Extended Abstract (140K)11D.4
Observed evolution of eyewall convection and low-wavenumber flow in Hurricane Guillermo (1997)
Matthew D. Eastin, NOAA/AOML/HRD, Miami, FL; and P. D. Reasor, J. F. Gamache, F. D. Marks, and M. L. Black
Recent observations and numerical simulations indicate that the azimuthal distribution of deep hurricane convection can be significantly influenced by environmental vertical wind shear and internal dynamical processes. In such instances, the convection can acquire a persistent low azimuthal wavenumber structure comprised of multiple transient convective cells. The roles played by such persistent and transient convective asymmetries in hurricane evolution are not well understood. Furthermore, how interactions between different evolving low-wavenumber flows influence the generation, organization, and evolution of asymmetric convection remains an open question. The objective of this study is to elucidate the organization and evolution of observed asymmetric eyewall convection within the context of the environmental vertical wind shear and low-wavenumber flow.
This study utilizes an extensive observational dataset collected during repeated dual-aircraft penetrations of Hurricane Guillermo on both 2 and 3 August 1997 over 6 h periods. Estimates of the environmental vertical wind shear and low-wavenumber flow are derived from three-dimensional dual-Doppler (3DDD) wind fields within 60 km of the storm center. Evolution of the flow is determined from the 10 unique 3DDD winds fields available each day (temporal resolution of ~35 min during the 6 h periods). The azimuthal distribution and evolution of transient convective cells is determined from animated radar imagery. Flight-level, GPS dropwindsonde, and vertically incident radar data is also used to elucidate various aspects of the eyewall convection.
Preliminary results suggest that, on each day, moderate northerly vertical wind shear was impinging upon the inner-core vortex. The eyewall convection exhibits a persistent wavenumber-one structure with enhanced convection in the southern and eastern quadrants. Transient convective cells episodically develop in the southern quadrant, and then advect cyclonically through the eastern quadrant before dissipating in the northern quadrant. The 3DDD wind fields depict an evolving asymmetric wind field. Currently, the evolution and interaction of each low-wavenumber wind component is being analyzed in order to document their relation to the episodic convective bursts in the southern eyewall.
Session 11D, tropical cyclone observations and structure VI
Wednesday, 5 May 2004, 3:45 PM-5:15 PM, Napoleon III Room
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