| 祁连山地区大气背景场及地形云降水过程的特征分析 | |
| Alternative Title | Characteristics analysis of atmospheric background field and topographic cloud precipitation process in Qilian Mountains |
| 把黎 | |
| Subtype | 硕士 |
| Thesis Advisor | 张文煜 |
| 2020-07-27 | |
| Degree Grantor | 兰州大学 |
| Place of Conferral | 兰州 |
| Degree Name | 理学硕士 |
| Degree Discipline | 气象学 |
| Keyword | 祁连山 背景场 地形云 降水过程 天气分析 回波分析 特征 |
| Abstract | ~为了合理利用祁连山的云水资源，对祁连山的背景场及地形云降水过程有更全面深入的理解，论文采用2017-2019年的常规地面观测数据、对应的天气雷达数据、探空数据、卫星数据及1979-2018年的ERA-interim再分析资料中的高低空风场数据，对控制祁连山的环流形势、高低空流场特征及地形云降水过程的天气背景场、物理量场、雷达回波变化特征进行了分析研究，得出以下主要结论： 控制祁连山的环流系统主要是西风带环流系统、高原季风系统和东亚、南亚季风系统，这一地区也是三个环流系统边缘影响的交汇带。有利于降水的天气形势主要有四类，分别为高空西风冷槽或冷平流型、蒙古冷涡（槽）型、高原低值系统（冷槽、切变和低涡）型和西南气流阻塞型。 祁连山地面流场盛行西南风和东南风，风速39年来有减小趋势，与三江源相比其值略小。夜间盛行辐散气流，辐散中心冬季主要位于祁连山西段、夏季主要位于祁连山中东段白天盛行辐合气流，辐合带主要位于祁连山中东段，夏季辐合带更清晰。结合祁连山降水分布落区分析发现，祁连山中段北坡降水较大时的原因，一方面是大尺度系统配合使地面辐合线维持时间较长，使气流不断抬升形成地形云另一方面是分散性地形云形成后，在高空引导气流的引导下，在移动过程中不断加强。 祁连山地面流场主要有七种类型：西北气流型、西北转东北气流型、东南或偏南气流型、东南转东北气流型、西北-东南气流辐合型、东北-西南气流辐合型、偏西或西南气流型。 祁连山降水过程：高空冷平流强迫型，云团主要向东南方移动副高外围的暖区降水型，云团主要向东或东北方移动低层暖平流强迫类，云团主要向东方移动。地形云降水云团的尺度主要以中&beta为主，云团形成后，在移动过程中经过祁连山中东段北坡的山脉，经历一个加强甚至是再生成的过程，在山脉的顶端至山腰间达到最强，移出山脉后，移至河西走廊平原时会逐渐减弱消亡。低层势函数在过程开始前表现为强辐合，势函数中心移过祁连山中段北坡后加强，说明地形云在祁连山生成后，向东移动的过程中，会经历再次增强的过程。垂直速度在过程开始前，于祁连山中段北坡加强，随时间变化梯度增大，中心强度在0.4-0.7pa/s，正的垂直速度大值区就是强上升气流区，也是地形云发展旺盛的地区。 祁连山降水过程：反射率因子演变特征表现为对流单体核心初始发展高度离地约5km，最强反射率因子可达45dbz，回波顶高可达10km，同时地形抬升作用，对中&alpha回波块的形成、加强有重要作用。速度场表现为底层气旋式辐合，高层反气旋式辐散，发展最强时的单体正负速度对达10.7m/s以上。对流单体发展至旺盛阶段，强反射率因子剖面可以看到>40dbz的对流单体核心发展的垂直深度可达6km, 对流单体的水平尺度达10km，低层到高层强反射率因子回波中心近于重合。 |
| Other Abstract | ~For the reasonable utilization of the rapid expanding of qilian mountain resources field and the atmospheric background of qilian mountain terrain cloud precipitation process have a more in-depth understanding, paper using conventional ground observation data in 2017-2019, the corresponding weather radar data and sounding data, satellite data, and ERA of 1979-2018 - interim reanalysis data of high and low wind field data, to control the circulation situation of qilian mountain, high and low flow field characteristics and terrain cloud precipitation process of weather background, physical quantity field, this paper studies the changing features of radar echo, the following main conclusions: The main circulation systems controlling the Qilian Mountains are westerly circulation system, plateau monsoon system and East Asian and South Asian monsoon system. There are four types of weather patterns in favor of precipitation, namely, upper westerly trough or cold advection, Mongolian cold vortex (trough), plateau low value system (trough, shear and low vortex) and southwest airflow blocking. The surface flow field of Qilian Mountain is dominated by southwest and southeast winds, and the wind speed has been decreasing in the past 39 years. Divergence flow prevailed in the night. The divergence center was mainly located in the western section of Qilian Mountains in winter and the Middle Section of Qilian Mountains in summer. Convergence airflow prevails in the daytime, and the convergence zone is mainly located in the Middle Section of Qilian Mountains. Combined with the analysis of precipitation distribution in The Qilian Mountains, it is found that the reasons for the high precipitation in the north slope of the middle part of The Qilian Mountains are, on the one hand, that the coordination of large-scale system makes the ground convergence line maintain for a long time and the air flow continuously lift to form topographic clouds. On the other hand, after the formation of dispersed topographic clouds, they are continuously strengthened in the process of moving under the guidance of high-altitude guiding airflow. There are seven main types of surface flow fields in Qilian Mountains: northwest to northeast, southeast to south, southeast to northeast, northwest to southeast, Northeast to southwest convergent, Northeast to southwest convergent, west or southwest convergent. Precipitation process in Qilian Mountains: the upper air cold advection is forced, and the clouds mainly move to the southeast. The precipitation type in the warm area outside the subtropical high, and the clouds mainly move to the east or northeast. Low layer warm advection forced class, the clouds are mainly moving east. The scale of the topographical cloud and precipitation cloud is mainly medium. After the formation of the cloud, it passes through the mountains on the north slope of the Middle East section of Qilian Mountains during its movement, and goes through a process of strengthening and even regeneration. It reaches its maximum from the top of the mountains to the mountainside. The low-level potential function showed strong convergence before the process began. The center of the potential function strengthened after moving over the north slope of the middle part of The Qilian Mountains, indicating that the terrain cloud would be strengthened again during its eastward movement after the formation of the Qilian Mountains. Before the beginning of the process, the vertical velocity was strengthened on the north slope of the central part of Qilian Mountains, and the gradient increased with time. The central intensity was between 0.4-0.7pA /s. The large positive vertical velocity area was the area of strong updraft, and also the area where the topographical cloud developed vigorously. Precipitation process in Qilian Mountains: The evolution characteristics of reflectivity factor are as follows: the initial development height of convective cell core is about 5km from the ground, the strongest reflectivity factor is up to 45dbz, and the echo top height is up to 10km. Meanwhile, topographic uplift plays an important role in the formation and strengthening of echo block. The velocity field is characterized by low-level cyclonic convergence and high-level anticyclonic divergence. The positive and negative velocity pairs of monomer at the strongest stage are over 10.7m/s. When the convective monomer develops to a vigorous stage, the strong reflectivity factor profile shows >The vertical depth of the convective cell core developed at 40dbZ was up to 6km, the horizontal scale of the convective cell was up to 10km, and the echo center of the strong reflectivity factor was nearly coincident from low to high level. |
| Pages | 68 |
| URL | 查看原文 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | https://ir.lzu.edu.cn/handle/262010/467395 |
| Collection | 大气科学学院 |
| Affiliation | 大气科学学院 |
| First Author Affilication | College of Atmospheric Sciences |
| Recommended Citation GB/T 7714 | 把黎. 祁连山地区大气背景场及地形云降水过程的特征分析[D]. 兰州. 兰州大学,2020. |
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