On the role of extratropical ocean circulation in the tropical-extratropical and interhemispheric interaction


This study shows that interhemispheric MOC asymmetry causing interhemispheric asymmetry in extratropical surface ocean heat exchange can control aspects of the tropical circulation and the position of ITCZ. We aim to further understanding of key teleconnection mechanisms hence we employ an intermediate complexity coupled climate model derived from GFDL CM2.0 through a set of modular simplifications in sector geometry.

A symmetric configuration with closed rectangular ocean randomly places the dominant source of deep water and heat release in one hemisphere. The advective and convective feedbacks in extratropical ocean cause this unforced hemispheric symmetry breaking that leads to positioning of ITCZ in the MOC dominant hemisphere. Sudden opening of circumpolar channel in subpolar region reduced ocean heat release there due to decrease of poleward salinity and heat transport. This forced hemispheric symmetry breaking moves the dominant region of deep-water production and heat release to opposite hemisphere that causes parallel shift of ITCZ across the equator.

Overall, in this simplified coupled system, ITCZ is always downstream (upstream) of the cross-equatorial OHT (AHT) controlled by interhemispheric asymmetry in extratropical ocean circulation and surface heat exchange. The result will hopefully spur further analysis of remote influence of the Southern Ocean, the North Atlantic and the North Pacific on the position of ITCZ around the globe in a hierarchy of models with different levels of complexity.