Analysis Of The Preceding Signals Of The Persistent Heavy Rainfall Events During Summer In Jiangnan

Based on daily averaged data derived from the NCEP/NCAR reanalysis dataset and the research of the persistent heavy rainfall events(PHR) during the period of 1951-2004,the preceding signals of the PHR that happened in Jiangnan during June are revealed by using correlation and composite methods.The characteristics of the signals, the interaction between themselves and the way by which the signals influence the PHR are discussed.The results show that most preceding signals happen in the mid-latitude. Furthermore,the east and west coast of the Pacific Ocean,the east coast of the northern Atlantic Ocean and the southern Indian Ocean are the key areas that influence the PHR. Finally,a conceptual model that the preceding signals influence the later PHR are established:(1) 3-4 weeks before the PHR,north Atlantic subtropical high strengthened, resulting in the trough near the Arabian Peninsula strengthened,and then strengthen the South Asia High and the Middle African Low;(2) 3-2 weeks before,the westerly trough at east of Australia intensified.With the trough moving eastward and a middle tropospheric high-pressure disturbance at northeast of Australia,the Australia High strengthened;(3) One week before,a high pressure disturbance moved from high to middle latitude at southwest Indian ocean,strengthen the Mascarene High.The two signals above may influence the PHR through telecormetion between the circulation system in southern and northern hemisphere;(4) Also one week before,500hPa altitude anomaly field behaves "+-+-+" semicircle pattern from west Pacific Ocean(165°E) to north America,and the west Pacific Ocean tropical high enhanced,extending more westward,which benefits the PHR in Jiangnan.