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University of Oklahoma
Supersonic winds in tornadoes?

Decades ago, it was thought that the highest tornadic winds at ground level might approach 250 meters per second (around 550 miles an hour). That figure has dropped in recent years to the neighborhood of 130 m/s, thanks to data from mobile Doppler radars and engineering analyses of tornado damage. Now, OU meteorology professor Brian Fiedler suggests that vertical tornadic winds of supersonic levels--nearly 350 m/s--could exist just above ground level inside small-scale suction vortices. The horizontal winds would be much less. Fiedler presented the results last month in San Francisco at the 18th American Meteorological Society Conference on Severe Local Storms.

Using a two-dimensional numerical model, Fiedler has examined the dynamics of vortex breakdown, where the size and structure of a tornado quickly and dramatically changes. During these transitions, Fiedler found, the pressure inside transient suction vortices along the tornado's edge could be up to 28 times what would be expected from standard hydrostatic behavior, which limits the majority of tornadic wind speeds. Friction at the ground near a tornado tends to turn the surface-level winds inward, creating tremendous convergence at the base of the suction vortex funnel. This helps sustain the suction vortices, which could be only a few tens of meters wide or even less, according to Fiedler. Thus far, he notes, "There's no smoking anemometer" that has measured any vertical winds in a suction vortex, not to mention supersonic winds. However, dual-Doppler studies using mobile radars could provide high-resolution, three-dimensional wind profiles to help shed light on the matter. For more information, contact Fiedler (405-325-6561 or fiedler@uoknor.edu).

University of Nebraska-Lincoln and Colorado State
Climate change and land use

The University of Nebraska-Lincoln (UNL) and Colorado State University (CSU) are engaged in a cooperative study to assess how climate change may influence land uses and important ecosystems in the U.S. Great Plains. The three-year project is funded by NSF and will focus not only on how climate changes might affect large-scale land uses such as agriculture, but how these changes in turn will interact with natural resources from surrounding ecosystems. For example, deliberate changes in land use may affect the ways agricultural and natural ecosystems exchange greenhouse gases with the atmosphere. Most previous studies have not addressed this issue. Another unique aspect of the research is that it blends economics with climatology and ecology. The research will begin with a survey of land managers in order to understand the reasoning process that goes into certain types of land-use decisions; results will be analyzed within regional ecological models. For more information, contact UNL project manager William Easterling (402-472-7887 or agme014@unlvm.unl.edu) or, at CSU, Dennis Ojima (970-491-1976).

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Last revised: Tue Apr 4 09:13:34 MDT 2000