Fatima-GB: Searching Clarity within Marine Fog

Fog constitutes a thick, opaque blanket of air hugging Earth’s surface, laden with small water droplets or ice crystals. Fog disrupts transportation, poses security threats, disorients human perception, and impacts communications and ecosystems. Collusion of atmospheric, terrestrial, and hydrologic processes produces fog droplets that pullulate over hygroscopic aerosols that act as condensation nuclei. Marine fog is particularly complex, since underlying dynamic, thermodynamic, and (bio)physicochemical processes span fifteen decades of spatial scales, from megameter-sized synoptic weather systems to nanometer-scale bioaerosols. This paper overviews the first international field campaign [Fog and Turbulence Interactions in the Marine Atmosphere-Grand Banks campaign (Fatima-GB)] of the project dubbed Fatima conducted during 1–31 July 2022 in the Grand Banks region of the North Atlantic. Therein, weather systems and commingling cold and warm oceanic waters provide entrée for fog genesis. Measurement platforms included an islet southwest of Nova Scotia (Sable Island), a research vessel ( Atlantic Condor ), an offshore oil platform, and autonomous surface vehicles. The instrument array comprised of extant remote and in situ sensors augmented by novel sensing systems prototyped and deployed in marine fog to penetrate the smallest scales of turbulence, examine aerosols, and quantify radiation budget. The comprehensive dataset so gathered, together with satellite and reanalysis products, mesoscale model, and large-eddy simulations, demonstrated that the long-held hypotheses of marine fog formation by warm air advection over colder water and in areas of enhanced (shelf) turbulence need to be revisited. The study also elicited new phenomena, for example, the fog shadow (clearings of fog downstream of islands). Significance Statement Fog research has escalated recently per climate change implications and directed energy (electromagnetic systems) applications. Here, we report selected findings of Fatima-GB, a comprehensive multidisciplinary field campaign conducted in Grand Banks, one of the world’s foggiest areas, for improving the understanding and predictability of marine fog. Our findings indicate historical understanding of marine fog life cycle requires a fundamental rethink to incorporate complexities of scale interactions. Fog covers 15 decades of spatial scales, wherein megameter-scale synoptic systems sway millimeter-scale turbulent eddies, within which micron-scale fog droplets spawn on either tens (bioaerosols) or hundreds (sea salt) of nanometer-sized marine aerosols. We demonstrate the collusion of meteorological, oceanographic, turbulence, thermodynamic, and (bio)physicochemical processes during marine fog evolution, which should help develop future subgrid parameterizations for numerical weather prediction (NWP) models.