Estimation of Melting-Layer Cooling Rate from Dual-Polarization Radar: Spectral Bin Model Simulations
Estimation of Melting-Layer Cooling Rate from Dual-Polarization Radar: Spectral Bin Model Simulations
复制标题
双偏振雷达熔化层冷却速率的估计：谱箱模型模拟
DOI：
10.1175/jamc-d-18-0343.1
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发表时间：
2019
影响因子：
3
通讯作者：
A. Ryzhkov
中科院分区：
文献类型：
--
作者：
Jacob T. Carlin;A. Ryzhkov
由于其社会和动力学后果，对业务预报员和建模者来说，层状融化层中由水流星相位变化引起的绝热冷却是非常感兴趣的。估计融化层冷却速率的尝试通常依赖于从反射率Z估计的水流星含量的预算，或根据明亮波段中Z的大小按比例缩放的模型生成的查找表。最近在开发观测融化雪的独特偏振特征及其可能包含的附加微物理信息的方法方面取得了进展。然而，到目前为止，还没有研究从极化雷达亮带特征中获得的热力学信息。本文采用融雪一维谱仓模型和耦合极化算符，研究了极化雷达亮带与融雪层冷却速率的关系。在固定粒径分布（PSD）和可变环境条件下的模拟结果表明，亮带的高度、厚度、最大亮带Z和比差相移对周围环境均敏感，而差反射率相对不敏感。另外，基于熔融层以上现场观测的2700个psd的模拟表明，最大Z、和熔化层内与最大冷却速率相关性较差，而与最大冷却速率相关性强。最后，模式模拟表明，除了边缘，聚集和降水强度的同步变化以及相关的冷却可能导致观测到的亮带特征下垂。
Diabatic cooling from hydrometeor phase changes in the stratiform melting layer is of great interest to both operational forecasters and modelers for its societal and dynamical consequences. Attempts to estimate the melting-layer cooling rate typically rely on either the budgeting of hydrometeor content estimated from reflectivity Z or model-generated lookup tables scaled by the magnitude of Z in the bright band. Recent advances have been made in developing methods to observe the unique polarimetric characteristics of melting snow and the additional microphysical information they may contain. However, to date no work has looked at the thermodynamic information available from the polarimetric radar brightband signature. In this study, a one-dimensional spectral bin model of melting snow and a coupled polarimetric operator are used to study the relation between the polarimetric radar bright band and the melting-layer cooling rate. Simulations using a fixed particle size distribution (PSD) and variable environmental conditions show that the height and thickness of the bright band and the maximum brightband Z and specific differential phase shift are all sensitive to the ambient environment, while the differential reflectivity is relatively insensitive. Additional simulations of 2700 PSDs based on in situ observations above the melting layer indicate that the maximum Z, , and within the melting layer are poorly correlated with the maximum cooling rate while is strongly correlated. Finally, model simulations suggest that, in addition to riming, concurrent changes in aggregation and precipitation intensity and the associated cooling may plausibly cause observed sagging brightband signatures.