Long term trends in ice fog occurrence in the Fairbanks, Alaska, region based on airport observations

Ice fog typically occurs at temperatures below about −30°C. Ice fog formation and persistence are affected by atmospheric processes at different spatial and temporal scales and can be influenced by anthropogenic activities that add vapor to the near surface atmosphere. Based on meteorological observations from Fairbanks International Airport and Eielson Air Force Base (Alaska, USA) from 1948/49 to 2021/22, we provide an overview of general ice fog climatology at the sites, changes over time, and synoptic scale upper-level weather patterns common during ice fog occurrence. On average, ice fog occurrence has decreased by 60-70% over the study period (median number of ice fog days at Fairbanks Airport in 1950/51-1979/80: 16.5; median in 1990/91-2019/20: 6). The average length of ice fog events and of the ice fog season have also decreased. Trends are not linear and rates of change vary over time. The greatest reduction in ice fog occurred during the 1970s and ‘80s. Trends in ice fog hours roughly track decreasing trends in hours with cold temperatures. However, the percentage of cold hours in which ice fog occurs has decreased since about the 1980s. This suggests that local changes in air pollution or near-surface moisture may also play an important role for trends in ice fog occurrence. We use self organizing maps to assess recurring synoptic scale weather patterns in the upper atmosphere during ice fog conditions in Fairbanks. Ice fog is typically associated with a northerly flow or low pressure gradients over the study area.