Validation of Satellite‐Based Cloud Phase Distributions Using Global‐Scale In Situ Airborne Observations

Understanding distributions of cloud thermodynamic phases is important for accurately representing cloud radiative effects and cloud feedback in a changing climate. Satellite‐based cloud phase data have been frequently used to compare with climate models, yet few studies validated them against in situ observations at a near‐global scale. This study aims to validate three satellite‐based cloud phase products using a compositive in situ airborne data set developed from 11 flight campaigns. Latitudinal‐altitudinal cross sections of cloud phase occurrence frequencies are examined. The Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) show the most similar vertical profiles of ice phase frequencies compared with in situ observations. The CloudSat data overestimate mixed‐phase frequencies up to 15 km but provide better sampling through cloud layers than lidar data. The DARDAR (raDAR/liDAR) data show a sharp transition between ice and liquid phase and overestimate ice phase frequency at most altitudes and latitudes. The satellite data are further evaluated for various latitudes, longitudes, and seasons, which show higher ice phase frequency in the extratropics in their respective wintertime and smaller impacts from longitudinal variations. The Southern Ocean shows a thicker mixing region where liquid and ice phases have similar frequencies compared with tropics and Northern Hemisphere (NH) extratropics. Two comparison methods with different spatiotemporal windows show similar results, which demonstrates the statistical robustness of these comparisons. Overall, this study develops a near global‐scale in situ observational data set to assess the accuracy of satellite‐based cloud phase products and investigates the key factors affecting the distributions of cloud phases. Plain Language Summary Accurate representations of cloud thermodynamic phase (i.e., ice, liquid, and mixed phase) play an important role in climate prediction. Even though satellite observations have been used to improve climate model simulations of cloud phase, few studies have validated satellite‐based cloud phase distributions on a global scale. This work develops a large data set based on in situ aircraft‐based observations from 11 flight campaigns in various regions. Three satellite‐based cloud phase products are evaluated. Satellite observations that are either in proximity to the aircraft samples or in a similar domain are used for comparisons. CALISPO data show the