PRISTINE - Polarimetric Radar simulations with realistic Ice and Snow properties and mulTI-frequeNcy consistency Evaluation

项目质朴的目的是开发一个极化雷达正演算子，是基于现实的雪粒子属性。可靠的前向算子是整个PROM程序的重要工具，因为它是数据同化算法和模型评估研究的核心组成部分。现有的基于t矩阵近似的均匀球状云和降水粒子正演算子与观测到的冰冻水成物的极化特征有很大的偏差。这些偏差与t矩阵近似引入的简化有关。PRISTINE将建立在有效的极化雷达模拟器框架EMVORADO之上，EMVORADO涵盖了雷达模拟的许多其他方面，并与天气模型COSMO和ICON相耦合。该项目将使用离散偶极子近似（DDA）方法进行新颖的单散射计算。精确的DDA计算需要关于水流星详细结构的额外假设。质朴将通过一种创新的建模技术来解决这个问题。雪粒子的形状将使用详细的拉格朗日云建模和一个明确的雪粒子模拟器的组合来生成。通过这样做，质朴的目的是找到雪的形状，是雪的综合平均属性的代表。此外，从雪生长过程的随机性和雪颗粒的不规则形状引起的雪颗粒微物理和极化散射特性的不确定性将被评估。单散射特性将用于取代EMVORADO中目前基于t矩阵近似的云冰和雪的散射模块。更新后的散射模拟性能将根据多频、多普勒分辨、极化雷达观测结果进行评估。EMVORADO和DDA散射数据的后续更新版本将提供给PROM项目伙伴和更大的科学界。

Project PRISTINE aims at developing a polarimetric radar forward operator that is based on realistic snow particle properties. A reliable forward operator is an essential tool for the overall PROM program since it is a core component of data assimilation algorithms and model evaluation studies. The existing forward operators based on the T-matrix approximation for homogeneous, spheroid-shaped cloud and precipitation particles have shown substantial deviations with respect to the observed polarimetric signatures of frozen hydrometeors. Those deviations have been linked to the simplifications introduced by the T-matrix approximation. PRISTINE will build upon the efficient polarimetric radar simulator framework EMVORADO, which covers many other aspects of radar simulation and is coupled to the weather models COSMO and ICON. The project will perform novel single-scattering computations using the Discrete Dipole Approximation (DDA) method. The accurate DDA calculations require additional assumptions regarding the detailed hydrometeor structure. PRISTINE will address this issue by means of an innovative modeling technique. The snow particle shapes will be generated using a combination of detailed Lagrangian cloud modeling and an explicit snow particle simulator. By doing so, PRISTINE aims at finding the snow shapes that are representative of the ensemble mean properties of snow. Moreover, the uncertainties, in terms of snow particle microphysical and polarimetric scattering properties, that arise from the stochastic nature of snow growth processes and the irregular shape of snow particles will be evaluated. The single-scattering properties will be used to replace the scattering modules for cloud ice and snow in EMVORADO that are currently based on the T-Matrix approximation. The performance of the updated scattering simulations will be evaluated against multi-frequency, Doppler-resolved, polarimetric radar observations. The successively updated versions of EMVORADO and of the DDA scattering data will be made available to the PROM project partners and the larger scientific community.