"The hook echo is usually thought to be a passive feature of tornadoes," he said. "I'm saying it's not passive, it's an active mechanism for tornado formation." His work is published in the August issue of Journal of the Atmospheric Sciences. Davies-Jones ran computer simulations of supercell storms to see if falling rain could provide the needed kick that turned diffuse updrafts rising off the warm plains into tight-spinning, lethal tornadoes. As the rain falls out of a rotating supercell cloud it is also twisting, and as it falls he found it transfers the rotational energy into the updrafting air adjacent to it. The rain also acts as a sort of wall, confining the swirling, rising air. As it continues to head skyward the air inside the rain curtain stretches out like a figure skater raising her arms. The spinning speeds up, and a tornado is born. "The mechanism is a good one," David Lewellen of the University of West Virginia said. "But until these things are seen more conclusively out in the field, it's not at all clear whether rain is involved in the formation of most tornadoes, a few, or none at all." Lewellen points out that rain is only one of myriad weather conditions that have to be just right for a tornado to form. A massive field campaign of experiments is scheduled for the spring season in 2009 and 2010 that he hopes will determine if the implications in the models are correct. Related Links: Michael Reilly's blog: Strike Slip |
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