AGU: Geophysical Research Letters

 

Editors' Highlight

Human-generated aerosols affect atmospheric circulation trends in the Southern Hemisphere

Though most human-generated aerosols reside in the Northern Hemisphere, a recent model study shows that in response to rising aerosol concentrations, the Southern Hemisphere's ocean circulation, including retroflecting eddies and the entire subtropical gyre, intensifies and shifts poleward. Cai and Cowen (2007) sought to determine if these ocean responses also manifest in the Southern Hemisphere's atmospheric circulation. Through analyzing data from two sets of 20th century simulations in a coupled ocean-atmosphere global climate model, the authors found that as a result of the poleward shift in oceanic circulation, maximum sea surface temperatures, midlatitude storms, and the westerly jet shift southward. This shift in air circulation intensifies the trend of the Southern Annular Mode, a low-frequency pattern of atmospheric variability near Antarctica, causing a poleward shift and intensification in zonal wind and vertical velocities generated from the atmosphere-ocean interface to the middle of the troposphere. These atmospheric circulation responses, in turn, reinforce the ocean circulation changes. Thus, the authors suggested a contribution by human-generated aerosols to the observed trend of the Southern Annular Mode.

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