Errors and Uncertainty in Absorbed Solar Radiation and the Hydrological Cycle

Thursday, December 13, 2018 - 17:45
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We use a global line-by-line benchmark quality tool to evaluate the impact of errors in the absorption of solar radiation by the atmosphere in two GCMs. Atmospheric absorption of solar radiation is important for the hydrological cycle, as it competes with latent heat of precipitation to balance long wave cooling. Recent work has hypothesized that errors in radiative transfer calculation of the absorption of solar radiation by greenhouse gases may be the leading cause of the intermodel spread in the intensification of the hydrological cycle under a warming climate.

However, for both models studied here we find that the impact of aerosol absorption is far larger than parameterization error associated with gaseous absorption. Global average radiative parameterization errors in aerosol effect on solar absorption are 20% for GFDL’s AM4 and 10% for CESM 1.2.2, with larger errors regionally. However, the range in shortwave absorption by aerosols between the two GCMs is still greater than the error in aerosol or gaseous absorption. Therefore, our results suggest that the spread in hydrologic cycle intensification between models may not be primarily due to inter-model differences in gaseous radiative parameterization, as hypothesized in the literature, but instead due to a combination of errors and uncertainty in how much shortwave radiation is absorbed by aerosol.

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