Analysis of systematic biases in equatorial resolved and parameterized wave forcing of the quasi-biennial oscillation in a multi-model ensemble
Abstract
The equatorial resolved and parameterized wave forcing of the quasi-biennial oscillation (QBO) in models participating in phase 2 of the Atmospheric Processes and their Role in Climate (APARC) Quasi-Biennial Oscillation initiative (QBOi) is analyzed. We compare two experiments performed by the multi-model ensemble, NoNudge and ObsQBO, covering the period from 1979 to 2020. In this study, NoNudge designates experiments where the QBO is generated internally without nudging, whereas ObsQBO represents experiments in which the QBO is bias-corrected by nudging stratospheric zonal-mean zonal winds toward ERA5, allowing investigation of modelling uncertainties originating from biases in the background winds. While the NoNudge simulations exhibit QBO biases typically seen in models, including eastward wind bias in the mid-stratosphere and underestimation of the QBO amplitude in the lower stratosphere, these discrepancies are effectively mitigated by nudging in ObsQBO simulations. In the NoNudge experiments, the models reveal weaker Kelvin and gravity wave forcing in the tropical lower stratosphere than ERA5, but these forcings are enhanced in the ObsQBO experiment, suggesting that weak wave forcing of internally generated QBOs results from reduced critical-level filtering of waves due to unrealistically weak vertical wind shear at these levels. However, in ObsQBO experiments, the models still exhibit insufficient Kelvin and gravity wave forcing in the lower stratosphere. This suggests that the weak QBO amplitude in the lower stratosphere may stem from the inherent deficit in wave forcing in the models. One notable feature of the ObsQBO experiments is the excessive eastward wave forcing in the mid-to-upper stratosphere during the easterly QBO phase in the lower tropical stratosphere. The correlation coefficient between the 10 hPa eastward wave forcing and westerly QBO amplitude is 0.8, indicating that excessive westerly QBO is associated with strong eastward wave forcing in the mid-to-upper stratosphere.
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BibTeX
@misc{lee2026analysis,
title = {{Analysis of systematic biases in equatorial resolved and parameterized wave forcing of the quasi-biennial oscillation in a multi-model ensemble}},
author = {Hyun-Kyu Lee and James Anstey and Hye-Yeong Chun and Shingo Watanabe and François Lott and Zhaoyang Chai and Yixiong Lu and Qi Tang and Jinbo Xie and Dong-Chan Hong and Seok-Woo Son and Federico Serva and Pu Lin and Martin Andrews and Neal Butchart and Aleena Jaison and Jeff Knight and Scott Osprey and Hiroaki Naoe and Kohei Yoshida and Yoshio Kawatani and Jadwiga Richter},
howpublished = {EGUsphere [preprint]},
year = {2026},
month = jun,
doi = {10.5194/egusphere-2026-2856},
url = {https://hal.science/hal-05842295v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Analysis of systematic biases in equatorial resolved and parameterized wave forcing of the quasi-biennial oscillation in a multi-model ensemble
AU - Hyun-Kyu Lee
AU - James Anstey
AU - Hye-Yeong Chun
AU - Shingo Watanabe
AU - François Lott
AU - Zhaoyang Chai
AU - Yixiong Lu
AU - Qi Tang
AU - Jinbo Xie
AU - Dong-Chan Hong
AU - Seok-Woo Son
AU - Federico Serva
AU - Pu Lin
AU - Martin Andrews
AU - Neal Butchart
AU - Aleena Jaison
AU - Jeff Knight
AU - Scott Osprey
AU - Hiroaki Naoe
AU - Kohei Yoshida
AU - Yoshio Kawatani
AU - Jadwiga Richter
PY - 2026
DA - 2026/06/05
PB - EGUsphere [preprint]
DO - 10.5194/egusphere-2026-2856
UR - https://hal.science/hal-05842295v1
AB - The equatorial resolved and parameterized wave forcing of the quasi-biennial oscillation (QBO) in models participating in phase 2 of the Atmospheric Processes and their Role in Climate (APARC) Quasi-Biennial Oscillation initiative (QBOi) is analyzed. We compare two experiments performed by the multi-model ensemble, NoNudge and ObsQBO, covering the period from 1979 to 2020. In this study, NoNudge designates experiments where the QBO is generated internally without nudging, whereas ObsQBO represents experiments in which the QBO is bias-corrected by nudging stratospheric zonal-mean zonal winds toward ERA5, allowing investigation of modelling uncertainties originating from biases in the background winds. While the NoNudge simulations exhibit QBO biases typically seen in models, including eastward wind bias in the mid-stratosphere and underestimation of the QBO amplitude in the lower stratosphere, these discrepancies are effectively mitigated by nudging in ObsQBO simulations. In the NoNudge experiments, the models reveal weaker Kelvin and gravity wave forcing in the tropical lower stratosphere than ERA5, but these forcings are enhanced in the ObsQBO experiment, suggesting that weak wave forcing of internally generated QBOs results from reduced critical-level filtering of waves due to unrealistically weak vertical wind shear at these levels. However, in ObsQBO experiments, the models still exhibit insufficient Kelvin and gravity wave forcing in the lower stratosphere. This suggests that the weak QBO amplitude in the lower stratosphere may stem from the inherent deficit in wave forcing in the models. One notable feature of the ObsQBO experiments is the excessive eastward wave forcing in the mid-to-upper stratosphere during the easterly QBO phase in the lower tropical stratosphere. The correlation coefficient between the 10 hPa eastward wave forcing and westerly QBO amplitude is 0.8, indicating that excessive westerly QBO is associated with strong eastward wave forcing in the mid-to-upper stratosphere.
ER -