Decadal variation of surface solar radiation in the Tibetan Plateau from observations, reanalysis and model simulations Qinglong You • Arturo Sanchez-Lorenzo • Martin Wild • Doris Folini • Klaus Fraedrich • Guoyu Ren • Shichang Kang Received: 4 February 2012 / Accepted: 23 April 2012 / Published online: 9 May 2012 Ó Springer-Verlag 2012 Abstract In this study, the annual and seasonal variations of all-sky and clear-sky surface solar radiation (SSR) in the eastern and central Tibetan Plateau (TP) during the period 1960–2009 are investigated, based on surface observational data, reanalyses and ensemble simulations with the global climate model ECHAM5-HAM. The mean annual all-sky SSR series shows a decreasing trend with a rate of -1.00 Wm -2 decade -1 , which is mainly seen in autumn and secondly in summer and winter. A stronger decrease of -2.80 Wm -2 decade -1 is found in the mean annual clear- sky SSR series, especially during winter and autumn. Overall, these results confirm a tendency towards a decrease of SSR in the TP during the last five decades. The comparisons with reanalysis show that both NCEP/NCAR and ERA-40 reanalyses do not capture the decadal varia- tions of the all-sky and clear-sky SSR. This is probably due to a missing consideration of aerosols in the reanalysis assimilation model. The SSR simulated with the ECHAM5-HAM global climate model under both all-sky and clear-sky conditions reproduce the decrease seen in the surface observations, especially after 1980. The steadily increasing aerosol optical depth (AOD) at 550 nm over the TP in the ECHAM5-HAM results suggests transient aero- sol emissions as a plausible cause. Keywords Surface solar radiation Á NCEP/NCAR Á ERA-40 Á ECHAM5-HAM Á Tibetan Plateau 1 Introduction Variations in solar radiation at the Earth’s surface (or surface solar radiation, SSR), profoundly affect the human and ter- restrial environment, which for example has significant implications for the intensity of the hydrological cycle, the carbon cycle, the cryosphere, and consequently for climate change scenarios. In recent decades, a decrease in SSR (also known as ‘‘global dimming’’) of about 7 Wm -2 was observed worldwide from the 1960s to 1980s at land stations and this topic has been widely studied (e.g. Gilgen et al. 1998; Liepert 2002; Stanhill and Cohen 2001; Qian et al. 2006, 2007; Kaiser and Qian 2002). More recent studies showed that the declining SSR faded during the 1980s, with an increase until the end of the twentieth century (also known as ‘‘brighten- ing’’) (Wild et al. 2005). The SSR records suggest a contin- uation of the brightening after 2,000 at numerous stations in Europe and the United States, although with a renewed Q. You (&) Á S. Kang Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences (CAS), Beijing 100085, China e-mail: yqingl@126.com Q. You Á K. Fraedrich Meteorological Institute, University of Hamburg, KlimaCampus, 21044 Hamburg, Germany Q. You Á G. Ren Laboratory for Climate Studies, National Climate Center, China Meteorological Administration (CMA), Beijing 100081, China A. Sanchez-Lorenzo Á M. Wild Á D. Folini Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland e-mail: arturo.sanchez@env.ethz.ch M. Wild e-mail: martin.wild@env.ethz.ch D. Folini e-mail: doris.folini@env.ethz.ch S. Kang State Key Laboratory of Cryospheric Science, Chinese Academy of Sciences (CAS), Lanzhou 730000, China 123 Clim Dyn (2013) 40:2073–2086 DOI 10.1007/s00382-012-1383-3