Deformation Band
Cloud bands or lines which form within a deformation field and stretch or dissolve under the influence of elongation.
Deformation zones are generated by opposing flows, where cloud systems of two synoptic or meso-scale cloud systems are brought closer to each other. A deformation zone needs a cyclonic and an anticyclonic circulation to form. As anticyclonic circulations tend to be rather dry, characteristic patterns for deformation zones can be best seen in water vapour image loops. After the deformation stage the cloudiness dissipates or merges with other cloudiness. The deforming band elongates in the direction of the upper level flow. Often there is sinking motion on the poleward side of the cloud band. This sinking air can be seen spreading in both directions with the upper level wind field.