Changes in the Dominant Mode of Summer Precipitation Over the Central-Eastern Tibetan Plateau Around the Mid-1990s

The interdecadal changes in the dominant mode of the summer precipitation over the central-eastern Tibetan Plateau (TP) are investigated around the mid-1990s. It is found that the leading empirical orthogonal function mode of the interannual variations of summer precipitation over the central-eastern TP is shown an out-of-phase pattern, with opposite variation between the southeastern and northeastern TP during 1961-1996, while the dominant mode become an in-phase pattern during 1997-2019. During 1961-1996, the dipole pattern of TP precipitation is mainly related to the North Atlantic Oscillation (NAO) and associated circulation anomalies. However, the impact of NAO on the dipole pattern of TP precipitation has weakened since the mid-1990s. In contrast, during 1997-2019, more pronounced positive height anomalies in the upper troposphere are observed over the whole TP regions. Meanwhile, the southerly moisture flux from the Bay of Bengal and the Philippine Sea is prevalent significantly with strong moisture convergence. Further analysis demonstrates that this interdecadal spatial change is mainly linked to the significant increasing of the sea surface temperature in the North Atlantic, South Atlantic, and Indo-Pacific warm pool, via wave trains propagation. The wave train-related positive height anomalies over the TP regions are in favor of the strengthening of the South Asian high (SAH). Moreover, the zonal and meridional mean temperature advections by SAH-related circulation anomalies are primarily responsible for the intense vertical flow anomalies. Consequently, the summer precipitation anomalies over the entire TP regions are largely enhanced and formed the mono-sign pattern during 1997-2019.