Three-dimensional structure of Hurricane Rita boundary layer from the IWRAP radar

Air-sea interactions and flux transport within the hurricane boundary layer (HBL) have been intensively studied to improve the understanding of the mechanisms responsible for hurricane intensity change. Secondary circulations in the HBL are believed to have an influence on vertical fluxes. Thus, a diagnosis of the structure of these small-scale features and their effect on the HBL is necessary.

The acquisition of data documenting the entire depth of the HBL over water, with a temporal resolution capable of resolving small-scale secondary circulations is rather challenging. In order to document the structure of these HBL secondary circulations, airborne wind data from Hurricane Rita (2005) were analyzed. The data were collected using the Doppler radar capability of the University of Massachusetts (UMASS) Imaging Wind and Rain Airborne Profiler (IWRAP). The IWRAP is a dual-frequency, vertically scanning airborne Doppler radar flown on the NOAA WP-3D airplane, and was operated during a UMASS and NOAA/NESDIS collaborative effort. Because the IWRAP scans conically in the vertical direction, analysis of the entire depth of the HBL could be conducted, and the 30-m range gate resolution provided high-spatial resolution data required to study HBL small-scale features. Thanks to its fast rotation speed (60 RPM) and the simultaneous scanning of two incidence angles for each wavelength (C and Ku), retrieval of high-resolution three-dimensional components of the wind was possible. We plan to show examples of the HBL wind structures in Hurricane Rita as observed with the IWRAP at the conference. For data comparison, vertical profiles of the horizontal and vertical wind from the airborne tail Doppler radar will be provided.