Direct influence of solar spectral irradiance on the high-latitude surface climate: a surface radiation budget perspective

Abstract:

Not only total solar irradiance (TSI) but the partitioning of the solar spectral irradiance (SSI) between the visible (VIS) and near-infrared (NIR) matter for the Earth’s radiation budget, as clouds and surfaces (especially the sea ice) can have different reflectivity for the VIS and NIR. However, the SSI used in current global climate models (GCMs) is not constrained as well as the TSI. Recent NASA TSIS-1 mission has provided more accurate SSI observations than before. The TSI observed by TSIS-1 differs from the one used by climate models by no more than 1 Wm^-2. However, the SSI difference in a given VIS or NIR band can be as large as 4 Wm^-2 between what TSIS-1 has observed and what is used by climate modelers. This study used the latest fully-coupled climate model by NCAR, CESM2, to study the extent to which such different VIS and NIR SSI partitions can affect the simulated climate. Two sets of simulations, one done with the current SSI used by mainstream climate models and the other with the TSIS-1 constrained SSI, have shown statistically significant differences in the absorbed VIS and NIR flux by the atmosphere and by the surface. Due to the different spectral reflective properties of ice and snow surfaces for VIS and NIR, the interplay among surface albedo, temperature, and sea ice rendered the high latitudes the most susceptible regions to such VIS and NIR SSI partition. The results underscore the importance of precise knowledge of SSI and its temporal variations on the simulated high-latitude surface energy budget and climate.