Helical circulations in the typhoon boundary layer
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2008
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University of Hawaii at Manoa
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Low-level wind data from the WSR-88D in Guam obtained in Typhoon Dale (1996) and Typhoon Keith (1997) are analyzed for coherent structures. Consistent with the results of previous studies of Atlantic hurricanes, velocity anomalies associated with coherent structures were found in the boundary layer of both storms. Coherent structures that are consistent with roll vortices were documented in 99 total cases during a six-hour evaluation periods during each storm. Storm relative roll location, roll vorticity, asymmetries in roll updrafts and downdrafts as well as differences in the upward and downward momentum fluxes associated with roll circulations are addressed in this study. A velocity azimuth display (V AD) technique is used to obtain wind profiles using Doppler velocity data to determine the depth of the roll circulation. My work shows the effects of terrain and convective elements, such as rainbands. on the formation and maintenance of rolls. Finally, signatures of transverse circulations normal to the mean flow are explored. Convergence and divergence patterns and transverse circulations of ~5 m s-1 were observed perpendicular to the mean flow are and presented here. This research supports and extends prior findings of roll observations and theory. The results presented here can be used to help validate theoretical and numerical models of coherent structures within tropical cyclones. Moreover, the wind variations documented in this study have application for wave run-up and the structural wind damage potential in tropical cyclones.
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Theses for the degree of Master of Science (University of Hawaii at Manoa). Meteorology; no. 4335
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