• The satellite image shows a cloud bulge at the rear edge of the cloud band of a Cold Front;
• in the VIS and IR images the area of the cloud bulge is white, indicating thick and/or multi-level cloudiness;
• in the IR image the grey shades sometimes are brighter than the rest of the cloud band;
• in the initial stage an S-shape of the rearward cloud edge is formed, which becomes more and more pronounced;
• at some later stages of development a cloud spiral develops from the cloud bulge:
  • in some cases the spiral develops directly from the white cloud bulge (see Occlusion: Warm Conveyor Belt Type );
  • in some cases the spiral develops within lower cloud tops emerging beneath the higher cloud layers; in this case it seems that two synoptic layers are decoupled (see Occlusion: Cold Conveyor Belt Type ).

The image shows a frontal zone from the Atlantic (south of 50N) across north France, Germany, Poland and further northward. The S-shape of the Wave bulge can be found above Germany and the Baltic Sea. An additional dominant feature is a Comma - like cloud spiral immediately on the cold rear side of the wave. This developing synoptic feature is responsible for deviations in the distributions of the key parameters of the Wave as well as for a delay in the cyclogenesis process in the wave area.
Grey shades in the IR image are brighter in the wave area than in the other parts of the cloud band. In the VIS image no differentiation in the grey shades between the Wave area and the rest of the cloud band can be observed. This indicates multi-layered thick cloudiness. The Wave point can be expected within the cloud band close to the point of inflexion of the S-shape of the Wave (see Key parameters). This example shows a very special situation with two Waves in one Cold Front cloud band. At 00.00 UTC the northern one can be observed over the North Sea, the southern one over south France and the Mediterranean. Until 12.00 UTC the cloud bulges become more and more pronounced leading to spiral structures. This is a case where the cloud spiral forms within the whole cloud layer. In the example of 27 September 1995 the spiral develops, in contrast to the example before, within the lower cloud layers which can be seen above Russia close to the Ladoga Lake and Estonia.

Appearance in AVHRR imagery

• AVHRR images (below left; third row left) show detailed cloud structures.
• Substructures in the wave area can be seen near the cyclonic and anticyclonic region of the wave.
• During both nighttime and daytime, RGB channel combinations (below left; second row) provide a quick overview of thin or thick, layered, low, middle or high level clouds.
• Image manipulation (eg. subtraction with thresholding; third row right) highlights cloud patterns and other features.

Several cloud types are involved with the Wave which are easily detected in the (manipulated) satellite images. The images show a Cold Front lying from Iceland to the Atlantic (37N/31W). The Wave is a striking feature in this Cold Front. To the rear of the front the cloudiness has a rather sharp borde and appears white to bluish white (above left). Along the anticyclonic side the clouds are much more fragmented and multi-layered. In Fig. 3 and 4 the Cold Front is decaying to the south of the Wave: In this region there is less high cloudiness (white) and more low and middle cloudiness. Multi-layer clouds are seen along the anticyclonic side of the Wave (warm sector) in both images, but the low clouds are more pronounced in the image above right (yellow areas). A lot of cloud features can be seen in the image above left. In the image above right the cloud contrast resulting from image manipulation sharpens the pattern recognition.