Hurricane Rita
wind field evolution

Team Leaders:
Robert Rogers (AOML/HRD)
Eric Uhlhorn (AOML/HRD)

Team members:
Peter Dodge (AOML/HRD)
John Gamache (AOML/HRD)
Frank Marks (AOML/HRD)
Shirley Murillo (AOML/HRD)
George Soukup (AOML/HRD)

Objective:
The purpose of this project is to examine the evolution of the wind field of Hurricane Rita (2005) as it evolved from a primarily symmetric storm to a storm with concentric eyewalls and finally to a storm becoming highly asymmetric as it made landfall in the northwest Gulf of Mexico.

Accomplishments
Used a combination of flight-level and surface wind measurements from the Stepped Frequency Microwave Radiometer (SFMR) to document the changes in the azimuthal location of the peak winds over time, and how those changes reflect changes in the vortex and its environment. The observations showed that the magnitude and azimuthal location (i.e., phase) of the peak asymmetry varied at both levels during the three days observed. The phase of the asymmetry at both levels was aligned to the right of storm track on the first day of sampling. By the third day, the phase of the asymmetry at both levels remained to the right of storm track, but there was a phase shift of nearly 45 degrees between the surface and flight-level. Such a change in the phase resulted in significant azimuthal variations in the surface to flight-level ratio of peak winds over the three days sampled. The locations of the radii of maximum winds at the surface and flight-level, indicative of the eyewall slope, also varied over time, indicating a vortex whose tilt was increasing over time. For some parameters, e.g., the phase of the wind asymmetries and ratio of peak winds, the measurements are consistent with previous modeling and observational studies, while for other parameters, e.g., the magnitude of the asymmetries and the evolution of the asymmetry phase, they are not fully explained by previous studies or have never been observed. These differences suggest that other processes are occurring in the storm.

Milestones
This work will be extended by including the airborne Doppler radar winds and dropsonde measurements and incorporating high-resolution numerical model simulations to provide temporal continuity. Attention will be focused on the role of vertical shear in driving the azimuthal wind asymmetries, and on the role of these asymmetries in determining the impact of encroaching dry air.

References:

Rogers, R.F., and E.W. Uhlhorn, 2007: Observations of the three-dimensional structure and evolution of wind asymmetries in Hurricane Rita (2005). Geophysical Res. Lett., In review.

Last modified: 8/28/2007