Differences in the Dominant Modes of the Interannual Variability of Eastern Tibetan Plateau Precipitation between Early and Peak Summers

The spatiotemporal variation of summer precipitation on the Tibetan Plateau (TP) is complex. In this study, we propose that there exist visible differences in the dominant modes of the interannual variability of eastern TP (ETP) precipitation between early (June) and peak (July–August) summers during 1979–2022. A north-south dipole pattern of the precipitation interannual variability appears in early summer, but in peak summer, the dominant mode is changed to be a monopole pattern. This phenomenon is mainly due to the intraseasonal transition of the dominant atmospheric circulation patterns over the TP and surrounding areas. In early summer, the north-south dipole pattern of the interannual variability of ETP precipitation is associated with the upper-level anomalous anticyclonic circulation over the western TP, which is primarily forced by the convective heating of South Asian summer monsoon. Under the control of anomalous northerlies on the eastern side of the anticyclonic circulation, the precipitation on the northern ETP is suppressed by both negative moist enthalpy advection and negative moisture advection. While in peak summer, the monopole pattern of the interannual variability of ETP precipitation is mainly regulated by the large-scale meridional displacement of the subtropical westerly jet. When the westerly jet shifts southward, the strengthened westerlies control the entire plateau and create unified positive moist enthalpy advection over the ETP, finally resulting in anomalous upward motions and increased precipitation; and vice versa. This study provides an insight that further investigations on the ETP summer precipitation should consider the intraseasonal difference.