Southward displacement of the upper atmosphere zonal jet in the eastern north Pacific due to global warming

Abstract

The jet stream over the eastern North Pacific (ENPJ) as a core of the atmospheric flow is known to strongly fluctuate meridionally, and its meridional displacement directly influences adjacent regional climate. Here, we investigate how this jet will be changed due to global warming. By analyzing the future scenario experiments of Climate Model Intercomparion Project Phase III (CMIP3) and Phase V (5), it was found that both ENPJ and the eastern tropical Pacific intertropical convergence zone (ITCZ) tend to move southward, which are closely related to the tropical eastern Pacific warming trend. Tropical eastern Pacific warming leads to not only the southward migration of ITCZ by southward-shifting the off-equatorial eastern Pacific warm pool, but also the southward shift of ENPJ by increasing baroclinic instability of the atmosphere in subtropical region through intensifying the meridional sea surface temperature (SST) gradient. Not primary but yet secondly the southward shift of ITCZ contributes to the southward shift of ENPJ through a kinematic connection bridged by local Hadley circulation.