POSSIBLE IMPACTS OF MADDEN-JULIAN OSCILLATION ON THE SEVERE RAIN-SNOW WEATHER IN CHINA DURING NOVEMBER 2009

Possible relationships between MJO and the severe rain-snow weather in Eastern China during November of 2009 are analyzed and results show that a strong MJO process is one of the strong impact factors. MJO is very active over the Indian Ocean in November 2009. Especially, it maintains 9 days in MJO phase 3, just corresponding to the two strongest rain-snow processes. Composites of MJO events show that when the MJO convective center is located over the Indian Ocean, the probability of rainfall is significantly increased and the temperature is lower than normal in eastern China, which is consistent with the situation in November of 2009. Atmospheric circulation anomalies of mid- and higher-latitudes can be influenced by the tropical MJO convection forcing and this influence could be realized by teleconnection. When the MJO is over the Indian Ocean, it is favorable for the maintenance of a circulation pattern of two ridges versus one trough at mid- and higher-latitudes. Meanwhile, the western Pacific subtropical high is stronger and more westward than normal, and a significant convective belt appears over eastern East Asia. All these circulation anomalies shown in the composite result also appeared in the observations in November 2009, which indicates the general features of relationships between the MJO and the circulation anomalies over the extratropics. Besides the zonal circulation anomalies, the MJO convection can also lead to meridional circulation anomalies. When the MJO convection is located over the Indian Ocean, the western Pacific is dominated by anomalous descending motion, and the eastern East Asia is controlled by strong convergence and ascending motion. Therefore, an anomalous meridional circulation is formed between the tropics and middle latitudes, enhancing the northward transportation of low-level moisture. It is potentially helpful to understanding and even forecasting such kind of rain-snow weather anomalies as that in November 2009 using MJO.