Observed modulation of wintertime Western Arctic mixed-phase cloud properties by sea ice conditions, their long-term variabilities and trends

To assess the long-term interaction between sea ice conditions and Arctic mixed-phase cloud (MPC) properties, fourteen winter seasons of observations from the North Slope of Alaska are analysed. MPC properties are set into context with sea ice conditions by determining the sea ice sectors which are most relevant to interact with the observed clouds. A conical sector of 6° and 50 km radius of upstream sea ice concentration (SIC) is considered based on the azimuth direction of the maximum water vapour transport (WVT) within the atmospheric boundary layer. The WVT height is used as indicator for the WVT interacting with the cloud, which is categorized as cloud-coupled or decoupled. The MPC properties are classified according to the presence of high or low pressure systems and analysed as a function of SIC. Results highlight which MPC properties do increase in magnitude as SIC decreases. The long-term time series evolution shows positive and negative trends in MPC properties, depending on the coupling status and the atmospheric pressure system. The study found statistically significant positive trends suggesting an increase of sea ice-MPC coupled liquid water path (+35.0±0.9 g m-2 decade-1), cloud base height (+44.0±0.7 m decade-1) and cloud top temperature (+2.2±0.7 K decade-1) under low pressure weather systems. It has been revealed that the evolution of MPC properties presents cyclical characteristics and it is hypothesized that those are in phase with climate oscillations like ENSO or PDO. Although the results support this hypothesis, a direct causation is not trivial.