Diagnosis Analysis on Relationship Between the Atmospheric Heat Source in the Northwest Pacific Ocean and the Meiyu of Mid-lower Reaches of the Yangtze

Based on the precipitation of Meiyu at 25 stations of mid-lower reaches of the Yangtze and the daily reanalysis geopotential height, wind field, humidity field and surface pressure field data (2.5°×2.5°) from 1954 to 2001, the relationship between the atmospheric heat source in the North Pacific Ocean and the abnormality of Meiyu precipitaion of mid-lower reaches of the Yangtze is investigated in terms of the Z index methold, empirical orthogonal function (EOF), composite analysis, singular value decomposition (SVD), and so on.The results of Z index methold indicate that there are notable multi (shored) Meiyu precipitation on mid-lower reaches of the Yangtze during the Meiyu period. There are 8 years in which the Meiyu precipitation is abnormally more and 6 years in which the Meiyu precipitation is abnormally less. The first mode of EOF shows the ENSO mode of the atmospheric heat source of North Pacific Ocean on mid-lower reaches of the Yangtze during the Meiyu period which express specifically the positive (negative) correlation between the atmospheric heat source in the mid-east Pacific Ocean and the north Pacific Ocean.The second mode of EOF shows the abnormal mode of the atmospheric heat source on the mid-lower reaches of the Yangtze during the Meiyu period which represents specifictly the positive (negative) correlation between the atmospheric heat source in the equatorial Pacific Ocean and the north Pacific Ocean of the middle-high latitudes. The results of SVD show that there are notable correlation between the Meiyu precipitation in the good (poor) Meiyu year and the atmospheric heat source in the Pacific Ocean. Through Monte-Carlo test at 95%, it shows there is positive (negative) correlation between the atmospheric heat source in the western (eastern) Pacific Ocean and the precipitation on mid-lower reaches of the Yangtze. When the SSTA around the Philippine island ocean and in the north-west Pacific Ocean are marked increasing (decreasing), convective activity is vigorous (weaken), the atmospheric heat in the north-west Pacific Ocean is increasing (decreasing), so the atmospheric heat in the eastern Pacific Ocean is decreasing (increasing), while the precipitation is marked increasing (decreasing) on mid-lower reaches of Yangtze river, and vice verse. The results of composite analysis and correlation analysis and SVD are identical congruent.