ABSTRACT
Thunderstorms Thunderstorms inevitably involve the transfer of large quantities of energy from one form to another. The mechanism for the creation of strong winds within a thunderstorm is through the viscous drag of very large quantities of water droplets on masses of air. This can create a strong down-draught, or even a downburst. Peak winds approaching 75 mJs are possible, and in the case of a 'supercell', 'derecho', or mesocyclone, the effects can spread over an area of 1500 km2 • In a recent event in Canada (Cummine et ai., 1992), a 'blowdown' of trees was produced over an area of 2000 km2 •
The effects noted above are the meteorological spawning grounds for major strong winds on the surface of the Earth. There are other effects (such as lee waves and effects associated with gravity or thermally induced movements of air in mountainous regions) that can amplify strong winds or can themselves produce isolated instances of very high wind speeds.
