Effects of surface flux parameterization on the numerically simulated intensity and structure of Typhoon Morakot (2009)

Abstract

The effects of surface flux parameterizations on tropical cyclone (TC) intensity and structure are investigated using the Advanced Research Weather Research and Forecasting (WRF-ARW) modeling system with high-resolution simulations of Typhoon Morakot (2009). Numerical experiments are designed to simulate Typhoon Morakot (2009) with different formulations of surface exchange coefficients for enthalpy (CK) and momentum (CD) transfers, including those from recent observational studies based on in situ aircraft data collected in Atlantic hurricanes. The results show that the simulated intensity and structure are sensitive to CK and CD, but the simulated track is not. Consistent with previous studies, the simulated storm intensity is found to be more sensitive to the ratio of CK/CD than to CK or CD alone. The pressure–wind relationship is also found to be influenced by the exchange coefficients, consistent with recent numerical studies. This paper emphasizes the importance of CD and CK on TC structure simulations. The results suggest that CD and CK have a large impact on surface wind and flux distributions, boundary layer heights, the warm core, and precipitation. Compared to available observations, the experiment with observed CD and CK generally simulated better intensity and structure than the other experiments, especially over the ocean. The reasons for the structural differences among the experiments with different CD and CK setups are discussed in the context of TC dynamics and thermodynamics.