THE RELATIONSHIP OF THE PRECEDING WINTER MJO ACTIVITIES AND THE SUMMER PRECIPITATION IN YANGTZE-HUAIHE RIVER BASIN OF CHINA

The first two series (RMM1 and RMM2) of RMM Index (all-Season Real-time Multivariate MJO Index) are computed to obtain the interannual variation of the preceding winter (preceding December to current February) MJO strength, according to which active (or inactive) years of preceding winter MJO are divided. By utilizing the data provided by NCEP/NCAR, CMAP and China's 160 stations from 1979 to 2008, we studied the preceding winter MJO strength and discovered that the summer precipitation in the basin are of significantly negative correlation, i.e. when the preceding winter MJO is relatively active, the summer precipitation in the basin decreases, and vise verse. We also analyzed the causes. When the preceding winter MJO is relatively active, its release of potential heat facilities Inter-Tropical Convergence Zone (ITCZ) to strengthen and locate northward in winter and propagate northeastward. This abnormal situation lasts from winter to summer. In mid-May, ITCZ jumps northward to the South China Sea, the western Pacific subtropical high withdraws eastward, and the South China Sea summer monsoon sets off and strengthens. In summer, ITCZ propagates to South China Sea-subtropical western Pacific, the zonal circulation of subtropical Pacific strengthens, and a local meridional circulation of the South China Sea to the basin area forms, giving rise to the East Asia Pacific teleconnection wave-train. An East Asian monsoon trough and the Meiyu front show opposite features from south to north, the East Asian summer monsoon strengthens and advances northward. As a result, the summer monsoon is weakened as the basin is controlled by the subtropical high continually, with less rain in summer. On the contrary, when the preceding winter MJO is inactive, ITCZ weakens and is located southward, the subtropical high is located southward in summer, and the basin is in a region of ascending airflow with prevailing southwest wind. The East Asian monsoon trough and EASM weaken so that summer monsoon is reduced in the basin where precipitation increases.