Turbulence structure of dusty cirrus and its relation to atmospheric conditions: A characterization using cloud-radar measurements and reanalysis data

Abstract. Several times per year, Saharan dust intrusions reach central Europe and lead to the so-called dusty cirrus phenomenon. Numerical weather prediction models often struggle to reproduce these dusty cirrus clouds . This study presents the first characterization of the atmospheric conditions associated with dusty cirrus formation, using long-term, height-resolved observations from ground-based remote sensing. Continuous measurements from the Cloudnet station at Schneefernerhaus throughout the year 2022 were evaluated using cloud-radar measurements to explore the turbulent structure of cirrus clouds in the presence of Saharan dust. Observations were compared with simulated dust concentrations from the EAC4 (European Centre for Medium range Weather Forecasts (ECMWF) Atmospheric Composition 4) Global Reanalysis product provided by the Copernicus Atmosphere Monitoring Service (CAMS) to investigate links between dust and turbulence in cirrus clouds. This study further explores the atmospheric mechanisms that lead to dusty cirrus formation including the influence of wind shear on the observed turbulence structure. The results reveal a clear link between elevated dust concentrations and increased turbulence. No cases of strong turbulence in the absence of elevated dust concentrations, or vice versa were observed. Increased turbulence and the associated higher frequency of vertical updrafts, may promote heterogeneous ice nucleation in dusty cirrus clouds. Wind shear does not seem to be a significant factor influencing the observed turbulence. Further analysis of the atmospheric conditions observed around dusty cirrus clouds suggest that current theories might not fully capture the processes involved in this phenomenon.