Delaminating the Marine Atmospheric Boundary and Saharan Air Layers: Observations and modeling by MAGPIE to understand marine boundary and lower free troposphere layer inhomogeneity over the Northwest Tropical Atlantic

Abstract

Simplifying the atmosphere into discrete layers, such as the Marine Atmospheric Boundary Layer (MABL) and its surface, mixed, and detrainment layers, as well as the Saharan Air Layer (SAL) aloft, is necessary in maritime meteorological modeling and data analysis. However, data reduction risks losing critical information. The ONR Moisture and Aerosol Gradients/Physics of Inversion Evolution (MAGPIE) experiment, centered on Ragged Point Barbados around August 2023, July 2024, and February 2025 used Synthetic Aperture Radar (SAR), High Spectral Resolution Lidar (HSRL), Doppler and Raman lidars coupled with ground-based instrumentation, as well as the CIRPAS/NOAA aircraft to document the four-dimensional variability and large to fine scale budgets of atmospheric state, clouds, sea salt, and dust. Results span three areas: 1) Regime identification: SAR winds and geostationary imagery easily identify MABL regimes that can be reproduced in large eddy simulations; 2) Vertical exchange: Lidar and aircraft show that cloud organization of MABL regimes are related to vertical exchange from the near surface through cloud water vapor halos, especially at regime boundaries. Copious dust was also found in the MABL; and 3) SAL stratification: The concept of the monolithic or multi-layer of Saharan Air is often realized as ultrafine Saharan Air Layer(s) stratified under influence by large scale forcing, shear, diabatic heating, and likely more complex coupled processes. These insights inform multiscale modeling to bridge MABL 'grey zone' processes too large for parameterization in large-domain models, yet too fine to be explicitly resolved due to computational constraints.