Preprints
https://doi.org/10.5194/egusphere-2026-1165
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/egusphere-2026-1165
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
06 May 2026
| 06 May 2026
Status: this preprint is open for discussion and under review for Geoscientific Model Development (GMD).
Experiment design, nudging protocol, and models participating in Phase 2 of the APARC Quasi-Biennial Oscillation initiative (QBOi)
Abstract. 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.
How to cite. Anstey, J. A., Butchart, N., Osprey, S., Kawatani, Y., Hamilton, K., Richter, J. H., Stockdale, T., Andrews, M. B., Chai, Z., Davini, P., Hong, D.-C., Huang, K., Jaison, A. M., Kerzenmacher, T., Knight, J. R., Lin, P., Lott, F., Lu, Y., Naoe, H., Serva, F., Simpson, I., Son, S.-W., Tang, Q., Watanabe, S., Xie, J., and Yoshida, K.: Experiment design, nudging protocol, and models participating in Phase 2 of the APARC Quasi-Biennial Oscillation initiative (QBOi), EGUsphere [preprint], https://doi.org/10.5194/egusphere-2026-1165, 2026.
Competing interests: JA serves as co-editor for the special issue to which this paper belongs.
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James A. Anstey
CORRESPONDING AUTHOR
Canadian Centre for Climate Modelling and Analysis (CCCma), Victoria, Canada
Neal Butchart
Met Office Hadley Centre (MOHC), Exeter, UK
Scott Osprey
National Centre for Atmospheric Science (NCAS), University of Oxford, Oxford, UK
Yoshio Kawatani
Faculty of Environmental Earth Science, Hokkaido University, Sapporo, Japan
Kevin Hamilton
International Pacific Research Center (IPRC), Honolulu, USA
Jadwiga H. Richter
National Center for Atmospheric Research (NCAR), Boulder, USA
Tim Stockdale
European Centre for Medium-Range Weather Forecasts (ECMWF), Reading, UK
Martin B. Andrews
Met Office Hadley Centre (MOHC), Exeter, UK
Zhaoyang Chai
Institute of Atmospheric Physics, Chinese Academy of Sciences (CAS), Beijing, China
Paolo Davini
Institute of Atmospheric Sciences and Climate, National Research Council (CNR-ISAC), Torino, Italy
Dong-Chan Hong
School of Earth and Environmental Sciences, Seoul National University, Seoul, 08826, Korea
Kai Huang
National Center for Atmospheric Research (NCAR), Boulder, USA
Aleena M. Jaison
National Centre for Atmospheric Science (NCAS), University of Oxford, Oxford, UK
Tobias Kerzenmacher
Karlsruher Institut für Technologie (KIT), Karlsruhe, Germany
Jeff R. Knight
Met Office Hadley Centre (MOHC), Exeter, UK
Atmospheric and Oceanic Sciences, Princeton University, Princeton, USA
Francois Lott
Laboratoire de Météorologie Dynamique (LMD), Paris, France
Yixiong Lu
Earth System Modeling and Prediction Centre, China Meteorological Administration (CMA), Beijing, China
Hiroaki Naoe
Meteorological Research Institute (MRI), Tsukuba, Japan
Federico Serva
Institute of Marine Sciences, National Research Council (CNR-ISMAR), Rome, Italy
Isla Simpson
National Center for Atmospheric Research (NCAR), Boulder, USA
Seok-Woo Son
School of Earth and Environmental Sciences, Seoul National University, Seoul, 08826, Korea
Lawrence Livermore National Laboratory, Livermore, CA, USA
Shingo Watanabe
Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokohama, Japan
Advanced Institute for Marine Ecosystem Change, WPI-AIMEC, Tohoku University, Sendai, Japan
Jinbo Xie
Lawrence Livermore National Laboratory, Livermore, CA, USA
High Meadows Environmental Institute (HMEI), Princeton University, Princeton, NJ, USA
Kohei Yoshida
Meteorological Research Institute (MRI), Tsukuba, Japan
Short summary
We describe experiments where modelled tropical stratosphere winds are adjusted by "nudging" them toward realistic time-evolving eastward and westward Quasi-Biennial Oscillation (QBO) winds. The effects of this bias correction on other atmospheric processes, such as the stratospheric polar vortex or tropical waves that force the QBO, can then be assessed. We describe details of the experiments, the multi-model ensemble that has performed them, and basic validation of the nudging response.
We describe experiments where modelled tropical stratosphere winds are adjusted by "nudging"...
review of "Experiment design, nudging protocol, and models participating in Phase 2 of the APARC Quasi-Biennial Oscillation initiative (QBOi)" by Anstey et al
This study introduces the protocol for phase 2 of the QBOi project, with the main addition being two nudged experiments. In Exp1-ObsQBO, the tropical stratospheric zonal winds are nudged to observed reanalysis wind, and in Exp1-NoQBO they are nudged to the climatological wind over the 1979-2020 period. The paper also introduces key aspects of the participating models, and also describes the data request. The paper also demonstrates that the models respond to nudging as expected.
I have no major comments - this study is very appropriate for GMD - and I look forward to reading the subsequent papers that report results. To be explicit, I don't think the authors should be asked to include any additional results in the current paper. It should be promptly accepted subject to the technical edits described below.
technical edits:
line 59-62 this sentence could be reworded for clarity
line 87 "seasonal" -> "subseasonal"
caption of figure 1: give- > given
line 227 "Sensitivity of QBO simulations to vertical resolution is not well quantified," is confusing. Do you mean "mechanisms are poorly understood"?
line 245, 502 Garfinkel et al 2025 seems appropriate in these two locations. Consider citing it.
line 275: therefore **are** not
line 302 nudged -> nudge
line 355 "responding" is superfluous
line 368 "and" is missing between Exp1-NoQBO and Exp1-ObsQBO
line 375 **the** simulated
line 396 consider a comma after "winds"
line 465 GCMs
line 506 superfluous "is"
section A2: it might be worth stating explicitly that the profile for Exp1-noQBO is the climatological mean over 1979-2020 to match the period for obsQBO, though this is probably obvious. For SNAPSI, the specific wind and temperature profiles to be relaxed towards were provided to model developers. For SNAPSI this was done because the initial spinup in the first few days after initialization needed to be handled somewhat carefully to avoid shocks for the runs nudged to climatology due to the fast nudging timescale. Presumably this is less of a problem for the QBOi runs.
Garfinkel, C. I., Avisar, D., Osprey, S., & Smith, D. (2025). The response of the QBO to external forcings: implications for disruption events. Journal of Geophysical Research: Atmospheres, 130(22), e2025JD044438.