华南沿海暖区辐合线暴雨地形动力机制数值模拟研究

华南沿海暖区暴雨是单一暖气团降水。本文采用客观分析方法确定暖区暴雨主要影响系统为两类辐合线低值系统:偏南向辐合线与西南向辐合线；此类辐合线系统具有强烈的辐合上升层次与暖心结构，是一类强烈的暖区暴雨天气系统。偏南向辐合线多出现在粤西沿海，而西南向辐合线多出现于粤东沿岸，分别具有短时团状与持续带状两类强降水。华南沿海地区山脉河口众多，其中珠江口以西的团状云雾山正面阻挡偏南向辐合线，河口以东的带状莲花山侧面阻挡西南向辐合线。利用WRF数值模式分别研究粤东和粤西山脉对两类辐合线及其暴雨的地形影响，包括正面阻挡和侧面摩擦。结果显示，将偏南向型辐合线所遇云雾山范围地形降低80%后，因正面阻挡缺失，辐合线及其降水向北推进，雨带强度减弱，形状改变。地形的正面阻挡促使低层辐合气流迅速抬升触发强降水。降水释放的凝结潜热，又加强系统的上升运动和暖心结构强度与层厚，进而增强暴雨。填充偏南向型狭管地形的试验显示，狭管效应构成对强降水位置和强度的直接强迫影响，加之与云雾山正面阻挡配合，两项作用造成粤西暴雨频繁特征。测试粤东西南向莲花山脉对西南向辐合线的侧向阻挡与摩擦效应，通过对比莲花山两种地表粗糙度环境模拟效果，获得显著的局地垂直上升速度差，显示粤东沿海山脉的侧向摩擦不仅增强西南辐合线强度也加强垂直上升运动强度，由于西南气流的持续，山脉走向与气流的配置，维持了降雨时长及雨带范围。同时对粤西近海西南辐合气流及河口的暴雨雨带也有连带增强与维持作用。进一步地山脉地形抬升以其抬升迅速，范围集中，层次深厚，而有别于锋面气团抬升。加之近海水汽充沛，抬升后中层凝结释放的配合，增强了辐合线低值系统强度，造成暖区降水雨强远高于华南锋面降水。

The Numerical Study of Terrain Dynamic Influence on Warm Area Heavy Rainfall of Convergence Lines in South China Coast

Heavy rainstorms in the coastal region of South China are often caused by single warm air mass. Based on objective analysis by computational program, two types of convergence line, i.e. the southerly convergence line and southwesterly convergence line, are determined to be the major systems affecting the warm area heavy rainstorms. The structure of such convergence lines is characterized by a strong and deep warm center and ascending motions. The convergence line is essentially a strong synopticstorm system in warm air mass area. The southerly convergence line often occurs at the western coast of Guangdong Province of South China, which can induce short-term heavy precipitation clusters. The southwesterly convergence line often appears at the eastern coast of Guangdong and results in continuous heavy precipitation belts. Terrain in coastal region of South China is complex with various mountains and estuaries. Mountain Yunwu at the western coast of Guangdong can block the southerly convergence line at a right angle, while Mountain Lianhua at the eastern coast of Guangdong curves laterally to meet the southwesterly convergence line and imposes significant frictional effects on it. The numerical model WRF3.5 is applied to investigate the influence of mountainous terrain on the two types of convergence line with a focus on the effects of blocking at the right angle and the lateral friction. The results show that after the height of Mountain Yunwu is reduced by 80%, the southerly convergence line and the accompanied rainstorm move northward without the mountain blocking. Rainfall pattern and location also change, and the intensity decreases. The mountain blocking forces the low convergence flow to rise fast and triggers heavy rainstorm, while the latent heat release caused by condensation strengthens the convergence line. The depth and intensity of the warm center and the ascending motion all intensify, which in turn increases precipitation. The experiment with the narrow valley between Mountain Yunwu and the Mountain Tianlu to its southeast filled shows that the tunneling effect of the valley can determine the rainfall location and intensity. Due to thejoint effects of the valley tunneling and the blocking of Mountain Yunwu, the storm happens frequently in the western coast of Guangdong. In the southwesterly convergence line experiment, a comparison between two kind of roughness coefficients of Mountain Lianhua surface were made. A remarkable difference of vertical velocity appeared; the result showed that the lateral friction of Mountain Lianhua can enhance southwesterly convergence line and its ascending motions. Due to the shape of mountain is the southwest wards, it leads southwester jet flowing along the mountain. They maintain the longer rainstorm duration and belt shape of rainfall location. Meanwhile, it can influence the rainstorm at west coast and the estuary to become narrow and slightly move southward. The influence of mountain terrain is different from the synoptic systems because mountain can cause local faster lifting and can make thick upwards motion. Especially there is plentiful moisture vapor along the coast, the moisture condenses and releases latent heat at high level, then it enhances convergence line systems. The process causes the rainstorm intensity in single warm airmass is larger than that of front rainfall in South China.