Numerical simulation of wind gusts in intense convective weather and terrain-disrupted airflow

P. W. Chan, C. C. Lam, P. Cheung

Abstract

Wind gust is an important element in weather forecasting. Gusts associated with squalls in intense convective weather may bring about injuries to the public. In aviation meteorology, the aircraft may not attempt to land on the runway in gusty crosswinds, which could disrupt air traffic and adversely affect airport efficiency. The conventional method of gust forecasting is mainly based on climatological information of wind excess due to gust on top of the mean wind for different synoptic and mesoscale conditions (e.g. subtropical squall line, monsoonal flow, tropical cyclone situation, etc.). This paper uses a physical approach to wind gust estimate in meso to microscale numerical weather prediction (NWP), namely, based on turbulent kinetic energy and vertical air motion as applied to Regional Atmospheric Modelling System (RAMS) version 4.4, and examines its performance in different conditions of gusty winds at the Hong Kong International Airport (HKIA). For the typical gusty wind events considered in the paper, the performance of the wind gust estimate is found to be satisfactory in comparison with actual wind measurements at the airport (yes-yes case, viz. the actual gusty winds are captured by the wind gust estimate method). To demonstrate that the method does not over-estimate the gust (null-null case, viz. the less gusty winds are not exaggerated in the estimate), an ordinary, moderate wind event with the winds crossing the mountains at the airport is also studied, and the estimated gust is reasonably close to the actual data. Gust estimate is apparently affected by the treatment of turbulence in the NWP model. As such, a sensitively study is also conducted on the impact of selecting different turbulence parameterization schemes available in RAMS 4.4 on the estimation of wind gusts for a case of terrain-disrupted airflow.

Keywords

Wind gust; squall line; terrain-disrupted airflow; tropical cyclone

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