Intensified melting in the Arctic lower troposphere from 1979 to 2023

Ice melting in the atmosphere has far-reaching impacts on cloud microphysical properties, precipitation intensity and type. However, this issue remains largely unexplored in the Arctic. This study adopted the melting level (ML) as a metric to investigate the changes in atmospheric ice over the Arctic over 1979—2023. The results showed that the melting level height (MLH) rose by an average of 28.0 m per decade (p < 0.01) across the Arctic. The largest increase in MLH was observed in the North Atlantic and North Pacific sectors, as well as over the New Siberian Islands and their surrounding areas. Further analysis indicated that sea ice retreat played an essential role in the long-term trend of MLH during the freezing period, whereas the interannual variability of MLH was largely regulated by atmospheric rivers (ARs). Moreover, the atmospheric melting extent migrated poleward at a rate of 53.9 km per decade (p < 0.01) and lay farther north than the surface 0 ℃ isotherm, which may lead to widespread freezing-rain events in high-latitude regions. With these changes in ML, the cloud properties and the different types of precipitation have been undergoing pronounced changes in the Arctic, which has had a profound impact on the local snow and ice processes and ecological environment.