Using annular rings and quadrants to clip polygons representing tropical cyclone rain shields in a GIS

One technique that researchers employ to investigate the rainfall patterns of tropical cyclones (TCs) is to divide the storm into sections using quadrants and annular rings surrounding the storm's circulation center. This study utilizes a GIS to perform this task. Base reflectivity radar returns from 13 U.S. landfalling TCs are georeferenced and imported into a GIS in hourly intervals. After merging returns from adjoining stations into one composite, these point data are interpolated to create polygon shapes. The perimeters of these shapes are defined by the 20 dBZ contour interval. The center of circulation of each TC at each observation time is then buffered with eight rings spaced 50 km apart. These rings are used to clip the polygon shapes. Radial lines emanating from the circulation center divide the polygon shapes into quadrants based on the direction of storm motion. The percentage of area occupied by polygons within each ring and quadrant is recorded. These data are examined to determine if a relationship exists among the spatial extent of precipitation in the inner, middle, and outer regions of the TCs and to track changes in the post-landfall precipitation distribution. As TCs can produce precipitation that is asymmetrical to their track, the distribution of precipitation among the quadrants is also examined. The TCs analyzed in this study encounter a variety of conditions that alter their post-landfall precipitation distribution (e.g., extratropical transition, mountainous terrain) and the effects of these conditions are apparent in plots depicting changes in the spatial distribution of precipitation over time for each TC.