A modelling study of temperature and humidity variations induced by mountain waves in the neighbourhood of Hong Kong International Airport

Hong Kong International Airport lies near mountainous terrain which strongly affects airflow for particular meteorological conditions; this results in wind shear that interrupts flight activity. Hong Kong Observatory deploys a wide range of measurement equipment, and there have been a number of published case studies describing the corresponding measurement analysis and application of models in the region. The current study focuses on a two-day wind shear event in March 2022 where measurements indicated not only flow convergence, but also sharp temperature fluctuations to the west of the high terrain; an earlier study concluded that these meteorological disturbances were caused by a Foehn wind. Here, the computationally efficient airflow model, FLOWSTAR, is configured to represent this event. In addition to calculating wind fields, a novel approach has been developed whereby the convergence, divergence and intersection of ‘pseudo-streamlines’ are used to generate 3D temperature and humidity fields. Comparisons between modelled and measured temperature and humidity parameters indicate that the model has some skill in predicting the time and magnitude of the meteorological fluctuations, although absolute temperature values are under-predicted. The study concludes that a combination of streamline convergence and mechanical mixing was the warming mechanism associated with this Foehn wind.