88th Annual Meeting (20-24 January 2008)

Monday, 21 January 2008
Conversion from Shear to Curvature Vorticity, Organization of Convection, and Hurricane Genesis
Exhibit Hall B (Ernest N. Morial Convention Center)
Benjamin Schenkel, Florida State University, Tallahassee, FL; and D. T. N. Krishnamurti, S. Pattnaik, M. K. Biswas, and A. Simon
This study examines the exchange between shear and curvature vorticity and the resulting organization of convection that is central to the formation of tropical cyclones from African Waves. Horizontal shear instability results in a strong transfer of shear vorticity into curvature vorticity, which implies a small radius of curvature of flow or an “organization of convection.” As curvature is maximized and convection organizes, convective heat release based baroclinic processes start to dominate in the genesis of the storm. This study uses high-resolution satellite data in combination with model data for Hurricane Nate (2005) and a non-developing African Easterly Wave to show that vorticity conversions are responsible for the organization of convection. Cloud liquid water is calculated from brightness temperatures using the algorithm given by Wentz (1997) from AQUA, the DMSP series, and TRMM at resolutions of 0.25º. These datasets are used to show that convection is organizing by displaying a time series of the growth of the power of the azimuthal wavenumber structure of cloud liquid water. Shear to curvature vorticity ratios are then computed from the MM5 at a resolution of 0.03º using the equations given by Bell and Keyser (1993). Contributions to vorticity exchanges from barotropic, baroclinic, and diabatic processes will be examined using a modified version of the MM5.

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