14A.4
The relationship between GPS dropsonde wind profiles and sea-surface temperature in Hurricane Bret (1999)
Michael L. Black, NOAA/AOML/HRD, Miami, FL; and E. W. Uhlhorn, S. E. Feuer, W. P. Barry, and L. K. Shay
Wind profiles in tropical cyclones from GPS dropsonde observations have shown remarkable variability. Multiple, low-level wind maxima and large differences in the wind speed as a function of height in the boundary layer, comprise most of this variability. The low-level wind maxima are frequently observed near the top of the atmospheric boundary layer (~500 m), are thought to be associated with individual convective elements, and are most pronounced in the hurricane eyewall. The boundary-layer wind profile in tropical cyclones, however, may vary from a logarithmic decrease with height towards the sea surface to a nearly constant wind speed profile, and, more rarely, to an increase in the wind velocity with decreasing height. Some of this variability is correlated with substantial vertical air motions, suggesting that vertical mixing of momentum may be contributing to the observed differences in the wind profiles.
Observations from a several hundred dropsonde wind profiles in hurricanes have shown differences in the mean wind structure as a function of storm intensity and strength of the vertical wind. Sea surface temperature (SST), which can affect the static stability of the boundary layer, may inhibit or enhance vertical mixing of momentum, thereby altering the shape of the boundary-layer wind profile. In this study, the HRD archive of dropsonde wind profiles is combined with simultaneous observations of SST from Airborne Expendable Bathythermographs (AXBT) to investigate the relation between ocean temperature and atmospheric boundary-layer wind structure. Since 1997, over two hundred AXBTs have been launched together with GPS dropsondes from NOAA WP-3D research aircraft in the convective cores of Atlantic basin tropical cyclones. The SST data from the AXBT observations will be stratified into cool, moderate, and warm regimes to investigate any systematic differences in the dropsonde wind profiles. Subsets of these stratifications may also be made according to storm strength, intensity change, and location relative to storm features such as the eyewall and rainbands in order to further refine the relation between wind structure, SST, and convective activity. Mean wind profiles based on these stratifications will be presented and discuss
Session 14A, Tropical Cyclone Observations and Structure III (Parallel with Sessions 14B, 14C, and 14D)
Thursday, 2 May 2002, 2:00 PM-3:30 PM
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