Exploring new EarthCARE observations for evaluating Greenland clouds in the regional climate model RACMO2.4

Abstract. Clouds present one of the major challenges for polar climate modeling and significantly contribute to uncertainties in climate and ice sheet mass balance projections, as their radiative effect can strongly impact ice and snow melt. Therefore, a reliable representation of clouds in polar climate models is essential, yet the observations necessary for their evaluation remain sparse. The launch of the Earth Cloud, Aerosol, and Radiation Explorer (EarthCARE) satellite in May 2024 helps bridge this gap by offering cloud observations in unprecedented detail using multiple instruments. Here, we demonstrate the potential of using these novel observations to evaluate cloud representation over the Greenland ice sheet in the regional climate model RACMO (version 2.4p1). To this end, we show along-track comparisons of co-located RACMO cloud profiles with EarthCARE lidar and radar observations. We compare both lidar backscatter and radar reflectivity observations, as well as retrieved cloud properties, with simulated RACMO profiles for two selected case studies. These first results indicate that RACMO simulates low- and mid-altitude ice clouds and snowfall at the correct locations, but fails to capture thinner high-altitude clouds. Additionally, RACMO typically underestimates cloud ice and snow water content, in particular in precipitating systems, where RACMO underestimates snowfall rates. Regarding supercooled liquid and mixed-phase clouds, RACMO does not always reproduce these, especially when they are located at higher altitudes. These first comparisons highlight the potential for using EarthCARE observations to evaluate regional climate models and provide directions for further development of RACMO.