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Observed Vorticity Structure in Hurricane Rita (2005) Methodology Improvements

Observed Vorticity Structure in Hurricane Rita (2005) Methodology Improvements. Michael M. Bell National Center for Atmospheric Research/ Earth Observing Laboratory Colorado State University Wen-Chau Lee National Center for Atmospheric Research/ Earth Observing Laboratory.

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Observed Vorticity Structure in Hurricane Rita (2005) Methodology Improvements

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  1. Observed Vorticity Structure in Hurricane Rita (2005)Methodology Improvements Michael M. Bell National Center for Atmospheric Research/ Earth Observing Laboratory Colorado State University Wen-Chau Lee National Center for Atmospheric Research/ Earth Observing Laboratory

  2. Vortex Rossby Waves • Waves retrograde and propagate outward when the radial gradient of mean vorticity is negative, similar to observed spiral bands in hurricanes (Montgomery & Kallenbach 1997) • Vorticity perturbations can change mean intensity via wave-mean flow interaction at a critical radius r* • Mesovortices can mix eye-eyewall air and provide a ‘turboboost’ to the hurricane engine (Persing & Montgomery, 2003; Bell & Montgomery, 2006)

  3. Radial Mean Vorticity Profiles • ELDORA’s 300 - 500 m spatial resolution can yield new insights into the 2D mean and 3D perturbation vorticity Reasor et al (2000); Mallen et al (2005)

  4. Methodology • Obtain u, v, w & Z in Cartesian space from dual-Doppler analysis using variational synthesis (Gamache, 1997) • Determine vortex center and mean wind at each altitude (Marks et al, 1992) • Convert to cylindrical coordinates • Determine azimuthal mean and perturbation quantities Hildebrandt et al. 1986

  5. Methodology Improvements • Do a first pass through the data and set the time of closest approach (TCA) to each gridpoint. • Restrict the closest approach of the beginning and ending of the track to either side of an azimuthal line • Define a 4-minute window from which data can be added to a gridpoint based on the time of closest approach. • Remove a small wedge (1-5 degrees) of data near the track overlap.

  6. Methodology Improvements

  7. Key Science Questions • Can we find observational evidence of VRWs and their contributions to intensity change in a moist-baroclinic-nonlinear-forced-dissipative vortex? • Empirical Normal Modes (Brunet, 1994; Chen et al, 2003) • Where is the critical radius for wave-mean flow interaction? • Is this radius a dynamically preferred region for secondary eyewall formation/growth? • Which spatial scales are the most important? (low azimuthal wavenumber vs. convective, 3D structure of filaments)

  8. Empirical Normal Modes Chen et al (2003) • Pseudomomentum and Pseudoenergy modes are orthogonal • ENM analysis allows for separation of vortical wave modes (VRWs) and their contribution to E-P flux

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