Hurricane Eyewall Slope as Determined from Airborne Radar Reflectivity Data: Composites and Case Studies

Understanding and predicting the evolution of the tropical cyclone (TC) inner core continues to be a major research focus in tropical meteorology. Eyewall slope and its relationship to intensity and intensity change is one example that has been insufficiently studied. Accordingly, in this study, radar reflectivity data are used to quantify and analyze the azimuthal average and variance of eyewall slopes from 124 flight legs among 15 Atlantic TCs from 2004 to 2011. The slopes from each flight leg are averaged into 6-h increments around the best-track times to allow for a comparison of slope and best-track intensity. A statistically significant relationship is found between both the azimuthal mean slope and pressure and between slope and wind. In addition, several individual TCs show higher correlation between slope and intensity, and TCs with both relatively high and low correlations are examined in case studies. In addition, a correlation is found between slope and radar-based eye size at 2 km, but size shows little correlation with intensity. There is also a tendency for the eyewall to tilt downshear by an average of approximately 10 degrees. In addition, the upper eyewall slopes more sharply than the lower eyewall in about three-quarters of the cases. Analysis of case studies discusses the potential effects on eyewall slope of both inner-core and environmental processes, such as vertical shear, ocean heat content, and eyewall replacement cycles. These results indicate that eyewall slope is an important measure of TC inner-core structure, and may prove useful for future study of the processes that drive changes in the TC core.