2026/06/08 by James Hlywiak, David D. Flagg, James D. Doyle +7
Earth and Planetary Sciences · #Oceanographic and Atmospheric Processes #Meteorological Phenomena and Simulations #Ocean Waves and Remote Sensing
paper · doi:10.1175/mwr-d-25-0072.1
Abstract Existing theories explain that fluid interactions with isolated island topography generate leeward turbulent wakes through internal processes, such as hydraulic dissipation or baroclinic tilting. Realistic island wake flows and resulting marine atmospheric boundary layer (MABL) structures subjected to diurnal changes in surface heat fluxes are not well understood, especially over islands with low topographic peaks (<1 km). Here, we elucidate diurnal characteristics of the MABL downstream of Barbados (maximum elevation = 340 m) during summertime conditions coinciding with the Moisture and Aerosol Gradients/Physics of Inversion Evolution (MAGPIE) campaign. We synthesize composited coupled ocean–atmosphere, mesoscale numerical weather prediction model solutions over 18 days in August with remote estimates of the 10-m winds obtained from synthetic aperture radar, revealing contrasting spatial and temporal characteristics of the downstream wake MABL between night and day. Overnight, windward surface drag and leeward boundary layer separation result in a laminar, shallow wake. Enhanced low-level stability reduces lateral mixing between the wake and environment, permitting retention of long, laminar wakes downstream. During the daytime, standing mountain waves weaken in favor of thermally induced leeward surface convergence, fueling a deep, buoyant MABL immediately offshore. Finally, we contrast the evolution of the simulated flow between 2 days which differ by the strength of the upstream wind forcing, thermal stratification, and surface heating over the island. We find that nuanced differences in these upstream parameters impact the downstream extent and diurnal transition of the wake, providing a link between the local MABL and regional environment. Significance Statement Understanding weather patterns near isolated islands is challenged by the drastic spatial variations in topography and surface type over small distances characteristic to these environments. Additionally, classical knowledge of atmospheric flow interactions with island topography relies on theory that does not consider gradients in land–sea surface heating, which drive coastal weather phenomena. Here, we use numerical weather prediction model simulations and estimates of near-surface winds from satellites to study differences in the near-surface weather downstream of Barbados between night and day during August 2023. Results reveal distinct diurnal variability in the wake of Barbados, confirming the importance of thermal processes in understanding and accurately forecasting island atmospheric flows.