Tropopause Folding Events to the East of Tibetan Plateau in Boreal Summer and their Remote Relation to the Circulation Anomalies over Northeastern Atlantic

Abstract

This study investigates the occurrence of tropopause folding (TF) events to the east of Tibetan Plateau (ETP) (TF–ETP) in boreal summer. Firstly, it is revealed that, anomalously frequent TF–ETP occurrence in summer, always corresponds to a significant dipole rainfall anomaly pattern over China, with negative rainfall anomalies over the upper and middle reaches of the Yangtze and Yellow river valleys, and positive rainfall anomalies over eastern China. Secondly, the South Asian High (SAH) center over Tibetan Plateau (TP) is found to be anomalously stronger when occurrence of TF–ETP events is frequent. Further diagnosis indicates that, the TF–ETP occurrence is related to an eastward propagating Rossby wave train (RWT) that originates from a barotropic low anomaly center over the northeastern Atlantic (NEA) about one–week before. The RWT propagates downstream via Western Europe, the west of Baikal and down to East Asia along the mid-latitude westerlies, and is connected to a high anomaly center over the north rim of TP, which enhances the SAH center over TP. The enhanced SAH in turn favors the southward and downward PV intrusion and the subsequent occurrence of TF–ETP. Furthermore, the low anomaly center that initiates the RWT is related to dynamical forcing of transient eddy activity over the NEA, which induces the low via eddy-forced upper divergence and its pumping. Finally, such local and remote processes are confirmed in a typical TF–ETP case. The ERA–Interim daily fields during 1979–2018 is used.