UC Berkeley

A number of key paleoclimate records in the Southern Hemisphere midlatitudes exhibit climate changes synchronous with abrupt climate changes in the North Atlantic. We advance a hypothesis - argued from consideration of model evidence, observational climate diagnostics, and atmospheric dynamics - that attributes said climate changes in the Southern Hemisphere to a modulation in the strength of the South Pacific Split Jet, a pronounced zonally asymmetric feature of the wintertime Southern Hemisphere westerlies. North Atlantic cooling is associated with a weaker Split Jet, characterized by weaker South Pacific subtropical and subpolar jets and a strengthened midlatitude jet. It leads to climate impacts over the South Pacific sector that coincides with regions with observed paleoclimate changes timed to the North Atlantic. These circulation changes are envisioned to operate in addition to the climate impacts resulting from the oceanic bipolar seesaw.A proposed global atmospheric teleconnection links North Atlantic cooling to the weakening of the Split Jet. North Atlantic cooling induces a southward shift of the marine Intertropical Convergence Zone and weakening of the Asian monsoon. The resulting Hadley circulation change weakens the wintertime South Pacific subtropical jet, and which in turn leads to a weaker South Pacific Split Jet. A weaker Split Jet leads to a southward shift of the zero wind-stress curl line, implying a shift in the same sense for the South Pacific subtropical front. Over land, it leads to winter warming over New Zealand, winter cooling over subtropical South America, drying over Western Patagonia, and winter warming and wetting of southernmost Patagonia. Our hypothesis also predicts reduced storminess over West Antarctica. Similar changes but of opposite sign occur in the Northern Hemisphere, where a stronger wintertime North Pacific subtropical jet increases precipitation over the Western United States.