甘南高原

为准确应用旁瓣回波作强冰雹预警，对湘西北地区5次强冰雹过程中9个风暴单体被观测到的159次旁瓣回波样本进行统计分析，并系统总结旁瓣回波的雷达产品图像特征和探讨影响旁瓣回波观测的主要原因，深入研究旁瓣回波随强度与空间的分布特征。结果表明：⑴产生旁瓣回波的风暴核最小反射率因子强度为60 dBz，其强度是能否产生旁瓣回波的决定因素，强度越强，越易产生旁瓣回波且特征越明显，旁瓣回波的面积与60 dBz以上的风暴核面积和强度成正比，旁瓣回波中心强度、最大值强度与相应的风暴核最大值强度相关性分别可达0.86和0.92。（2）旁瓣回波在高度4 km左右、仰角3.4°、距离75 km左右出现频次达到峰值，风暴核回波强度的垂直分布特点是造成这种分布特征的主要影响因素。（3）旁瓣回波在270 °-360°方位区间出现频次最多，具有明显的方位分布特点，强风暴单体的生成源地及其路径决定旁瓣回波的方位分布。（4）旁瓣回波分布在风暴核切向方向梯度大值区一侧，另一侧由于存在真实回波，导致旁瓣回波特征被真实回波覆盖而不易被观测到。（5）旁瓣回波特征可以作为S波段天气雷达强冰雹预报预警的充分条件。

VIL density as a hail indicator

In order to accurately apply the side-lobe echo for the severe hail warning, statistical analysis was performed on 159 samples of side-lobe echo in 9 storm supercells from 5 severe hail events in Northwest Hunan area. The radar product image characteristics of side-lobe echo were summarized systematically and the influence of side-lobe echo on observation was discussed. The distribution characteristics of side-lobe echo with intensity and space were studied in depth. The results show that:(1) For producing side-lobe echo, the minimum reflectivity factor intensity of storm core is 60 dBz. And its intensity is the decisive factor. The stronger the storm core is, the more easily side-lobe echo is generated and the more obvious feature is. The area of side-lobe echo is proportional to the area and intensity of storm core above 60 dBz. The correlation coefficients between side-lobe echo center intensity and the corresponding storm core maximum intensity, and between maximum intensity and the corresponding storm core maximum intensity can reach 0.86 and 0.92, respectively. (2) Side-lobe echo occurs the most in the following cases:about 4 km in height, 3.4° elevation, about 75 km in distance. The vertical distribution characteristic of storm nucleus echo intensity is the main factor affecting the distribution feature. (3) The frequency of the side-lobe echo occurs the most in the azimuth range of 270°-360° with obvious azimuth distribution, and the origin and path of severe storm cells determine the azimuth distribution of the side-lobe echo. (4) The side-lobe echo is distributed on one side with large echo gradient in the tangential direction of the storm. The other side exists true echo, which causes the feature of the side-lobe echo to be masked by the true echo. (5) Side-lobe echo characteristics can be regarded as a sufficient condition for severe hail warning using S-Band weather radar.