The role of Earth’s major cloud systems in the hemispheric albedo symmetry

We conduct an in-depth investigation of the role of major climatological cloud systems in the well-known near symmetry at multi-annual scales between the Northern and Southern hemisphere reflected solar radiation (RSR). Here we quantify the degree of symmetry for the entirety of a recent 22-year period, while also analyzing how its interannual variability is modulated by cloud systems which we have previously termed “regimes of regimes” or RORs. By pairing RORs with monthly RSR values from the CERES EBAF dataset we elucidate how several large RSR asymmetries at the ROR level, mainly due to strong ROR hemispheric population contrasts, combine in a compensatory way to produce near-symmetry at the hemispheric level. We also investigate how interannual variations of small RSR asymmetries relate to interannual asymmetry variations at the ROR level, which we also find to be mainly because of trends in ROR populations. Overall, we find statistically significant darkening in both hemispheres, but have lower confidence in the darkening’s hemispheric contrast. Finally, we probe the role of the complementary symmetry in absorbed solar radiation (ASR), and specifically of its atmospheric component, in the broader context of hemispheric energetics. Our analysis sheds light on the role of major global cloud systems in modulating the mean state and variability of the equitable contribution of the two hemispheres to the global RSR.