INFLUENCE OF THE DOUBLE RIDGES OF WEST PACIFIC SUBTROPICALHIGH ON THE SECOND MEIYU OVER THE YANGTZE RIVER VALLEY DURING 1998

Based on the NCEP/NCAR reanalysis data and the TBB data from Meteorological Institute Research of Japan, the reason that the ridge of the west Pacific subtropical high (WPSH) in July 1998 suddenly locates much more southward than its normal position is investigated. The results show that the view point on the sudden retreat southward of the WPSH ridge has its limit to some extent. T his is in fact a rebuilding process of the WPSH ridge in the south. It is found that there simultaneously exist two WPSH ridges in the same longitude over the west Pacific subtropical region in the first and middle of ten days of July 1998.