Modeling and Analysis of the Landfalling Hurricane Boundary Layer

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Prior analysis of high-resolution mobile Doppler radar observations collected during Hurricane Fran (1996) has revealed evidence of highly organized sub-kilometer scale circulations termed boundary-layer "rolls," which embody organized rotation about a horizontal axis and develop within strongly sheared winds beneath some storms. Along with the more widely recognized presence of mesovortices (identified by locally-intense spin about a vertical axis), these organized features superposed on the intense, broadly cyclonic low-level airflow within hurricanes are thought to have potential to significantly influence overall storm intensity (via vertical transports of heat, moisture and momentum) and, more locally, to influence the duration and peak intensity of strong surface winds responsible for extreme property damage and loss of life. This new research effort will allow detailed examination of an extensive archive of existing data from the NSF-supported "Doppler on Wheels" (DOW) mobile radar facility for a number of more recent hurricane landfalls. In conjunction with large-eddy simulations aimed at the computer-based numerical representation of organized features within low-level wind fields, these analyses will allow quantification of turbulence structure, intensity and resultant fluxes beneath landfalling hurricanes. Where available, ancillary observations of surface wind speeds (as from surviving anemometers) and time-tagged damage to trees and engineered structures will also be considered to better relate these novel radar observations to conditions at the earth's surface. The intellectual merit of this study rests on improved documentation and dynamical understanding of the low-level ("boundary layer") atmospheric processes involved in hurricane intensity changes at far finer spatial scales than have previously been observed, and in relating these quantities both to storm intensity/structure and characteristics of the underlying surface (e.g., land-sea contrasts, type of vegetation, concentration of built structures etc.). Broader impacts will be derived through increased understanding of turbulent low-level airflows within landfalling tropical cyclones that can be implied to forecast model improvement and more accurately tuned building codes, as well as through support for an early-career scientist drawn from an underrepresented group.