Atmospheric boundary layer in the Atlantic: the desert dust impact

Abstract

We investigate the dynamics of the atmospheric Boundary Layer (BL) over the Atlantic Ocean, with a focus on the region surrounding Cabo Verde during the Joint Aeolus Tropical Atlantic Campaign (JATAC) and the ASKOS experiment, using a combination of ground-based PollyXT and Doppler lidars, satellite lidar data from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), radiosondes, and the model outputs of the Integrated Forecasting System (IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF). The comparison of CALIPSO lidar results with ECMWF/IFS reanalysis for 2012–2022, revealed good agreement for BL top over open ocean regions but weaker relation over dust-affected areas of the African continent. In these regions, daytime CALIPSO retrievals typically indicate lower BL tops than ECMWF, while at night CALIPSO often detects aerosols within the residual layer, leading to higher estimates than the model. Observations in Cabo Verde highlight distinctive Marine Atmospheric Boundary Layer (MABL) characteristics, such as limited diurnal evolution, but also show the potential for BL heights to reach up to 1 km, driven by factors like strong winds that increase mechanical turbulence. Additionally, the technical and physical challenges in estimating the BL height using different datasets and methods are discussed, examining cases with different thermodynamical conditions and aerosol load that directly affect the dynamics of the BL. The findings underline the strengths and limitations of different observational and modeling approaches, and emphasizes on the importance of considering local meteorology and aerosol conditions when interpreting BL height.