K. C. Wang¹, R. E. Dickinson², M.Wild³, and S. Liang⁴

¹ State Key Laboratory of Earth Surface Processes and Resource Ecology, College of Global Change and Earth System Science, Beijing Normal University, Beijing, 100875, Beijing, China;

² Department of Geological Sciences, The University of Texas at Austin, Austin, TX 78712, USA;

³ Institute for Atmospheric and Climate Science, ETH Zürich, 8092 Zürich, Switzerland;

⁴ Department of Geography, University of Maryland, College Park, MD 20742, USA.

 

Abstract: The Earth’s climate is driven by surface incident solar radiation (R_s). Direct measurements have shown that R_s has undergone significant decadal variations. However, a large fraction of the global land surface is not covered by these observations. Satellite-derived R_s has a good global coverage but is of low accuracy in its depiction of decadal variability. This paper shows that daily to decadal variations of R_s, from both aerosols and cloud properties, can be accurately estimated using globally available measurements of Sunshine Duration (SunDu). In particular, SunDu shows that since the late 1980’s R_s has brightened over Europe due to decreases in aerosols but dimmed over China due to their increases. We found that variation of cloud cover determines R_s at a monthly scale but that aerosols determine the variability of R_s at a decadal time scale, in particular, over Europe and China. Because of its global availability and long-term history,SunDu can provide an accurate and continuous proxy record of R_s, filling in values for the blank areas that are not covered by direct measurements. Compared to its direct measurement, R_s from SunDu appears to be less sensitive to instrument replacement and calibration, and shows that the widely reported sharp increase in R_s during the early 1990s in China was a result of instrument replacement. By merging direct measurements collected by Global Energy Budget Archive with those derived from SunDu, we obtained a good coverage of R_s over the Northern Hemisphere. From this data, the average increase of R_s from 1982 to 2008 is estimated to be 0.87Wm⁻² per decade.