Correlations between Topography and Land Cover with Tornado Intensity using Rapid-Scan Mobile Radar Observations and Geographic Information System Data

Although many avenues of tornado research have been opened and investigated over the past 50+ years, very little work has been done to investigate the role of geographic surface features on tornadoes.  Specifically, observational studies targeting this topic are minimal; and those that have been performed almost ubiquitously examine an isolated event and/or suffer from poor resolution.  As such, the impact that topography and/or surface friction has on tornado behavior is poorly understood.  The goal of this work is to begin to fill the knowledge gap that exists around this topic by examining the statistical relationships between tornado intensity and i) topographic features, or ii) land cover type (e.g. forest, grassland, water, shrubs, etc.).  Radial velocity data acquired from two rapid-scan mobile radars: the Mobile Weather Radar 2005 X-band Phased Array, (MWR-05XP) and the Rapid Scan X-band Polarimetric radar (RaXPol) are used as a proxy for tornado intensity for four case studies: the 2009 Goshen, WY tornado; the 2011 El Reno, OK tornado; the 2013 Carney, OK tornado, and the 2013 Shawnee, OK tornado. 

Nearly 400 radar observations of the tornadoes (latitude/longitude of tornado center, intensity, diameter of the 35 ms^-1 isodop) from the lowest elevation angle data available (ranging from ~50-550 m above radar level) are coupled with digital elevation model (DEM) GIS data and 2011 national land cover database (NLCD) GIS data using ArcMap.  The categorical NLCD data are reclassified with quantitative values of roughness lengths as specified by the EPA’s AERSURFACE user guide.  A singular dataset is constructed that couples intensity, elevation, and land cover classification for the location of the tornado center (for elevation) and within the specified 35 ms^-1 tornado radius (for land cover).  The high spatio-temporal resolution of the radar dataset (2 – 56 s updates, range gate spacing as low as 30 m) supersedes the resolution of any previous observational study relating tornadoes with topography or land cover in the pier-reviewed literature.  The high resolution data allows for improved confidence in the geographic placement of tornado features in the context of the land cover/topography.  Statistical correlations, composite analysis, and multivariate linear regression models are used to evaluate the quantitative relationships between tornado intensity and both topography and land cover type, and their statistical significance.