Linkage between the boreal spring Antarctic oscillation and the temperature dipole mode over the Tibetan Plateau in summer

Abstract

As the extratropical Southern Hemispheric most prominent atmospheric mode, Antarctic oscillation (AAO) can impact the climate system via multi-spherical interactions, whereas its potential influence on the temperature anomaly over the Tibetan Plateau (TP) remains unclear. By employing ERA5 reanalysis during 1979–2018, we have identified a significant in-phase relationship between April–May AAO and the boreal summer (June–August) temperature anomaly over the TP. The AAO significantly modulates the meridional circulation in the Atlantic sector where the climatic subtropical jet is weaker than other regions in the subtropics as well as the equatorward extension of midlatitude jet. The divergence of transient eddy momentum related to the positive AAO strengthens the northward movement of the South American meridional circulation and cross-equatorial airflow in the low troposphere. Due to the Coriolis force, the cross-equatorial airflow turns southwesterly above the tropical North Atlantic, weakening the climatic northeasterly and the feedback of wind-evaporation-sea surface temperature (SST). Consequently, an anomalous warm SST persists into the boreal summer and triggers a Rossby wave train, which propagates along the North Atlantic-TP pathway. As a result, the positive phase of TP's temperature dipole mode with an eastern warm anomaly and a western cold anomaly appears. The numerical experiments conducted by the linear baroclinic model provide further evidence for the Rossby wave origination and propagation. The AAO, therefore, may act as a valuable predictor for the climate predictions around the TP.