Large Eddy Simulation of Tropical Cyclone Evolution

Large Eddy Simulation of Tropical Cyclone Evolution
Liguang Wu, Qingyuan Liu and Yubin Li
Pacific Typhoon Research Center and Key Laboratory of Meteorological Disaster of Ministry of Education, Nanjing University of Information Science and Technology, Nanjing, China

Corresponding author address: Dr. Liguang Wu
Pacific Typhoon Research Center
Nanjing University of Information Science and Technology, Nanjing, Jiangsu 210044
E-mail: liguang@nuist.edu.cn

Abstract
Tropical cyclones receive their primary energy from the warm ocean surface in the form of sensible and latent heat (moist enthalpy) fluxes, which are transported to the free atmosphere through the turbulent planetary boundary layer (PBL), and thus the PBL is known to play a critical role in transporting energy and controlling tropical cyclone intensity. In the tropical cyclone PBL, previous studies suggest that roll vortices prevail with sub-kilometer to multi-kilometer wavelengths have significant implications for the vertical transport of energy in tropical cyclones. With improvements in computational capability, the large-eaddy simulation (LES) technique has been increasingly used in tropical cyclone modeling. Rotunno et al. (2009) found that the mean tropical cyclone intensity starts to decrease, while the maximum wind increases sharply in the turbulent gusts in their sub-100-m integrations. Green and Zhang (2015) showed that the size of the simulated PBL eddies depends upon the horizontal resolution, suggesting that convergence to true LES has not yet been reached when the model resolution is 111 m.
Since previous studies strongly suggest the dependence of tropical cyclone intensity on the effects of resolved turbulence, it is necessary to evaluate the effects of various horizontal resolutions in numerical experiments on the simulated roll vortices and associated tropical cyclone evolution. Using the LES technique, the objective of this study is to simulate tropical cyclones with three different innermost horizontal resolutions of 333 m, 111 m and 37 m. The tropical cyclones are embedded in a realistic monsoon trough in the western North Pacific. Our focus is on how the horizontal resolution affects the tropical cyclone evolution. Numerical experiments are conducted with the Advanced Weather Research and Forecast (WRF) model (version 3.2.1) in this study. We will present comparisons of the simulated PBL rolls with various horizontal resolutions and the associated influences on tropical cyclone evolution and the near-surface wind structure.