Environmental Drivers of Arctic Low-Level Clouds: Analysis of the Regional and Seasonal Dependencies Using Space-Based Lidar and Radar

Abstract. Low-level clouds play a crucial role in the Arctic surface energy budget and hydrological cycle. However, their representation in climate models remains challenging due to limited observations and complex interactions between local processes and large-scale environmental conditions. This study analyzes eight years 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). Our results show that 51 % of low-level clouds are located below 3 km. A reassessment of cloud-type frequencies reveals that MPCs occur 17 % of the time, ice-only clouds 20 %, and USLCs 12 %. Notably, this work provides the first satellite-based assessment of USLCs over the Arctic, showing that their occurrence can reach up to 25 % in oceanic regions during transition seasons. The Svalbard region and Bering Seas emerge as the cloudiest areas, where liquid-containing clouds are prevalent, while ice clouds dominate over Alaska and Siberia. Using multiple linear regression, we quantify the influence of key environmental drivers on cloud-phase occurrence. Surface temperature, lower tropospheric stability, mid-tropospheric humidity, and marine cold air outbreaks (MCAOs) are identified as dominant factors. MPCs are particularly linked to dynamic conditions such as MCAOs, especially over oceanic regions and during transition seasons, whereas USLCs are more associated with stable and drier mid-tropospheric environments. The results highlight the impact of air mass intrusions on the regional distribution of the cloud phase partitioning, offering guidance for improving their representation in climate models.