Mobile Radar and In-Situ Observations of Supercell Tornadoes and Hurricane Boundary Layers at Landfall

 

Curtis Alexander

University of Oklahoma and Center for Severe

Weather Research

 

High-resolution mobile radar observations of supercell tornadoes and hurricane boundary layers during landfall have been collected by the Doppler On Wheels (DOWs) platform between 1995 and present.  The result of this ongoing effort is a large observational database spanning over 100 separate supercell tornadoes and 9 landfalling hurricanes with a typical data resolution of O(50 m X 50 m X 50 m) and updates every O(60 s).  Stemming from this database is a multi-tiered effort to characterize the structure and dynamics of the high wind speed environments in and near supercell tornadoes and hurricane boundary layers.  Applications of individual tornado cases have included a comparison of observed and damage-derived tornado intensity estimates using a simple observation-constrained analytic wind model, the estimation of tornado impacts on densely-populated urban areas using the wind model, an estimate of tornado wind speeds within 20 m of the ground using a combination of the radar and in-situ instrumentation, and the formation of a conceptual model for tornadogenesis involving convective storm mergers.  The integration of observations across tornado cases in the database has provided an estimate of observed tornado size and intensity distributions that differ significantly from the damage-reported distributions.  Vertical structure of the tornadoes has been examined to characterize differences between near-surface tornado wind speeds and those associated with the larger scale mesocyclonic flow aloft observed by operational radars.  The evolution of angular momentum near the surface in many of the tornado cases has provided some insight into possible modes of scale contraction for tornadogenesis and failure.  Wind speed variations in the hurricane boundary layer extending down to 3-10 m above ground are also being examined with preliminary comparisons of radar-measured and in-situ observations yielding significant correlation of small-scale fluctuations in speed at various elevations within 50 m of the surface in commonly observed wind streaks.