Quantifying aerosol-cirrus cloud interactions using reanalyses and satellite lidar-radar observations

Cirrus clouds play a key role in the Earth’s radiation budget due to their high-altitude location, ice-only composition, and interactions with both longwave and shortwave radiation. Their radiative impact is highly sensitive to variations in ice crystal number concentration, size, and morphology, which are controlled by ice nucleation pathways and aerosol properties. Aerosol–cloud interactions (ACIs) remain one of the largest sources of uncertainty in the climate forcing, particularly through their contribution to the effective radiative forcing (ERFaci). While progress has been made over the past decades in understanding aerosol impacts on liquid clouds using satellite observations, the impact of aerosols on ice cloud formation and evolution is still poorly understood, leading to large uncertainties in the radiative forcing associated with aerosol–ice cloud interactions.

This study provides insights into aerosol-cirrus interactions by combining cirrus properties such as ice crystal number concentration (Ni) and ice water content (IWC) retrieved from the synergistic lidar-radar (DARDAR) remote sensing technique, notably the DARDAR-Nice product, with aerosol reanalysis products from the Copernicus Atmospheric Monitoring Service (CAMS). We quantified the sensitivity of cirrus parameters to aerosol concentration and subsequently infer the associated global aerosol-ice cloud radiative forcing. A variety of cloud regimes is considered to disentangle meteorological effects from the aerosol–cirrus interaction signal, including cirrus classifications based on their formation mechanisms as well as seasonal and regional bins.