Spatial and temporal patterns of fog and low clouds in the Polar regions

Low-level clouds and fog play a crucial role in the surface energy balance of polar regions, where even small perturbations in radiative fluxes can trigger amplified climatic responses. In these environments, the frequent presence of fog and stratiform low clouds strongly modulates both shortwave and longwave radiation, exerting a dominant control on near-surface temperature. The radiative effect of these clouds is highly sensitive to their thermodynamic phase: liquid-containing clouds generally enhance downwelling longwave radiation, promoting surface warming, whereas ice-dominated clouds are more transparent in the infrared and can contribute to surface cooling, particularly during polar night. As both the Arctic and Antarctic undergo rapid warming accompanied by shifts in cloud phase partitioning, understanding the occurrence and temporal variability of liquid and ice fog and low clouds is essential for accurately representing polar climate feedbacks and their role in ongoing climate change.

Using 11 years of cloud observations from the active satellite sensor CALIPSO, we characterize the spatial and temporal patterns of fog and low clouds (FLCs) across the polar regions, stratified by season and light conditions. Our results show a pronounced reduction in ice FLCs over Antarctica (~1% per year), while the Southern Ocean exhibits a decrease in liquid FLCs during winter under both daytime and nighttime conditions. In the Arctic, both liquid and ice FLCs decrease over land and sea-ice-covered regions from fall to spring. Over the Arctic Ocean, however, we find an increase in liquid FLCs during these seasons regardless of solar angle, whereas ice FLCs increase only under conditions of available solar radiation.

Overall, the observed trends in fog and low-level clouds suggest a potentially important role in modulating polar surface energy budgets.