Correlation analysis of persistent heavy rainfall events in the vicinity of the Yangtze River valley and global outgoing longwave radiation in the preceding month

Based on the National Oceanic and Atmospheric Administration (NOAA) daily satellite datasetof global outgoing longwave radiation (OLR) for the period of 1974--2004 and the NCEP-NCAR reanalysisfor 1971--2004, the linkage between persistent heavy rainfall (PHR) events in the vicinity of the YangtzeRiver valley and global OLR leading up to those events (with 1- to 30-day lag) was investigated. Theresults reveal that there is a significant connection between the initiation of PHR events over thestudy area and anomalous convective activity over the tropical Indian Ocean, maritime continent, andtropical western Pacific Ocean. During the 30-day period prior to the onset of PHR events, the majorsignificantly anomalous convective centers have an apparent dipole structure, always with enhancedconvection in the west and suppressed convection in the east. This dipole structure continuously shiftseastward with time during the 30-day lead period. The influence of the anomalous convective activityover the tropical oceans on the initiation of PHR events over the study area is achieved via an interactionbetween tropical and extratropical latitudes. More specifically, anomalous convective activity weakensthe Walker circulation cell over the tropical Indian Ocean first. This is followed by a weakening ofthe Indian summer monsoon background state and the excitation and dispersion of Rossby wave activityover Eurasia. Finally, a major modulation of the large scale background circulation occurs. As a result,the condition of a phase-lock among major large scale circulation features favoring PHR events isestablished over the study area.