The Retrieval of Drop Size Distribution Parameters Using a Dual-Polarimetric Radar
The Retrieval of Drop Size Distribution Parameters Using a Dual-Polarimetric Radar
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DOI：
10.3390/rs15041063
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发表时间：
2023-02
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通讯作者：
Gyuwon Lee;V. Bringi;M. Thurai
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文献类型：
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作者：
Gyuwon Lee;V. Bringi;M. Thurai
雨滴大小分布(DSD)对于定量估计降水、理解微物理过程以及验证/改进两矩总体微物理方案等应用至关重要。我们从函数形式(指数、伽马和广义伽马模型)及其归一化(非归一化、单/双矩归一化)追溯DSD表示的历史及其与极化雷达观测值的联系。四参数广义伽马模型很好地代表了DSD的变异性。一个雷达散度计被发现描述了五个典型的形状(来自加拿大蒙特利尔)，包括毛毛雨、较大的雨滴和在细雨和较大尺寸的降水之间经常出现的“S”形状的曲率。通过结合光学阵列探头上的小水滴和2DVD上的大水滴的视盘测量，我们复制了类似的S形状的DSD。描述了基于双矩标度归一化的统一理论。该理论假定矩和DSD之间的多重幂定律由表示为任意两个矩的组合的两个特征参数来归一化。归一化的DSD非常稳定。因此，将平均下垫面形状拟合到广义Gamma模型中，从该模型中获得了两个最优形状参数。分布的其他矩是参考矩M3和M6与两个形状参数的幂定律的乘积。这些参考矩可以来自双偏振测量：M6来自经衰减校正的反射率，M3来自经衰减校正的差分反射率和特定的差分传播相位。因此，可以计算出分布的所有矩，并可以推断DSD的微物理演化。这是本文的主要发现之一。
The raindrop size distribution (DSD) is vital for applications such as quantitative precipitation estimation, understanding microphysical processes, and validation/improvement of two-moment bulk microphysical schemes. We trace the history of the DSD representation and its linkage to polarimetric radar observables from functional forms (exponential, gamma, and generalized gamma models) and its normalization (un-normalized, single/double-moment scaling normalized). The four-parameter generalized gamma model is a good candidate for the optimal representation of the DSD variability. A radar-based disdrometer was found to describe the five archetypical shapes (from Montreal, Canada) consisting of drizzle, the larger precipitation drops and the ‘S’-shaped curvature that occurs frequently in between the drizzle and the larger-sized precipitation. Similar ‘S’-shaped DSDs were reproduced by combining the disdrometric measurements of small-sized drops from an optical array probe and large-sized drops from 2DVD. A unified theory based on the double-moment scaling normalization is described. The theory assumes the multiple power law among moments and DSDs are scaling normalized by the two characteristic parameters which are expressed as a combination of any two moments. The normalized DSDs are remarkably stable. Thus, the mean underlying shape is fitted to the generalized gamma model from which the ‘optimized’ two shape parameters are obtained. The other moments of the distribution are obtained as the product of power laws of the reference moments M3 and M6 along with the two shape parameters. These reference moments can be from dual-polarimetric measurements: M6 from the attenuation-corrected reflectivity and M3 from attenuation-corrected differential reflectivity and the specific differential propagation phase. Thus, all the moments of the distribution can be calculated, and the microphysical evolution of the DSD can be inferred. This is one of the major findings of this article.