Summer atmospheric bridging between Europe and East Asia: Influences on drought and wetness on the Tibetan Plateau

Abstract

Based on the ERA-40 reanalysis data, dryness and wetness over the Tibetan Plateau are categorized according to the monthly standardized precipitation index. The atmospheric features associated with severe and extreme dryness and wetness reveal two cross-Eurasia wave trains: the Scandinavia-East Asia wave train and the Mediterranean-East Asia wave train. Severe and extreme dryness is associated with an anomalous cyclone over south and southeast Asia, which directs the moisture supply from the Arabian Sea, the Bay of Bengal, and the South China Sea directly eastward towards the western Pacific, thus bypassing the Tibetan Plateau. This cyclone anomaly constitutes part of the Scandinavia-East Asia wave train, which is sustained by the divergence and convergence of the anomalous transient eddy heat transport associated with a more southwest-northeast oriented North Atlantic storm track and a northward shift of the polar front jet in the North Atlantic. In contrast, severe and extreme wetness over the Tibetan Plateau is associated with a more zonally elongated North Atlantic storm track; wave trains excited from there have a high probability to reach the Mediterranean region and to propagate eastward following the subtropical westerly jet. This Mediterranean-East Asia wave train generates anticyclonic anomalies around the Tibetan Plateau and East China, which bring more moisture supply from the Arabian Sea, the South China Sea, and the western Pacific towards the Tibetan Plateau and enhance the moisture convergence there. This paper demonstrates how atmospheric bridging processes affect regional climate variability under present day climatic conditions, which are also relevant for understanding past climates.