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

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.