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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
29 Mar 2017
Review status
This discussion paper is under review for the journal Atmospheric Chemistry and Physics (ACP).
Aerosol trends as a potential driver of regional climate in the central United States: Evidence from observations
Daniel H. Cusworth1, Loretta J. Mickley2, Eric M. Leibensperger3, and Michael J. Iacono4 1Department of Earth and Planetary Sciences, Harvard Univ ersity, Cambridge, 02138, USA
2School of Engineering and Applied Sciences, Harvard University, Cambridge, 02138, USA
3Center for Earth and Environmental Science, State University of New York at Plattsburgh, Plattsburgh, 12901, USA
4Atmospheric and Environm ental Research, Lexington, 02421, USA
Abstract. In situ surface observations show that downward surface solar radiation (SWdn) over the central and southeastern United States (U.S.) has increased by 0.58–1.0 W m−2 a−1 over the 2000–2014 timeframe, simultaneously with reductions in U.S. aerosol optical depth (AOD) of 3.3–5.0 × 10−3 a−1. Establishing a link between these two trends, however, is challenging due to complex interactions between aerosols, clouds, and radiation. Here we investigate the clear-sky aerosol–radiation effects of decreasing U.S. aerosols on SWdn and other surface variables by applying a one-dimensional radiative transfer to 2000 2014 measurements of AOD at two Surface Radiation Budget Network (SURFRAD) sites in the central and southeastern United States. Observations characterized as clear–sky may in fact include the effects of thin cirrus clouds, and we consider these effects by imposing satellite data from the Clouds and Earth's Radiant Energy System (CERES) into the radiative transfer model. The model predicts that 2000–2014 trends in aerosols may have driven clear-sky SWdn trends of +1.35 W m−2 a−1 at Goodwin Creek, MS, and +0.93 W m−2 a−1 at Bondville, IL. While these results are consistent in sign with observed trends, a cross-validated multivariate regression analysis shows that AOD reproduces 20–26 % of the seasonal (June–September, JJAS) variability in clear-sky direct and diffuse SWdn at Bondville, IL, but none of the JJAS variability at Goodwin Creek, MS. Using in situ soil and surface flux measurements from the Ameriflux network and Illinois Climate Network (ICN) together with assimilated meteorology from the North American Land Data Assimilation System (NLDAS), we find that sunnier summers tend to coincide with increased surface air temperature and soil moisture deficits in the central U.S. The 1990–2015 trends in the NLDAS SWdn over the central U.S. are also of a similar magnitude as our modeled 2000–2014 clear-sky trends. Taken together, these results suggest that climate and regional hydrology in the central U.S. are sensitive to the recent reductions in aerosol concentrations. Our work has implications for severely polluted regions outside the U.S., where improvements in air quality due to reductions in the aerosol burden could inadvertently increase vulnerability to drought.

Citation: Cusworth, D. H., Mickley, L. J., Leibensperger, E. M., and Iacono, M. J.: Aerosol trends as a potential driver of regional climate in the central United States: Evidence from observations, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2017-208, in review, 2017.
Daniel H. Cusworth et al.
Daniel H. Cusworth et al.
Daniel H. Cusworth et al.


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Short summary
Since 1990, light-scattering pollution known as aerosols have declined as a result of tightening U.S. air quality regulations. Our study finds that U.S. surface solar radiation has increased simultaneously. We establish a link between aerosols and radiation through physical and statistical models. We find the strongest relationship between aerosols, radiation, and climate at a site in the Midwest. Our work underscores the importance of regional pollution on climate in the U.S. and abroad.
Since 1990, light-scattering pollution known as aerosols have declined as a result of tightening...