A Addison Alford- April 8

Examining the Hurricane Boundary Layer at Landfall

A. Addison Alford

Wednesday, April 8^th  

3:00pm Central Time (US and Canada)/Zoom Meeting

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https://oklahoma.zoom.us/j/505651584

Meeting ID: 505 651 584

The hurricane boundary layer (HBL) has been well observed offshore by operational and research aircraft. GPS dropwindsonde data have been used to characterize the kinematic structure of the mean HBL over the ocean. These data show that the vertical structure of the horizontal wind is a function of radial distance from the center of circulation, of storm features (e.g., rainbands), and of storm intensity. However, relatively few studies have focused on the structural changes (i.e., changes in the vertical wind profile) to the HBL during landfall, and no study has yet compared the HBL over water and over land for a single hurricane.

            During the landfall of Hurricane Irene (2011), a Shared Mobile Atmospheric Research and Teaching (SMART) radar was deployed near the WSR-88D in Morehead City, NC (KMHX). A dual-Doppler wind retrieval region extended across the coastal region, including portions of several large coastal waterways. Wind analyses were conducted for a period of approximately 13 hours (27 August 2011 00 UTC to 27 August 2011 13 UTC) at high spatial resolution (250 m). During this observational period, the National Oceanic and Atmospheric Administration (NOAA) tasked the Air Force C-130, NOAA G-IV, and NOAA WP-3D Orion reconnaissance aircraft sampled Irene as it moved toward landfall.

            Using kinematic dropwindsonde data and ground-based dual-Doppler radar analyses, the vertical structure of Irene’s HBL over water and across the coastal interface can be quantitatively compared. Specifically, the mean state of the HBL across the coastal transition will be discussed and compared to the HBL observed over water. The evolution of the tangential wind maximum, which has been shown to reside within the HBL over water, and the impacts of the internal boundary layer response on the vertical distribution of momentum will be examined. Finally, the temporal evolution of the near-coast HBL observed via dual-Doppler analysis and via velocity azimuth display (VAD) retrievals from the Rapid Scanning X-Band Polarimetric Radar (RaXPol) will be discussed, focusing on the contrasts between the outer band, inner core, and eyewall flow regimes.