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The Atlantic Multidecadal Oscillation: Key Drivers and Climate Impacts

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University Grant
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Atlantic Multidecadal Variability (AMV), the leading mode of low-frequency, sea-surface temperature (SST) variability in the Atlantic Ocean, has been shown to impact a wide spectrum of earth systems ranging from Atlantic hurricanes to fish distribution. Given its inherent scientific value as well as its enormous socio-economic implications, it is in great demand to enhance process-level understanding of the AMV—also called the Atlantic Multidecadal Oscillation, AMO—and to identify its predictability. However, the effort towards this end has been challenging primarily due to the multidecadal time scale and the intricate interactions among various subcomponents of the climate system involved in the AMV, not to mention the limited observation—the key bottleneck for advancing the understanding. Some studies identify the ocean circulation, primarily the Atlantic meridional overturning circulation, as the main driver of the AMV, while others argue that the AMV is predominantly driven by random atmospheric noise. Aerosol or solar radiative forcing has also been suggested as the key driver of the AMV. These different views imply not only very different physical processes, but also drastically different predictive skills of the AMV and its impact. For example, the Atlantic meridional overturning circulation is deemed to be the most predictable source of the decadal variability, while predictability arising from random atmospheric noise is very limited.

The AMV is primarily considered as a mode of internal climate variability stemming from coupled ocean-atmosphere interaction, which may evolve as the climate changes. However, external radiative forcings are also likely to contribute to the multidecadal SST variability, and they must be distinguished from the natural AMV variability. Some of the previous inferences on the role of the external forcing were highly dependent on the choice of model, suggesting a multi-model approach to properly advance understanding. Importantly, these key drivers co-exist, and their roles are not mutually exclusive. Instead, they are timescale-dependent and geographically varying, with feedbacks between different drivers. Therefore, a systematic modeling approach is needed to quantify the relative importance of different AMV drivers, to understand the feedback between them, to clearly identify AMV impacts, and to assess its future evolution as the climate system changes.

Scientists will investigate the AMV using a hierarchical modeling framework to advance process level understanding on the respective roles of, and the feedback between, the key drivers of the AMV, in particular the ocean circulation associated with the Atlantic meridional overturning circulation and random atmospheric noise, which is primarily due to the variability of the North Atlantic Oscillation. The focus will be primarily on the AMV due to natural variability, but the investigation will be extended to the possible modulation of the main characteristics of the AMV under external climate forcing. Furthermore, the impact of the AMV will be examined, with a special emphasis on the possible augmentation of predictability that the AMV may bring to the regional weather and climate of North America, Western Europe, and the Arctic. Based on the improved dynamical understanding of the key drivers and impacts of AMV, a set of metrics for the AMV will be developed to assess the DOE’s E3SM v.1 among the latest generation of earth system models.

A kick-off meeting will be held on February 1, 2019.

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