Extended Abstract (292K)4A.2
The structure and evolution of a hurricane in vertical wind shear: Hurricane Elena (1985)
Kristen L. Corbosiero, SUNY, Albany, NY
The thermodynamic and kinematic properties of a hurricane in vertical wind shear are examined using radar and reconnaissance aircraft data from Hurricane Elena (1985). Elena is a unique case for study as it was a slow moving, intensifying, convectively active tropical cyclone in the Gulf of Mexico in an environment with a nearly constant direction, but changing magnitude of vertical wind shear for over 36 hours. It was during this time that one of the most complete data sets of a single tropical cyclone was ever recorded with 1,142 ground-based radar scans, 86 radial flight legs and 47 vertical incidence scans collected aboard NOAA P3 aircraft and processed by Michael Black at the Hurricane Research Division of NOAA.
Elena’s reflectivity pattern was highly asymmetric throughout the period of study. The highest values of reflectivity in the eyewall and inner rainbands appeared upshear of the center. Convection in the eyewall took the form of discrete cells that generally first become visible slightly right of directly downshear of the center and could be tracked cyclonically around the eye into the upshear quadrants. Radius-time and azimuth-time hovmollers of reflectivity show that the cells propagated cyclonically slower than the local tangential wind and radially outward, consistent with vortex Rossby waves.
Eighteen hours of reflectivity and vertical velocity data were composited with respect to the vertical wind shear vector from the radius of maximum winds out to 36 km from the radius of maximum winds. The composites show distinct differences in structure between quadrants. The downshear right quadrant vertical velocity composite shows the clearest lower to upper tropospheric continuous, sloping updraft channel in the eyewall, while the downshear left quadrant contains the greatest percent coverage of updrafts. Both the upshear left and right composites feature strong upper tropospheric downdrafts just outside the eyewall. Finally, the 20 dBZ contour is 3-4 km higher in the upshear quadrants of Elena as compared to the downshear quadrants.
The above results are consistent with the theoretical vertical motion pattern induced by vertical wind shear in tropical cyclones in which updrafts initiate downshear, rise helically, condense, and carry rain water/ice to their highest levels in the upshear quadrants. In the talk, more comparisons will be made between the observed structures in Elena and the results of numerical studies that have modeled tropical cyclones in vertical wind shear.
Uploaded Presentation File(s):
Corbosiero_Miami2004.ppt
Session 4A, Tropical Cyclones and Vertical Shear
Monday, 3 May 2004, 3:45 PM-5:30 PM, Le Jardin Room
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