Deformation is a feature of a varying wind field, changing cloud formations and humid areas affected by it.

In satellite images Deformation Band is a cloud line which

• elongates, becoming narrower and longer, usually keeping its orientation
• thins out in the middle, eventually breaking
• can be straight or slightly arched

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.

Typical appearances for Deformation Bands in different channels:

• In VIS images grey, partly translucent fibres with well confined, even sharp, edges
• In IR images grey or white narrow, fibrous cloud band with well confined edges
• In WV images grey or white band, often with dark area on the poleward side
• In RGB combination images the Deformation Cloud Band can be distinguished from the background and nearby cloud systems more clearly than in the single channel images:
  • In WV6.2-WV7.3; IR9.7-IR10.8; WV6.2 combination the cloud band is seen white over a blue or green background. The sinking air polewards of the cloud band is seen as a reddish band.

On the 18th of February there were remains of an occluded cloud band, that became a Deformation Band stretching from Poland to White Sea: The development of the Deformation Band can best be seen in an animation: In this loop a Deformation Band stretching from Poland to White Sea gradually narrows and elongates while being stationary. Loop shows WV 6.2 images 18 February 2009 hourly from 00.00 UTC to 07.00 UTC.

Appearance in AVHRR imagery

AVHRR images can be used to more accurately locate the Deformation Band, where upper level cirrus bands are best seen in the IR channels or a suitable combination image. A Deformation Band, just north of the Alps, is seen in all the AVHRR channels as a long, and rather narrow band of clouds, mostly consisting of thin upper level cloudiness. The sharp southern edge of the cloudiness is clearly seen in all the channels. The 124 combination image clearly shows that the cloudiness is cirrus (bluish tones - see Basics for more explanation).