Parametrization of Planetary Boundary-Layer Height with Helicity and Verification with Tropical Cyclone Prediction

摘要

To reduce the discrepancy between simulated and observed tropical cyclones, we consider a new parametrization scheme for planetary boundary-layer (PBL) height based on helicity, intended to provide an improved description of the overall helical structures of the tropical cyclone PBL simulated in a numerical model. This scheme was preliminarily tested in the Yonsei University (YSU) PBL scheme integrated within the National Center for Atmospheric Research Weather Research and Forecasting model. Based on verification of track simulations for seven tropical cyclones that made landfall over China, tropical cyclone Morakot (2009) was selected for further evaluation of the new scheme. Compared with the original scheme based on the Richardson number (Ri), the new scheme elevated the PBL height associated with intense convection, which is consistent with observation. Importantly, the new scheme improved the numerical simulation of intense rainfall by modulating the PBL environment for convection evolution. Furthermore, the PBL height and 2-m temperature over land at night, which are frequently overestimated by the original YSU scheme, were improved using the new scheme. Because of its effects on PBL structures and convection evolution, the simulation of tropical cyclone Morakot intensity was improved by the new scheme.