15A.4
Influences of asymmetric heating on tropical cyclone evolution in a full-physics numerical model
J. Dominique Möller, University of Munich, Munich, Germany; and L. J. Shapiro
Research has confirmed the important influence of flow features that are asymmetric with respect to the center of a tropical cyclone, represented as potential vorticity (PV) anomalies, in determining the structure and intensity of the cyclone. Studies without convection for strong vortices in two (Moeller and Montgomery 1999) and three (Moeller and Montgomery 2000) dimensions have provided fundamental insights into the influence of PV asymmetries on a tropical storm. Simple relaxation ("axisymmetrization") experiments with monochromatic azimuthal-wavenumber PV disturbances and PV blobs showed that vortex Rossby (PV-) waves propagate both radially and vertically, transporting tangential momentum and thereby intensifying the symmetric vortex. When persistent convection was simulated by adding PV anomalies, one after another, to the symmetric vortex, the tropical storm intensified to hurricane strength. The results confirmed that there exists an alternate means of tropical cyclone intensification to the symmetric mode.
In order to incorporate the feedback between the PV anomalies, the vortex and convection, a model that includes moist physics is required. Shapiro (2000) used a three-layer numerical including a convergence-based convective parameterization scheme to understand the role of cumulus convection and the atmospheric boundary layer in the interactions between asymmetric PV anomalies and a hurricane vortex. This study showed that convection plays an important role in determining how a hurricane responds to the anomalies in its environment. It was shown that the interactions between the asymmetries and the symmetric hurricane vortex at early times depend on realistic features of the model hurricane. The response is constrained to the extent that moving the PV anomaly radially inward or outward has no qualitative effect on the results. The longer-term evolution of the vortex is more problematic, and may depend on the convective parameterization use . The three-layer model is limited in the realism of its representation of convection.
In the present study the NCAR/Pennsylvania State full-physics nonhydrostatic multi-level numerical model (MM5) is used to evaluate and extend the results from the simpler three-layer model in a more realistic setting. The impact of asymmetric convective heating and PV generation on a symmetric hurricane vortex is investigated. The impact of diabatically-generated asymmetries (individual azimuthal-wavenumber disturbances, or blobs) on hurricane intensification, and the dependence of the hurricane's response on the duration, location, amplitude, radial and vertical structure of the convective anomalies will be evaluated. The conditions under which multiple convective pulses are effective in intensifying the vortex will be established. Preliminary results indicate that the early evolution of the hurricane vortex in the presence of the asymmetric heating may be similar to that with imposed PV asymmetries in the three-layer model. The physical mechanism responsible for the results will be established using budgets of azimuthally-averaged tangential momentum and asymmetric vorticity. The longer-term evolution of the vortex will also be investigated. Results from the analysis will be presented as available.
.Session 15A, Tropical cyclone intensity change IV: Numerical Modeling Studies
Thursday, 6 May 2004, 3:45 PM-5:00 PM, Le Jardin Room
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