Relationship Between East Asian Winter Monsoon and Summer Monsoon

Using National Centers for Environmental Prediction/National Centre forAtmospheric Research (NCEP/NCAR) reanalysis data and monthly Hadley Centersea surface temperature (SST) data, and selecting a representative EastAsian winter monsoon (EAWM) index, this study investigated the relationshipbetween EAWM and East Asian summer monsoon (EASM) using statistical analysesand numerical simulations. Some possible mechanisms regarding thisrelationship were also explored. Results indicate a close relationshipbetween EAWM and EASM: a strong EAWM led to a strong EASM in the followingsummer, and a weak EAWM led to a weak EASM in the following summer.Anomalous EAWM has persistent impacts on the variation of SST in thetropical Indian Ocean and the South China Sea, and on the equatorialatmospheric thermal anomalies at both lower and upper levels. Through theseimpacts, the EAWM influences the land--sea thermal contrast in summer andthe low-level atmospheric divergence and convergence over the Indo-Pacificregion. It further affects the meridional monsoon circulation and otherfeatures of the EASM. Numerical simulations support the results ofdiagnostic analysis. The study provides useful information for predictingthe EASM by analyzing the variations of preceding EAWM and tropical SST.