There are often also lines of convective cloud which occur independently from orographic obstacles (see Orographically Induced Convergence Lines ). They are often more or less stationary or at least show a much slower propagation than the surrounding cloud systems. Such a phenomenon can be observed with convection lines

• in advance of a frontal cloud band
• within cold air behind frontal systems.

Regions where these phenomena can be frequently observed during summer time include Germany, Poland, Czech Republic and the Baltic States.

Convective lines with very strong convective activity are indicated by high brightness in VIS, IR and WV channels.

Less active convective lines appear white in the VIS, grey in the IR image and mostly do not show up in the WV image. Sometimes they are even situated in a dry (black) zone in WV images.

The example from 01 July 1999/12.00 UTC shows a convective Convergence Line immediately in front of a frontal cloud band; the distance between the frontal cloud band and the convective Convergence Line seems to be closer in IR and WV than in VIS which is caused by higher cloud elements and high upper level humidity at the leading side of the frontal cloud band.

The AVHRR channels show a more detailed structure. Some cellular substructures within the lines can be detected which are not visible in Meteosat images.

Some slight difference can be found between the VIS1 and VIS2 channels: VIS2 shows the line being more distinct and continuous. The combination channel 124 shows the Convergence Lines as a white to light blue cloud band. A discrimination between thick cloudiness and the thin cirrus clouds at the edge can be done. Use of combination channel 345 shows a more a white to bluish appearance.

Both channel combinations show the Convergence Lines very distinctly. The main area is white, the edges are bluish representing only high cloud.