Increased Impact of the Tibetan Plateau Spring Snow Cover to the Mei-yu Rainfall over the Yangtze River Valley after the 1990s

This study investigated the increased impact of the spring (March-May) snow-cover extent (SCE) over the western Tibetan Plateau (TP) (SSTP) to the mei-yu rainfall [June-July (JJ)] over the Yangtze River valley (YRV) (MRYRV) after the 1990s. The correlation between the MRYRV and SSTP is significantly increased from the period of 1970-92 (P1) to 1993-2015 (P2). In P1, the MRYRV-related SSTP anomalies are located over the southwest TP, which causes a perturbation near the subtropical westerly jet (SWJ) core and favors an eastward propagation in the form of a wave train. The wave train results in a southward shift of the SWJ over the ocean south of Japan in JJ and exerts a limited effect on the MRYRV. Differently, in P2, the MRYRV-related anomalous SSTP causes an anomalous cooling temperature and upper-level cyclonic system centered over the northwestern TP. The cyclonic system develops and extends eastward to the downstream region with time and reaches coastal East Asia in JJ. The anomalous westerly winds along its south flank cause an enhanced SWJ, which is accompanied by an anomalous lower-level air convergence and ascent motion near the YRV region, favoring enhanced MRYRV. In addition, the forecast experiments performed with empirical regression models illustrate that the prediction skill of the MRYRV variation is clearly increased in P2 with the additional forecast factor of the SSTP.

Automated summary

This study found that the increased spring snow-cover extent over the western Tibetan Plateau after the 1990s has a significant impact on the mei-yu rainfall in the Yangtze River valley. The correlation between the two factors has changed over time, leading to different weather patterns and ultimately affecting the precipitation in the MRYRV.