It is known that the Tibetan Plateau (TP) can weaken the transient eddies (TEs) transported along the westerly jet stream. This study investigates the effects of the persistently suppressed TEs by the TP on the East Asian summer monsoon and the associated mechanisms using the NCAR Community Earth System Model. A nudging method is used to modify the suppression of the TEs without changing the steady dynamic and thermodynamic effects of the TP.The suppressed TEs by the TP weaken the East Asian westerly jet stream through the weakened poleward TE vorticity flux. On the one hand, the weakened jet stream leads to less (more) rainfall in northern (southern) East Asia by inducing anomalous moisture convergence, mid-tropospheric warm advection, and upper-level divergence, particularly in early summer when the eastward propagation of TE suppression by the TP is strong. On the other hand, the precipitation anomalies can shift the East Asian westerly jet stream southward and promote the moisture convergence in southern East Asia through latent heat release. Therefore, the persistent suppression of the TEs leads to a southward shift of the East Asian rain belt by a convective feedback, as previously found that the steady thermodynamic and dynamic forcings of the TP favored a northward shift of the rain belt. This study suggests that the anomalously weak TEs can lead to the south-more-north-less rainfall change over East Asia.

Investigation into the interannual variation of the Middle East jet stream (MEJS) and its influence on the Asian monsoon indicates that the eastward extension of MEJS is closely related with a wetter and colder winter in southern China and a later onset of the subsequent Asian summer monsoon, compared with normal conditions. When the MEJS extends eastward, a significant barotropic anomalous anticyclone is located over the Arabian Sea (AS), associated with the southeastward propagating wave train from Europe. Intense divergence in the southwest of the AS anomalous anticyclone favors more convection over the western tropical Indian Ocean, which excites an anomalous upper-level anticyclone to the north as a Rossby wave response, further intensifying the AS anticyclonic anomaly. This positive feedback loop maintains the AS anomalous anticyclone and results in the eastward extension of the MEJS. Accordingly, intense northeasterly anomalies over the Mediterranean Sea and the subtropical westerly anomalies bring abundant cold air from the middle-higher latitudes to subtropical regions, resulting in a widespread cooling in subtropical Eurasia including southern China. Barotropic anomalous westerlies occur around the Tibetan Plateau in the south and deepen the India-Burma trough, favoring more water vapor transport from the Bay of Bengal to southern China. This wetter and colder conditions in subtropical Eurasia can persist from winter to spring, leading to the much later onset of the Asian summer monsoon. Therefore, the winter MEJS variability can be considered as an important indicator for the Asian monsoon.

East Asian summer precipitation (EASP) displays salient intraseasonal variability (ISV). For example, the record-breaking Meiyu in 2020 was related to the phase change of ISV (Ding et al., 2021; B. Liu et al., 2020a). The most significant flood over East China in 1991 was also argued to be caused by strong ISV (Mao & Wu, 2006). Although ISV is the dominant source of subseasonal predictability (Meehl et al., 2021;Vitart et al., 2017), our understanding of EASP ISV, especially its origins from external forcings in the tropical and mid-to-high latitudes or from local oscillation, remains limited.