【作者】 李江萍；

【导师】 王式功；

【作者基本信息】 兰州大学 ， 气象学， 2012， 博士

【摘要】 高原低涡(高原涡、西南涡和西北涡)是影响高原及其东部邻近地区强降水过程的重要天气系统,可造成高原上及周边地区夏秋季节严重的洪水灾害,甚至引发泥石流等地质灾害。因此,加强高原低涡研究既有重要的科学意义,又有广泛的社会意义,同时也可为该地区暴雨、泥石流等灾害的防御提供科学依据和技术支撑。本文利用1980—2000年夏半年(5-9月)逐日08、20时(北京时)500hPa和700hPa历史天气图、2001—2010年探空资料及相应时期的NCEP资料,在分析了高原低涡的时空分布及环流形势的基础上,探讨了高原低涡与其它天气系统之间的关系,研究了高原低涡频发期强降水过程的水汽输送轨迹以及由低涡引发的强降水及其衍生灾害。主要研究结果及结论如下：1.高原低涡的气候特征(1)时间变化特征：1980—2010年期间,总体上三种高原低涡发生频数的逐年变化都呈下降趋势,其最大差异是三种低涡出现频数最多的月份有明显不同,虽然它们在5、6、7三个月发生频数都比较高,但高原涡7月发生频数最多,西南涡也是7月份,西北涡则是5月份发生频数最多。高原涡与西北涡夜间发生频数小于白天,而西南涡则是夜间发生频数大于白天。进一步分析高原低涡在1980—2010年期间的年代际变化特征,发现西北涡在每个年代出现频数最多的月份与前述结果一致；而高原涡与西南涡的逐月分布有显著的年代际变化,说明它们比西北涡对气候变暖的响应程度更敏感。此外,高原涡的群发／间歇性特征显著,但是高原涡的群发期最明显的时间并不对应间歇期最明显的时间,并且高原涡群发性显著的年份不完全对应高原涡发生次数最多的年份。(2)空间分布特征：高原涡主要位于那曲、松潘,有两个集中区,且以那曲中心为主；西南涡最活跃的地区是四川盆地,小金次之,九龙最少；西北涡则主要集中在柴达木盆地。2.高原低涡的环流形势及与其它天气系统的关系(1)高原涡群发与间歇期的大气环流形势存在显著差异：群发期,200hPa上南亚高压(夏季位于青藏高原上空时也称其为青藏高压,下同)位置偏西,500hPa上天气系统的强度均比间歇期强。(2)东移西北涡的大气环流形势,200hPa以南亚高压的东部型为主,5500hPa上高空槽的强弱直接影响西北涡的东移发展。另外,东移西北涡与高原涡同时出现时的大气环流形势与东移西北涡的环流形势基本一致,说明高原涡与西北涡的同时出现也有利于西北涡的东移。总之,三类高原低涡与南亚高压的关系密切,同时有高原涡出现的西南涡与南亚高压的相对位置随时间有变化,且南亚高压以带状型为主,东部型次之；东移西北涡位于南亚高压的东北方向,南亚高压则以东部型为主,带状型次之。(3)三类高原低涡之间的关系：东移西北涡出现时产生高原涡的几率大于高原涡出现时有东移西北涡产生的几率,说明西北涡的东移会受到高原涡及其相关环流形势和天气系统的影响。3.高原低涡频发期强降水天气过程的水汽输送轨迹后向轨迹模型可作为判断降水过程中水汽来源的有效方法之一,本文运用此方法对高原低涡频发期强降水天气过程的水汽输送轨迹进行了初步分析。结果表明,不同类型的高原低涡,由于其水汽来源不同、移动方向也不同,可影响不同地区的降水。其中,西北涡向东北移动所影响的河套地区的强降水,其水汽主要来自孟加拉湾和印度洋；高原涡东移所影响的四川盆地的强降水,其水汽主要由东亚季风输送来的；西南涡向东南移所影响的华南地区的强降水,其水汽来源除了赤道西太平洋和南海外,可能还含有来自南半球的越赤道气流的输送。4.高原低涡的衍生灾害高原涡与西南涡的耦合作用,可引起相关地区的暴雨和大暴雨天气,进而引发山体滑坡、泥石流等自然灾害；而西北涡一般不太可能与其它低涡发生作用。西南涡与西北涡产生的暴雨,通常是在其它天气系统(如冷锋活动、西南急流、偏南气流等)配合下完成的。更多还原

【Abstract】 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).更多还原