PNNL

Abstract

Atmospheric ice-nucleating particles (INPs) play a critical role in cloud freezing processes, with important implications for precipitation formation and cloud radiative properties, and thus for weather and climate. Additionally, INP emissions respond to changes in the Earth System and climate, e.g., desertification, agricultural practices, and fires, and therefore may introduce climate feedbacks that are still poorly understood. A better understanding of INP sources, their atmospheric variability, and cloud responses to INPs is required to improve Earth System predictability. As knowl-edge of the nature and origins of INPs has advanced, regional and global weather, climate, and Earth system models have increasingly begun to link cloud ice processes to model-simulated aerosol abundance and types. While these recent advances in nu-merical modeling of INPs are exciting, coupling cloud processes to simulated aerosol also makes cloud physics simulations increasingly susceptible to errors and uncertain-ties in simulation of INPs that are poorly constrained. Advancing INP predictability will require an increased focus on research that bridges the measurement and modeling communities. This review summarizes the current state of knowledge and identi?es critical knowledge gaps from both observational and modeling perspectives. In partic-ular, we emphasize the need for research that advances our understanding and capa-bilities in two key areas: (1) observational closure between aerosol and INP quantities and (2) skillful simulation of INPs within existing weather and climate models. We discuss the state of knowledge on various INP particle types as it relates to both of these goals, and brie?y discuss the challenges faced in understanding cloud impacts of INPs with present-day models. Finally, we identify priority research directions for both observations and models to improve understanding of INPs and their interactions with the Earth System.