The Amplification Effect Of The Intraseasonal Oscillation Of The Atmospheric Heat Source Over The Qinghai-Tibet Plateau In Summer On Precipitation In Southern China And Its Possible Mechanism

Based on the daily reanalysis data of JRA-55 from 1979 to 2018,the characteristics of Intra-Seasonal Oscillation(ISO)of the atmospheric heat source over the Tibetan Plateau(TP)and its surrounding areas(TPSR)are analyzed.The linkage between the 10-30-day ISO of atmospheric heat source over the TPSR and “amplified" intraseasonal precipitation anomalies in the south of the middle and lower reaches of the Yangtze River(MLYR,22°-32°N,105°-122°E)and possible mechanisms are revealed.The coordinated influence of the TP and lowlatitude heat sources on the intraseasonal precipitation in the south of MLYR are also discussed.In summer,the eastern and southern TP are the most active regions for 10-30-day ISO.When the positive(negative)anomaly of atmospheric heat source over the TPSR strengthens and reaches the peak(valley)phase(the third(seventh)phase),an anomalous thermal low(cold high)develops and almost runs through the upper and middle troposphere,leading to positive(negative)vorticity anomalies over the TPSR.In the middle and upper troposphere,positive(negative)vorticity anomaly of the mid-and high-latitude EU-type wave train is enhanced when it passes through the northeast side of TP and combines with the deep positive(negative)vorticity region over the TPSR,and the positive(negative)vorticity anomaly region across the TP and eastern China is formed.The wave activity flux turns southward with the positive vorticity anomaly propagates to the southeast of China.The absolute positive vorticity advection in the south of MLYR increases with height,which is conducive to the occurrence of convergence,upward motion,and the enhancement of positive precipitation anomalies.When the atmospheric heat source over the TP is weak(the second phase),precipitation anomaly in the south of MLYR is closely related to the ISO over the South China Sea(SCS).The downward(upward)movement over the SCS produces the high-level convergence(divergence)and low-level divergence(convergence)anomalies,forms the compensation and stimulates the meridional vertical circulation circle.The circle is favorable for the convergence(divergence)of water vapor flux in the south of the MLYR.In addition,the meridional nonuniformity of diabatic heating between the bay of Bengal and the TP causes zonal wind anomalies at 200 h Pa,and contributes to the precipitation anomalies in the south of MLYR by favoring the zonal transport of upper absolute vorticity advection.