Horseshoe Vortex Over Ursel, Belgium
October 07, 2006
The photo above showing a very nice example of a horseshoe vortex was taken over Ursel, Belgium on August 4, 2005. These vortices are one of the more bizarre cloud forms. They can only form if there's a lot of vorticity (a measure of rotation) in the lower atmosphere. Shallow cumulus seem to be ideal for the formation of horseshoe-vortices, although the vortices are rare nevertheless. They're believed to form when small cumulus updrafts interact with the surrounding air to create a dipole vortex. If the cumulus cloud is small, it'll dissipate more quickly than the spinning vortex, so the leftover vortex is seen at the top of the cumulus -- the vortex remains visible longer since it interacts (mixes) less well with the ambient air. See the Earth Science Picture of the Day for September 2, 2004.