| Based on the monthly NCEP/NCAR Reanalysis data from 1958-2013 and average monthly precipitation data from the 160 stations re-organized by China National Center of Climate and the SODA (Simple Ocean Data Assimilation) deep sea surface temperature data provided by University of Maryland, the India Ocean vertical circulation anomalies and their relation to decadal variations of summer rainfall in Yangtz-Huaihe valley is analyzed. It’s pointed out that the relationship between them is because of the Interdecadal and interannual scale change, and further study revealed the possible causes of West India vertical circulation anomalies. The following conclusions were obtained:(1) The relationship between the vertical circulation over West India Ocean (WIOVC) and precipitation in Yangtz-Huaihe valley is closed to the variation of the background. The relationship between summer rainfall in Yangtz-Huaihe valley is the best of them. But both of them in the context of different decadal, relationship has a big difference. During 1958-1978 WIOVC has no significant correlation with summer rainfall in Yangtz-Huaihe valley, linear correlation coefficient is-0.2; during 1979-1993, which is in the negative phase, the correlation coefficient is-0.56; during 1994-2013, their trends are the same, and correlation coefficient is 0.71.(2) The relationship between Interdecadal variation of precipitation in summer and WIOVC is closely related to the shift of East Asian circulation background. Before 1979, Baikal Lake South high is significantly low, East China prevailed southerly wind, East summer monsoon is strong, cold air is weak, warm air is strong, as a result, rain balt in this stage is located in north China; after 1979, the atmospheric circulation is changed, and the circulation distribution in last two stages are similar, just different in strength and range. Baikal Lake South high is strong, the west Pacific subtropical high is significantly enhanced, the summer monsoon has waned, warm air gradually weakened, the cold air enhanced, moisture convergence gradually move south, as a result the rain belt in L2 stage is located in Yangtz-Huaihe valley, L3 stage in southern China.(3) The interannual influence of WIOVC anomalies of East Asian circulation is always the same, when the anomalous ascending(descending) motions occur over Western Indian Ocean, the East-Asian Summer Monsoon is strengthen(weaken) and the rain belts in east China are likely to shift northward (southward), which is (not)benefit for moist air northward propagating. Interannual WIOVC exception plays an important role in the relationship of WIOVC and summer rain fall in Yangtz-Huaihe valley.(4) The Interdecadal relationship between summer rainfall in Yangtz-Huaihe valley and WIOVC is perpendicular to the coupled regions of Pacific circulation. Before 1979, West India coupled mainly with the Eastern Pacific Ocean; after 1979, West India Ocean coupled with the west Pacific Ocean but not the Eastern Pacific. They have a negative correlation which means when there occurs ascending (descending) motions over West Indian Ocean, there is descending (ascending) motions over Pacific Ocean. Before the 1980s, There occurs a strong Walker circulation in tropical ocean while over the Pacific Ocean there’s an anomalous descending motion corresponding to the East-Asian Summer Monsoon is strengthen, vapor transport goes northward easily and the rain belt locate northeast China. At this stage, the relationship was not significant. After 1980s, the tropical Eastern Pacific atmosphere had an unusually strong upward movement corresponding to the east Asian summer monsoon was weaken, rain belt was located in Yangtz-Huaihe valley. WIOVM made the rain belt northward. As a result, WIOVM has a significant negative correlation with summer rainfall in Yangtz-Huaihe valley. After 1990s, the background present descending motion over the tropical mid-Pacific Ocean and ascending motion over tropical East Pacific Ocean corresponding the East summer monsoon in north of the Yangtze river further weakened, the rain belt located in south China. At this stage, the effect of WIOVM is conductive to rainfall in Yangtz-Huaihe valley; they present an obvious positive correlation. Interdecadal variations of the background and the interannual variations of WIOVC made the variation relationship between summer rainfall in Yangtz-Huaihe valley and WIOVC.(5) WIOVC produced exception in early sea temperature, ahead of 5 months India Ocean Council to sea temperature with good related relationship, also ahead of 3 months of North Atlantic sea temperature. That means the early spring of Atlantic sea temperature exception can be a signal of the summer India ocean vertical circulation exception. |
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