edu.ucar.opensky::articles:23863 UCAR/NCAR - Library OpenSky Support PO Box 3000 Boulder CO 80307-3000 opensky@ucar.edu http://opensky.ucar.edu/ homepage pointOfContact 2025-12-25T06:40:49.129721 ISO 19115-2 Geographic Information - Metadata - Part 2: Extensions for Imagery and Gridded Data ISO 19115-2:2009(E) https://n2t.org/ark:/85065/d7765jnd Attribution of NAO predictive skill beyond 2 weeks in boreal winter 2020-11-28T00:00:00Z publication https://n2t.org/ark:/85065/d7765jnd https://doi.org/10.1029/2020GL090451 Sun, L. author Perlwitz, J. author Richter, Jadwiga H. author Hoerling, M. P. author Hurrell, J. W. author UCAR/NCAR - Library publisher Weeks 3-6 averaged winter North Atlantic Oscillation (NAO) predictive skill in a state-of-the-art coupled climate prediction system is attributed to two principle sources: upper and lower boundary conditions linked to the stratosphere and El Nino-Southern Oscillation (ENSO), respectively. A 20-member ensemble of 45-day reforecasts over 1999-2015 is utilized, together with uninitialized simulations with the atmospheric component of the prediction system forced with observed radiative forcing and lower boundary conditions. NAO forecast skill for lead times out to 6 weeks is higher following extreme stratospheric polar vortex conditions (weak and strong vortex events) compared to neutral states. Enhanced weeks 3-6 NAO predictive skill for weak vortex events results primarily from stratospheric downward coupling to the troposphere, while enhanced skill for strong vortex events can be partly attributed to lower boundary forcing related to the ENSO phenomenon. Implications for forecast system development and improvement are discussed. UCAR/NCAR - Library OpenSky Support PO Box 3000 Boulder CO 80307-3000 opensky@ucar.edu http://opensky.ucar.edu/ homepage pointOfContact PDF Text theme Resource Type 2016-01-01T00:00:00Z publication Copyright 2020 American Geophysical Union. None eng geoscientificInformation