Wider impacts of Subpolar North Atlantic decadal variability on the ocean and atmosphere (WISHBONE)

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The Subpolar North Atlantic (SNA), which is the region of the Atlantic Ocean between 45-65N latitude, is a highly variable region. Surface temperatures and surface salinity here have varied on a range of time-scales, but the changes are dominated by large and slow changes on decadal or longer timescales. This decadal timescale variability appears to form a key component of a larger climate mode, the Atlantic Multidecadal Variability, which has been linked to a broad range of important climate impacts, including rainfall in the North African and south Asian monsoons, floods and droughts over Europe and North America, and the number of hurricanes. The SNA is also one of the most predictable places on Earth at decadal timescales, which suggests the potential for improved predictions of regional climate and high-impact weather years ahead. However, the origins of this variability in the SNA, and the processes controlling its impacts, are far from fully understood. There is significant evidence to suggest that anomalous heat loss from the subpolar North Atlantic Ocean to the atmosphere can instigate a cascade of changes across the North Atlantic basin in both the ocean and atmosphere. For example, changes in the SNA can change the strength of the ocean circulation to the south, affect the northward transport of heat and freshwater in the North Atlantic, and subsequently affect the upper ocean temperatures and salinity across the whole North Atlantic basin, and into the Arctic. Changes in the subpolar North Atlantic surface temperature are also thought to affect the atmospheric circulation - i.e. wind patterns - in both summer and winter. However, observational records are very short, and so there are significant problems with understanding causality, and considerable uncertainty about how well many of the important processes are represented in current climate models. WISHBONE will make use of new advanced climate simulations and forecast systems to make progress in understanding the impact of the subpolar North Atlantic on the wider North Atlantic basin. It will also test specific hypotheses related to understanding the specific role of heat loss over the subpolar North Atlantic in driving changes throughout the basin including the role of surface anomalies in driving wind patterns. WISHBONE is a collaboration between the National Centre for Atmospheric Science at the University of Reading, The National Oceanography Centre Southampton, The University of Oxford, and The University of Southampton from the U.K., and The National Center for Atmospheric Research, from the U.S.