Thermodynamic and microphysical properties of summertime marine fog observed from Sable Island

Abstract This study focuses on the physical processes in marine fog and its impact on optical attenuation using measurements from Sable Island during the 2022 FATIMA Grand Banks field campaign. The analyses used the water‐droplet size distribution from a fog monitor (FM‐120) and the meteorological optical range (MOR) measured by a present weather sensor (PWD22) as primary data sources, augmented by frequent radiosonde launches collocated with other FATIMA instruments. Analyses of the frequent radiosonde launches revealed the presence of fog associated with frequent frontal passages throughout the intensive measurement period. Based on the 35 days of microphysics measurements, we also identified and analyzed nine reduced visibility events (RVEs) when the mean MOR was less than 1 km. Furthermore, the data were categorized based on the weather code to characterize the observed hydrometeor further into clear, mist, fog, and precipitation categories. This study shows evidence of persistent stable thermal stratification in the fog layer, often accompanied with low‐level jets in or above the fog layer. The droplet spectra in fog indicated a bimodal distribution below the droplet size of 50 m. Our results also show a consistent power‐law relationship between visibility and fog liquid water content for pure marine advection fog events, which are different from coastal fog, only. In particular, a power‐law fit seems to resemble closely the theoretical relationship given by previous studies of the marine fog.