武夷山及周边复杂地形对强降水对流系统启动、组织和发展影响的机理研究

TThe formation and development of heavy-rain-producing convective system inducing flash floodings and mud slides over complicated terrains are often effected by dynamically and thermodynamically topographic forcings. However, the forecasting ability of numerical model for heavy rain in complicated topographic areas is extremely limited, and the knowledges about the physical mechanism of heavy-rain-producing convective system in complicated terrains are insufficient. The program sponsored here aims at the fact that the Wuyi Mountains and its surrounding complicated topography is one of areas with rainfall maximum during Spring and Summer in China, an area with frequent occurrences of heavy-rain-producing convective systems during pre-summer flood period in south China, and a source region of deep convective cloud clusters. In this program, with multiple observed data, and through observational analysis and diagnosis, cloud-resolving numerical simulation, and idealized, ensembled and sensitive experiments, the predominant synoptic patterns and enviromental features favorable for the formation of heavy-rain-producing convective systems will be revealed. The main physical mechanism for the impacts of dynamically and thermodynamically topographic forcings upon the initiation, organization and development of heavy-rain-producing convective system will be examined. Lastly, the main physical concept models for the effects of the Wuyi Mountains and its surrounding complicated topography on the initiation, organization and development of heavy-rain-producing convective system over there or nearby will be summarized under typical weather patterns and enviromental fields. Scientific explanations for the observed facts will be conducted. New knowledges about the physical mechanism for the effects of the complicated topography on the heavy rain formation may be made through hard working of this program's members. Scientific and useful advices will be proposed for the improvements of meso- micro-scale physics in numerical models.

复杂地形环境下引发山洪、泥石流等地质灾害的强降水对流系统的形成和发展往往受地形动力热力强迫的影响，而数值模式对复杂地形区强降水的预报能力还非常有限，有关复杂地形区强降水对流系统演变机制的认识还很不充分。本项目针对武夷山及周边山地为我国春夏季降水极大值中心之一，且为华南前汛期强降水对流系统频发地，深对流云团重要生成地的观测事实，拟利用多源观测资料，通过观测诊断分析、积云分辨尺度数值模拟、理想、集合和敏感性数值试验，摸清有利于强降水对流系统形成的主要天气背景及其环境场特征，研究复杂地形的动力热力强迫对强降水对流系统启动、组织和发展影响的主要物理机制，建立典型天气背景和环境场下武夷山及周边山地对其上空和附近强降水对流系统启动、组织和发展影响的物理概念模型，对上述观测事实做出科学合理的解释，力争在复杂地形对强降水影响物理机制的认识上取得新进展，并为改进数值模式中小尺度物理过程等提出科学有益的建议。

复杂地形区造成山洪、泥石流等地质灾害的强降水对流系统（Heavy-Rain-Producing Convective System，HRPCS）形成和发展往往受地形动力热力强迫影响，而模式对复杂地形区强降水预报能力非常有限，有关HRPCS演变机制认识还很不充分。本项目研究了强、弱天气尺度强迫下武夷山及周边复杂地形区HRPCS形成的动力热力与水汽环境场特征，地形动力、热力扰动、上游地形和局地地形、边界层过程及其与HRPCS形成发展的关系，地形动力、热力扰动对HRPCS影响过程与主要物理机制及其相对重要性。结果发现：（1）强天气尺度强迫下,地形阻滞作用造成山前辐合,为暖云HRPCS发展和准静止维持提供动力条件，地形强迫抬升效应使暖云HRPCS在山坡增幅降水；地形暖云HRPCS在山前引发的大气次生效应如在山前大气边界层形成冷池，近地面冷出流与环境气流碰撞，对对流系统前沿新生单体触发以及对流系统准静止长时间维持有重要作用；地形对移动性HRPCS的增幅和拖曳减速作用决定降水增幅与否。（2）强天气尺度强迫下,复杂地形区傍晚地面热通量减少，边界层高度降低和低空急流增强，暖湿气流在地形动力强迫作用下激发对流，夜间该效应维持使低空急流继续增强，另外对流激发形成的降水凝结潜热也增强低空急流及其前部辐合，对流系统在高地形阻挡下准静止维持于山前产生极端强降水。（3）弱天气强迫条件下，复杂地形区受太阳短波辐射加热，高地形区与周边大气温度梯度很快激发出地形热力流，气流沿山爬升在山顶形成辐合产生上升运动激发出零散的热对流系统，其向山下移动遭遇海风锋后快速发展增强，形成组织化的HRPCS并产生局地强降水。（4）上游地形影响水汽和动量等输送分布，增强迎风坡一侧降水而改变台风环流内非绝热加热分布进而影响台风移动及强降水形成，其阻挡和摩擦效应影响低层环流内高温高湿气团输送，形成湿静力能锋区，并在下游产生弱风区和正涡度带影响HRPCS发展。研究结果对于深入认识复杂地形效应对HRPCS的影响及改进模式中小尺度物理过程具有重要意义，对强降水业务预报也具有重要应用价值。