PNNL

Abstract

Despite its significant socio-economic impacts, the reliable simulation, prediction, and complete theoretical understanding of atmospheric blocking remain a great challenge. Generations of climate models have notoriously underestimated blocking frequency, particularly over the Euro-Atlantic sector. Understanding the factors controlling blocking frequency and dynamics is crucial for improving simulation accuracy and advancing our knowledge of the underlying physical processes. Here, we present new evidence unveiling the previously unknown impact of cloud radiative effects (CREs) --- the radiative heating resulting from the presence of clouds --- on blocking. Using a cloud-locking technique in the U.S. DOE’s Energy Exascale Earth System Model, we find that CREs significantly increase the formation of Euro-Atlantic blocking. Supported by the finite-amplitude local wave activity (LWA) budget analysis, the interactive CREs increase LWA mainly by enhancing diabatic source of wave activity upstream of the block region, feeding to the development of the blocks downstream. Qualitatively similar results are obtained when analyzing multi-model experiments that make clouds transparent (radiatively inactive) to longwave radiation, albeit with a larger impact due to changes in the mean state. This study underscores the necessity of correctly representing CREs in weather and climate models to accurately simulate and predict blocking events.