Diurnal variation in the near-global planetary boundary layer height from satellite-based CATS lidar: Retrieval, evaluation, and influencing factors

Diurnal variations in planetary boundary layer height (PBLH) are essential for regulating the diffusion of pollutants and controlling heat and moisture exchange in the lower atmosphere. However, owing to the lack of continuous large-scale observations, the global behavior of diurnal variation in the PBLH remains poorly understood. This study seeks to bridge this knowledge gap by examining 33 months of profiles from Cloud Aerosol Transport System (CATS) lidar to retrieve the PBLH on a near-global scale. The retrievals were compared with other datasets, including radiosonde, CALIPSO, reanalysis, and CMIP6. The results suggest that the CATS retrievals were significantly consistent with the radiosonde and CALIPSO retrievals, with correlations of 0.6 (clearsky) and 0.74, respectively. Spatially, the CATS PBLH exhibits correlations of 0.11-0.72 with several CMIP6 and reanalysis outputs. For diurnal variations, the CATS PBLH showed a higher correlation (reaching 0.7) with reanalysis outputs during midday and early afternoon. However, there were considerable differences between them in the morning and late afternoon, owing to the influences of the residual layer and algorithm differences. Notably, deserts, plateaus and tropical areas exhibited more discrepancies between the CATS and reanalysis PBLH, which may be attributed to multilayer aerosol structures, heterogeneous surfaces, and deep convection. Based on the CATS derived PBLH dataset, we further investigated the meteorological impacts on interannual variability in the near-global PBLH using multiple stepwise regression and contribution calculations. The results indicate that meteorological factors explain 39-58% of the interannual variability in the CATS PBLH, and their contributions are land cover dependent and exhibit diurnal variations. Lower tropospheric stability dominated the interannual variability over land, with a diurnal pattern of its contribution aligned with the PBLH itself, whereas humidity factors contributed the most over oceans and wetlands. These findings have important implications for understanding the diurnal and temporal variability in the near-global PBLH, as well as the PBL parameterization.