Winter North Atlantic Oscillation Index Reconstruction from Tree-Rings since 910 C.E. Cook, E.R.; Kushnir, Y.; Smerdon, J.E.; Williams, A.P.; Anchukaitis, K.J.; Wahl, E.R. Cook, E.R. Kushnir, Y. Smerdon, J.E. Williams, A.P. Anchukaitis, K.J. Wahl, E.R. Atmospheric and Oceanic Circulation Patterns Reconstruction earth science/paleoclimate/reconstructions (North Atlantic Oscillation>LATITUDE >LONGITUDE ) We develop a new reconstruction of the winter North Atlantic Oscillation (NAO) index using a network of 97 Euro-Mediterranean tree-ring series. The reconstruction covers the period 910-2018 C.E., making it the longest annually resolved estimate of winter NAO variability available. We use nested correlation-weighted principal components regression and the Maximum Entropy Bootstrap method to generate a 2400-member ensemble of reconstructions for estimating the final reconstruction and its quantile uncertainties. Extensive validation testing of the new reconstruction against data withheld from the calibration exercise demonstrates its skill. The skill level of the new reconstruction is also an improvement over two NAO reconstructions published earlier. Spectral analyses indicate that the new reconstruction behaves like a "white noise" process with intermittent band-limited power, suggesting that the winter NAO is stochastically forced. The "white noise" properties of our reconstruction are also shown to be consistent with the spectral properties of long instrumental NAO indices extending back to 1781 and NAO indices extracted from a large number of forced climate model runs covering the last millennium. In contrast, an annually resolved multi-proxy NAO reconstruction of comparable length, based in part on speleothem data, behaves more like externally forced "red noise" process, which is inconsistent with our reconstruction, long observations, and forced model runs. STUDY NOTES: In the NAO reconstruction data table, -05%CL is an amount to be subtracted from the median and +95%CL is an amount to be added to the median. NCDC-Paleoclimatology https://www.ncdc.noaa.gov/data-access/paleoclimatology-data - Bauer Bruce Investigator : Cook, E.R. Investigator : Kushnir, Y. Investigator : Smerdon, J.E. Investigator : Williams, A.P. Investigator : Anchukaitis, K.J. Investigator : Wahl, E.R. 2019-05-14 ONLINE Files online, ASCII https://www.ncdc.noaa.gov/paleo/study/26810 https://www1.ncdc.noaa.gov/pub/data/paleo/reconstructions/cook2019/cook2019-ensemble.txt https://www1.ncdc.noaa.gov/pub/data/paleo/reconstructions/cook2019/cook2019-nao.txt https://www1.ncdc.noaa.gov/pub/data/paleo/reconstructions/cook2019/cook2019-ensemble.txt https://www1.ncdc.noaa.gov/pub/data/paleo/reconstructions/cook2019/cook2019-nao.txt English https://www.ncdc.noaa.gov/paleo/study/26810 https://www1.ncdc.noaa.gov/pub/data/paleo/reconstructions/cook2019/cook2019-ensemble.txt https://www1.ncdc.noaa.gov/pub/data/paleo/reconstructions/cook2019/cook2019-nao.txt Cook, Edward R., Yochanan Kushnir, Jason E. Smerdon, A. Park Williams, Kevin J. Anchukaitis, and Eugene R. Wahl2019A Euro-Mediterranean tree-ring reconstruction of the winter NAO index since 910 C.E.Climate Dynamics10.1007/s00382-019-04696-2 Jones, P. , Davies, T. , Lister, D. , Slonosky, V. , Jónsson, T., Bärring, L., Jönsson, P. , Maheras, P. , Kolyva-Machera, F. , Barriendos, M. , Martin-Vide, J. , Rodriguez, R. , Alcoforado, M. , Wanner, H. , Pfister, C. , Luterbacher, J. , Rickli, R. , Schuepbach, E. , Kaas, E. , Schmith, T. , Jacobeit, J. and Beck, C.1999Monthly mean pressure reconstructions for Europe for the 1780-1995 periodInternational Journal of Climatology10.1002/(SICI)1097-0088(19990330)19:4<347::AID-JOC363>3.0.CO START YEAR: 910 AD * END YEAR: 2018 AD -50 38 -10 65