2026/06/18 by Stephanie S. Rushley, James D. Doyle, James Hlywiak +8
Earth and Planetary Sciences · Environmental Science · #Meteorological Phenomena and Simulations #Atmospheric aerosols and clouds #Climate variability and models
paper · doi:10.1175/mwr-d-26-0004.1
Abstract Saharan air layer (SAL) events transport warm, dry, and dusty air from Africa across the tropical Atlantic, but how they influence the marine atmospheric boundary layer (MABL) is not well understood. Using unique observations from the August 2023 Moisture and Aerosol Gradients/Physics of Inversion Evolution (MAGPIE) field campaign on Barbados, we test the hypothesis that the SAL’s impact on the MABL is indirect, driven by large-scale dynamic adjustments. The SAL’s thermodynamic properties enhance large-scale subsidence, strengthening the trade-wind inversion. This enhanced inversion then acts as a “synoptic-scale governor,” controlling MABL depth and temperature from above. We verify this mechanism using a high-resolution mesoscale model and its adjoint, which provides quantitative evidence that MABL depth is most sensitive to the temperature of the SAL air mass far upstream, not local mixing. While global models capture the broad environmental changes, their coarse vertical resolution fails to resolve the fine-scale inversion structure. Our findings demonstrate that the evolution of the MABL under SAL conditions is influenced by a competition between the thermodynamic suppression from the warm, dry air and the dynamic deepening from shear-driven turbulence of the midlevel jet. This highlights a key process for improving tropical weather and climate models. Significance Statement The Saharan air layer (SAL) is a large-scale plume of dry, dusty air that extends from Africa into the Caribbean Sea that alters the temperature, humidity, cloud cover, and wind in this area, as well as negatively impacting public health. In this study, we examine the environment when the SAL is present and when it is absent in observations and models. We find that the SAL drastically changes the environment and modifies the near-surface conditions.