Modulation of QBO on the relationship between stratospheric polar vortex and surface air temperature over Eurasia during early winter.

This study investigates the potential role and mechanism of the quasi-biennial oscillation (QBO) in influencing the relationship between the stratospheric polar vortex (SPV) and surface air temperature (SAT) over Eurasia during boreal early winter. Our results show that there are variations in the SPV-related SAT anomalies over Eurasia between different phases of QBO, i.e., SAT anomalies exhibit a south- north pattern (colder south and warmer north over Eurasia) in easterly phase of QBO (EQBO) compared to westerly phase of QBO (WQBO) in strong SPV years (SSPV), while a northeast-southwest pattern (colder northeast and warmer west over Eurasia) in weak SPV years (WSPV). On average, the contributions of SPV and QBO to SAT anomalies are approximately 29.4% and 12.6%, respectively. Further analysis suggested that these SAT differences between EQBO and WQBO under different SPV conditions are associated with the corresponding atmospheric circulation in the troposphere over Eurasia. The south-north pattern of SAT anomalies during SSPV is attributed to a stronger amplitude of the anomalous anticyclone in western Eurasia, which shifts westward, and the eastward shifting of anomalous cyclonic center in northwestern Eurasia in EQBO. But the southwest-northeast pattern during WSPV is related to anomalous cyclone over western Eurasia and the eastward shifting of anticyclone over northwestern Eurasia in EQBO. These tropospheric circulation anomalies are influenced by the propagation of planetary waves induced by QBO. The SPV weakens in EQBO compared to WQBO, which is accompanied by the strengthened (weakened) low-latitude waveguide and reinforced (shifting southward) subtropical jet stream during SSPV (WSPV) years. The different responses of subtropical jet are mainly related to the tropopause and the meridional temperature gradient around the tropopause caused by QBO via the meridional circulation and Holton-Tan relationship. [ABSTRACT FROM AUTHOR]