Observations of Supergradient Winds in Hurricane Rita (2005)

Presentation Type: 
Michael Bell (University of Hawaii)
Shannon L. McElhinney (University of Hawaii at Manoa)

Tropical cyclone (TC) eyewall convection plays a critical role in intensity change. Recent theoretical studies have suggested that the radial location of eyewall convection relative to the radius of maximum wind (RMW) is critical to intensification efficiency, but our understanding of the physical forcing mechanisms that determine the location and strength of eyewall convection is still incomplete. Numerical models suggest that a supergradient jet in the boundary layer associated with strong convergence may play a crucial role in the formation of eyewalls, but the magnitude of the jet is sensitive to turbulence parameterizations.

Kinematic and thermodynamic fields with adequate spatial resolution to resolve the observed magnitude of supergradient winds are difficult to obtain due to limitations in our observational capabilities. Airborne Doppler radar, dropsondes, flight level in situ sensors, and Stepped Frequency Microwave Radiometers (SFMR) can all make measurements in the boundary layer, but each of these has its own limitations. This study will present an analysis of supergradient winds in the primary and secondary eyewalls of Hurricane Rita (2005) using aircraft observations from the RAINEX/IFEX field campaign. A spline-based, 3-D variational analysis technique called SAMURAI is used to retrieve high-resolution low-level TC winds and pressure gradients from the field observations as close to the surface as possible. An error analysis using synthetic data from a WRF simulation will be presented along with the real observations.

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