The Study Of Characteristics, Circulation Situation And Vapor Track Of Low Vortex On The Qinghai-Tibet Plateau

The low vortex on the plateau, i.e. plateau low vortex, southwest low vortex, and northwest low vortex play an important role in the strong rainfall process in plateau and the eastern part of China. It induces disastrous weather, even debris flow and other geological disasters of plateau and the surrounding area in summer. Therefore, it is not just scientific but social as well to strengthen research on the low vortex on the plateau. Meanwhile, it also provides scientific evidences for disaster prevention and reduction on heavy rain, debris flow, and other geological disasters.The data of historical weather map from1980to2000, radiosonde data from2001to2010and the data NCEP/NCAR from1980to2000were used in this paper. Firstly, the climate characteristics and circulation situations of low vortex were analysed; secondly, interactions of low vortex and other weather system were expounded; thirdly, vapor track of heavy rain caused by low vortex was studied; lastly, the strong rainfall and derivative disaster caused by low vortex on the plateau were represented. The primary results were as follows:1. Climate characteristics of low vortex on the Plateau(1) Temporal characteristics: During1980-2010year, the yearly variations of low vortex on the plateau was decreasing, the most difference was months that the most frequently presented of the low vortex. July was the most frequently represented of the plateau low vortex and the southwest low vortex; May was the most frequently occurred of the northwest low vortex. Frequency of plateau vortex and northwest low vortex in night is less than that in day, while the southwest low vortex is on the contrary. When the years of1980-2010were divided into three time periods evenly, May was still the most frequently occurred of the northwest low vortex in each time period, while the months which the most frequently represented of the plateau vortex and southwest low vortex existed some significant change in different years. July was the most frequently represented of the plateau vortex before2000, the most frequently represented of the plateau vortex was in May from2001to2010. June, July and May were the most frequently occurred of the southwest low vortex during the three time period, respectively. It indicated that the plateau vortex and the southwest low vortex were more sensitive than the northwest low vortex in response to the warming climate.(2) Spatial characteristics:the vorticity source of the plateau low vortex concentrated on Nagqu and Songpan, especially Nagqu. The vorticity source of southwest low vortex mainly concentrated on Sichuan Basin, the second is xiaojin region, last is Kowloon. The vorticity source of northwest low vortex mainly concentrated on Qaidam Basin.2. The circulation situation of low vortex on the Plateau and relationship between low vortex on the Plateau and other weather systems(1) The circulation situation was remarkably different in simultaneous occurrence and intermittent of plateau low vortex. In the period of simultaneous occurrence, the position of South Asia high was toward west in200hPa, and intensity of weather system in500hPa is stronger than intermittent.(2) The circulation situation of eastward the northwest low vortex in200hPa was dominated by eastern pattern of South Asia high, the upper troughs of500hPa is strong or weak that directly affect moving eastwards of the northwest low vortex. In addition, the simultaneity circulation situation of eastward the northwest low vortex and the plateau low vortex were in accordance with eastward the northwest low vortex. It suggested that the plateau low vortex and southwest low vortex occurring simultaneously is benefit for moving eastwards of the northwest low vortex.In a word, the relationship between low vortex on the Plateau and South Asia high is close, when the southwest low vortex was associated with the plateau low vortex, the southwest low vortex was locate in northeast of South Asia high before July, while locate in east of South Asia high after July (including July); the circulation situation in200hPa was mainly banding pattern of South Asia high, followed by eastern pattern. Eastward northwest low vortex was locate in northeast of South Asia high, the circulation situation in200hPa was eastern pattern-dominated of South Asia high, followed by banding pattern.(3) The relationship within low vortex on the Plateau:the probability that occurrence of the plateau low vortex along with eastward the northwest low vortex was higher than that occurrence of eastward the northwest low vortex along with the plateau low vortex. It suggested that moving eastwards of the northwest low vortex was influenced by the plateau low vortex and relevant circulation situation and weather system.3. Analysis of vapor track of heavy rain during the frequency of low vortex on the PlateauThe HYSPLIT model is one of the ways that can be used to study the vapor track. Different low vortex on the Plateau affect different areas precipitation due to the difference of movement direction; because of the difference of location, the different area precipitations have different water steam sources. Vapor source of Hetao region which affected by the northwest low vortex comes from Bay of Bengal; vapor source of Sichuan Basin which affected by the plateau low vortex comes from south-west stream brought by East Asia Monsoon; vapor source of South China which affected by the southwest low vortex comes from South hemisphere cross-equatorial flow.4. Derived disasters of low vortex on the PlateauCoupled action of the plateau low vortex and the southwest low vortex may cause rainstorms and big rainstorms, and then cause natural disaster like landslides, debris flow; while the northwest low vortex dose not react with other low vortex on the Plateau. The northwest low vortex and the southwest low vortex can cause hard rain unless the match of other weather systems (such as cold front, southwest jet, and southerly stream).