Assimilation and validation of Millennium-length seasonal moisture over North America

Abstract:

The paleoclimate data assimilation (PDA) is widely used to study past climate change. Based on the seasonally resolved tree ring chronologies, the PDA is used to reconstructed warm season (MJJ) and cool season (DJFMA) precipitation over North America during the past two millennia in this study. The new reconstructions are compared with the North American Seasonal Precipitation Atlas, which is reconstructed by the point-by-point regression method based on the same proxy dataset. Validation against various instrumental data shows that the reconstruction skill is significantly improved over most area except the Western United States. The new reconstructions can provide the reliable estimation of past climate and can be used to study the differences in the timing, pattern, and intensity of cool and warm season moisture regimes in the past. Meanwhile, the pseudoproxy experiments are also applied to determine the basic parameter settings of PDA and evaluate the fidelity of the PDA method in estimating seasonal precipitation. The results indicated that uneven distribution of proxies in time and space led to different reconstruction skills in different regions.