During certain weather conditions, the constant stream of air over hilly areas would produce small, electrically charged whirlwinds. These could build up into columns and then break down again, creating a circle of flattened crops.
This theory may even explain the formation of complex patterns in certain crops. The electrical energy created when the whirlwind discharges could be sufficient to create complicated patterns in the landscape. This discharge could also be accompanied by light and sound, explaining why witnesses report seeing flashing lights and hearing humming noises.
Meaden claims examinations of soil and crop samples suggest that a short-lived force flattens the crops. But as yet, the existence of these 'plasma-vortices' has not been proven.
http://www.bbc.co.uk/science/space/l...s/vortex.shtml