EGUsphere EGUsphere EGUsphere EGUsphere Copernicus Publications Göttingen, Germany 10.5194/egusphere-2026-1165 Experiment design, nudging protocol, and models participating in Phase 2 of the APARC Quasi-Biennial Oscillation initiative (QBOi) Anstey James A. 1 Butchart Neal 2 Osprey Scott https://orcid.org/0000-0002-8751-1211 3 Kawatani Yoshio https://orcid.org/0000-0003-3260-8830 4 Hamilton Kevin https://orcid.org/0000-0002-3560-8097 5 Richter Jadwiga H. 6 Stockdale Tim 7 Andrews Martin B. 2 Chai Zhaoyang https://orcid.org/0000-0002-8064-9066 8 Davini Paolo https://orcid.org/0000-0003-3389-7849 9 Hong Dong-Chan 10 Huang Kai 6 Jaison Aleena M. 3 Kerzenmacher Tobias https://orcid.org/0000-0001-8413-0539 11 Knight Jeff R. 2 Lin Pu https://orcid.org/0000-0003-2577-6094 12 Lott Francois https://orcid.org/0000-0003-2126-5510 13 Lu Yixiong https://orcid.org/0000-0001-9823-9367 14 Naoe Hiroaki https://orcid.org/0000-0002-6261-0854 15 Serva Federico https://orcid.org/0000-0002-7118-0817 16 Simpson Isla 6 Son Seok-Woo https://orcid.org/0000-0003-2982-9501 10 Tang Qi https://orcid.org/0000-0003-2959-0203 17 Watanabe Shingo 18 19 Xie Jinbo https://orcid.org/0000-0002-3003-9155 17 20 Yoshida Kohei https://orcid.org/0000-0002-2422-5584 15 Canadian Centre for Climate Modelling and Analysis (CCCma), Victoria, Canada Met Office Hadley Centre (MOHC), Exeter, UK National Centre for Atmospheric Science (NCAS), University of Oxford, Oxford, UK Faculty of Environmental Earth Science, Hokkaido University, Sapporo, Japan International Pacific Research Center (IPRC), Honolulu, USA National Center for Atmospheric Research (NCAR), Boulder, USA European Centre for Medium-Range Weather Forecasts (ECMWF), Reading, UK Institute of Atmospheric Physics, Chinese Academy of Sciences (CAS), Beijing, China Institute of Atmospheric Sciences and Climate, National Research Council (CNR-ISAC), Torino, Italy School of Earth and Environmental Sciences, Seoul National University, Seoul, 08826, Korea Karlsruher Institut für Technologie (KIT), Karlsruhe, Germany Atmospheric and Oceanic Sciences, Princeton University, Princeton, USA Laboratoire de Météorologie Dynamique (LMD), Paris, France Earth System Modeling and Prediction Centre, China Meteorological Administration (CMA), Beijing, China Meteorological Research Institute (MRI), Tsukuba, Japan Institute of Marine Sciences, National Research Council (CNR-ISMAR), Rome, Italy Lawrence Livermore National Laboratory, Livermore, CA, USA Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokohama, Japan Advanced Institute for Marine Ecosystem Change, WPI-AIMEC, Tohoku University, Sendai, Japan High Meadows Environmental Institute (HMEI), Princeton University, Princeton, NJ, USA 06 05 2026 2026 1 38 Copyright: © 2026 James A. Anstey et al. 2026 This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/ This article is available from https://egusphere.copernicus.org/preprints/2026/egusphere-2026-1165/ The full text article is available as a PDF file from https://egusphere.copernicus.org/preprints/2026/egusphere-2026-1165/egusphere-2026-1165.pdf

We describe the protocol for coordinated experiments in phase-2 of the Quasi-Biennial Oscillation initiative (QBOi) and the participating models. The experiments involve nudging tropical stratospheric zonal-mean zonal winds in the models toward observations, enabling analysis of the impact of QBO biases on simulated teleconnections. Additionally, nudging the tropical winds allows investigation of the origins of QBO biases by examining the behaviour of resolved and parameterized equatorial waves under realistic equatorial wind shear conditions. We document here the scientific rationale and design of the nudging experiments, summarize the QBOi data request, and provide an overview of participating models. An initial evaluation is given of tropical stratospheric winds simulated by the multi-model ensemble for both nudged and free-running cases, and the overall impact of nudging on climatological aspects of the atmospheric circulation is examined.