Spatial variation of surface drag coefficient in tropical cyclones

Several years of GPS sonde wind profiles were examined to understand spatial variation of the drag coefficient (Cd) in tropical cyclones. Findings indicate that Cd varies with radius and azimuth. Cd is lower at radii within the median eyewall diameter (30 km) and highest in the left front sector beyond 30 km. High Cd values appear to be related to the nature of wave breaking in the location of the storm where the most energetic waves propagate across the near surface wind. Examples of wave breaking behavior will be shown as well as Cd estimates extended to higher mean boundary layer wind speeds than previously observed.