Assessing EarthCARE Cloud Profiling Observations in Arctic Clouds Using Coordinated Airborne Radar and Lidar Underflights

Abstract. Accurate characterization of Arctic clouds, particularly at low levels, remains challenging due to sparse observations and uncertainties hindering their representation in climate and weather models. The Earth Cloud, Aerosol and Radiation Explorer (EarthCARE) mission provides unique spaceborne observations of clouds and precipitation, including novel Doppler measurements from the Cloud Profiling Radar (CPR) and lidar observations from the Atmospheric Lidar (ATLID). To assess the potential of EarthCARE's CPR and ATLID for Arctic cloud studies, the "Clouds over cOMPlEX environment – EarthCARE" (COMPEX-EC) airborne campaign was conducted in April 2025 from Kiruna, Sweden. Seven research flights collected approximately 5.6 h of along-track measurements coincident with EarthCARE overpasses. The Alfred Wegener Institute's Polar 5 aircraft carried high-resolution active and passive instrumentation, including the 94 GHz Microwave Radar/Radiometer for Arctic Clouds (MiRAC) with a passive channel for liquid water path (LWP) retrievals, the Airborne Mobile Aerosol Lidar (AMALi) for independent cloud top height (CTH) retrievals, complemented by dropsondes for collocated thermodynamic and wind profiles. We assess EarthCARE products using airborne measurements from underflights with a ±15 min temporal distance (about 150 km) from match. In a close range (±10 km), the CPR reflectivity shows little bias below 1 dBZ relative to MiRAC, given EarthCARE's geometry and the Orbital-Radar simulator. This indicates generally good radiometric consistency in Arctic mixed-phase cloud and precipitation systems. The matched segments further allow us to characterize cloud fraction and precipitation rate from MiRAC and AMALi, complementing the EarthCARE assessment with additional information on mixed-phase clouds in downstream regions of marine cold-air outbreaks (MCAOs), which are particularly challenging for Numerical Weather Prediction. Due to strong sublimation occurring in the convective cells, EarthCARE's CPR overestimates surface snowfall in these cases because of its blind zone at 500 m above ground level. The airborne measurements show, on average, 80 m higher CTH from lidar than from radar, which hints at a supercooled liquid layer aloft. While having a much lower number of retrieved ATLID CTH values, EarthCARE shows the opposite, with higher CPR than ATLID CTH. These findings highlight the combined value of active radar and lidar observations for interpreting EarthCARE's cloud and precipitation products in the Arctic.