Toward Spectrally Consistent Solar Radiation Across Components in Earth System Models

math_shortcuts Earth system models (ESMs) often exchange solar fluxes and albedos between components using only two spectral bands (visible (VIS) and near-infrared (NIR)). Surface models often repartition spectrally coarse incident solar fluxes into higher resolutions using prescribed, time-invariant weights. This is particularly prevalent over cryospheric surfaces, where spectral albedos vary significantly throughout the NIR region. Here, we resolve the exchange of solar fluxes and albedos from two bands to eight (one VIS and seven NIR bands) between the atmosphere and snow-covered land surfaces within an ESM. The exchange of higher resolution fluxes and albedos allows the surface to dynamically weight the spectral albedos throughout the NIR region, and thereby respond to changes in the spectral distribution of solar insolation. Diagnostic experiments show that the induced forcing on surface absorption caused by utilizing a dynamic NIR insolation relative to prescribed weights ranges between -1.90-4.73 Wm-2. Water vapor absorption strongly modulates this forcing such that low/high humidity generally increases/reduces surface absorption. Regional surface net flux and temperature responses over snow-covered surfaces are consistent with the applied forcing. Furthermore, replacing the two-band surface albedo with an eight-band albedo better captures the steep drop of snow reflectance at longer NIR wavelengths. This reduces the solar warming rate of the lower atmosphere by up to 0.1 K/day. These results provide a framework for, and quantify the impacts of implementing a high resolution spectrally consistent treatment of solar radiation between the atmosphere and cryospheric surface components in coupled ESMs.