Study On Tropospheric Quasi-Biennial Oscillation (TBO) Of East China Precipitation

Using 160 stations precipitation of China from 1951-2005, NCAR/NCEP reanalysis data set and ERSST (Extended Reconstruction of Global Sea Surface Temperatures) data, east China summer precipitation TBO's climate characteristics are studied and argued and further to discussed their mechanism by many statistical methods. The results as followed:1. The main rainfall is in the period of summer for China with the obvious feature of TBO, the areas with distinct TBO of summer rainfall for China are respectively in northeast of Tibet, south of Northeast China, the basin of Yangzi and Huaihe, south China to southwest China and north of Xinjiang.2. Based on the characteristic of summer rainfall TBO, east China is divided into 7 sections including northeast China, Hetao basin, Huaihe basin, Yangzi basin, west South China, centre South China and east South China. The divisions own different evolution. 1950s, the rainfall of all divisions have strong TBO except west of south China, from early 1960s to late, all divisions own weaker TBO besides west of south China and Hetao basin, in the period of mid-late 1970s to mid-1980s, there are obvious TBO for Hetao basin, Huaihe basin, Yangzi basin and centre of south China, mid-1980s to early 1990s, only Huaihe and Yangzi basin have marked TBO signal, from to early 1990s to today, almost all divisions represent the tendency of reinforcing of TBO but Hetao basin. Huaihe basin is the key area and the sensitive area of summer rainfall TBO for east China.3. POP analysis of summer rainfall TBO of east China get two main modes. The real part mode is called transition mode which represent two small negative center in center-low Yangzi basin and southwest China, other areas all be zero, the imaginary part is called peak value mode which have a big extent positive value center in Yangzi and Huaihe basin. The first POPs' variance is 18.2% and the period is about 2 years. By analysis and theory of the POP and ACP, the first summer, east and central Pacific SST rise as following stronger convection meanwhile west Pacific SST decrease with weaker convection, zonal wind anomaly in equator troposphere, weaker Hadley cell and anomaly cyclone cover the SCS-East China reducing Asia summer monsoon. The second summer, the circulation revise, SCS and anomaly anticyclone cover East China and reinforce summer monsoon.4. The EOF's analysis of east China summer rainfall shows that TBO of summer rainfall exist two main modes. The first mode's variance is 20.15% with bigger amplitude which reflects out phase change between north and south by 27°N. The second mode's variance is 13.06% with smaller amplitude which shows the relationship of out phase for Heitao-north Chian belt with its north and south zone, which center is far north than that of first.East China summer rainfall TBO is closed with air circulation anomaly. When summer rainfall TBO is the first mode, there is distinct circulation anomaly in troposphere from equator to mid-high latitude, while anomaly extent is bigger, which means the first mode have tight relationship with interaction between low and mid-high latitude, and it is important to for the effect of air circulation anomaly of south Hemisphere. When the summer rainfall TBO is the second mode, circulation anomaly is almost in subtropical zone and mid-high latitude.5. The SEOF analysis on summer rainfall TBO of East China shows the first two modes are main modes which reflect primary features in seasons for summer rainfall TBO. The SEOF1 is called ENSO-TBO mode which principal characteristic of SSTA and circulation background is, by the developing of ENSO, that equator and subtropical circulation anomaly move to east gradually, anomaly east wind, generated in India Ocean, moves to east and became an anomaly anticyclone in martin of east China and northwest Pacific which maintains to the second summer, so it is the key system of ENSO-TBO of east China summer rainfall. The SEOF2 is called non-ENSO-TBO mode which is not on obvious SSTA background, the corresponding air circulation analysis suggests SEOF2 mode is closely relationship with the anomaly of mid-high latitude circulation.6. ECHAM4 can simulate the average climate state of air circulation. However, the simulation of winter is that of summer, and that of Asia rainfall is weak. The main period of mode of Asia summer rainfall is able to find weaker TBO signal but for the main period of 4-6 years.