12/11/2012
Shortcut to Calculating Aerosol-Cloud Signals
Summary
Aerosol particles brighten clouds and contribute to climate cooling, but to
calculate these effects in climate models requires lengthy calculations to average out the natural “noisiness” of clouds. Now, U.S. Department of Energy researchers from the Scripps Institute of Oceanography, University of Washington, and Pacific Northwest National Laboratory have shown that by nudging the winds simulated in the Community Atmosphere Model (CAM5) toward the winds measured in the atmosphere, the aerosol effects on cloud brightness can be identified much more quickly. This nudging greatly reduced variations in the column liquid water in clouds without changing the sensitivity of the column liquid water to the aerosol, thus
permitting global estimates of aerosol effects on clouds in much shorter simulations. Simulations with preindustrial and present-day emissions of aerosol and aerosol precursor gases were both nudged toward the same winds so that the weather systems were similar in both simulations. They also performed simulations with preindustrial and with present-day emissions without nudging such that the weather systems could evolve freely in order to check their results. This study gives climate researchers a valuable tool for important climate change projection experiments.
References
Kooperman, G. J., M. S. Pritchard, S. J. Ghan, R. C. J. Sommerville, and L. M. Russell. 2012. “Constraining the Influence of Natural Variability to Improve Estimates of Global Aerosol Indirect Effects in a Nudged Version of the Community Atmosphere Model 5,” Journal of Geophysical Research-Atmospheres 117, DOI: 10.1029/2012JD018588.