The Characteristics Of Atmospheric Water Budget Over The Eastern China Monsoon Wetness Region

Using daily and monthly means of the reanalysis datasets from the NCAR/NCEP1,NECP/NCAR2,ECMWF(ERA40),rainfall data from 160 and 757(June～August)surface stations in China for the period 1958 to 2007 and referring to atmospheric circulations in eastern China monsoon wetness region. We use the empirical orthogonal function decomposition (EOF), wavelet analysis, singular value decomposition (SVD), Mann-Kendall test and other statistical methods and related synthetic,composite diagnosis methods, systematic analyzing the climatic character of moisture budgets in Eastern China monsoon wetness region and the spatial temporal distribution of precipitation and water vapor transport. We analyze the winter and summer moisture balance in high and low values years(decadal years) which corresponding to water vapor transport anomaly, atmospheric circulation anomalies, winter and summer monsoon strength, the meridional wind anomalies, precipitation anomalies and so on. At the same time, we use the RegCM3 mode to simulation the winter and summer anomaly of water vapor transport,moisture flux divergence and precipitation in high and low values years(decadal years) in Eastern China monsoon wetness region.The major conclusions can be summarized as follows:⑴For yearly moisture budgets in this area, moisture has incoming, and the same results for spring, summer, autumn, winter. Based on different method to calculate moisture balance, we have got that water vapor transport and moisture budgets are stronger in spring and summer, while in winter and autumn are relative weak.⑵For the meridional water wapor transport, water vapor enters this area mainly in south boundary, and enters through west boundary and departs from east boundary all the year For the zonal. For whole area, the moisture budget which is calculated by water wapor transport method is positive from February to October. Meanwhile, moisture budgets which are calculated by moisture flux divergence method or P ? Emethod, the results are positive in February to September in the same time.⑶Based on water wapor transport and moisture flux divergence methods which calculate the vertical distribution of moisture budgets under climatically, the values manifest positive anomaly between 800～500hPa. We have got that moisture output at 850hPa, other layers input under climatically. The vertical distribution of moisture budgets is different for seasons, the values manifest positive in the lower troposphere in spring and summer, while manifesting negative in autumn and winter. The values manifest positive in the upper troposphere for seasons. The interannual variability of four seasons is explicitly and shows a significant linear trend in the decades.⑷Using M-K tests to analyze the the time series of moisture budgets for annual and four seasons, revealed the existence of abrupt change from each time series; Using wavelet analysis, revealed the period of each time series mainly in 2 to 4 years.⑸Using EOF method in winter and summer to analyze precipitation and water vapor transport field, revealed the character of the temporal and spatial distribution. Using SVD method in winter and summer to analyze precipitation and water vapor transport field, found out that there have a relationship with the phase change.⑹The high values of moisture budgets are not only reflecte the variations of the anomaly of meridional winds but also indicate an intensity of winter monsoon and an anomaly of rainfall along the valleys in the Eastern China monsoon wetness region. Corresponding to the higher value years, the high and cold pressure centering in Mongolia and the low pressure centering in Aleutian are weaker. Meanwhile, the southerly wind anomalies prevail in the lower troposphere and anomaly cyclone circulation in the vertical troposphere over the mainland of China, therefore intensifying the convergence and upward motion in south of 30°N and coordinating with the water vapor transport of Bay of Bengal and South China Sea. It causes the moisture budgets and anomaly rainfall to increase, but the lower value years are oppositely. The difference in composites for water vapor transport importes between 900 to 600 hPa, western or southern boundary is the major input region, the remains are the contrary. The larger difference in composites for moisture budgets is in meridional, accounting for 91.3% for net incoming change, the difference in composites for the zonal moisture budgets is smaller. The difference in composites for rainfall is above 40mm in center. The difference in composites for decadal rainfall is above 30mm in center. The mean flow brings about moisture convergence, and transient eddy brings about divergence. In higher value years, the southerly transient eddy of water vapour transport is weaker in the South China Sea, and stronger in the eastern China.⑺The moisture budgets sequence display the significant interannual variations in summer, Not only reflecte the variations of the anomaly of meridional winds but also indicate an intensity of summer monsoon and an anomaly of rainfall along the valleys in the Eastern China monsoon wetness region. The difference between high and low values of integrated water vapor transport to East Asia-Western Pacific Region shows the three-pole type. Different levels of atmospheric circulation anomalies in composite are conducive to water vapor input, increaseing the moisture and precipitation. Differences between high and low values of precipitation in composite mainly causes to the change of income and expenditure meridional moisture budgets, but the change of zonal budget contributes to this difference only by 1/4.⑻The interdecadal variations of summer moisture budgets, in high value era, the summer monsoon is weak, subtropical high is wester and stronger; Asian thermal low pressure is weak, the lower troposphere appears anomalous cyclonic circulation, and prevails anomalous southerly wind, as more water vapor enter from the outside, accompanies with the strong upward motion, so it is easy to the generation of precipitation. The difference in composite for water vapor transport importes between 900 to 500 hPa, Accompanying with the difference and significant anomaly for rainfall, the main reason is changes by the incoming and expenditure in meridional moisture budgets. Before May, the precipitation is less than normal, corresponding to the negative anomaly of water vapor transport in meridional and zonal; between June to August, the precipitation is more than normal, corresponding to the positive anomaly of water vapor transport; after October, the precipitation is negative and water vapor transport is positive. But the low value era is oppositely.⑼The high values region of water vapor flux by transient eddy northerly in summer than winter. In higher value era, the southerly and westerly transient eddy of water vapour transport is stronger in the eastern China and the South China Sea. The interdecadal variability of moisture budgets can reflect from NECP1,NECP2,ERA-40 reanalysis datasets, and the same difference of distribution in composite for water vapor transport and moisture flux divergence.⑽RegCM3 model has a good ability to simulate the interdecadal variation of precipitation, the difference in composite for SWT2 is better than SWT1, it can reveal one of the reasons that land-sea thermal difference will affect the atmospheric circulation anomalies in summer.