Interannual variability of Eastern China Summer Rainfall: the origins of the meridional triple and dipole modes

Abstract

The Eastern China Summer Rainfall (ECSR) has a strong interannual variability, and the leading mode of interannual ECSR variability is characterized by either meridional triple or dipole structures as claimed by previous studies. In this study, decadal differences of the leading ECSR modes are investigated, using observational data and long-term integrations of climate models. Observational analyses show that the leading mode of ECSR is characterized by a meridional triple structure during 1979–1993 whereas a meridional dipole structure during 1994–2014. In the 200-year air–sea coupled simulation of Community Climate System Model version 4 (CCSM4), the leading mode of ECSR is characterized by triple structure in some decades whereas dipole structure in other decades, and decadal shifts between the triple and dipole structures are seen. In the 200-year simulation of the stand-alone atmospheric component of CCSM4 (i.e., CAM4) forced by fixed SST annual cycle, the triple mode and dipole mode are also identified, suggesting both of these two modes and their decadal shift can be generated by atmospheric internal dynamics without air–sea interaction. As agreed by observation, CCSM4 and CAM4 simulations, the positive (negative) phase of the triple leading mode is associated with enhanced (weakened) western north Pacific subtropical high, southward (northward) shifted East Asian jet, and meridional wave train along the East Asian coast. The positive (negative) phase of the dipole leading mode is associated with enhanced (weakened) western north Pacific subtropical high, enhanced (weakened) East Asian jet, and zonal wave train over mid-latitude Eurasian continent.