Geographical features of changes in surface shortwave irradiance in East Asia estimated using the potential radiative forcing index

Abstract

Using a recently-proposed index of the potential radiative forcing (PRF), we quantified 2-dimentional relative contributions of atmospheric parameters (clouds, aerosols and precipitable water) on the change of surface shortwave irradiance ( S) over East Asia in July from 2003 to 2004. 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’. For example, the S change of totally about –70 (W/m 2) was estimated in the south China case because of all the negative factors. On the other hand, the S change of nearly 20 (W/m 2) was calculated as a result of a small negative aerosol effect and a moderate positive effect by the cloud optical depth in the central China case. Like these cases, PRF is useful in determining which of the parameters has a dominant effect on the overall change in S. Comparison of the summation of each PRF-derived contribution and the difference in S from the ISCCP products were fairly favorable (the correlation coefficient of 0.84). Regardless of a few shortcomings, obtained results demonstrated the usefulness of PRF for various climate investigations. Nonetheless, rigid validation against estimated S changes using PRF should be done with independent observations such as ground-based pyranometer measurements.