Temporal and spatial variations of atmospheric contributions to shortwave surface irradiance in East Asia

Relative contributions of atmospheric parameters (clouds, aerosols and precipitable water) on the change of surface shortwave irradiance (S) were quantified over East Asia from 2001 to 2007 using an index of the potential radiative forcing (PRF) for climatological studies. Analyses at some points revealed that contributions of the cloud optical depth, cloud amount and aerosol optical depth took various values, including the sign, depending the combination of atmospheric parameters' values and differences. The contribution of precipitable water was rather small compared to other parameters'. Then the slopes of the linear regressions for the S variation due to the atmospheric parameters during the period were illustrated spatially, together with the standard deviation of the S variation. Consequently, the magnitudes of the temporal changes in the S variation due to them were shown to be highly variable geographically. Moreover, the variation between one parameter and the S variation due to that parameter was temporally coincident and basically opposite. And the contribution behaved nonlinearly and was determined by a combination of other relevant parameters. Based on above findings, it is concluded that PRF can be a promising tool for research of the long-term S variation.