UC Berkeley

Abstract Previous studies have shown that the extratropical-to-tropical teleconnection exhibits seasonal dependence, but the underlying mechanisms remain unclear. In this study, we use an idealized framework to explore the teleconnection and its underlying dynamics. We impose extratropical thermal warming in an aquaplanet model coupled to a mixed layered ocean under two idealized control climates: a perpetual winter-like climate and a perpetual summer-like climate. The extratropical-to-tropical teleconnection is more pronounced in the perpetual summer-like case, primarily due to differences in eddy momentum flux behavior. The unstable environment in the summer-like climate leads to vertically extended warming, which suppresses baroclinicity effectively and results in a subtropical eddy momentum flux convergence anomaly. This in turn drives adjustments in the Hadley cell. Moreover, the summer-like climatological Hadley cell is in a regime that responds effectively to anomalous eddy momentum flux. The anomalous eddy momentum flux convergence weakens the Hadley cell, triggering air–sea interactions and bringing the extratropical influence to the deep tropics. The strong mean-state dependence of the extratropical-to-tropical teleconnection provides insight into the atmospheric response to more realistic extratropical forcings, such as volcano eruptions, ozone depletion, and aerosol emission.