Reconciling Aerosol Indirect Effect from Satellite Observations and Numerical Simulations

Aerosol indirect effect (AIE) remains one of the largest uncertainties in the estimated radiative forcing associated with human activities, both in current climate and in future projections. Satellite and ground-based observations have shown both positive and negative responses in cloud liquid water path (LWP), and, consequently, cloud albedo due to aerosol perturbations. In contrast, climate models mostly simulate strong positive (cooling) responses.

We utilize geostationary satellite retrievals, ground-based observations from DOE Atmospheric Radiation Measurement program in the eastern North Atlantic, and observation-constrained LES with a grid resolution of less than 200 meters to understand this discrepancy. Our study focuses on the AIE of the warm marine boundary layer clouds at scales equivalent to climate model resolutions. Specifically, we select more than ten marine boundary layer cloud cases using both geostationary satellite and ground-based observations to represent a range of cloud states within the observational statistics. Our findings indicate that cloud drying response modeled by LES is significantly less robust than the estimates derived from satellite observations.

To reconcile AIE derived from satellite observations and model simulations, this presentation will explore the impact of different estimation methods, the settings of numerical simulations, and the microphysical variability of clouds, including the covariation of LWP and droplet number concentration (Nd) due to cloud processes instead of aerosol perturbations.

Acknowledgment: This work is supported by the DOE Office of Science Early Career Research Program and the ASR Program. This work was performed under the auspices of the U.S. DOE by LLNL under contract DE-AC52-07NA27344. LLNL-ABS-868694