Collaborative Effects Of MJO And Intraseasonal Oscillations Over The Tibetan Plateau On The Spring Rainfall In South China

In this paper, NCEP/NCAR reanalysis data and China’s753stations daily precipitation data are used to study the tropical low-frequency oscillation (MJO) and the oscillations of the500hPa zonal wind over Tibetan Plateau and their relationship with spring rainfall in South China. Then this paper also studies the collaborative effects of MJO and intraseasonal oscillations over the Tibetan Plateau on the spring rainfall in South China. Main results are listed as follows:(1) MJO has a significant impact on anomalies of spring rainfall in southern China, when the MJO approaches the Indochina peninsula and its nearby, it can cause a positive contribution to precipitation in southern China, and in other stages, precipitation anomalies caused by MJO is basically not so obvious. The analysis of synthesis of the atmospheric circulation anomalies shows that in phase4-5, the central and western regions of China are mainly controlled by an abnormal low pressure, with abnormal south airflow over the southern China, which makes a positive contribution to the increased precipitation. From the analysis on vapor flux anomalies and vertical velocity anomalies, it can be found that when precipitation in south China is larger, vapor flux is southerly anomaly and the vertical velocity is negative anomaly over the area, showing that an abnormal ascending motion is conducive to the increase of precipitation.(2) Intraseasonal oscillation of500hPa zonal winds over the Tibetan Plateau in spring demonstrates its main oscillation period which is about10-30d, characterized by its eastward propagation in zonal and southward propagation in meridional. The occurrence of the maximum (minimum) precipitation anomalies over the southern China is about2days lagged behind the peak (valley) phase of the intraseasonal oscillation over the plateau. Intraseasonal oscillation of500hPa zonal winds over the Tibetan Plateau in spring is associated with the500hPa low-frequency waves in mid-high-latitude Eurasia spreading from west to east.The intraseasonal oscillation of zonal winds has an impact on spring rainfall in southern China by its passing from east to west. When low-frequency zonal winds are at phase2-3, the configuration of high and low level circulation anomalies is conducive to the spring precipitation; when low-frequency zonal winds are at phase6～7, its configuration is not conducive to the precipitation in southern China in spring.(3) When MJO spread to the Indochina Peninsula (phase4～5) and the intraseasonal oscillation of500hPa zonal wind prevails westerly anomalies (phase2～3), their collaborative effects on the precipitation in South China is obviously greater than the separate effect. When MJO spread to the western Indian Ocean and the equatorial Pacific dateline (phase8～1) and the intraseasonal oscillation of500hPa zonal wind prevails easterly anomalies (phase6～7), precipitation in South China will decrease abnormally. In these above two different stages, the corresponding potential height field anomaly, wind field anomaly,850hPa vapor flux anomaly and500hPa vertical velocity anomaly are all exactly opposite.