September 02, 2004
The above photo showing horseshoe vortices was taken above Amersfoort, Netherlands in early July, 2004. On occasion, the rotating updraft core of a relatively shallow cumulus cloud (towering cumulus) will remain visible after the cloud itself has dissipated. When this happens, a horseshoe-shaped vortex may be left behind. Evidently, the vortex remains visible longer since it doesn't readily mix with the ambient air.