The Holton-Tan mechanism under stratospheric aerosol intervention

The teleconnection between the quasi-biennial oscillation (QBO) and the Arctic stratospheric polar vortex, or the Holton-Tan (HT) relationship, may change in a warmer climate or one with stratospheric aerosol intervention (SAI) compared to the present-day climate (PDC). Our results from an Earth system model indicate that, under both global warming (based on RCP8.5 emission scenario) and SAI scenarios, the HT relationship weakens in early winter (November-December), although it is closer to PDC under SAI than under the RCP8.5 scenario. In contrast, the HT relationship in the middle to late winter period (January-February) does not change considerably in response to either RCP8.5 or SAI scenarios compared to PDC. While the weakening of the HT relationship under the RCP8.5 scenario is likely due to the weaker QBO wind amplitudes at the Equator, another physical mechanism must be responsible for the weaker HT relationship under SAI scenarios, since the amplitude of the QBO wind is comparable to the PDC. The strength of the polar vortex does not change under the RCP8.5 scenario compared to PDC, but it becomes stronger under SAI; we attribute the weakening of the HT relationship under SAI to a stronger polar vortex. In general, the changes in the HT relationship cannot be explained by changes to the critical line; the changes in the residual circulation (particularly due to the gravity wave contributions) are important in explaining the changes in the HT relationship under RCP8.5 and SAI scenarios.