The Madden–Julian oscillation during the 2016 summer and its possible impact on rainfall in China

Abstract

ABSTRACTThe summer rainfall in China in 2016 exhibited a substantial intraseasonal feature, with an intensification in June and July but a suppression in August over the Yangtze River Basin and North China. The Madden–Julian oscillation (MJO) during the summer and its impact on rainfall in China are investigated by conducting observational analyses and diagnostic linear baroclinic model (LBM) experiments. A significant MJO activity in the summer is observed with three MJO episodes corresponding to three stages of rainfall in China. The LBM is utilized to diagnose the circulation response to the tropical heating forcing associated with each MJO episode. The results suggest that much of the atmospheric circulation linked to the anomalous rainfall is attributed to the strong MJO episodes. During June–July (August), the enhanced (suppressed) convection over the tropical Indian Ocean along with the suppressed (enhanced) convection over the South China Sea (SCS) to the western Pacific excite an ‘East Asian–Pacific’ north‐eastward‐propagating Rossby wave train, inducing anomalous low‐level anticyclonic (cyclonic) flows over the northern SCS and the western North Pacific but cyclonic (anticyclonic) flows over North China. They lead to a westward (eastward) shift and strengthening (weakening) of the western Pacific subtropical high, thus favouring the intensification (suppression) in rainfall over the Yangtze River Basin and North China along with the opposite variation over South China. Relative to the first MJO episode, the MJO convection in the second episode causes a northward movement of the anomalous rainfall band from the Yangtze River Basin to North China. Apart from the impact on the above regions, the first (second and third) MJO episode favours an increase (reduction) in rainfall over Northeast China.