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  • Vecchi, G.A., and B.J. Soden, 2007: Global Warming and the Weakening of the Tropical Circulation. J. Climate. In press.

This study examines the response of the tropical atmospheric and oceanic circulation to increasing greenhouse gases using a coordinated set of 21st Century climate model experiments performed for the Intergovernmental Panel on Climate Change’s 4th Assessment Report (IPCC-AR4). The strength of the atmospheric overturning circulation decreases as the climate warms inall IPCC-AR4 models, in a manner consistent with the thermodynamic scaling arguments of Held and Soden (2006). The weakening occurs preferentially in the zonally-asymmetric (i.e., Walker) rather than zonal-mean (i.e., Hadley) component of the tropical circulation and is shown to induce substantial changes to the thermal structure and circulation of the tropical oceans. Evidence suggests that the overall circulation weakens by decreasing the frequency of strong updrafts and increasing the frequency of weak updrafts; although the robustness of this behavior across all models cannot be confirmed due to lack of data. As the climate warms, changes in both the atmospheric and ocean circulation over the tropical Pacific Ocean resemble “El Niño-like” conditions; however, the mechanisms are shown to be distinct from those of El Niño and are reproduced in both mixed-layer and full ocean dynamics coupled climate models. The character of the Indian Ocean response to global warming resembles that of Indian Ocean Dipole Mode events. The consensus of model results presented here are also consistent with recently-detected changes in sea level pressure since the mid-19thCentury.

Full Article: http://www.gfdl.noaa.gov/~gav/REPRINTS/VS_07_GWnCIRC.final.pdf

Last Updated: 2007-04-12

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