A study recently published in the Journal of Climate emphasizes the importance of the North Atlantic Ocean for Atlantic Multidecadal Variability (AMV), which can lead to improved rainfall predictions in the United States and other parts of the globe.
Using the GFDL CM2.1 and the NCAR CESM1 coupled climate models, CPO-supported researchers show how the AMV leads to precipitation anomalies in the tropics. For example, warmer phases of the AMV lead to reduced rainfall in west United States.
This mode of decadal variability is important to understand because it could improve skill in precipitation predictions.
The study was supported by the CPO Climate Variability and Predictability program.
Read the paper:
Ruprich-Robert, Y., R. Msadek, F. Castruccio, S. Yeager, T. Delworth, and G. Danabasoglu, 2017: Assessing the Climate Impacts of the Observed Atlantic Multidecadal Variability Using the GFDL CM2.1 and NCAR CESM1 Global Coupled Models. J. Climate, 30, 2785–2810, doi: 10.1175/JCLI-D-16-0127.1.
The climate impacts of the observed Atlantic multidecadal variability (AMV) are investigated using the GFDL CM2.1 and the NCAR CESM1 coupled climate models. The model North Atlantic sea surface temperatures are restored to fixed anomalies corresponding to an estimate of the internally driven component of the observed AMV. Both models show that during boreal summer the AMV alters the Walker circulation and generates precipitation anomalies over the whole tropical belt. A warm phase of the AMV yields reduced precipitation over the western United States, drier conditions over the Mediterranean basin, and wetter conditions over northern Europe. During boreal winter, the AMV modulates by a factor of about 2 the frequency of occurrence of El Niño and La Niña events. This response is associated with anomalies over the Pacific that project onto the interdecadal Pacific oscillation pattern (i.e., Pacific decadal oscillation–like anomalies in the Northern Hemisphere and a symmetrical pattern in the Southern Hemisphere). This winter response is a lagged adjustment of the Pacific Ocean to the AMV forcing in summer. Most of the simulated global-scale impacts are driven by the tropical part of the AMV, except for the winter North Atlantic Oscillation–like response over the North Atlantic–European region, which is driven by both the subpolar and tropical parts of the AMV. The teleconnections between the Pacific and Atlantic basins alter the direct North Atlantic local response to the AMV, which highlights the importance of using a global coupled framework to investigate the climate impacts of the AMV. The similarity of the two model responses gives confidence that impacts described in this paper are robust.