Comparative Evaluation of Boundary Layer Height Estimation Using Multi-Source Observations and WRF Simulations under Complex Topography

Abstract. The planetary boundary layer (PBL) height determines the vertical scale of transport and mixing, making it a critical parameter in air pollution studies, weather forecasting, climate modelling, and many other applications. However, the accuracy of boundary layer height (BLH) representation by models in complex terrain conditions still requires further in-depth research. To address this critical scientific issue, the present study investigates the BLH from various simultaneous observations of multi-remote sensing instruments radiosonde (RS), wind profiler radar (WPR), and microwave radiometer (MWR) and six PBL parameterization schemes (Asymmetrical Convective Model version 2 (ACM2), Yonsei University (YSU), Mellor-Yamada-Janjic (MYJ), Mellor-Yamada-Nakanishi-Niino Level 2.5 (MYNN2), Mellor-Yamada-Nakanishi-Niino 3 (MYNN3) and Bougeault-Lacarrère (BouLac)) within the Weather Research and Forecasting (WRF) model from the Liangshan Prefecture (LSP) region during complex mountainous conditions. The findings are as follows: (1) The continuous wavelet transform (CWT) method is suitable for retrieving daytime convective boundary layer height (CBLH) in complex terrain, although aerosol layers interfere with the retrievals, and results from traditional threshold methods using MWR closely simulate the diurnal variation of BLH in the LSP. (2) WRF model simulates potential temperature and mixing ratio (𝜃 and R) profiles well, but shows discrepancies in wind speed simulation, particularly in capturing the weak near-surface inversion layer, leading to biases in BLH estimation. (3) Among the various PBL schemes, ACM2 and MYNN3 perform best in simulating BLH, with ACM2 recommended for convective conditions and MYNN3 for stable boundary layers, while YSU and MYJ consistently underestimate BLH. (4) The daytime atmosphere in mountainous regions typically exhibits a multi-layered structure, with mountain-induced exchange processes transporting high-suspended aerosol layers, causing discrepancies between thermodynamic-determined CBLH and actual BLH. In valleys and urban areas where BLH is higher than in the surrounding mountains.