Observational study of atmospheric boundary layer height in Hong Kong based on 20-year multi-source measurements

Abstract

Investigating atmospheric boundary layer height (ABLH) holds significant value for the understanding and numerical simulations of the atmospheric boundary layer (ABL). Based on the 20 years (2003−2022) of radiosonde data and 10 years (2013−2022) of microwave radiometer observations, this study applied two methods to determine the ABLH and comprehensively investigated the ABLH characteristics over Hong Kong, a densely populated subtropical city strongly influenced by tropical cyclones (TC). The analysis includes the interannual and seasonal variability of ABLH, as well as its relationships with atmospheric stability and wind shear exponent (WSE) under both TC and non-tropical cyclone (NTC) conditions. The results indicate higher ABLH in summer and autumn compared to spring and winter, and higher ABLH under weakly unstable boundary layer conditions. Nevertheless, the interannual variation in the ABLH is insignificant. Notably, the relationships between ABLH, atmospheric stability, and WSE exhibit distinct differences under TC and NTC conditions. It is revealed that on NTC days, the ABLH increases with the WSE under neutral or weakly stable stratification, while this increase is not significant during TC days due to turbulence saturation. The findings of this study are expected to enhance the understanding of ABL dynamics and provide scientific insights for wind energy assessment, urban pollutant dispersion modeling, and thermal comfort evaluation.