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Abstract:
Exploration of the diurnal pattern of global dimming and brightening has been limited by the paucity of high-temporal resolution observations. Based on 22 years’ continuous observations of hourly surface solar radiation (Rs) over 96 stations across China for 1993–2014, this study evidences higher relative changes in diurnal Rs in terms of both frequency and magnitude at sunrise and sunset, with a longer pathway for the sun passing through the atmosphere, than the hours in between. Rs is comprised of two components, the direct radiation (Rd) and the diffuse radiation (Rf). Over the solar energy resource region, we observe a loss of Rd which is relatively large near sunrise and sunset at low solar elevation angles when the sunrays pass through the atmosphere on a longer pathway. However, the concentrated Rd energy covering an average 10-hr period around noon during a day is relatively unaffected. Over the agricultural crop resource region, the large amounts of clouds and aerosols scattering more of the incoming light result in Rf taking the main proportion of Rs during the whole day. Rf resources and their fertilization effect in the main crop region of China further enhances since 1993 over almost all hours of the day.
