Recent poleward shift of tropical cyclone formation linked to Hadley cell expansion

Abstract

Recent research indicates that the annual-mean locations of tropical cyclones have migrated toward higher latitudes. Concurrently, an anthropogenically forced tropical expansion has been observed, yet the connection between the two processes remains little-explored. Here, using observational and reanalysis data, we investigate how large-scale dynamical effects, combined with coherent changes in the regional Hadley circulation, explain recent changes in regional tropical cyclone genesis over 1980–2014. We show that the recent anomalous upper-level weakening of the rising branch of the Hadley circulation in the deep tropics, possibly induced by the increased vertical stability, has likely suppressed the low-latitude tropical cyclone genesis in most ocean basins via anomalous large-scale subsidence. Regional Hadley circulation variations have also favoured a poleward displacement of tropical-cyclone-favourable climate conditions through poleward shift of the Hadley circulation’s meridional extent. With projections indicating continued tropical expansion, these results indicate that tropical cyclone genesis will also continue to shift poleward, potentially increasing tropical-cyclone-related hazards in higher-latitude regions.