Using GIS to Investigate Land–Atmosphere Interactions Involved in Tornadogenesis

Northern Alabama is among the most tornado-prone regions in the United States. Due to is proximity to the southern Appalachian Mountains and Cumberland Plateau, this region has a higher degree of spatial variability in terrain and land cover than the more frequently studied North American Great Plains region. Several modeling and simulation studies stretching back to the 1970’s have found that variations in the land surface induce tornadic-like flow near the surface, illustrating a need for further investigation. More research is needed to understand how the variable land surface influences tornadogenesis in North Alabama given its high tornado frequency. This presentation introduces a geospatial methodology developed to quantify and understand the dynamic interaction between the land and during tornadogenesis. This research investigates the hypothesis that horizontal gradients in land surface roughness, normal to the direction of flow in the boundary layer, induce vertically oriented vorticity at the surface that can potentially aid in tornadogenesis. A novel approach was implemented to test this hypothesis using a GIS-based quadrant pattern analysis method. This method was developed to quantify spatial relationships and patterns between horizontal variations in land surface roughness and locations of tornadogenesis. Land surface roughness was modeled using MODIS 500 m and Landsat 30 m data following the Noah land surface model parameterization scheme in order to compare the relationship between tornadogenesis locations and roughness gradients at different spatial scales. This analysis found a statistical relationship between areas of higher roughness located normal to flow surrounding tornadogenesis locations that supports the tested hypothesis. In this presentation, the innovative use of satellite remote sensing data and GIS technologies to address interactions between the land and atmosphere will be highlighted in order to demonstrate alternative applications for GIS within the weather focus area.