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Tropical Expansion Driven by Poleward Advancing Midlatitude Meridional Temperature Gradients
Author(s) -
Yang Hu,
Lohmann Gerrit,
Lu Jian,
Gowan Evan J.,
Shi Xiaoxu,
Liu Jiping,
Wang Qiang
Publication year - 2020
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1029/2020jd033158
Subject(s) - climatology , subtropics , middle latitudes , tropics , zonal and meridional , sea surface temperature , global warming , coupled model intercomparison project , convergence zone , southern hemisphere , temperate climate , environmental science , climate model , atmospheric sciences , geology , climate change , oceanography , ecology , biology
Abstract An abundance of evidence indicates that the tropics are expanding. Despite many attempts to decipher the cause, the underlying dynamical mechanism driving tropical expansion is still not entirely clear. Here, based on observations, multimodel simulations from the Coupled Model Intercomparison Project phase 5 (CMIP5) and purposefully designed numerical experiments, the variations and trends of the tropical width are explored from a regional perspective. We find that the width of the tropics closely follows the displacement of oceanic midlatitude meridional temperature gradients (MMTG). Under global warming, as a first‐order response, the subtropical ocean experiences more surface warming because of the mean Ekman convergence of anomalously warm water. The enhanced subtropical warming, which is partially independent of natural climate oscillations, such as the Pacific Decadal Oscillation, leads to poleward advance of the MMTG and drives the tropical expansion. Our results, supported by both observations and model simulations, imply that global warming may have already significantly contributed to the ongoing tropical expansion, especially over the ocean‐dominant Southern Hemisphere.