Collapses of Hemispheric Available Potential Energy

Abstract The atmospheric circulation in the midlatitudes is maintained against dissipation by converting available potential energy (APE) into kinetic energy (KE). During boreal winter this energy reservoir occasionally collapses, releasing up to 10% of hemispheric APE within days. Using the ERA5 reanalysis and a locally defined APE framework, we identify 83 such collapse events and show that most of them arise from intense conversion within a single storm track. These events are driven by the export of Arctic APE into the storm tracks along two main pathways and are accompanied by explosive cyclones, extreme surface winds, and continental cold‐air outbreaks. The amplification of synoptic‐ and planetary‐scale KE, accompanied by a weakening of the zonal mean KE, reveals a reorganization of the midlatitude circulation during APE collapses. These results show that sudden Arctic energy exports can cascade through the midlatitudes, fueling extreme storms, surface wind events and large‐scale variability.