14C.3 Assessing the Influence of Downdrafts and Surface Enthalpy Fluxes on the Intensity Change of Tropical Cyclones in Moderate Vertical Shear

Thursday, 19 April 2018: 2:00 PM
Champions ABC (Sawgrass Marriott)
Leon Nguyen, NOAA/AOML/HRD, Miami, FL; and R. F. Rogers, J. Zawislak, and J. Zhang

It is well-known that tropical cyclone (TC) intensification is often associated with a more symmetric distribution of precipitation and diabatic heating. Recent case studies have shown that in the presence of environmental vertical wind shear, lower-tropospheric cooling by downdrafts, particularly in the left of shear quadrants, and insufficient recovery via surface enthalpy fluxes can help to prevent the development of a more symmetric precipitation distribution. In this study, the effects of downdraft-induced cooling and downstream recovery via surface fluxes on TC intensity change are evaluated using dropsonde observations collected from 1996-2017. The dropsonde data are analyzed in a shear-relative framework and binned according to TC intensity change, allowing for comparison between intensifying and non-intensifying cases. Of particular interest are tropical depressions, tropical storms, or weak hurricanes subjected to at least moderate (>5 m s-1) levels of environmental vertical wind shear. Potential relationships between the downdraft-induced cooling, the frequency and intensity of downdrafts, and the tilt of the vortex are also assessed using airborne tail-Doppler radar analyses in select cases. Time permitting, the shear-relative kinematic structure of the boundary layer in differing TC intensity change regimes will also be discussed.
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