【作者】 李祥；

【导师】 杨书运； 杨帅；

【作者基本信息】 安徽农业大学 ， 气象学， 2021， 硕士

【摘要】 暴雨每年频繁发生,所致洪涝灾害严重。但我国地域广阔,暴雨类型多样,形成条件和机制各有不同,导致预测预报难度大。在我国西部地区,在青藏高原大地形的热动力作用影响下,夏季对流活跃,暴雨频发。尤其是高原东南侧地形复杂地区,一旦发生暴雨,很容易引发严重的地质灾害,并中断运输,农业和工业活动,造成严重的经济损失并威胁人民生命安全。因此,急需对高原东侧复杂地形地区暴雨的发生发展机制进行理论和模拟研究,这也是暴雨预报的基础。本文针对2019年8月5-6日四川一次东传型强降水事件,揭示了高原东侧多涡旋接力发展导致降水发展和传播的现象。利用涡度方程对诊断分析了影响不同涡旋发展的要素;并从能量演变的角度,揭示了涡旋降水加强、对流增长的原因。同时通过构建地形、开展地形坡度变化敏感性试验,评估青藏高原、横断山脉和四川盆地三大地形对高原东侧涡旋演变的作,研究坡度的改变对涡旋传播的影响。所得结果如下:(1)通过2019年夏季8月5-7日四川暴雨过程的逐小时降水和涡旋演变分析,发现高原东侧多涡旋的接力发展,导致降水向东发展和传播的现象。在研究区域和降水时段内,主要受三个涡旋影响:将高原北部向东北方向移动的部分称为高原涡1(PLV1),将高原南部向东移动的部分称为高原涡2(PLV2),在四川盆地上空生成的西南涡(SWV)。PLV1在0500时于高原上空生成之后向东北向移动并于0517时逐渐消散,PLV2在0508时开始在高原上空逐渐加强并东移,在0522时左右和西南涡合并,SWV在0511时左右在四川盆地附近生成并和PLV2在0522时左右合并,之后一起东移,于0615时左右逐渐移出模拟区域。降水发展和传播与多涡旋的路径的强度演变密切相关。(2)通过涡度方程诊断分析了影响不同涡旋发生的主导因子,剖析三个涡旋发展的机制有何异同。发现PLV1以垂直平流项和拉伸项为主要贡献项;对于PLV2,主导项为垂直平流项和拉伸项;而SWV2的主要贡献项为垂直平流项和水平平流项;利用能量方程,揭示了局地总能量异常的演变特征。发现在对流系统的东部出现正能量异常,可指示对流系统的发展方向,即向东传播。(3)通过青藏高原、横断山脉和四川盆地等多尺度地形的敏感性试验,探讨各大地形对涡旋发展的作用。结果表明,横断山脉对西南涡的形成起主导作用,而四川盆地对西南涡的形成起次要作用。对于高原涡旋(PLV2)的传播,四川盆地只会影响涡旋的强度,而不会影响高原涡旋的传播路径。一旦横断山脉被移除,高原涡旋的传播现象将不再出现;在青藏高原、横断山脉和四川盆地交界的陡峭地形处,地形坡度改变的敏感性实验表明,坡度越陡,高原涡(PLV2)的传播速度越快,同时盆地内的西南涡越强。而高原涡发展的高度(即最强涡度垂直伸展的高度),几乎稳定维持在地形上空相同高度位置,受(陡坡/缓坡)坡度变化的影响较小。更多还原

【Abstract】 Heavy rains occur frequently every year,causing serious flood disasters.However,China has a vast area and various types of rainstorms,and their formation conditions and mechanisms are different,which makes it difficult to forecast.Especially in the western region of China,under the influence of the thermal power of the Qinghai-Tibet Plateau,the convection is active in summer and the rainstorm is frequent.In particular,in the complex terrain area on the southeast side of the plateau,heavy rain is likely to cause geological disasters such as mud-rock flow,mountain torrents and landslides,which will cause serious losses to the national economy and the safety of people’s lives and property.Therefore,it is urgent to conduct theoretical and simulation research on the occurrence and development mechanism of rainstorm in the complex terrain area on the east side of the Plateau,which is also the basis of rainstorm forecast.Based on an eastward heavy precipitation event in Sichuan Province during August 5-6,2019,this paper reveals the phenomenon of precipitation development and transmission caused by multiple vortices relay development on the eastern side of the Plateau.The factors affecting the development of different vortices are analyzed by using the vorticity equation.From the Angle of energy evolution,the reasons for the strengthening of eddy precipitation and the increase of convection are revealed.At the same time,the influence of slope change on the evolution of vortices on the eastern side of the Plateau was evaluated by constructing topography and carrying out sensitivity tests of topographic gradient change.(1)For the vortices in the studied region and period,the northern part of the Plateau Vortex moving to the northeast is called Plateau Vortex 1(PLV1),and the southern part of the Plateau Vortex moving to the east is called Plateau Vortex 2(PLV2),and the southwest vortex(SWV)generated over the Sichuan Basin.PLV1 after over the plateau generated when in 0500 east north to mobile and dissipating,during the 0517PLV2 began in 0508 when gradually strengthened and eastward over the plateau,in at around0522 and southwest vortex merging,SWV generated near the Sichuan basin and around 0511 and PLV2 around 0522 when the merger,after the east together,in 0615 when gradually removed from the simulation area.(1)Based on the analysis of hourly precipitation and eddy evolution during the rainstorm in Sichuan Province during August 5-7,2019,it is found that the evolution of multiple vortices on the eastern side of the Plateau leads to the eastward development and propagation of precipitation.In the study area and precipitation period,there are three vortices: the northeast moving part of the northern part of the Plateau is called Plateau Vortex1(PLV1),and the eastward moving part of the southern part of the Plateau is called Plateau Vortex 2(PLV2),and the southwest vortex(SWV)generated over the Sichuan Basin.PLV1 was generated over the Plateau at 0500 and then moved eastward and northward and dissipated gradually at 0517.PLV2 gradually strengthened over the Plateau at 0508 and moved eastward,and merged with the southwest vortex at about 0522.SWV was generated near the Sichuan Basin at about 0511 and merged with PLV2 at about 0522.Then they moved eastward together and gradually moved out of the simulation area at about 0615.The development and propagation of precipitation are closely related to the intensity evolution of multi-vortex paths.(2)Based on the vorticity equation,the dominant factors affecting the occurrence of different vortices were diagnosed and analyzed,and the similarities and differences of the development mechanisms of the three vortices were analyzed.It is found that the vertical advection term and the tensile term are the main contribution items of PLV1.For PLv2,the dominant term is vertical advection term and tensile term.The main contribution of SWV2 is vertical advection and horizontal advection.Using the energy equation,the evolution characteristics of local total energy anomalies are revealed.It is found that the positive energy anomaly in the east of the convective system indicates the development direction of the convective system,that is,eastward propagation.(3)Based on the sensitivity tests of multi-scale topography,such as the Qinghai-Tibet Plateau,Hengduan Mountains and Sichuan Basin,the effects on the development of vortices are discussed.The results show that the Hengduan Mountains play a leading role in the formation of the southwest vortex,while the Sichuan Basin plays a secondary role in the formation of the southwest vortex.For the propagation of the Plateau Vortex(PLV2),the Sichuan Basin only affects the intensity of the vortex,but does not affect the propagation path of the Plateau Vortex.Once Hengduan Mountains are removed,the Plateau vortex propagation phenomenon will no longer appear.In the steep terrain at the junction of Qinghai-Tibet Plateau,Hengduan Mountains and Sichuan Basin,the sensitivity experiments of topographic slope change show that the steeper the slope is,the faster the propagation speed of the Plateau Vortex(PLV2)is,and the stronger the Southwest Vortex in the basin is.On the other hand,the height of the Plateau vortex development(i.e.,the height at which the strongest vorticity extends vertically)is almost stable at the same height over the terrain,and is less affected by(steep/gentle slope)slope change.更多还原