Synoptic-Scale Effects of Atmospheric Heat Source over Key Areas of the Tibetan Plateau on Its Downstream Rainfall in Summer

This study demonstrates the synoptic-scale relationship between the atmospheric heat source over the Tibetan Plateau (TP) (TP<Q1>) and summer rainfall in eastern China. The results show that the summer TP<Q1> has three key areas [eastern, western, and northeastern TP (TPE, TPW, TPNE, respectively)] and 3-8-day dominant oscillation periods on the synoptic time scale for each subregion. Analogously, on the synoptic scale, the downstream rainfall of the TP in China has six sensitive regions (zone I to zone VI), each with 3-8-day dominant periods. The TPE<Q1>, TPW<Q1>, and TPNE<Q1> lead rainfall by 4 days with a southeastward propagation pathway, by 5 days with both southeastward and northeastward propagation routes, and by 4 days with an eastward route, respectively. Mechanistically, when TP<Q1> lies in the positive-to-negative transition phase, the rainfall moves off the TP and reaches the maximum in its most inactive phase; the jet cores embedded in the subtropical westerly jet band and the trough from the region of the TP<Q1> lead the eastward movement of the rainfall by the propagation of the divergence center and generalized moist potential vorticity. Besides, the southwest vortex and northwest vortex generated at the southeastern and northeastern flank of the TP are the main cause for the southeastward and northeastward or eastward movement of the precipitation. Further internal atmospheric dynamic structures indicate that both the horizontal moisture advection and generalized moist potential vorticity advection act on the entire propagation processes of the synoptic-scale signals for each TP<Q1> key area. In conclusion, the study has obvious theoretical significance and application value for the development of plateau synoptics.