MITIGATION AGAINST EXTREME WINDSTORMS

This paper treats various manifestations of atmospheric wind in relation to the effects these have on human safety and comfort. We concentrate on more recent advances in our knowledge of the geophysical structure and behavior of extreme windstorms. Particular attention is given to severe thunderstorms and their attendant mesoscale offspring, tornadoes and downbursts, as well as the extratropical and tropical cyclones. It appears that the highest credible wind speed estimates in any of these windstorms so far are for tornadoes, about 135 m s-1; these have been derived from photogrammetric analyses of eyewitness photography and remote sensing from in situ and portable Doppler radars. On the other hand, it is found from extensive aerial and ground poststorm damage surveys that the vast majority of all tornadoes have peak wind speeds no higher than those measured by sparse surface networks and reconnaissance aircraft in mature hurricanes. New in situ and remote sensing (Doppler radars) weather observing networks currently being deployed across the United States and other countries, combined with greater public awareness, may significantly alter our current assessment of the climatology of extreme windstorms in these areas. Advances in the field of wind engineering are shown to afford cost-effective techniques for mitigating against extreme windstorms, including tornadoes. However, the rather unique sociopolitical framework of building codes and practices in the United States presently hinders effective technology transfer and mitigation practice. Important implications of these findings accrue to forecasts and warnings of forest fires and airborne dispersal (loss of containment) of toxic materials, including nuclear processing by-products.