贺兰山地形对强降水触发和发展的影响机理研究

Helan Mountain is located at the border of Ningxia and Inner Mongolia. It stretches for more than 200 kilometers in the north-south direction. The main peak is 3556 meters above sea level. It is a medium-scale terrain and one of the important climatic boundaries in China. In recent years, the extreme heavy rainfalls in Helan Mountain has increased and easy occur in relatively fixed areas, which was repeatedly broken historical records and suffered heavy losses. The studies and the existing weather forecasting theories indicate that the topography of Helan Mountain has significant effect on the occurrence and development of heavy rainfall, but its influence mechanism, characteristics and area differentiation of heavy rainfall are still unclear. Which is the greater contribution of the terrain or the weather system to the heavy precipitation? These issues have not been studied in depth so far, and there is no clear answer. The project is based on the study of the temporal and spatial distribution of heavy rainstorm in Helan Mountain and use some methods of adopt diagnostics, numerical simulations and terrain sensitivity tests to analyze the terrain effects and the dynamic and thermal effects of the small-scale terrain on heavy precipitation, discuss the role of topography and weather system in heavy rainfall and the possible causes of the regional differences in Helan Mountain rainstorm. It is aimed at enhancing cognition of the disciplinarian and mechanism of heavy rainfall in Helan Mountain, which can promoted monitoring capacity of heavy precipitation in Helan Mountain and supported for improving the parameterization scheme of the medium-scale numerical prediction model in the local area.

贺兰山近南北向位于宁夏与内蒙古交界的地方，主峰3556米，为中尺度地形，是我国重要的气候分界线之一。近年监测显示，贺兰山强降水天气增多且易发生在相对固定的区域，屡次打破历史记录，灾害损失惨重。研究和已有的天气预报认知表明，贺兰山地形对强降水发生发展有明显作用，但其影响机理和特征、强降水区域差异的可能原因也不是很清楚，地形对其贡献大还是天气系统？这些问题迄今没有得到深入研究，没有明确答案。因此，项目拟在对贺兰山强降水时空分布规律研究的基础上，采取诊断分析、数值模拟和地形敏感性试验等方法，研究贺兰山地形及包含在其中的小尺度地形动热力效应对强降水的影响，探讨地形与天气系统在强降水事件中的作用，以及强降水区域差异的可能原因，旨在提升对贺兰山强降水发生规律及地形对强降水影响机理的认知能力，促进强降水监测预警水平，可为改进本地区域中尺度数值预报模式参数化方案优化提供支持。

利用高时空分辨率观测资料和数值模拟等方法，分析研究发现贺兰山区降水呈现东多西少、南多北少、自东南向西北逐渐减少分布特征，沿山是暴雨高发区，中心在主峰南偏西0.1个经度处，日降水极值西侧高于东侧，小量降水日数多范围大，对区域总降水量贡献较大，暴雨点发、日数少，对总降水量贡献较小但对沿山贡献大。强降水集中在7、8月午后到前半夜。对流风暴生命史多小于30 min，移速9～13 m∙s-1，以东移为主。.贺兰山中尺度地形、主峰屏障、喇叭口地形收窄汇聚和狭管效应使主峰东南侧成为强降水易发区。主峰附近降水量东坡大于西坡，随高度东、西坡每百米增加2.1mm、5.1mm。地形对东麓迎风坡降水正贡献35%-57%，对西侧背风坡腾格里沙漠降水负贡献26%-63.6%。地形通过影响中小尺度系统发生发展、动热力差异及其日变化、水汽强弱及输送差异等影响暴雨位置、强度和时间。暴雨发生时低空急流与山脉夹角近30-90度。东麓暴雨中低层水汽来源为东南路，高层为偏西路；西麓相反，低层以西路为主，本地为辅，高层为偏南路；东西麓中低层以西路为主，高层为西南路；西麓和东西麓越往高层，偏南路输送占比越大。.地形作用使低层偏东风增强并强烈抬升，诱发气旋性环流发展成中小尺度系统；傍晚到前半夜，山地平原温差形成山风吹向平原，谷峰局地热力环流形成小尺度山风加强吹向平原的大尺度山风强度，与低层东南暖湿气流相遇，高低空急流耦合效应加剧层结不稳定，暖湿气流沿山风爬升至自由对流高度，使对流云团在东坡强烈发展，抬升释放潜热又进一步增强了层结不稳定，强降水拖曳下沉形成冷池出流向东扩展，更进一步加剧冷暖气流汇聚抬升，形成“正反馈机制”，加之异常环流背景和弱天气尺度强迫作用导致特大暴雨爆发，也是滑雪场至滚钟口成为强降水中心原因之一。构建了多尺度天气系统与地形相互作用概念模型。.完成研究论文18篇，核心发表9篇，全国交流3篇；入选晋升培养各类人才16人次，宁夏局创新团队1个；大北方区域数值模式联盟突出贡献奖等表彰4人次。