North Atlantic Oscillation 1000 Year Model-Tested Reconstruction Ortega, P.; Lehner, F.; Swingedouw, D.; Masson-Delmotte, V.; Raible, C.C.; Casado, M.; Yiou, P. Ortega, P. Lehner, F. Swingedouw, D. Masson-Delmotte, V. Raible, C.C. Casado, M. Yiou, P. Atmospheric and Oceanic Circulation Patterns Reconstruction North Atlantic Oscillation earth science/paleoclimate/climate reconstructions (North Atlantic Oscillation Index,multiple proxies,two standard error upper bound,standard deviation unit,Dec-Feb,climate reconstructions,null,null,N,regression uncertainty as departure from the ensemble mean of 2 standard errors) earth science/paleoclimate/climate reconstructions (North Atlantic Oscillation Index,multiple proxies,two standard error lower bound,standard deviation unit,Dec-Feb,climate reconstructions,null,null,N,regression uncertainty as departure from the ensemble mean of -2 standard errors) earth science/paleoclimate/climate reconstructions (North Atlantic Oscillation Index,multiple proxies,null,standard deviation unit,Dec-Feb,climate reconstructions,null,null,N,ensemble of 100 model-constrained NAO reconstructions) earth science/paleoclimate/climate reconstructions (age,null,null,year Common Era,null,climate reconstructions,null,null,N,null) earth science/paleoclimate/climate reconstructions (North Atlantic Oscillation Index,multiple proxies,range lower bound,standard deviation unit,Dec-Feb,climate reconstructions,null,null,N,ensemble spread) earth science/paleoclimate/climate reconstructions (North Atlantic Oscillation Index,multiple proxies,range upper bound,standard deviation unit,Dec-Feb,climate reconstructions,null,null,N,ensemble spread) earth science/paleoclimate/reconstructions (Northern Hemisphere>LATITUDE >LONGITUDE ) The North Atlantic Oscillation (NAO) is the major source of variability in winter atmospheric circulation in the Northern Hemisphere, with large impacts on temperature, precipitation and storm tracks, and therefore also on strategic sectors such as insurance, renewable energy production, crop yields and water management. Recent developments in dynamical methods offer promise to improve seasonal NAO predictions, but assessing potential predictability on multi-annual timescales requires documentation of past low-frequency variability in the NAO. A recent bi-proxy NAO reconstruction spanning the past millennium suggested that long-lasting positive NAO conditions were established during medieval times, explaining the particularly warm conditions in Europe during this period; however, these conclusions are debated. Here, we present a yearly NAO reconstruction for the past millennium, based on an initial selection of 48 annually resolved proxy records distributed around the Atlantic Ocean and built through an ensemble of multivariate regressions. We validate the approach in six past-millennium climate simulations, and show that our reconstruction outperforms the bi-proxy index. The final reconstruction shows no persistent positive NAO during the medieval period, but suggests that positive phases were dominant during the thirteenth and fourteenth centuries. The reconstruction also reveals that a positive NAO emerges two years after strong volcanic eruptions, consistent with results obtained from models and satellite observations for the Mt Pinatubo eruption in the Philippines. STUDY NOTES: This is a new reconstruction of North Atlantic Oscillation evolution during the last millennium. It has been produced by generating an ensemble of 100 different multi-proxy reconstructions, each one calibrated over a different time period. In each case, the final selection of proxies is constrained through the use of reanalyses and last millennium model simulations. For additional information about the data and the methodology please refer to Ortega et al. 2015. Provided Keywords: Last millennium, North Atlantic Oscillation, Perfect Model Analysis NCDC-Paleoclimatology https://www.ncdc.noaa.gov/data-access/paleoclimatology-data - Bauer Bruce Investigator : Ortega, P. Investigator : Lehner, F. Investigator : Swingedouw, D. Investigator : Masson-Delmotte, V. Investigator : Raible, C.C. Investigator : Casado, M. Investigator : Yiou, P. 2015-07-02 ONLINE Files online, ASCII https://www.ncdc.noaa.gov/paleo/study/18935 https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/ortega2015/ortega2015nao.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/ortega2015/ortega2015nao.txt English https://www.ncdc.noaa.gov/paleo/study/18935 https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/ortega2015/ortega2015nao.txt Pablo Ortega, Flavio Lehner, Didier Swingedouw, Valerie Masson-Delmotte, Christoph C. Raible, Mathieu Casado, and Pascal Yiou 2015A model-tested North Atlantic Oscillation reconstruction for the past millenniumNature523755871-7410.1038/nature14518http://www.nature.com/nature/journal/v523/n7558/full/nature14518.html START YEAR: 1049 AD * END YEAR: 1969 AD -180 0 180 90