Feature Of Stratospheric Circulation Transition In Northern Hemisphere And Relationship With Troposphere Circulation

The stratosphereric circulation (SC) is closely related to the tropospheric circulation (TC) and has significant seasonal variations. The seasonal transition of the SC is earlier than that of the TC, and the abnormal signals in the stratosphere may be used as a pre-signal to predict the variations of the TC. So it is significant to study the seasonal transition date in the stratosphere and the poential influence of the SC.According to the different circulation features in the stratosphere in winter and summer, a transition date index (TDI) is defined to indicate the transition date from summer to winter circulations in the stratosphere in the Northern Hemisphere. Based on TDI, this thesis shows the climate features of TDI as well as the relationship between TDI and south China sea onset (SCS), relationship between TDI and the subtropical high over the west pacific. Some conclusions are drawn as follows.1) The circulation patterns in the stratosphere are different in winter and summer. In winter, the cold cyclone system and westerly winds prevail in high latitudes, while in summer it is characterized as anticyclone system and weak easterly winds. Monthly circulation variations in the stratosphere and troposphere are significant in winter and weak in summer, and increase with heights from the troposphere to the stratosphere.2) Based on the inversion of potential height gradient and wind direction, a transition date index (TDI) in the stratosphere is defined to reflect the circulation from winter pattern to summer pattern, which occurs firstly in higher levels and then spreads to lower levels. The spreading speed becomes slow from the high level to the low level of the stratosphere. Furthermore, although the regions in the Northern Hemisphere show different dates at each level in the stratosphere, it is proved that they share some decadal similarities, which are characterized as later to earlier period and earlier to the late stage. The time scales of TDI show Quasi-biennial oscillations, approximate 3～6 years,9～12 years,21～24 years.3) The relationship between TDI and SCS, the subtropical high and summer precipitation in two different periods ranging from 1958 to 1990 and from 1991 to 2008 shows that the average TDI is earlier than the SCS onset. In 1990s, the 21-year sliding correlation coefficients between the TDI, the SCS onset date, and the western Pacific subtropical high have changed greatly and turned into a negative correlation from a significant positive correlation. Before 1990s, it presents a significant positive correlation and vice versa after 1990s. Further analysis illustrates that the seasonal transition in the SC has provided key information for prediction of variations of the western Pacific subtropical high in the period of 1958-1990. In addition, the relationship between the TDI and 500hPa height anomaly field in June mainly shows a negative correlation.This thesis intends to study the basic features of the stratospheric circulation transition in the northern hemisphere and to explore the relationship between the TDI and the SCS, the West Pacific subtropical high. Results suggest that the TDI has annual and decadal variations. The abnormal signal in the stratosphere should be fully considered when the TDI is used as the pre-signal to predict the SCS and the subtropical high over the West Pacific.