Using formvar to capture atmospheric ice crystals and retrieve roughness parameters

Abstract. Atmospheric ice crystal roughness is a poorly observed and understood parameter, yet it significantly influences ice crystal scattering properties and consequently impacts radiative transfer in the atmosphere, contributing to uncertainties in climate forecasting. We introduce a novel approach, as a proof-of-concept, to obtain high-resolution roughness measurements, building on the traditional formvar method for capturing ice crystals and validated through comparison of the roughness parameters of salt crystals and salt crystal replicas. In this study, ice crystals were grown in the Manchester Ice Cloud Chamber, collected, and subsequently imaged using a scanning optical profilometer, which enabled the identification of roughness features as small as 0.8 µm. This approach has potential to provide critical insights into roughness characteristics that are significant for improving radiative transfer models and forecasts.