出流边界触发对流新生的机理

Nowcasting of warm-season convection initiation (CI) in both temporal and spatial dimension is a worldwide challenge. Outflow boundary (gust front) produced by original convective system, as one of important and common types of boundary layer convergence lines is important triggering factor of CI. Study on mechanism of CI triggered by outflow boundaries is a key point in enhancing nowcasting and warning of localized and strong convection, also one of open and primary scientific problems to be solved for convective-scale numerical weather forecast in the world. However, there is little systematical research of the topic in China. The project will perform the study on mechanism of CI triggered by outflow boundaries, which is based on convective-scale numerical simulation with very high temporal and spatial resolution and update cycling frequency using rapid-refresh 4-D variational assimilation techniques of multi-radar observations and 3-D cloud-scale numerical models, and also analysis on observations from radars, satellites, auto surface stations, and other instruments. The study will focus on localized and rapidly intensified convection occurred over Beijing-Tianjin-Hebei region, also analyze some typical localized convection cases in Yangtze-Huaihe region. The research of the project is expected to solve some key scientific problems that is closely related to CI triggered by outflow boundaries, and shape several conceptual models and retrieve some key indicators in dynamical and thermodynamical aspects for representing CI triggered by outflow boundaries. The research findings from the project will potentially provide scientific basis for nowcasting and warning localized and rapidly intensified convection over the regions.

暖季对流新生（CI）的临近预报，不论是时间还是空间上，都是世界性难题。而原有对流系统形成的出流边界（阵风锋），作为一类重要且常见的边界层辐合线，是CI的重要触发因子。出流边界触发CI的机理研究是提升局地突发强对流临近预报、预警水平的关键所在，也是对流尺度数值天气预报所需要解决的基本科学问题之一，但在国内开展的系统性研究较少。本项目拟以京津冀地区的局地突发和快速演变对流为重点研究对象，并结合江淮地区的典型局地突发对流个例，基于雷达资料快速刷新四维变分同化技术和三维数值云模式，开展高时间分辨率和更新频次的对流尺度数值模拟，并结合雷达、卫星、自动站等观测资料分析，对出流边界触发CI的机理进行研究，回答出流边界能否触发CI的多个动力和热动力方面的关键科学问题，形成出流边界触发CI的概念模型，建立相应的的动力和热动力关键指标，为局地突发和快速演变强对流的临近预报和预警提供科学依据。

暖季对流新生（CI）的临近预报是世界难题。原有对流系统形成的出流边界（阵风锋）是CI的重要触发因子。出流边界触发CI的机理是提升局地突发强对流临近预报预警水平的关键所在，也是对流尺度数值天气预报所需解决的基本科学问题之一。项目以京津冀局地突发和快速演变对流为重点研究对象，并结合江淮地区典型局地突发对流个例，基于加密观测及高时空分辨率数值模拟，对出流边界触发CI的机理进行研究，回答出流边界能否触发CI的动力和热动力方面的关键科学问题，为局地突发和快速演变强对流的临近预报和预警提供科学依据。.借鉴国际先进技术，采用快速更新雷达四维变分同化（RR4DVar）和三维数值云模式，构建了项目模拟研究的重要工具——雷达四维变分分析系统，并在此基础上进一步研发了适合于京津冀局地突发强对流预警应用的快速更新临近数值预报系统（RMAPS-NOW）。.深入开展了北京及周边出流边界发生、演变及其触发CI特征的观测统计研究，获得了复杂地形下出流边界与对流新生和快速演变的基本关系，为京津冀出流边界导致的局地突发强天气临近预报预警提供了基本科学背景。基于高分辨率模拟数据统计分析，形成了京津冀复杂地形下出流边界影响CI和对流快速演变的概念模型，结合RMAPS-NOW系统实时模拟产品，为京津冀出流边界导致的局地突发强天气临近预报预警提供了有力判据。.通过多个典型个例的观测及模拟分析，深入认识了京津冀复杂地形下出流边界触发对流新生和快速演变的不同机理，包括：出流边界对强对流局地新生及快速增强的动力效应；冷锋与干线、出流边界相遇触发强对流过程的机制；弱天气系统强迫下对流下山演变热动力机制差异；京津冀南部平原出流边界与水平对流滚轴云（HCRs）交叉碰撞导致对流新生的机制；阵风锋导致对流快速加强形成短时大风的机制；导致北京局地突发强降水维持的云桥单体形成的关键机制。另外，对江苏平坦地区中尺度对流系统中与出流边界密切相关的不同单体新生的关键机制进行了对比分析研究。