shaped and show a cellular structure.

Another case was found which showed that similar convective Convergence Lines can develop in southern France under different synoptic situations, namely, in the region of a decaying frontal system.

4. Alpine Convergence Lines

Also in the area of the Alps orographic Convergence Lines can be observed but these events have to be differentiated a bit more:

• there are Convergence Lines very similar to the ones already mentioned; they appear in the N-S oriented part of the W. Alps and are quite bright;
• there are Convergence Lines in the W-E oriented part of the Central and E. Alps mainly along the highest mountain chains; these lines are usually less bright and also more narrow than the other types just mentioned; they are most easily seen when developing in front of approaching fronts from the W.