The representation of the Earth radiation budget in reanalyses

The Earth’s radiation balance fundamentally determines the climatic conditions on our planet. While the radiation balance at the Top-of-Atmosphere (TOA) determines the overall heat uptake in the climate system, the radiation balance at the surface governs the thermal changes in our environments, and defines the energy that drives the evaporative flux and with it the global water cycle.

The present study investigates the representation of the global mean radiation balance components in 10 atmospheric reanalyses, and  compares their magnitudes with independent reference estimates as well as the ones simulated by the latest generation of climate models from the 6^th phase of the coupled model intercomparison project (CMIP6).

Despite the assimilation of comprehensive observational data in reanalyses, we find that the spread amongst the magnitudes of their radiation balance components generally remains substantial, up to more than 20 Wm^-2 in some quantities, and their consistency is typically not higher than amongst the much less observationally constrained CMIP6 models. A comparison of reanalysis runs in full assimilation mode with corresponding runs constrained only by sea surface temperatures reveals marginal differences in their global mean radiation balance components. This indicates that discrepancies in the global radiation balance components caused by the different model formulations amongst the reanalyses are hardly alleviated by the imposed observational constraints from the assimilation process. Similar to many climate models, reanalyses overestimate the global mean surface downward shortwave radiation and underestimate the surface downward longwave radiation by 3 - 7 Wm^-2. While reanalyses are of tremendous value as references for many atmospheric parameters, they may not yet be suited to serve as references for the magnitudes of the global mean radiation balance components.

Parts of the results of this study have been published in Wild, M. and Bosilovich, M., 2024: The Global Energy Balance as Represented in Atmospheric Reanalyses, Surveys in Geophysics, 45, 1799–1825. https://doi.org/10.1007/s10712-024-09861-9.