Observations of Fog‐Aerosol Interactions Over Central Greenland

Abstract

Supercooled fogs can have an important radiative impact at the surface of the Greenland Ice Sheet, but they are difficult to detect and our understanding of the factors that control their lifetime and radiative properties is limited by a lack of observations. This study demonstrates that spectrally resolved measurements of downwelling longwave radiation can be used to generate retrievals of fog microphysical properties (phase and particle effective radius) when the fog visible optical depth is greater than ∼0.25. For 12 cases of fog under otherwise clear skies between June and September 2019 at Summit Station in central Greenland, nine cases were mixed‐phase. The mean ice particle (optically‐equivalent sphere) effective radius was 24.0 ± 7.8 µm, and the mean liquid droplet effective radius was 14.0 ± 2.7 µm. These results, combined with measurements of aerosol particle number concentrations, provide evidence supporting the hypotheses that (a) low surface aerosol particle number concentrations can limit fog liquid water path, (b) fog can act to increase near‐surface aerosol particle number concentrations through enhanced mixing, and (c) multiple fog events in quiescent periods gradually deplete near‐surface aerosol particle number concentrations.

A climatology of Arctic fog along the coast of East Greenland

“…Cloud condensation nuclei occur in lower concentrations over Arctic pack ice than over the open ocean (Heintzenberg et al, 2006; Mauritsen et al, 2011). With perennial sea ice cover near Danmarkshavn, it is possible that the boundary layer at this high‐Arctic location has a lower aerosol load, but this will need to be determined by field measurements of fog microphysics (Gultepe et al, 2021; Guy et al, 2021; Guy et al, 2023). According to Meyer et al (1991), aerosol load alone cannot account for the lower visibility observed in the Arctic.…”