23 March 2015

The 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. They found that sea salt aerosol variability may contribute to short-wave cloud forcing (SWCF) variability in the tropical Pacific, explaining up to 20-30% 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.


This research was supported by NSF AGS1048995 and by DOE DE-SC0006679 as part of the U.S. Department of Energy, Office of Science, Biological and Environmental Research, Decadal and Regional Climate Prediction using Earth System Models (EaSM) program. The Pacific Northwest National Laboratory is operated for the DOE by Battelle Memorial Institute under contract DE-AC05-76RLO 1830. We are grateful for the NASA MEaSUREs project providing the SeaWiFS AOD satellite data and for Joseph M. Prospero and Michael Schulz providing the long-term measurements of aerosols over the global ocean. All model results are available at http://portal.nersc.gov/project/m1374/SeaSalt/ in the National Energy Research Scientific Computing Center (NERSC).