Regional and Seasonal Distribution of Arctic Low-Level Cloud Types and Their Relationship to Large-Scale Environmental Conditions

Abstract. Low-level clouds strongly influence the Arctic surface energy budget and hydrological cycle, yet their representation in climate models remains challenging due to limited observations and complex interactions between local processes and large-scale conditions. This study analyzes eight years (2007–2016) of active remote sensing observations from CALIPSO and CloudSat to investigate the regional and seasonal distribution of four types of low-level clouds: warm liquid, ice-only, mixed-phase clouds (MPCs), and unglaciated supercooled liquid clouds (USLCs). 51 % of Arctic clouds occur below 3 km. The statistical analysis of cloud-type frequencies shows that MPCs account for 17 %, ice-only clouds for 21 %, and USLCs for 12 %. This study provides the first satellite-based assessment of USLCs over the Arctic, revealing occurrences up to 20 % over marine regions during transition seasons. Multiple linear regressions are used to quantify the influence of key environmental drivers on the cloud type distribution. MPCs are linked to dynamically unstable conditions such as marine cold-air outbreaks, especially over open sea regions and during transition seasons. USLCs preferentially develop under stable and relatively dry mid-tropospheric environments as opposed to ice clouds. Cloud–surface coupling shows that, on average, 32 % of low-level clouds are coupled to the surface. In winter, USLCs are four times more frequently coupled with the open ocean than with sea ice, emphasizing the strong thermodynamic control of the underlying surface. These results provide new insight into Arctic cloud-phase variability and offer guidance for improving their representation in large-scale models.