Definition of the core zone of the “westerlies-dominated climatic regime”, and its controlling factors during the instrumental period

The term "westerlies-dominated climatic regime" describes the pattern of precipitation/moisture variations between westerliesdominated arid Central Asia(ACA) and mid-latitude monsoon-dominated Asia on decadal to multi-millennial time scales. However, no attempts have been made to define its core region and the possible physical mechanisms responsible during the period of instrumental observations. The present study investigates the spatiotemporal variations of summer and winter precipitation on interannual to decadal time scales over mid-latitudes of the Eurasian continent using Empirical Orthogonal Function(EOF) analysis. Our results suggest the existence of an opposing pattern of summer precipitation variations between ACA and mid-latitude monsoon-dominated Asia and Mediterranean on decadal time scales. Based on these results, the core region influenced by the westerlies is outlined, including arid central Asia and Xinjiang in China(36°–54°N, 50°–90°E). By using monthly NCEP-NCAR reanalysis, the relationship between the "westerlies-dominated climatic regime" and atmospheric circulation were also analyzed. The combination of the zonal climatic teleconnection pattern and anomalous Indian Summer Monsoon Precipitation(ISMP) causes the precipitation characteristics of the "westerlies-dominated climatic regime" precipitation pattern. In addition, the Atlantic Multidecadal Oscillation(AMO) may also have an important effect on the "westerlies-dominated climatic regime".