Influence of tropospheric temperature gradient on the boreal wintertime precipitation over East Asia

Recently it has been found that the summertime tropospheric temperature gradient (hereafter TT gradient) over East Asia provides a natural characterization of the local climate variability, particularly, the precipitation variability, and can help forecast the onset of summer monsoon. In this study we extend the study to the winter months, using the National Center for Environmental Prediction (NCEP) - DOE AMIP 2 reanalysis daily datasets. It is shown that the TT gradient during the El Nino years is significantly smaller than that during the La Nina years, and the difference in TT variation in the two ENSO phases leads to a distinctly different pattern of variability of precipitation over East Asia. The corresponding variabilities of circulation and moisture transport are in agreement with the observation, which are further substantiated in a causal inference using the traditional regression analysis and a newly developed causality analysis technique with time series.