Evaluation of Climatic Impacts of Ice-Nucleating Particles through Precipitation Process with a GCM

Abstract Uncertainties abound regarding the climatic impacts of the cloud thermodynamic phase. This is partly due to the complexity of cloud microphysical processes involving ice-nucleating particles (INPs), which act as nuclei for cloud ice particles. To understand the link between INP-driven microphysics and the mean state of the present-day global climate, we conducted a suite of experiments with a global climate model (GCM) that assumed various temperature dependencies of INP concentrations and compared the results with satellite observations. These experiments were performed using the MIROC6 GCM equipped with two different microphysics schemes: the traditional diagnostic (DIAG) and the latest prognostic (PROG) precipitation schemes with single and multiple ice categories, respectively. Comparisons with satellite observations revealed that the PROG better reproduced the radar reflectivity profiles with more sophisticated representation of interactions between ice particles than the DIAG. These differences in microphysical representation lead to opposite responses of cloud radiative effects (CREs) to INP perturbations between the two schemes through differing interactions between ice particles and their impact on the cloud ice budget. Additionally, this study conducted sensitivity experiments mitigating the biases in cloud ice–snow interactions found in the PROG. The results imply that models that excessively produce snow potentially overestimate the CRE perturbations due to INPs. These results provide novel insights into the microphysics involving INPs through the cloud thermodynamic phase and cloud particle growth to precipitation. Furthermore, our findings underscore the importance of using GCMs capable of representing the interactions between ice particles to adequately evaluate the climatic impacts of INPs.