Abstract
A prominent feature of recent climatic change is the strong Arctic surface warming that is contemporaneous with broad cooling over much of Antarctica and the Southern Ocean. Longer global surface temperature observations suggest that this contrasting pole-to-pole change could be a manifestation of a multi-decadal interhemispheric or bipolar seesaw pattern, which is well correlated with the North Atlantic sea surface temperature variability, and thus generally hypothesized to originate from Atlantic meridional overturning circulation oscillations. Here, we show that there is an atmospheric origin for this seesaw pattern. The results indicate that the Southern Ocean surface cooling (warming) associated with the seesaw pattern is attributable to the strengthening (weakening) of the Southern Hemisphere westerlies, which can be traced to Northern Hemisphere and tropical tropospheric warming (cooling). Antarctic ozone depletion has been suggested to be an important driving force behind the recently observed increase in the Southern Hemisphere's summer westerly winds; our results imply that Northern Hemisphere and tropical warming may have played a triggering role at an stage earlier than the first detectable Antarctic ozone depletion, and enhanced Antarctic ozone depletion through decreasing the lower stratospheric temperature.
Highlights
A prominent feature of recent climatic change is the strong Arctic surface warming that is contemporaneous with broad cooling over much of Antarctica and the Southern Ocean
Longer global surface temperature observations suggest that this contrasting pole-to-pole change could be a manifestation of a multi-decadal interhemispheric or bipolar seesaw pattern, which is well correlated with the North Atlantic sea surface temperature variability, and generally hypothesized to originate from Atlantic meridional overturning circulation oscillations
The results indicate that the Southern Ocean surface cooling associated with the seesaw pattern is attributable to the strengthening of the Southern Hemisphere westerlies, which can be traced to Northern Hemisphere and tropical tropospheric warming
Summary
Robustness of the multi-decadal bipolar seesaw after 1950. To enhance credibility in our examination of interhemispheric or bipolar seesaw robustness, we employed two state-of-the-art compilations of SST data, including the Extended Reconstructed SST v3b7 (ERSSTV3b; no satellite data are used in this version) and the Hadley Centre Global SST (HadISST) data[8] to derive decadal-scale linear trends in annual mean global SSTs. ERA-40 data are available from September 1957 to August 2002, covering a cooling period (before roughly 1970) and a warming period, permitting analysis of concurrent changes in global temperatures at different levels of the atmosphere for the periods with opposite surface temperature changes We highlight those temperature changes that are consistent with surface temperature changes and relevant to multi-decadal SAM variability. The second feature, characterized by amplified tropical-upper tropospheric warming due to increased latent heat release through enhanced moist convection[19,28,31,32], indicates an increased equator-to-pole temperature gradient in the SH upper troposphere/lower stratosphere, leading to a strengthened upper-layer mid-latitude eastward wind[19,31,32] This increased midlatitude upper-layer wind is known to increase the eastward propagation speed of the mid-latitude eddies, which pushes the wave-breaking region and the eddy-driven jet poleward[33]. Long-term sustained monitoring of AMOC in the North Atlantic, which is currently being undertaken (see http://www.noc.soton.ac.uk/rapidmoc/), is important for understanding the combined effects of atmospheric and oceanic circulation changes on multi-decadal climate variability
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