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Zusammenfassung:
The Tibetan Plateau (TP) is an important forcing in the global climate system. Compared to the extensive studies on the influence of the TP on surrounding climates, the variability of the surface potential vorticity (PV) over the TP (TPSPV) in response to other forcings is seldom discussed. In this article, the influence of the interannual mode of North Atlantic tripole sea surface temperature (NAT) on the TPSPV during boreal summer is investigated. Results show that the negative (positive) anomalous TPSPV is associated with anomalous unstable (stable) surface air, cyclonic (anticyclonic) surface circulation and rising (sinking) motion, which favors the stronger (weaker) East Asian summer monsoon and weaker (stronger) Indian summer monsoon. Further analysis indicates that the negative TPSPV is significantly correlated with a positive NAT mode with a cold center in the middle and warm centers in the subtropic and subpolar regions. This relationship is further testified by numerical experiments. The results further demonstrate that the positive NAT forcing can stimulate a Rossby wave train aloft, which passes Scandinavia, Ural and arrives at the TP and eventually triggers a low-level positive PV over the TP. Constrained by the PV-θ mechanism, the low-level positive PV favors a decrease in static stability near the surface and thus leads to a negative TPSPV. Under the positive feedback between TPSPV and vertical motion, the negative TPSPV could further strengthen. Therefore, the positive NAT phase could intensify the thermal and dynamic forcings of the TP in association with TPSPV during boreal summer.
