Mechanisms of Decadal Climate Variability Associated with the Atlantic Meridional Overturning Circulation

• Main Author: Replogle, Lauren Elaine
• Other Authors: Giese, Benjamin, Chang, Ping, Mask, Andrea
• Format: Thesis
• Language: English
• Published: 2019
• Subjects: physical oceanography; circulations; climate variability; Pacific; North Atlantic; North Atlantic oscillation
• Online Access: https://hdl.handle.net/1969.1/174170

To further identify physical mechanisms responsible for decadal climate variability, a combination of ocean reanalyses and coupled climate models were used. A pronounced trend is observed in the first EOF of SST that exhibits a spatial pattern of increasing global temperatures. An analysis of SST, the atmospheric meridional mass streamfunction, and precipitation minus evaporation illustrates a weakening Hadley circulation consisting of an expanded Northern Hemisphere Hadley cell, contracted Southern Hemisphere Hadley cell, and strong Southern Hemisphere Ferrell cell. There is also pronounced decadal variability that exhibits a prominent meridional and latitudinal temperature structure, an expanded Southern Hemisphere Hadley cell, and a poleward shift of the Northern Hemisphere Hadley circulation. This variability resembles a La Niña-like pattern that occurs in both the reanalysis, and the coupled model. As a consequence of tropical Pacific temperature variability, the Hadley circulation influences extratropical atmospheric circulation in the North Pacific and Atlantic Oceans via an atmospheric teleconnection. A correlation analysis shows a connection between the North Atlantic Oscillation Index and tropical Pacific Ocean temperature, with the Pacific Ocean SST leading by 19 months. North Atlantic related wind patterns force buoyancy changes in deep water formation regions and wave propagations along the western boundary of the North Atlantic Ocean. Thus, it is proposed that SST in the tropical Pacific Ocean forces atmospheric circulations in the North Atlantic Ocean that influence decadal variability in North Atlantic circulations.