The Impact of the AMO on the Tropical Pacific

Seminar by Aaron Levine from University of Washington

28 November 2019
14:00 - 15:00

The Seminar is being held in Room 1010 (Jasmin) - Intergrated mechanical engineering building. Click here for the campus map.

The Atlantic multidecadal oscillation (AMO) has been shown to play a major role in the multidecadal variability of the Northern Hemisphere, impacting temperature and precipitation, including intertropical convergence zone (ITCZ)-driven precipitation across Africa and South America. Studies into the location of the intertropical convergence zone have suggested that it resides in the warmer hemisphere, with the poleward branch of the Hadley cell acting to transport energy from the warmer hemisphere to the cooler one. Given the impact of the Atlantic multidecadal oscillation on Northern Hemisphere temperatures, we expect the Atlantic multidecadal oscillation to have an impact on the location of the intertropical convergence zone. We find that the positive phase of the Atlantic multidecadal oscillation warms the Northern Hemisphere, resulting in a northward shift of the intertropical convergence zone, which is evident in the Pacific climate proxy record. Using a coupled climate model, we find that the Pacific changes are driven in large part by the warming of the tropical Atlantic and not the extratropical Atlantic.

Given the known record of multidecadal ENSO variability and the sensitivity of ENSO to the tropical Pacific mean state, we explore the role of the AMO on the multidecadal variability of ENSO.  We find a strong influence of the Atlantic on the multidecadal variability of ENSO.  Changes in AMO-related tropical Atlantic SSTs are known to force changes in the Walker circulation in the tropical Pacific Ocean. Using conceptual and coupled model experiments, we show that these changes to the Walker circulation modify ENSO stability on both annual and multidecadal time scales leading to a distinctive pattern of multidecadal ENSO variability that we find in observations and ocean reanalyses.

Finally, recent research has suggested that the weakening of the Walker Circulation and its poor replication in coupled climate models is related to the SSTs in the tropical Atlantic.  We will explore the connection between the AMO influence on the tropical Pacific mean state and on ENSO and the recent trends in the Walker circulation and their representation in climate models.