Statistical analysis of Doppler weather radar Side-lobe echo for severe hail in Northwest Hunan area

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.