Characteristics of moisture transport in middle and lower reaches of Yangtze River and its variation trend

The structure of vapor transport and its decadal variation trend in the middle and lower reaches of Yangtze River in the processes of drought or flooding are studied by means of comprehensive analysis on whole layer moisture net budget and boundary flow of box-web structure in atmosphere. It is found that there is a region with significant varying subtropical high pressure in West Pacific and South China Sea, which is located at low latitude area. The annual variation of the high pressure is closely related to the East Asian summer monsoon water vapor transport structure in mid-low latitude area and precipitation in middle and lower reaches of Yangtze Riven. The analysis result of the deviation from average of whole layer vapor transport budget on boundaries of box structure at low-mid latitude for weak or strong monsoon shows that an anticyclone or a cyclone type of vapor transport relation chain structure will appear correspondingly. The analysis also shows that the anticyclone type vapor transport correlation characteristic is obvious in 1980s to 1990s, in this period the summer monsoon is comparatively weakened. This tendency is consistent with the precipitation variation in these two decades.