Abstract
Abstract. This study investigates dimming and brightening of surface solar radiation (SSR) during 1961–2005 in China as well as its relationships to total cloud cover (TCC). This is inferred from daily ground-based observational records at 45 pyranometer stations. A statistical method is introduced to study contributions of changes in the frequency of TCC categories and their atmospheric transparency to the secular SSR trend. The surface records suggest a renewed dimming beyond 2000 in North China after the stabilization in the 1990s; however, a slight brightening appears beyond 2000 in South China. Inter-annual variability of SSR is negatively correlated with that of TCC, but there is a positive correlation between decadal variability of SSR and TCC in most cases. The dimming during 1961–1990 is exclusively attributable to decreased atmospheric transparency, a portion of which is offset by TCC frequency changes in Northeast and Southwest China. The dimming during 1961–1990 in Northwest and Southeast China primarily results from decreased atmospheric transparency under all sky conditions and the percentage of dimming stemming from TCC frequency changes is 11% in Northwest and 2% in Southeast China. Decreased atmospheric transparencies during 1991–2005 in North China in most cases lead to the dimming. TCC frequency changes also contribute to the dimming during this period in North China. This feature is more pronounced in summer and winter when TCC frequency changes can account for more than 80% of dimming. In South China, increased atmospheric transparencies lead to the brightening during 1991–2005. A substantial contribution by TCC frequency changes to the brightening is also evident in spring and autumn.
Highlights
Based on analysis of inter-annual changes in solar radiation at the Earth’s surface (SSR) from pyranometer measurements or proxy data, a number of studies have pointed to a widespread decrease of surface solar radiation (SSR) from the early 1960s to the late 1980s (“global dimming”) (Liepert, 2002; Stanhill and Cohen, 2001)
Using daily SSR and total cloud cover (TCC) data from 45 sites in China during 1961–2005, the first objective of this study is to investigate how SSR is further evolving into the new millennium
One focus of this study is to present how SSR is further evolving into the new millennium
Summary
Based on analysis of inter-annual changes in solar radiation at the Earth’s surface (SSR) from pyranometer measurements or proxy data, a number of studies have pointed to a widespread decrease of SSR from the early 1960s to the late 1980s (“global dimming”) (Liepert, 2002; Stanhill and Cohen, 2001). More recent studies have used data records updated to include the 1990s, and these studies suggest that the decline in SSR diminished during the 1980s, and leveled off or even reversed towards an increase during the 1990s (“brightening”) (Wild et al, 2009a, b, and references therein). Analysis of SSR data updated through 2005 from 9 pyranometer sites in China suggests that to some extent the phase of stabilization/brightening during the 1990s may no longer be continuing in the new millennium (Wild, 2009b). This is supported by analysis of sunshine duration data updated through 2005 from 618 sites in China (Xia, 2010). Aerosol optical depth is estimated to increase from 0.38 in 1960 to 0.47 in 1990
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