Analysis of Hurricane Eye Slope Using Reflectivity Data From Airborne Doppler Radar: Composites and Case Studies

The structure and evolution of the hurricane core continues to be a major research focus in the field of tropical meteorology. In this study, we analyze one particularly fascinating aspect of the inner-core region: the slope of the hurricane eye. The slope of the hurricane eye/eyewall has been documented observationally since the 1960s, and the Sawyer-Eliassen (1951) model for tropical cyclone structure describes theoretical reasons why the eyewall must slope. However, finding the relationship (if any) between eye slope and intensity has proven to be difficult. Recent studies such as Stern and Nolan (2009) have shown that the slope of the radius of maximum wind has little to no relationship with the intensity of a tropical cyclone (TC), even on the scale of a single storm. However, the radius of maximum wind is not necessarily the same as the actual edge of the eye, and may be determined by different processes than those that determine the extent of the eye. In this study, we use airborne Doppler radar reflectivity data from Hurricane Hunter flights and field campaigns to determine the edge of the eye, calculate the slope, explore the relationship between slope and intensity, and investigate the dynamical processes that determine the slope of the eye .

After developing the dataset of eye slopes, we analyze the relationship between slope and the core structure and intensity of the TCs.The usable data consists of 96 different measurement times from a total of 16 storms from 2004 to 2010. We then compare this slope with storm intensity, and find that overall there is a statistically significant relationship between slope and intensity for these 96 points (r = 0.38, p = 0.0001). The relationship is stronger when the slopes are averaged around the “Best Track” points. In addition, the statistical relationship is much stronger for several of the individual storms. However, some of the storms show little relationship between slope and intensity, possibly due to changes in core structure such as eyewall replacement cycles. We also explore the possibility of using the relationship between slope and intensity to develop a statistical tool that can be used to observe and predict TC intensity. Finally, our study also looks at some of the physical reasons for the changes in slope and relationship with intensity, in order to better understand the dynamics that drive changes in the inner-core structure of a hurricane.