06/16/2017

Marine Aerosols Offer Insight into Variability of Tiny Atmospheric Particles

Researchers move a step closer to developing a simplified representation of aerosol subgrid variability for use in global climate models.

The Science

Most global aerosol-climate models cannot resolve the spatial variability of aerosol properties at scales smaller than the model grid. This lack of detail makes it difficult to predict cloud formation and Earth system changes. Researchers at the U.S. Department of Energy’s Pacific Northwest National Laboratory found that aerosol subgrid variability—the variability of atmospheric particles on scales smaller than a model grid—is strongly correlated with the subgrid variability of sea spray production at the surface and of vertical velocity in the atmosphere.

The Impact

Without more accurate information about subgrid variability of clouds and aerosols, estimates of aerosol particles’ effect on Earth’s energy balance will continue to be uncertain. This research identifies key correlations between marine aerosols and meteorological variables. These correlations can be used to develop a simplified representation (parameterization) of aerosol subgrid variability for use in global climate models.

Summary

To inform the development of aerosol subgrid variability schemes for global climate models, researchers analyzed the aerosol subgrid variability over the southern Pacific Ocean simulated by the high-resolution Weather Research and Forecasting-Chemistry (WRF-Chem) model. They found that within a typical global model grid, the subgrid variability of the aerosol mass concentration was 15 percent of the grid-box average near the surface, and increased up to 50 percent in the troposphere. Scientists investigated the relationships between the sea-salt mass concentration, meteorological variables, and sea-salt aerosol production rate under both clear and cloudy conditions. Under clear conditions, researchers found a high correlation between the subgrid variability of sea spray aerosol mass and the subgrid variability of vertical velocity, cloud water mixing ratio, and of the rate of sea spray coming from the ocean surface. The sea-spray aerosol subgrid variability was also strongly connected to the grid-box average aerosol concentration in the free troposphere (between 2-4 kilometers). In the cloudy portion, researchers found a higher correlation between the subgrid variabilities of aerosol mass concentration and vertical velocity. Scientists also discovered that decreasing the model grid size reduced the sea-salt aerosol subgrid variability, but it also could strengthen correlations between the aerosol subgrid variability and the total water concentration (sum of water vapor, cloud liquid, and cloud ice concentrations).

Principal Investigator(s)

Steven Ghan
Pacific Northwest National Laboratory
Steve.Ghan@pnnl.gov

Funding

The U.S. Department of Energy Office of Science supported this research as part of the Scientific Discovery through Advanced Computing (SciDAC) program.

References

Lin, G., Y. Qian, H. Yan, C. Zhao, S.J. Ghan, R. Easter, and K. Zhang. “Quantification of Marine Aerosol Subgrid Variability and its Correlation with Clouds Based on High-Resolution Regional Modeling.” Journal of Geophysical Research: Atmospheres 122(12), 6329-6346 (2017). [DOI: 10.1002/2017JD026567].