This study presents the first comprehensive analysis of the seasonal characteristics of raindrop size distribution (DSD) in Metro Manila, Philippines, using two years of measurements (2018–2020) from the PARSIVEL2 disdrometer. Seasonal properties of DSD for both stratiform and convective rain types were examined during the Southwest Monsoon (SWM; June–September), Northeast Monsoon (NEM; October–February), and pre-SWM or Transition period (March–May). Key findings reveal the dominance of small raindrops (<1 mm) during the NEM period, while mid-sized (1–3 mm) to large raindrops (>3 mm) are more prevalent during the SWM and Transition periods. The study highlights notable seasonal differences in DSD at moderate rain rates (5–10 mm hr−1), indicating variations in microphysical processes between stratiform and convective rain. Furthermore, the microphysical properties of convective rain in Metro Manila are found to be influenced by both oceanic and continental convective processes based on their mass-weighted mean diameter and generalized intercept parameter for all the monsoon periods. The DSD-derived dual-polarimetric radar variables are also shown to vary with the monsoon periods. Rainfall estimates using the DSD-derived dual-polarimetric relations statistically outperformed the empirical rainfall retrieval equation currently used by operational weather radars in the Philippines. Additionally, the Gamma shape parameter found in this study aligns with existing rainfall retrieval algorithm assumptions in space-borne radars. This similarity, along with the derived microphysical relations, could provide potential improvements in rainfall retrievals of ground-based and space-borne radars in tropical coastal environments like Metro Manila.

中文翻译：

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菲律宾马尼拉大都会雨滴粒径分布的季节特征及其对雷达降雨反演的意义


本研究首次对菲律宾马尼拉大都会雨滴粒径分布 （DSD） 的季节性特征进行了全面分析，使用了 PARSIVEL2 度计的两年测量（2018-2020 年）。在西南季风期间 （SWM;6 月至 9 月）、东北季风 （NEM;10 月至 2 月）以及 SWM 前或过渡期（3 月至 5 月）。主要研究结果显示，小雨滴（<1 mm）在NEM期间占主导地位，而中型（1-3 mm）到大型雨滴（>3 mm）在SWM和过渡期更为普遍。该研究强调了在中等降雨率 （5-10 mm hr-1） 下 DSD 的显着季节性差异，表明层状降雨和对流降雨之间的微物理过程存在差异。此外，根据马尼拉大都会对流过程的质量加权平均直径和所有季风周期的广义截距参数，发现马尼拉大都会对流的微物理特性受海洋和大陆对流过程的影响。DSD 衍生的双极化雷达变量也显示随季风周期而变化。使用 DSD 衍生的双极化关系的降雨量估计在统计上优于菲律宾业务天气雷达目前使用的经验降雨反演方程。此外，本研究中发现的 Gamma 形状参数与星载雷达中现有的降雨反演算法假设一致。这种相似性，以及由此衍生的微物理关系，可以为在热带沿海环境（如马尼拉大都会）中地面和星载雷达的降雨反演提供潜在的改进。