Influence of Sea Salt Variability on Clouds
The aerosol indirect effect, by altering cloud radiative forcing, is one of the largest uncertainties in understanding climate change. Researchers, including Department of Energy scientists at Pacific Northwest National Laboratory, examined multi-year climate variability associated with sea salt aerosols and their contribution to the variability of pre-industrial shortwave cloud forcing (SWCF) using a 150-year simulation of the Community Earth System Model version 1.0 (CESM1). The results suggest that changes in sea salt and related cloud and radiative properties on interannual timescales are dominated by the El Niño-Southern Oscillation (ENSO) cycle. Sea salt variability on longer timescales is associated with low-frequency variability in the Pacific Ocean similar to the Interdecadal Pacific Oscillation, but does not show a statistically significant spectral peak. The researchers found that sea salt aerosol variability may contribute to short-wave cloud forcing (SWCF) variability in the tropical Pacific, explaining up to 20 percent to 30 percent of the variance in that region. Elsewhere, there is only a small sea salt aerosol influence on SWCF through modifying cloud droplet number and liquid water path that contributes to the change of cloud effective radius and cloud optical depth (and hence cloud albedo), producing a multi-year aerosol-cloud-wind interaction.
Xu, L., D. W. Pierce, L. M. Russell, A. J. Miller, R. C. J. Somerville, C. H. Twohy, S. J. Ghan, B. Singh, J. H. Yoon, and P. J. Rasch. 2015. “Interannual to Decadal Climate Variability of Sea Salt Aerosols in the Coupled Model CESM1.0,” Journal of Geophysical Research Atmospheres 120(4), 1502–19. DOI:10.1002/2014JD022888.