Effect of Surface Exchange Coefficients on the Development of Inner-Core Asymmetries in Simulated Tropical Cyclones

It has been known for some time that the maximum potential intensity of tropical cyclones is related to the surface exchange coefficients of enthalpy (c_e) and momentum (c_d). This relationship has been explored primarily through the use of two-dimensional, axisymmetric models. However, scant attention has been given to the effect these exchange coefficients can have on the development of asymmetries, particularly in the tropical cyclone core. Changes in the exchange coefficients can modify the radial profile of potential vorticity, which is important to the development of features such as Vortex Rossby Waves and mesovortices. These features can result in fluctuations in maximum intensity (i.e. wind speed) as well as changes in the location and horizontal extent of gale force winds. The purpose of this study is to explore how variations in the enthalpy and momentum exchange coefficients impact the development of inner-core asymmetries in idealized, three-dimensional simulations. As a first step, the simulations will utilize constant values (in both time and space) for both c_e and c_d and warm rain microphysics. Of particular interest is determining if the type and/or duration of inner-core asymmetric structure changes when different values of c_e and c_d are specified. Analysis will focus on Fourier decomposition of model output, as well as a comparison between the development of asymmetric structures in the model to that predicted by linear stability and wave propagation theories. This work is supported by NSF grant AGS-1101713.