Impacts of the MJO on Winter Rainfall and Circulation in China

Impacts of the MJO on winter rainfall and circulation in China are investigated using a real-time multivariate MJO index. Composite results using the daily rainfall anomalies and ``rainy day'' anomalies according to eight different MJO phases show that the MJO has considerable influence on winter rainfall in China. Rainfall anomalies show systematic and substantial changes (enhanced/suppressed) in the Yangtze River Basin and South China with the eastward propagation of the MJO convective center from the Indian Ocean to the western Pacific. When the MJO is in phase 2 and 3 (MJO convective center is located over the Indian Ocean), rainfall probability is significantly enhanced. While in phase 6 and 7 (MJO convective center is over the western Pacific), rainfall probability is significantly reduced. MJO in winter influences the rainfall in China mainly through modulating the circulation in the subtropics and mid-high latitudes. For the subtropics, MJO influences the northward moisture transport coming from the Bay of Bengal and the South China Sea by modulating the southern trough of the Bay of Bengal and the western Pacific subtropical high. For the mid-high latitudes, the propagation of the low frequency perturbations associated with the eastward-propagating MJO convection modulate the circulation in the mid-high latitudes, e.g. the East Asian winter monsoon and the low trough over central Asia.