This study investigates the link between rain and ice microphysics across the melting layer in stratiform rain systems using measurements from vertically pointing multi-frequency Doppler radars. A novel methodology to examine the variability of the precipitation rate and the mass-weighted melted diameter (D_m) across the melting region is proposed and applied to a 6 h long case study, observed during the TRIPEx-pol field campaign at the Jülich Observatory for Cloud Evolution Core Facility and covering a gamut of ice microphysical processes. The methodology is based on an optimal estimation (OE) retrieval of particle size distributions (PSDs) and dynamics (turbulence and vertical motions) from observed multi-frequency radar Doppler spectra applied both above and below the melting layer. First, the retrieval is applied in the rain region; based on a one-to-one conversion of raindrops into snowflakes, the retrieved drop size distributions (DSDs) are propagated upward to provide the mass-flux-preserving PSDs of snow. These ice PSDs are used to simulate radar reflectivities above the melting layer for different snow models and they are evaluated for a consistency with the actual radar measurements. Second, the OE snow retrieval where Doppler spectra are simulated based on different snow models, which consistently compute fall speeds and electromagnetic properties, is performed. The results corresponding to the best-matching models are then used to estimate snow fluxes and D_m, which are directly compared to the corresponding rain quantities. For the case study, the total accumulation of rain (2.30 mm) and the melted equivalent accumulation of snow (1.93 mm) show a 19 % difference. The analysis suggests that the mass flux through the melting zone is well preserved except the periods of intense riming where the precipitation rates were higher in rain than in the ice above. This is potentially due to additional condensation within the melting zone in correspondence to high relative humidity and collision and coalescence with the cloud droplets whose occurrence is ubiquitous with riming. It is shown that the mean mass-weighted diameter of ice is strongly related to the characteristic size of the underlying rain except the period of extreme aggregation where breakup of melting snowflakes significantly reduces D_m. The proposed methodology can be applied to long-term observations to advance our knowledge of the processes occurring across the melting region; this can then be used to improve assumptions underpinning spaceborne radar precipitation retrievals.

中文翻译：

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将降雨与层状降雨中整个融化层的冰微物理学联系起来：一项封闭研究

这项研究使用垂直指向的多频多普勒雷达的测量数据，研究了层状雨水系统中整个融化层中雨水和冰微物理之间的联系。一种新颖的方法来检查沉淀速率和质量加权熔体直径（D _m）提出了跨融化区的研究，并将其应用于长达6小时的案例研究，该研究在朱利希云演化核心设施天文台的TRIPEx-pol野外活动期间观察到，涵盖了整个冰微物理过程。该方法基于对熔融层上方和下方应用的多频雷达多普勒观测光谱的粒径分布（PSD）和动力学（湍流和垂直运动）的最佳估计（OE）检索。首先，将检索应用于雨水地区；基于雨滴到雪花的一对一转换，检索到的雨滴大小分布（DSD）向上传播，以提供雪的质量保持量的PSD。这些冰PSD用于模拟不同雪模型在融化层以上的雷达反射率，并评估它们与实际雷达测量值的一致性。其次，进行OE降雪检索，在该OE降雪检索中，将根据不同的降雪模型模拟多普勒频谱，从而一致地计算下降速度和电磁特性。然后，将与最佳匹配模型相对应的结果用于估算雪通量和D _m，直接与相应的雨量进行比较。对于案例研究，雨水的总累积量（2.30 毫米）和融化的等效雪的累积量（1.93 毫米））显示出19％的差异。分析表明，通过融化区的质量通量得到了很好的保留，除了强烈的边缘时期外，在降雨期间降雨率高于在上面的冰中。这可能是由于熔化区域内的额外冷凝所致，这与高相对湿度以及与云雾状液滴的碰撞和聚结相对应，云雾状液滴的出现在边缘普遍存在。结果表明，冰的平均质量加权直径与下雨的特征大小密切相关，除了极端聚集的时期外，融化的雪花破裂会大大降低D _m。。所提出的方法可以应用于长期观测，以提高我们对整个融化区域中发生的过程的认识；然后可以将其用于改进支撑星载雷达降水检索的假设。