The Partition Of East China Based On The Summer Rainfall Isotropy And Its Climatological Analysis

In this thesis, the conception 'isotropy' is introduced to study partition of East China according to summer precipitation. East China is divided into eight subareas. Based on this, the characteristic of summer precipitation and its relation with the anomalies of atmospheric circulation and sea surface temperature (SST) in every subarea are studied. The main results obtained from this thesis are summarized as followed:1) East China is divided into eight subareas according to the conception 'isotropy', and the precipitation index is given to depict the characteristic of summer precipitation in every subarea. The summer rain belt in East China advanced gradually from south, and it is same with the advance of monsoon in East China. It is obvious of the interannual varability of summer precipitation in every subarea, and there exist the turn points in the end of 1970s, the middle of 1960s and the early 1990s.2) The four water inflow corridors play an important role in the summer precipitation in every subarea. The water vapor source affecting subareas is different from each other. Although the pressure level of water vapor transport according to subareas is different, the water vapor transport is mainly above 850 hPa. The water vapor divergences over the middle and lower reaches of Changjiang River, Yellow River, and Northeast China 2 subareas, whereas convergences over other five subareas. The characteristics of interannual variability about water vapor's budget over every subarea are very different.3) The atmospheric circulation anomalies are analyzed during the flood and the drought years in every subarea. During the flood years, the anomalous updraft is dominant and the cyclonic anomaly centers at 850 hPa over the every subarea, and the western Pacific subtropical high (WPSH) ridge line shifts northward. They display the reverse feature in the drought years. While the rain belt moves northward, the difference regions of the vertical velocity at 850 hPa between the flood and drought years moves northward, and the western Pacific subtropical high ridge line and the axis of subtropical westerly jet also shift northward. The rain belt locates in the area which lies north of the WPSH ridge line and south of the axis of subtropical westerly jet.4) The relationship between the precipitation in every subarea and the global SST is discussed. The results show that the summer precipitation in eight subarea is affected by the SST of the different ocean areas. It is found that the summer precipitation in the middle and lower reaches of Changjiang River positively correlates with the SST in the western Pacific, and the strongest correlation coefficients between the summer precipitation and the summer SST in the western Pacific exceeds 0.60. While the SST in the west Pacific is warmer (colder), the summer WPSH ridge line shifts northward (southward) , implying that the SST in the west Pacific affect the summer precipitation in the middle and lower reaches of Changjiang River through its influence on the summer WHPS.5) The characteristics of the autumn precipitation in the south China is discussed simply in the last character. Results indicate a strong interannual variability of autumn precipitation over South China. In the flood years, the WPSH ridge line lies over the south of South China and the strengthened ridge over North Asia triggers the cold air southward moving, and there exist significantly anomalous updraft and cyclone with the northward stream strengthened at 850 hPa and a positive anomaly center of meridional moisture transport strengthening the northward warm and humid water transport over South China. They display the reverse feature in the drought years. The autumn precipitation interannual variability over South China positively correlates with the SST in the western Pacific and the North Pacific, whereas a negative correlation occurs in the South India Ocean in July. The further discussion about the linkage among the July SST in the western Pacific, it suggests that the SST anomalies might contribute to the autumn precipitation through its closed relation to the autumn WPSH.