Poleward expansion of the hadley circulation in CMIP5 simulations

Observational analyses have demonstrated that the Hadley circulation has expanded poleward in recent decades. Important issues are what caused the widening of the Hadley circulation and whether the observed widening is related to anthropogenic forcing. In the present study, we use currently available simulations of the Coupled Model Intercomparison Project Phase-5 (CMIP5) to analyze changes in the width of the Hadley circulation. It is found that CMIP5 historical simulations with greenhouse gas (GHG) forcing generate a total widening of similar to 0.15A degrees A +/- 0.06A degrees in latitude (10 yr)(-1) for the period 1979-2005, and the widening in CMIP5 historical simulations with all forcings is similar to 0.17A degrees +/- 0.06A degrees per decade. Similar to that in CMIP3, the simulated poleward expansion in CMIP5 is much weaker than the observational reanalyses. In CMIP5 projection simulations for the 21st century, magnitudes of widening of the Hadley circulation increase with radiative forcing. For the extreme projected radiative forcing of RCP8.5, the total annual-mean widening of the Hadley circulation is similar to 0.27A degrees +/- 0.04A degrees (10 yr)(-1) in the 21st century. Although CMIP5 underestimates observed poleward expansion of the Hadley circulation, the results of this study suggest that the observed trends in the width of the Hadley circulation are caused by anthropogenic forcing and that increasing GHGs play an important role in the observed poleward expansion of the Hadley circulation, in addition to other forcings emphasized in previous studies.Meteorology & Atmospheric SciencesSCI(E)中国科技核心期刊(ISTIC)中国科学引文数据库(CSCD)8ARTICLE3790-7953