Tower and Doppler Radar Observations from the Boundary Layer of Hurricanes Isabel (2003) and Frances (2004)

Research on sub-kilometer coherent features found in the boundary layer of hurricanes at landfall has been problematic, as it involves structures for which the data collection has proven to be quite challenging. For a long time, technical limitations prevented the identification of such features. Recently, with the improvement of remote sensing instruments such as mobile Doppler radars, small-scale linear features of the HBL have been identified and documented, revealing the prevalence of such features in the HBL. Although some physical characteristics of these linear features are now better understood, their impact on the surface windfield is still a topic that raises numerous questions. To be able to fully understand the relationship between the HBL small-scale features and underlying surface windfield, it is essential to acquire near surface wind data, along with data from the general HBL. Instrumented towers have been valuable instruments to collect surface wind data, but their limited vertical extent does not allow any access to the general HBL. On the other hand, Doppler radars have been very efficient in documenting HBLs, however, technical limitations such as ground clutter has made data acquisition in the lowest part of the HBL very challenging. In an attempt to address those issues, the Texas Tech University Hurricane Intercept Team (TTUHIT) has combined the two types of instruments to document the influence of the HBL small-scale features with the surface windfield. During the landfalls of Hurricanes Isabel (2003) and Frances (2004), the TTUHIT deployed SMART radars and instrumented towers close to each other to collect a coupled dataset. The processing of the Doppler velocity data revealed very fine coherent features in the HBL. The goal of the study is to be able to correlate these features' kinematic signature to the surface windfield recorded by the instrumented towers.