Airborne Radar Observations of Eyewall Replacement Cycles in Hurricane Gonzalo

As part of multiple field projects including NASA's Hurricane and Severe Storm Sentinel (HS3) experiment, airborne Doppler radars successfully captured detailed observations of the inner core convection in Hurricane Gonzalo (2014) over three consecutive days. During this period, satellite observations indicate that Gonzalo underwent two complete eyewall replacement cycles (ERCs). The data were collected by NASA's Ku/Ka band HIWRAP radar and by NOAA's X-band P3 Tail radar. The HIWRAP radar flew on board NASA's WB-57 which was tasked for ONR's Tropical Cyclone Intensity experiment. These radars provided three-dimensional winds and reflectivity of Gonzalo's concentric eyewalls at different stages of each ERC. Here we explore these observations with particular focus on the asymmetric structures. We then compare with past observational and modeling studies, and interpret their dynamical roles in the context of hypothesized eyewall replacement mechanisms. Observations show kinematic structures in the rainbands that contributed to the development of the outer eyewall. This strengthening outer eyewall developed an asymmetric secondary circulation that was organized by the environmental wind shear. The decaying inner eyewall displayed an increasingly asymmetric kinematic and reflectivity structure, with a clear disconnection from the boundary layer inflow. These observations corroborate past studies of satellite and modeling data and also highlight asymmetric features that may play an important role in determining the fluctuating intensity and structure of TCs during ERCs.