Interannual variation of the onset of the Tibetan Plateau rainy season and its relationship with the sea surface temperature in the North Pacific

The onset of the Tibetan Plateau rainy season (OTPRS) marks the transition from dry season to wet season in situ, which has a great impact on the water cycle and atmospheric heating in extensive areas. This analysis found that the earlier OTPRS is controlled by the weakened westerly wind, a dipole vortex pair with an anomalous anti-cyclone over Lake Baikal but an anomalous cyclone over the Tibetan Plateau, the intensified southerly water vapour transportation on the southern edge of the Tibetan Plateau, the active convection and the increased humidity over the Tibetan Plateau in spring. And the opposite circulation anomalies correspond to the later OTPRS. The interannual variation in the OTPRS is closely related to sea surface temperature anomalies (SSTA) in the North Pacific in the previous winter, with the opposite phase between the 'tongue' extending eastward from the China East Sea and the surrounding 'semi-circle' in the east. This pattern features the third leading mode of the winter SSTA in the North Pacific and can persist to spring. The vertical motion, convergence and divergence associated with the direct thermal effect from the significant SSTA centres in the southeastern and northwestern North Pacific form two opposite zonal circulation circles along 30 degrees N. The zonal circulation circles bridge the SSTA in the North Pacific and the circulation anomalies over the Tibetan Plateau and have a delayed impact on convection over the Tibetan Plateau, thereby affecting the OTPRS.