Evaluation of the Ice Nucleating Abilities of Various Aerosol Types through a Combination of Satellite Data and Cloud-Resolving Modeling

Ice nucleation by aerosols in the Earth’s atmosphere changes cloud amount, lifetime, particle size and radiative properties, thereby affecting the global radiative balance, hydrological cycle, and climate. While mineral dust has been known as effective ice nucleating particles (INPs), the ice nucleating abilities of many anthropogenic aerosols are still under debate. Previous studies on ice nucleation abilities have mainly relied on laboratory experiments, which were limited to certain aerosol compositions and atmospheric conditions. Here we provide a top-down evaluation of the ice nucleation triggered by various aerosol types by employing 11-year continuous observations from multiple satellites, as well as cloud-resolving modeling. For both deep convective clouds and convection-generated cirrus clouds, we find that the responses of ice crystal effective radius (R_ei) to aerosol loadings are modulated by convective strength in conjunction with several other meteorological parameters. Our cloud-resolving simulations using an aerosol-aware Weather Research and Forecasting (WRF) model suggest that convective strength modulates the relative importance of homogeneous and heterogeneous nucleation, leading to the opposite aerosol impacts between strong and weak convective conditions observed in satellite measurements. When we classify aerosols into various types based on the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) and other satellite datasets, the preceding convective-strength modulation remains in effect for either dust or anthropogenic pollution aerosols, indicating that they both contain substantial amount of INPs. This conclusion is further supported by our cloud-resolving model simulations. Our study demonstrates the ice nucleating ability of anthropogenic aerosols, which is essential for an accurate estimate of the radiative forcing produced by aerosol-cloud interactions.