Revised Estimates of Aerosol Indirect Effects in Thin, Liquid-Containing Arctic Clouds

Of the uncertainties surrounding our understanding of global climate, one of the largest involves the relationships between aerosols and clouds along with the resulting impacts on atmospheric radiation and precipitation. Due to very limited profiling of aerosol properties, traditionally aerosol-cloud interactions have been evaluated using surface aerosol measurements as a proxy for aerosol at cloud height. At low- and mid-latitudes, clouds often form atop a well-mixed atmospheric boundary layer, meaning that the use of surface-based aerosol measurements is not necessarily unreasonable. At high latitudes, however, the atmosphere is often very stable. This stability limits vertical mixing of aerosols, meaning aerosol properties (e.g. number, hygroscopicity, scattering, size) observed at the Earth's surface may be very different from those at cloud height. This limitation makes it challenging to interpret previous efforts to understand the impacts of aerosols on liquid-containing Arctic clouds. In this work, we first use a variety of measurements from high-latitude measurement campaigns that included some form of aerosol profiling to demonstrate the relationship between surface and elevated aerosol properties under different stability regimes. Then, using surface-based remote sensors we derive and validate estimates for atmospheric mixing state. This mixing state product is subsequently used to provide revised estimates on the influence of aerosol effects in thin, liquid-containing Arctic stratiform clouds using only cases in which the lower atmosphere is well mixed.