Vertical Structure of the QBO in Observations and CMIP6 Models: Influence on Eastern China Winter Temperature.

Using the observations and Coupled Model Inter-comparison Project Phase 6 (CMIP6) models, this study analyzes the performance of CMIP6 models in simulating the vertical structure of the Quasi-Biennial Oscillation (QBO) and its impacts on the Eastern China surface air temperature (SAT), using the empirical orthogonal function (EOF) analysis. The first leading mode (EOF1) of QBO leads to an overall cooling/warming over Eastern China via QBO’s subtropical path and Holton-Tan effect, while the second leading mode (EOF2) of QBO tend to cause an east-west dipole of SAT anomalies between Eastern and western China due to the strong Holton-Tan effect. Most models with self-generated QBO can capture both westerly and easterly QBO anomalies in the mid-lower stratosphere in EOF1 and only westerly anomaly in EOF2. The multi-model ensemble mean can reproduce the Eastern China SAT anomalies that are statistically significant and related to EOF1-like QBO events. However, the intensity of these anomalies is relatively weaker, attributed to the weak Pacific response to the subtropical effect of the QBO. In contrast, most models fail to induce a strong Holton-Tan effect and a Northern Annular Mode (NAM) pattern in the polar region during the EOF2-like QBO events, resulting in weak and insignificant Eastern China SAT anomalies on average. Overall, the models with a better representation of polar and Pacific response to the QBO’s vertical structure exhibit a more reasonable Eastern China SAT response, although such a response is weaker than the observations.