| In recent years, new features of rainfall in eastern China have brought new challenges to the forecast of flood season precipitation. Water cycle, especially water vapor transport plays an irreplaceable role in regional precipitation. At present, it is a fundamentally flawed that water cycle is not taken into account in power and statistical forecasting, power-statistical forecasting and integrated forecasting. Because the direction and intensity of water vapor transport path affect precipitation directly, this article focuses on the study of the water vapor transport path and objectiving and quantitativing the water vapor transport path effecting the precipitation in eastern China. At first, based on the global Palmer Drought Severity Index (PDSI) data and monthly precipitation data from China, using linear trend analysis, comparative analysis and EOF methods, the spatiotemporal evolution of the droughts and floods over China during 1961-2010 is analyzed. Then North China and the middle and lower reaches of the Yangtze River are selected to study the moisture transport that influences summer rainfall.Then, based on the data of daily wind and specific humidity, surface pressure from NCEP/NCAR and the data of monthly average precipitation of 160 stations in China from National Climate Center, and according to correlation filed of precipitation and water vapor transport, the water vapor transport which is perpendicular to a cross section is defined as objective indicators of vapor transport path, and six mainly vapor transport paths are found out for North China. The results show that the confluent water vapor path, the water vapor path which outputs to the east, the water vapor path which inputs from the west and the water vapor path from the South China Sea have obvious inter-decadal variation and the inter-decadal variation is basically the same as the inter-decadal variation of summer precipitation in North China. It is found that the water vapor path which outputs to the east and the water vapor path which inputs from the west have main impact on the precipitation in North China on summer though sliding correlation analysis. It is influenced by westerly. Second, the water vapor transport of water vapor path which is from the west of North China increased, at the same time which is from the southeast of Pacific Ocean enhanced obviously. Then water vapor which by passing the middle and lower Yangtze river and the South China and directly transporting to the North China and Northeast China results in heavy precipitation of North China and Northeast China and slight precipitation of the south and the Yangtze. However, the water vapor from the bay of Bengal began to influence the precipitation in North China in summer from 2000. Daily wind, specific humidity, and surface pressure data from NCEP/NCAR, and monthly average rainfall data from 160 stations of National Climate Center in China are used to examine summer rainfall-influencing moisture transport in the middle and lower reaches of the Yangtze River. Results show the moisture originates along the south boundary. On the basis of this, area, center intensity, eastern ridge point, and boundary intensity indices are defined. It can be found that the moisture transport influences rainfall in different areas over China in summer through correlation analysis. A significant turning point comes in the 1990s to all indices. There're obvious interdecadal changes in indices of area, central intensity, and zonal intensity in the boundary. Correlation analysis shows that moisture transport influences summer rainfall in different areas over China, and that area and center intensity indices are negatively correlated with the western Pacific SST, but positively correlated with the eastern and equatorial Pacific SST. It also shows that higher winter eastern Pacific SST strengthens moisture transport from the western Pacific during summer, which enhances summer rainfall in the middle and lower reaches of the Yangtze River. |
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