The stratospheric Brewer–Dobson circulation under different phases of the Stratospheric Polar Vortex Oscillation combined with different phases of the Quasi-Biennial Oscillation

Based on long-term WACCM5 simulations initialized with the climatology around the year 2000, the anomalous distribution of planetary wave and gravity wave fluxes was studied during distinct phases of the boreal stratospheric polar vortex (BSPV) and Quasi-Biennial Oscillation (QBO). The contributions of these two types of wave to the Brewer-Dobson circulation (BDC) anomalies were further analyzed. The results reveal that under four distinct phases, the Northern Hemisphere BDC is primarily governed by planetary waves, while gravity waves counteract approximately half of the planetary wave influence on the BDC in the upper stratosphere. The QBO regulates the position of the centre of the BDC's descending branch anomaly in the Northern Hemisphere. In particular, during WQBO, the center of this anomalous descending branch is located in the upper stratosphere; during EQBO, it is located in the lower stratosphere. Southern Hemisphere BDC anomalies is more regulated by QBO activity: during WQBO, it shows synchronous changes with the BDC anomaly in the northern hemisphere, whereas during EQBO, it exhibits an anti-phase relationship with the BDC anomaly in the northern hemisphere. Mesospheric circulation anomalies are predominantly driven by gravity waves activity. The circulation weakens during weak BSPV and strengthens during strong BSPV. Additionally, the descending branch anomaly of the Northern Hemisphere circulation is more pronounced during the WQBO, while the ascending branch anomaly of the Southern Hemisphere circulation is more significant during the EQBO.