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Atmospheric Sciences & Global Change
Research Highlights

October 2017

Clearing the Air in East Asia

A new study showed how monsoon wind's effects on dust influence winter temperatures and precipitation.

Monsoon map
The maps show differences in East Asian winter monsoon-related variables (changes between the strongest and weakest monsoon years) between the variable dust and fixed dust simulations. The top map shows dust direct radiative forcing (W m-2), while the bottom shows temperature (K). Enlarge Image.

The Science                       

Dust particles can change regional and global energy balances by scattering and absorbing radiation from the sun and Earth's surface, but in East Asia, the strength of the East Asian winter monsoon (EAWM) largely controls dust's influence on wintertime temperature and precipitation changes. A study by scientists at the U.S. Department of Energy's Pacific Northwest National Laboratory and the Scripps Institution of Oceanography revealed the amount of influence that dust has on winter temperatures and precipitation over East Asia.

The Impact

Little research exists about the role dust plays in yearly variations of winter temperatures and precipitation in East Asia. This study sheds light on how changes in wind and precipitation from the EAWM affect the volume, transport, and removal of dust in East Asia, and how dust can influence climate.

Summary

EAWM events are characterized by cold and dry air with northwesterly wind in the lower troposphere. Researchers used two 150-year pre-industrial simulations of the Community Earth System Model—one with variable dust sources and the other with fixed dust sources—to understand the effects of wind on dust concentration during the EAWM season.

The simulated dust concentrations decreased with increasing intensity of the EAWM over north China. The decrease in dust led to an increase in heat energy at the surface. EAWM-related wind and precipitation changes and their effects on dust volume contributed 67 percent to the direct heating—or radiative forcing—at the surface. These effects also offset the cooling that occurred as the EAWM strengthened.

Between the strongest and weakest EAWM years, surface air temperature variations induced by changes in wind and dust decreased by up to 0.4 Kelvin from eastern coastal China to the Sea of Japan, and 0.6 K over northeastern China. These results indicated that the dust reduced the variations in surface air temperature by 3-18 percent in eastern coastal and northeastern China. Therefore, the surface air temperature rose with increasing intensity of the EAWM in these regions. The warming resulted from the combined effects of changes in direct heating and wind-driven heat energy transfer at the surface, and northwesterly wind anomalies bringing cold and dry air from Siberia to these regions. Meanwhile, in eastern coastal China, variations of large-scale precipitation dropped by 10-30 percent in winter as a result of changes in dust concentration from EAWM-related wind feedbacks.

Funding

The U.S. Department of Energy Office of Science, Biological and Environmental Research, and National Science Foundation supported this research as part of the joint Decadal and Regional Climate Prediction using Earth System Models (EaSM) program. The research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science user facility.

Publications

S. Lou, L.M. Russell, Y. Yang, Y. Liu, B. Singh, S.J. Ghan, "Impacts of Interactive Dust and its Direct Radiative Forcing on Interannual Variations of Temperature and Precipitation in Winter over East Asia." Journal of Geophysical Research: Atmospheres 122(16), 8761-8780 (2017). [DOI: 10.1002/2017JD027267]


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