Giant Cloud Condensation Nuclei (GCCN) Dampen Precipitation Susceptibility to Submicron Aerosol

April 23, 2026

Robert Wood

Hosted by Christine Chiu

Abstract

This presentation examines the role of giant cloud condensation nuclei (GCCN)—large, hygroscopic aerosol particles, primarily sea salt—in regulating warm rain formation in marine low clouds. Using theory, observations, and a new minimal Lagrangian cloud model, we show that aerosol impacts on precipitation depend strongly on particle size, not just number concentration. While submicron (accumulation‑mode) aerosols tend to suppress precipitation by increasing cloud droplet numbers and reducing droplet size, GCCN with dry radii ≳1 µm act as efficient precipitation nuclei, accelerating condensational growth even at very low supersaturation. This rapid growth allows GCCN‑formed droplets to reach sizes favorable for collision–coalescence much faster than droplets formed on standard CCN. A minimal parcel‑based model is developed that includes condensational growth, collision–coalescence, and sedimentation of GCCN and drizzle embryos. Model results demonstrate that precipitation enhancement scales approximately linearly with GCCN mass loading, making GCCN mass a better predictor than number concentration. GCCN are especially important in polluted or marginally raining clouds, where they can enable precipitation and substantially reduce precipitation susceptibility to submicron aerosol. Overall, the work concludes that GCCN dampen aerosol–precipitation sensitivity, help reconcile models with observations, and are largely missing from current cloud and climate model parameterizations, despite their potentially important role in marine cloud–climate interactions.

Robert Wood is Professor of Atmospheric Sciences at the University of Washington. Wood’s research work focuses upon understanding processes controlling clouds and precipitation in the Earth’s atmosphere and the roles that aerosol, cloud and precipitation play in determining climate variability and change. Wood’s research uses a combination of global datasets, including satellite and global climate models together with high resolution and theoretical models. Wood has served in leadership roles on several major international field experiments supported by NASA, the US National Oceanographic and Atmospheric Administration, and the US Department of Energy. Wood is a member of the NASA CloudSat/CALIPSO Science Team. At the University of Washington, Wood serves on the advisory board for the Program on Climate Change, a framework of intense cross-disciplinary collaboration that furthers research and education in climate science. Wood was awarded the 2001 L. F. Richardson Prize from the Royal Meteorological Society, the 2010 Henry Houghton Award from American Meteorological Society, and was awarded an AGU Ascent Award in 2017. He became a fellow of the American Meteorological Society in 2021, and a fellow of the American Geophysical Union in 2024.