QBO Disruption–like Events in the China Meteorological Administration (CMA) Climate Model

As a prominent mode of variability in the tropical stratosphere on the interannual timescale, the quasi-biennial oscillation (QBO) can significantly influence global atmospheric circulation and weather patterns. This study explores dynamic processes of the QBO disruptions using the China Meteorological Administration (CMA) integrated model by nudging the tropical zonal winds toward observations. A comparative analysis with ERA5 reanalysis data shows that the nudged runs accurately replicate the general characteristic of the QBO, including the alternating QBO wind regimes and QBO disruption events. The evolution of the QBO wind is diagnosed using the Empirical Orthogonal Functions (EOF) and root mean square difference (RMSD) analyses, and the rarity of the disruption events is confirmed in the CMA model. Different aspects of the QBO disruption and the relevant dynamics are present in the model. Firstly, the momentum budget analysis highlights the crucial roles of extratropical Rossby waves and non-orographic gravity waves in the transition from westerly to easterly winds during the disruption. Secondly, Kelvin waves and non-orographic gravity waves explain much of the transition from easterly to westerly winds near 40 hPa. Thirdly, the positive tendency from enhanced vertical advection further accelerates westerly momentum development via secondary meridional circulation. These findings underscore the importance of nudging techniques in understanding the QBO dynamics, which provides valuable insights for future climate model improvements in better forecasting QBO-related climate variability. Notably, due to model limitations, no QBO disruptions were simulated in the free-run experiments.