ABSTRACT

Based on the daily Japanese 55-year Reanalysis (JRA-55) from 1979 to 2015, this study shows that atmospheric heat sources over the Tibetan Plateau (TP) and its surrounding areas (TPSR) in summer have a significant 10- to 30-day intraseasonal oscillation (ISO). The linkage of the ISO with the amplified precipitation to the south of the middle and lower reaches of the Yangtze River (MLYR) is also investigated. The results show that when anomalous positive heat sources over the TPSR strengthen, an anomalous thermal low pressure develops, leading to anomalous positive vorticity over the TPSR. Meanwhile, a mid-high latitude wavetrain with alternating positive and negative vorticity anomaly centres over the Eurasian continent propagates eastward across the TP. The anomalous positive vorticity over the northeastern TP is enhanced when combined with a deep positive vorticity anomaly over the TPSR. The wave-activity flux in the eastern TPSR turns southward or southeastward, with a positive vorticity anomaly propagating to the southeast of China. As a result, positive vorticity advection to the south of the MLYR increases with height and is conducive to convergence, upward motion, and increased precipitation. The situation is the reverse when negative anomalous heat sources develop over the TPSR. Therefore, the 10- to 30-day ISO of the atmospheric heat source over the TPSR in summer could contribute to the amplification of the intraseasonal precipitation anomalies to the south of the MLYR by regulating the range and intensity of the anomalous vorticity of the Eurasian wavetrain.