Simulated variability in the mean atmospheric meridional circulation over the 20th century

The variability in the zonally averaged atmospheric meridional circulation over the last 150 years is investigated using two atmospheric general circulation models (GCMs). A multi-decadal signal, with an approximately 70 year timescale, is identified in the cross-equatorial circulation. This signal is associated with a latitudinal shift in the ascending branch of the Hadley cell and precipitation in the tropics, as well as a change in the atmospheric meridional heat transport. These changes are well-correlated with the inter-hemispheric SST difference: When Northern Hemisphere sea surface temperatures (SSTs) are colder than the Southern Hemisphere, the ITCZ and precipitation shift to the south in a zonal mean sense, and the northward atmospheric energy transport increases. Previous studies with idealized climate forcings have shown similar results, but the findings presented here highlight the potential relevance of the inter-hemispheric SST contrast for understanding 20th century climate changes. Citation: Mantsis, D. F., and A. C. Clement (2009), Simulated variability in the mean atmospheric meridional circulation over the 20th century, Geophys. Res. Lett., 36, L06704, doi: 10.1029/2008GL036741.