Interaction between the East Asian summer monsoon and westerlies as shown by tree-ring records

Abstract. Atmospheric circulation changes, their driving mechanisms, and interactions are important topics in global change research. Local changes in the East Asian summer monsoon (EASM) and the midlatitude westerlies will inevitably affect the climate and ecology of the arid zone of northwestern China. Hence, it is important to study these regional changes. While previous studies in this area are all single-point climate reconstruction studies, there is a lack of research on the interaction areas and driving mechanisms of the two major circulations. Dendroclimatology can provide high-resolution, long-term, and reliable multi-point proxies for the study of interannual and interdecadal climate change. We chose to observe these changes in the Alxa Plateau using dendrochronological methods. We assembled ring-width records of Qinghai spruce (Picea crassifolia) in the mountain regions surrounding the Alxa Plateau: the Helan Mountains, Changling Mountain, and Dongda Mountain. The results show that radial growth was indeed affected by changes in the monsoon and westerlies. The heterogeneity of precipitation and climatic wet–dry changes in different regions is primarily influenced by the interactions between atmospheric circulation systems, each with its own dominant controlling factors. In the case of the Helan Mountains, both of these major atmospheric circulation systems play a significant role in shaping climate changes. Changling Mountain in the southern part of the Alxa Plateau is mainly influenced by the EASM. Dongda Mountain is mainly influenced by the westerlies. Understanding these local conditions will help us predict climate changes in northwestern China.