The asymmetric wind structure of tropical cyclones in various shear environments

The Hurricane Research Division (HRD) of NOAA Atlantic Oceanographic and Meteorological Laboratories conducts an annual field program involving research flights into tropical cyclones with NOAA research aircraft. As part of this program, dropwindsondes are launched from the aircraft during a variety of airborne experiments. Since 1996, dropsondes based on satellite navigation from built-in Global Positioning System (GPS) modules have been deployed in and around the tropical cyclones. These GPS sondes demonstrate a remarkable ability to accurately measure kinematic and thermodynamic quantities, including winds to an accuracy of 0.5-2.0 m s^-1 at approximately 5 m resolution, as they descend from flight level to the surface. This study focuses on documenting the vortex-scale wind structure in the middle and lower troposphere of three hurricanes: Bonnie (1998), Guillermo (1997), and Bret (1999), which had experienced high, moderate, and low environmental shear, respectively. These hurricanes are all well sampled by GPS sondes released within 300 km of the center during HRD's vortex motion and evolution and modified air-sea interaction experiments. Objective analyses of the dropsonde data are performed to resolve significant wind features approximately 50-300 km from the center and filter out smaller scales. Using the analyzed fields, the distribution of kinematic asymmetries is contrasted among the storms and is related to the shear and to reflectivity fields simultaneously collected from airborne radar systems. Also, variations in the height of analyzed wind features are described.