The Distribution of Kinetic Energy of the Near-Surface Winds in Pacific Typhoons: An Analysis of WSR-88D Radar and Anemometer Data

Low-level wind data from the Weather Surveillance Radar-1998 Doppler (WSR-88D) from seven tropical cyclones impacting Guam between 1995-2003 are analyzed for coherent structures. Consistent with the results of previous studies of Atlantic hurricanes, velocity anomalies associated with roll vortices are found in the Typhoon Boundary Layer or (TBL). The helical transverse circulation associated with roll vortices produce alternating bands of enhanced and reduced azimuthal winds with the mean wind direction. In addition to documenting the wavelength, depth, magnitude and track of these anomalies, new statistics reveal roll height above sea level, distance from storm center, and their relationship to storm intensity. There is evidence that these secondary circulations become more prevalent in stronger tropical cyclones, and thus contribute commensurately more to the energy budget of stronger storms. In addition to data from the WSR-88D, four timeseries of wind data from land-based anemometers are analyzed. An energy spectrum is created from the anemometer data to help describe the kinetic energy distribution of the winds in a tropical cyclone. Results of spectrum analysis suggest that secondary circulations play a significant role in the total energy of the storm. The results presented here will serve as a reference point for the creation of both theoretical and numerical models of secondary circulations within tropical cyclones. Moreover, the wind variations documented in this study improve our overall understanding of the kinetic energy available for wave run-up and the structural- damage potential in tropical cyclones.