Abstract. Multiyear measurements from Joss-Waldvogel disdrometer (5 years) and X-band dual-polarization radar (2 years) made at Gadanki (13.5 N, 79.18 E), a low latitude station, are used to i) retrieve appropriate raindrop size distribution (DSD) relations for monsoonal rain, ii) understand their dependency on temperature, raindrop size-shape model and season and iii) assess polarimetric radar DSD retrievals by various popular techniques (Exponential-Exp, Constrained Gamma – CG, Normalized Gamma – N-Gamma and β methods). The coefficients obtained for different DSD relations for monsoonal rain are found to be different from that of existing relations elsewhere. The seasonal variation in DSD is quite large and significant and as a result the coefficients also vary considerably between the seasons. The slope of the drop size - shape relation, assumed to be constant in several studies, vary considerably between the seasons with warmer seasons showing smaller slope value than cold season. It is found that the constant (0.062) used in linear drop shape models is valid only for cold season. The derived coefficients for CG method for different seasons coupled with those available in the literature reveals that the warm seasons/regions typically have larger curvature and slope values than in cold seasons/regions. The coefficients of mass weighted mean diameter (D_m) – differential reflectivity (Z_DR) exhibit strong dependency on drop shape model, while those for the derivation intercept parameter exhibit strong seasonal dependency. Using the retrieved relations and X-band polarimetric radar at Gadanki, four popular DSD methods are evaluated against disdrometer measurements collected over 12 events. All the methods estimated D_m reasonably well with small root mean square error, however failed to estimate intercept parameter accurately. Only N-gamma method estimated the normalized intercept parameter reasonably. Problems associated with specific differential phase (K_DP)-based estimates close to the radar location, particularly during overhead convection, are also discussed.

中文翻译：

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使用 X 波段双极化雷达反演季风降雨的微物理参数：它们的季节相关性和评估

摘要。Joss-Waldvogel 测距仪（5 年）和 X 波段双极化雷达（2 年）在低纬度站 Gadanki（13.5 N，79.18 E）进行的多年测量用于 i) 检索适当的雨滴尺寸分布（ DSD) 与季风雨的关系，ii) 了解它们对温度、雨滴大小-形状模型和季节的依赖性，以及 iii) 通过各种流行技术（指数-Exp、约束伽玛 – CG、归一化伽玛 – N-伽玛）评估极化雷达 DSD 反演和β方法）。发现针对季风降雨的不同 DSD 关系获得的系数与其他地方的现有关系不同。DSD 的季节性变化非常大且显着，因此系数在季节之间也有很大差异。液滴大小 - 形状关系的斜率，在几项研究中假设为常数，在季节之间变化很大，较暖的季节显示出比寒冷季节更小的斜率值。发现线性水滴形状模型中使用的常数（0.062）仅对寒冷季节有效。不同季节 CG 方法的导出系数与文献中可用的系数相结合表明，暖季/地区通常比冷季/地区具有更大的曲率和斜率值。质量加权平均直径系数（D _m ) – 差分反射率 ( Z _DR ) 表现出对水滴形状模型的强烈依赖性，而推导截距参数表现出强烈的季节性依赖性。使用 Gadanki 的检索关系和 X 波段极化雷达，根据在 12 个事件中收集的测距仪测量值对四种流行的 DSD 方法进行了评估。所有方法都可以很好地估计D _m，均方根误差小，但未能准确估计截距参数。只有N-gamma方法可以合理估计归一化截距参数。与特定微分相位相关的问题 ( K _DP) 还讨论了靠近雷达位置的基于估计，特别是在头顶对流期间。