Global decrease of ice fog VS increase in the Arctic Ocean: a global analysis of ice fog and aerosols using 17 years of CALIOP measurements

Fog is typically a very low cloud touching the ground and consists of tiny liquid droplets or ice particles. Ice fog can form in very cold areas such as polar regions or high mountains at temperatures below -30°C. Few field campaigns have focused on ice fog and fewer have shown the presence of ice fog at warmer temperatures, suggesting that limitation in time and space may lead to an underestimation of this phenomenon with implications on the biosphere and the estimation of the Earth's energy budget.

By analysing CALIOP data from 2006 to 2023, we have found a reduction of both liquid fog (~ -33% up to 0.5km; ~ -32% up to 2km) and ice fog (~ -29% up to 0.5km; ~ -30% up to 2km) over time.
The geographical distribution of ice fog shows that ice fog mainly occurs at latitudes above 50°, where ice is more likely to form due to low temperatures.
Separating the regions with ice fog occurrence into North/South and continental/maritime sub-regions, we have found an increase in ice fog of about 35% (up to 0.5km; +30% up to 2km) over time in the maritime region at latitudes above 60° North, despite a decrease in ice fog in the other areas analysed.
Our results show that the increase in both liquid and ice fog from 2006 to 2023 is well correlated with the increase in aerosols over the same period. However, when ice fog over snow and ice covered surfaces is removed, the correlation between aerosols and ice fog is poor.
The aerosol types provided by CALIOP have been analysed for two temperature ranges to distinguish the homogeneous glaciation (T < -38°C) and the heterogeneous glaciation (-38°C ≤ T ≤ 0°C) of possible ice nucleating particles. This analysis have been used to derive probability density functions of single aerosol types, from which glaciation temperatures have been estimated over continental and maritime surfaces.