Comparisons of Electromagnetic Scattering Properties of Real Hailstones and Spheroids
Comparisons of Electromagnetic Scattering Properties of Real Hailstones and Spheroids
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DOI：
10.1175/jamc-d-17-0344.1
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发表时间：
2019-01-01
影响因子：
3
通讯作者：
Heymsfield, Andrew J.
中科院分区：
文献类型：
--
作者：
Jiang, Zhiyuan;Kumjian, Matthew R.;Heymsfield, Andrew J.
严重(2.5厘米)冰雹在美国每年造成50亿美元的损失。然而，雷达测量冰雹的大小仍然具有挑战性。通常，球体被用来表示雷达前进算子中的冰雹，并为雷达冰雹大小算法提供信息。然而，天然冰雹可能具有不规则的形状和波瓣；这些细节显著影响冰雹的散射特性。2016-17年度商业和家庭安全保险研究所(IBHS)冰雹现场研究期间收集的冰雹激光扫描仪获取了真实冰雹的高分辨率3D结构。还扫描了几个创纪录的冰雹(例如，南达科他州维维安，2010年)的石膏模型。用离散偶极子近似方法计算了这些冰雹的S波段散射特性。为了进行比较，用T矩阵计算了每个冰雹的球状近似(具有相同的最大和最小尺寸和质量)的散射特性。极化雷达变量在使用椭球体时会产生误差，即使是小冰雹也是如此。与真正的冰雹相比，球体在偏振变量上的变化通常较小。这种增加的可变性是观测中的相关系数往往比使用椭球体的正向模拟情况下更低的原因之一。后向散射差分相位增量也有很大的变化，特别是对大冰雹。薄液层的不规则冰雹与干冰雹相比，水平偏振反射因子HH(HH)、差分反射率Z(DR)、比差相K-DP、线去偏振比(LDR)和增量的变化值增大且变化量大，也显著减小。
Severe (>2.5 cm) hail causes >$5 billion in damage annually in the United States. However, radar sizing of hail remains challenging. Typically, spheroids are used to represent hailstones in radar forward operators and to inform radar hail-sizing algorithms. However, natural hailstones can have irregular shapes and lobes; these details significantly influence the hailstone's scattering properties. The high-resolution 3D structure of real hailstones was obtained using a laser scanner for hail collected during the 2016-17 Insurance Institute for Business and Home Safety (IBHS) Hail Field Study. Plaster casts of several record hailstones (e.g., Vivian, South Dakota, 2010) were also scanned. The S-band scattering properties of these hailstones were calculated with the discrete dipole approximation (DDA). For comparison, scattering properties of spheroidal approximations of each hailstone (with identical maximum and minimum dimensions and mass) were calculated with the T matrix. The polarimetric radar variables have errors when using spheroids, even for small hail. Spheroids generally have smaller variations in the polarimetric variables than the real hailstones. This increased variability is one reason why the correlation coefficient tends to be lower in observations than in forward-simulated cases using spheroids. Backscatter differential phase delta also is found to have large variance, particularly for large hailstones. Irregular hailstones with a thin liquid layer produce enhanced and more variable values for reflectivity factor at horizontal polarization Z(HH), differential reflectivity Z(DR), specific differential phase K-DP, linear depolarization ratio (LDR), and delta compared with dry hailstones; is also significantly reduced.