Variation in Sunshine Duration and Related Aerosol Influences at Shangdianzi GAW Station, China: 1958-2021

Sunshine duration (SD) is adopted widely to study global dimming/brightening. However, long-term simultaneous measurements of SD and closely related impact factors require further analysis to elucidate how and why SD has varied during the past decades. In this study, a long-term (1958-2021) SD data series obtained from the Shangdianzi Global Atmosphere Watch (GAW) station in China was analyzed to detect linear trends, climatic jumps, and climatic periods in SD using linear fitting, the Mann-Kendall trend test, and the continuous wavelet transform method. Annual SD exhibited steady dimming (-67.3 h decade-1) before 2010, followed by a period of brightening (189.9 h decade-1) during 2011-2020. An abrupt jump in annual SD occurred in 1995, and the annual SD anomaly exhibited significant oscillation with & SIM;3-yr periodicity during 1960-1978. Partial least squares analysis revealed that annual SD anomaly was associated with variations in relative humidity, gale days, cloud cover, and black carbon (BC). Further analysis of the clear-sky daily sunshine percentage (DSP) and simultaneous measurements of aerosol properties, including aerosol optical depth, aerosol extinction coefficient, single scattering albedo (SSA), BC, and total suspended particulates, suggested that variation in DSP was affected primarily by aerosol scattering and absorption. Furthermore, the hourly clear-sky SD at high aerosol loading was approximately 60% and 56% of that at middle and low aerosol loadings, respectively. The pattern of diurnal variation in clear-sky hourly SD, as well as the actual values, can be affected by the fine particulate concentration, aerosol extinction coefficient, and SSA.