Long-term changes in wintertime persistent heavy rainfall over southern China contributed by the Madden-Julian Oscillation

During the boreal winter, abundant persistent heavy rainfall (PHR) amount and significant rainfall variability at subseasonal timescale are generally observed over the southern sector of East China, where the large-scale circulation and moisture transport are tightly connected with the equatorial Madden-Julian Oscillation (MJO). As the MJO convections occur over the equatorial Indian Ocean (MJO phases 1-4), the low-level moisture convergence is enhanced over southern China (SC, 108 degrees-120 degrees E, 21 degrees-26 degrees N) with the divergence to the north. Thus, a positive anomaly of PHR amount appears in SC but a negative anomaly of PHR amount is seen in the Yangtze River valley (YR, 113 degrees-122 degrees E, 28 degrees-30 degrees N). In contrast, the divergence (convergence) of moisture flux anomalies in the SC (YR) associated with the western equatorial Pacific MJO convections (phases 5-8) limits (benefits) the occurrence of PHR in the SC (YR). The wintertime PHR over southern China is found to undergo a long-term change over the past three decades (1979-2011) with a decreasing (an increasing) trend of PHR amount in the SC (YR). The change in PHR amount occurs consistently with the decadal change in MJO activity. In the earlier decade (1979-1994, E1), the active Indian Ocean (western Pacific) MJO events appeared more frequently while they became less frequent in the recent decade (1995-2011, E2). Accordingly, the Indian Ocean (western Pacific) MJO-related moisture convergence (divergence) anomalies in the SC tend to be weakened (enhanced), contributing to the decrease in PHR amount over the SC in the recent decade.