Global Riming Signatures from EarthCARE CPR Doppler velocity measurements

Riming, the growth of ice particles by accretion of supercooled liquid droplets, is a key microphysical pathway in mixed-phase clouds, strongly influencing precipitation formation and cloud radiative effects. However, its global occurrence and variability have remained poorly constrained by observations, as riming is typically inferred indirectly at the global scale, while more direct evidence has been obtained primarily from limited regions or specific field campaigns. The Earth Cloud, Aerosol and Radiation Explorer (EarthCARE), launched in May 2024, carries the first spaceborne Doppler Cloud Profiling Radar (CPR), enabling near-global measurements of vertical motions within clouds. In this study, we exploit EarthCARE CPR Doppler observations to investigate microphysical signatures embedded in retrieved ice sedimentation velocity, with a particular focus on vertical gradients as an indicator of riming. The physical basis is that rimed ice particles often undergo rapid mass growth over short vertical distances, leading to corresponding changes in fall speed and producing localized acceleration patterns in sedimentation velocity profiles. We develop a gradient-based riming detection algorithm to derive riming probability at near-global scale and present the first maps of its spatial distribution and seasonal variability. The resulting climatology reveals where riming is most prevalent and how its occurrence shifts with season, providing observational constraints that were previously inaccessible from space. Because riming remains a major source of uncertainty in weather and climate model microphysics, these global statistics offer a new benchmark for evaluating and improving riming parameterizations in numerical models, including emerging km-scale modeling efforts.