Influence of the circumglobal teleconnection on the following ENSO: From the perspective of the freezing level height over the Tibetan Plateau

Abstract

The freezing level height (FLH) reflects the thermal conditions in the troposphere and implies cryospheric changes on the Tibetan Plateau (TP). This study aims to understand whether variations in the FLH over the TP are linked to midlatitude and tropical signals, which is currently unknown. An empirical orthogonal function analysis is utilized to investigate the east-west dipole pattern of the summer FLH over the TP during the period of 1961–2019. The results show that the dipole pattern of the FLH is mainly associated with the circumglobal teleconnection (CGT) waves, propagating from the North Atlantic Ocean to East Asia. A pair of anomalous cyclone and anticyclone related to the CGT pattern is observed, in favor for cooling and warming over the western and eastern TP, respectively. The thermodynamic equation diagnosis demonstrate that the CGT-related upward and downward motions accompanied by adiabatic cooling and heating, primarily contribute to the decreases and increases of FLH. As the thermal effect of the east-west dipole FLH occurs, the CGT waves are strengthened downstream to North Pacific and North America. Meanwhile, the lower-level easterly anomalies and westerly anomalies winds appear over the Indian Ocean and tropical Pacific. From summer to the following winter, anomalous westerly winds persistently prevail over the tropical Pacific, weakening the Walker circulation and leading to subsequent El Niño–Southern Oscillation (ENSO) events. Without the dipole mode of the TP FLH impact, the CGT-ENSO relationship could be weakened. The results suggest that the dipole pattern of the TP FLH acts as a linking bridge between the CGT pattern and ENSO events, which also verify the key role of TP in connecting the midlatitude and tropical climate variabilities.