Airborne Radar Observations of Rainband Structure in Hurricane Ophelia (2005)

A better understanding of the dynamics of tropical cyclone (TC) intensity change is needed to improve forecast skill. One of the mechanisms proposed for the spin-up of the TC mean tangential circulation is the convergence of absolute angular momentum above the boundary layer. This mechanism is important for the outer primary circulation and results in the broadening of the TC wind field. We hypothesize that the mid-level inflow associated with the stratiform precipitation in TC rainbands may be instrumental in spinning up the broader circulation, and may be important in the development of secondary eyewalls. These physical processes are investigated using airborne radar observations in Hurricane Ophelia (2005) during the Hurricane Rainband and Intensity Change Experiment (RAINEX). Data was collected from the single-parabolic X-band radar aboard the National Oceanic and Atmospheric Administration P-3 aircraft (NOAA43) and from the dual-beam X-band Electra Doppler Radar aboard the National Center for Atmospheric Research (NCAR) P-3 aircraft. The two aircraft flew simultaneously along Ophelia’s primary rainband during a research flight beginning around 1700 UTC on 11 September 2005, allowing for quad-Doppler wind retrievals over the entire rainband. The data were analyzed using a spline-based three-dimensional variational wind synthesis technique. Preliminary results show the concurrent presence of an elevated tangential wind maximum and a distinct mid-level inflow in the stratiform region that are consistent with the proposed mechanism for TC intensity change.