Linking Arctic ice cloud properties to atmospheric stability and vertical motion using lidar observations

Ice clouds play a crucial role in the Earth’s atmosphere system. They interact with both the incoming shortwave and outgoing longwave radiation and thus have a strong influence on the atmospheric radiation budget. Their net radiative effect is still not well-quantified and is highly sensitive to their macrophysical and microphysical characteristics. However, determining these properties remains a challenging task. As a consequence, ice clouds are frequently under- or misrepresented in weather and climate models, contributing substantially to uncertainties in climate research.

The Arctic climate system is undergoing rapid and complex changes, in connection to global warming. While various properties and processes are affected, most notably the Arctic troposphere is warming at an accelerated rate, compared to the global average. The term Arctic Amplification, has been introduced to describe the unique changes occurring in the Arctic. Ice clouds are expected to play an important role in Arctic Amplification, either directly by interacting with radiation or as part of new or altered feedback loops. Despite their potential significance, there is a scarcity of observations of their macro- and microphysical properties in the Arctic and a missing link between hose crucial properties and the ambient dynamical conditions.

The Arctic Study of Cloud, Circulation and Climate (ASCCI) campaign took place in the Arctic during the Spring of 2025. For this campaign the German research aircraft HALO was used. With its high flight ceiling and long range, HALO is perfectly suited for the study of remote ice clouds in the Arctic. On-board HALO was, among others, the WALES (Water Vapour Lidar Experiment in Space) lidar system. WALES is an airborne water vapor differential absorption (DIAL) and high spectral resolution (HSRL) lidar system. It provides 2D vertically resolved measurements along the flight track, of water vapor concentration, aerosol backscatter and linear depolarization ratio, as well as the two-way atmospheric transmission. These capabilities allow for a detailed characterization of ice clouds including their vertical structure.

In this study we use observations from WALES during ASCCI. In the generated dataset, first we identify and extract the ice clouds and then derive properties, including the Relative Humidity over ice (RHi) and optical depth. In addition, we use reanalysis data from ERA5, and more precisely the large-scale vertical velocity and static stability in order to characterize the dynamical environment in which the ice clouds were detected. The ice clouds are then grouped according to these environmental regimes, allowing us to investigate how their macro-, microphysical and optical properties vary with large-scale ascent or subsidence and atmospheric stability. Our aim is to improve our understanding of Arctic ice cloud characteristics and their sensitivity to state of the atmosphere. The results provide observational constraints important for the representation of ice clouds in weather and climate models and for reducing uncertainties regarding the role of ice clouds in the rapidly changing Arctic climate system.