Relating Tornado Intensity with Surface Topography and Ground Cover Using Rapid-Scan Mobile Radar Observations and a Geographical Information System Framework

Over the past several decades, much work has been done investigating atmospheric characteristics and storm-scale features on tornadoes and a storm’s ability to produce them. However, very few studies have examined the role of geographic surface features – specifically topography and ground cover – over which tornadoes are translating on the vortex’s properties and behavior. Observational studies are particularly sparse and those completed almost ubiquitously investigate an isolated event and/or suffer from poor temporal and/or spatial resolution. As such, the impact that topography and ground cover (a proxy for surface friction) have on tornado intensity and evolution is poorly understood. The goal of this work is to begin to fill the knowledge gap that exists around this topic by statistically examining relationships between instantaneous tornado intensity and changes in tornado intensity with: i) topographic features, and/or ii) ground cover type (e.g. forest, grassland, water, shrubs, etc.). Radial velocity data acquired from the Rapid Scan X-band Polarimetric radar (RaXPol) are used as a proxy for tornado intensity for multiple case studies. These high spatio-temporal resolution observations are coupled with topography information acquired from digital elevation model data and ground cover type obtained from the National Land Cover Database (NLCD) in a GIS framework to investigate relationships between the tornadoes and the underlying surface features. Qualitative ground cover categories are quantified via surface roughness lengths assigned by the EPA specifically for the NLCD dataset, enabling quantitative statistical evaluation. Monte Carlo bootstrapping techniques are employed to evaluate quantitative relationships between tornado intensity and surface properties.