Lidar-based methods to determine PBLH and cloud coupling: algorithm development and application

The planetary boundary layer (PBL) height (PBLH) is a key parameter to affect the accumulation of pollutants and the dynamics of the lower atmosphere. However, it is still challenging to accurately obtain PBLH by using remote sensing techniques, especially under cloud interferences. Moreover, the coupling and decoupling of low clouds have not been understood as well over land, partly due to more complex thermodynamic structures. To address these issues, we developed lidar-based algorithms to simultaneously retrieve PBLH and coupled states of cloud, by using long-term measurements acquired by lidar and a suite of surface meteorological instruments at the ARM SGP site. The coupled states derived from lidar show strong consistency with those derived on the basis of thermodynamics. Contrasting to the sensitive responses of coupled cloud to changes in PBL depth and buoyancy, the decoupled clouds are weakly related to PBL. For lidar remote sensing, it has been a persistent problem to retrieve PBLH under cloudy conditions, which is solved in this study. Our methods offer high-quality retrievals of PBLH under both clear-sky and cloudy conditions, and the identifications of cloud states and PBLH complement each other. As coupled and decoupled clouds show distinct relationships with PBL thermodynamics, our new method offers an advanced tool to further investigate the integrated aerosol-cloud-PBL interactions.