Synchronized Heat Extremes in the Northern Hemisphere Based on a Complex Network

Abstract

Heat extremes occurring synchronously in multiple regions often result in more severe impacts than isolated heat events. Here we analyze observational and reanalysis data to objectively detect and examine the synchronization of heat extremes in the Northern Hemisphere and identify the regions that have remote linkages, particularly in western Europe (WEU), western North America (WNA) and the Yangtze-Huai River Basin (YHRB). The results indicate that the intensity and frequency of synchronized heat extremes show increasing trends during 1979–2023 summer, with most events occurring in the past 20 years. The synchronized heat extremes are triggered by a quasi-stationary Rossby wave with wavenumber 6, resembling a circum-global teleconnection (CGT)-like pattern along the subtropical jet. While large-scale atmospheric circulation provides a common dynamical background, the sustaining mechanisms differ across regions. Land-atmosphere interactions and surface processes jointly reinforce the persistence of synchronized heat extremes, providing new insights on compound event analysis.