11/13/2011
Nature Publication Reports Pollution Impacts on Clouds and Precipitation
Summary
Using a 10-year set of extensive measurements made at the Department of Energy’s Atmospheric Radiation Measurement (ARM) Climate Research Facility in the U.S. Southern Great Plains, researchers found unprecedented strong evidence that aerosols drastically alter clouds and precipitation. Aerosols— tiny particles in the air, like dust or soot—affect clouds and precipitation through different mechanisms. Aerosols can serve as cloud condensation nuclei (CCN) that impact cloud microphysics and precipitation processes, or they can directly modulate radiative and latent energy, changing the atmospheric stability dynamics and thermodynamics that dictate cloud development. The interplay of these effects can either suppress or foster cloud and precipitation processes, depending on the specific circumstances. This study showed that increased aerosol concentrations increased the cloud top height and thickness—most significantly in the summer by up to a factor of 2—for clouds with a warm base (above 15°C) and mixed-phase tops (below -4°C). Precipitation frequency increased with aerosols for deep clouds with high water content and decreased for clouds with little water. The observational findings are successfully reproduced with a state-of-the-art cloud-resolving model demonstrating that these aerosol processes are well represented in the model.
References
Li., Z., F. Niu, J. Fan, Y. Liu, D. Rosenfeld, Y. Ding. 2011. “Long-Term Impacts of Aerosols on the Vertical Development of Clouds and Precipitation,” Nature Geoscience 4, 888-94. DOI:10.1038/ngeo1313.