ESRL/PSD Seminar Series

Sensitivity of Tropical Cyclone Simulations to Air-Sea Flux Parameterizations and Implications for Parameter Estimation

Benjamin Green
National Science Foundation (NSF) Graduate Research Fellow, Ph.D. Candidate
Department of Meteorology, The Pennsylvania State University


Tropical cyclones (TCs) are fueled by large fluxes of sensible and latent heat from the air-sea interface. These fluxes (as well as momentum fluxes) cannot be explicitly resolved by numerical weather prediction (NWP) models and therefore must be parameterized. Unfortunately, there is a great deal of uncertainty as to the behavior of air-sea surface fluxes, especially under strong (hurricane-force) winds. Thus, the numerous NWP parameterizations of surface fluxes introduce model error into TC forecasts, which limits the accuracy of predictions of TC intensity. In this talk, the sensitivity of WRF-ARW simulated TCs to parameterizations of the surface exchange coefficients for drag (Cd) and moist enthalpy (Ck) is examined. In agreement with theory, increased Ck yields a stronger TC both in terms of minimum central pressure and maximum 10-m wind speed. The impacts of Cd are not as straightforward: increased drag does reduce the maximum 10-m wind speed (in agreement with theory), but also deepens the minimum central pressure (opposite of what is predicted by theory) - in other words, Cd changes the pressure-wind relationship of simulated TCs. Cd also profoundly impacts TC structure, such that increased drag yields a more compact primary circulation. The implications of these findings for using data assimilation to estimate model parameters related to Cd and Ck are discussed. Finally, some preliminary results of a Large Eddy Simulation of Hurricane Katrina (2005) are shown.

Wednesday, July 16th
10:00 am

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