Coherent Summertime Precipitation Variability over East Asia and North America during the past millennium

Observations suggested that summertime precipitation anomalies in the North America and in the Asian monsoon regions may be linked by teleconnection patterns. To test the robustness of these teleconnections, this study firstly reconstructed the gridded warm season precipitation in North America based on seasonally sensitive tree rings, and Asia based on documentary and other rainfall sensitive proxies during 800-2000AD using the paleoclimate data assimilation method. The global gridded warm season 500hPa geopotential height and sea surface temperature (SST) conditions during the same period were also reconstructed. The summer precipitation teleconnections between the two continents and their links to SST were examined using the singular value decomposition (SVD) method. The first SVD mode suggested that the dipolar precipitation between mid-western United States and the Great Lakes is linked to opposite rainfall variations between southwest China and northeast China as well as Indochina. The second SVD mode suggested that the excess precipitation in western US is linked to excess rainfall in northern and southern China and less rainfall in the Yangtze River Valley. The third SVD mode suggested that dry/wet fluctuations in the Central US are linked to dipolar precipitation variations between regions north and south of the Yangtze River. The first, second and third SVD modes are closely linked to the El NinoSouthern Oscillation, Atlantic Multidecadal Oscillation, and the Indian Ocean Dipole, respectively. The large-scale atmospheric teleconnections that facilitating the links between North America and East Asia were also analyzed. The results suggested that the teleconnections vary on multidecadal and longer time scales during the past millennium.