The intrinsic small spatial scales and low-reflectivity structure of oceanic warm precipitating clouds suggest that millimeter spaceborne radars are best suited to providing quantitative estimates of cloud and rain liquid water paths (LWPs). This assertion is based on their smaller horizontal footprint; high sensitivities; and a wide dynamic range of path-integrated attenuations associated with warm-rain cells across the millimeter wavelength spectrum, with diverse spectral responses to rain and cloud partitioning. State-of-the-art single-frequency radar profiling algorithms of warm rain seem to be inadequate because of their dependence on uncertain assumptions about the rain–cloud partitioning and because of the rain microphysics. Here, high-resolution cloud-resolving model simulations for the Rain in Cumulus over the Ocean field study and a spaceborne forward radar simulator are exploited to assess the potential of existing and future spaceborne radar systems for quantitative warm-rain microphysical retrievals. Specifically, the detrimental effects of nonuniform beam filling on estimates of path-integrated attenuation (PIA), the added value of brightness temperature (T_B) derived adopting radiometric radar modes, and the performances of multifrequency PIA and/or T_B combinations when retrieving liquid water paths partitioned into cloud (c-LWPs) and rain (r-LWPs) are assessed. Results show that (1) Ka- and W-band T_B values add useful constraints and are effective at lower LWPs than the same-frequency PIAs; (2) matched-beam combined T_B values and PIAs from single-frequency or multifrequency radars can significantly narrow down uncertainties in retrieved cloud and rain liquid water paths; and (3) the configuration including PIAs, T_B values and near-surface reflectivities for the Ka-band–W-band pairs in our synthetic retrieval can achieve an RMSE of better than 30 % for c-LWPs and r-LWPs exceeding 100 g m⁻².

中文翻译：

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注意差距–第2部分：使用星载雷达改进海洋暖雨中云层和雨水路径的定量估计

海洋温暖的降水云固有的小空间尺度和低反射率结构表明，毫米波星载雷达最适合提供云和雨水路径的定量估计。该断言基于它们较小的水平足迹；高灵敏度；以及与毫米波光谱范围内的温雨单元相关的路径积分衰减的动态范围宽，对雨水和云分区的光谱响应也各不相同。先进的暖雨单频雷达分析算法似乎不足，因为它们依赖于不确定的雨云分区假设以及雨水的微观物理学。这里，利用高分辨率的云解析模型模拟了海洋上积云中的降雨，并利用了星载前向雷达模拟器来评估现有和未来星载雷达系统在定量暖雨微物理探测中的潜力。具体来说，光束填充不均匀对路径积分衰减（PIA）的估计，亮度温度的附加值（T _B）采用辐射雷达模式得出，并评估了多水PIA和/或T _B组合在检索划分为云（c-LWPs）和雨水（r-LWPs）的液态水路径时的性能。结果表明：（1）Ka和W波段的T _B值增加了有用的约束，并且在低于同频PIA的LWP时有效；（2）来自单频或多频雷达的匹配波束组合的T _B值和PIA可以显着缩小所取回的云层和雨水路径中的不确定性；和（3）包括配置PIA的， Ť_乙在我们的合成反演中，Ka波段-W波段对的热值和近地表反射率可以使c-LWP和r-LWP超过100 g m ^-2时的RMSE优于30％。