UC San Diego

Marine fog impacts human health, naval strategy, and biological productivity. Despite itsimportance, the skill of operational and global environmental models in forecasting marine fog and its optical properties remain limited due to our incomplete understanding of the physical processes that drive fog, particularly over its broad range of temporal and spatial scales. The Gulf Stream and the Labrador Sea currents meet in Atlantic Canada and the Grand Banks off Newfoundland, Canada, making it a productive region for biodiversity with a wide range of physical oceanographic features present. This region has one of the two highest fog occurrences in the world (Dorman et al., 2020). In this work, we present findings from a 71-year climatological analysis covering a broad range of spatial and temporal scales. Using ICOADS observations from 1950-2020, ERA5 reanalysis products, and satellite imagery, we discuss fog formation and annihilation in this region. Spatially, the Atlantic Canada continental shelf induces submesoscale ocean features along its rapid variation in bathymetry. These structures influence the fog life cycle. Sharp sea surface temperature gradients and air-sea temperature differences coincide with the over-the-shelf fog maxima in summer (June, July and August). The air-sea temperature differences show a clear signal that fog occurrence is higher with negative air-sea temperature differences (SST - air temperature). This higher occurrence of fog is mainly isolated on the continental shelf, where colder SST typically exists. Temporally, climatological trends confirm correlations between air-sea temperature differences and high fog occurrence within sample regions on and off-shelf. Satellite imagery of a fog event during the 2022 ONR FATIMA MURI campaign highlights the complicated interplay of shelf break dynamics and near-surface atmospheric conditions. A fog bank is shown to form in the colder water regions over the shelf, outlining the shelf break and pointing to boundary layer and smaller-scale processes that are driving fog formation. These observations are crucial in characterizing the spatial and temporal structure of the fog life cycle and provide a better understanding of fog occurrence in this region.