Importance of the Southern Ocean for translating the ozone hole influence from the stratosphere to the surface climate

The late 20th century was marked by a significant summertime climatic trend associated with poleward shifting of near-surface westerlies, which was attributed to downward translation of stratospheric changes induced by the Antarctic ozone depletion (so-called "ozone hole"). Still, dynamical processes involved in this downward translation remain to be understood.

Professor Hisashi Nakamura and Research Associate Kazuaki Nishii (Climate Science Research), jointly with Dr. Fumiaki Ogawa and his collaborators of University of Bergen (Norway), performed idealized numerical experiments with a state-of-the-art atmospheric model and analyzed the Intergovernmental Panel on Climate Change (IPCC) climate simulations, to reveal that frontal temperature gradients in the midlatitude Southern Oceans are critical for translating ozone-induced strengthening of stratospheric westerlies down to the surface. They have demonstrated that the oceanic temperature fronts energize cyclones and organize a tropospheric westerly jetstream in mid-latitudes, which allows effective connection between the dominant variability in the tropospheric and stratospheric westerly jetstreams. Thus, improved representation of the midlatitude oceanic fronts in global climate models can help reduce uncertainties in simulating the climate changes observed over the Southern Hemisphere and possible future changes due to ozone recovery.