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

Pristine项目旨在开发一种基于真实雪粒属性的极化雷达前向算子。可靠的正演运算符是整个PROM计划的重要工具，因为它是数据同化算法和模式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的正演算符与观测到的冻结水流星的偏振特征有很大的偏差。这些偏差与T-矩阵近似引入的简化有关。Pristine将建立在高效的极化雷达模拟器框架EMVORADO的基础上，该框架涵盖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)方法进行新颖的单次散射计算。准确的DDA计算需要关于详细的水流星结构的额外假设。Pristine将通过一种创新的建模技术来解决这个问题。雪粒形状将使用详细的拉格朗日云模型和显式雪粒模拟器的组合来生成。通过这样做，Pristine的目标是找到代表雪的整体平均特性的雪形。此外，还将评估由于雪生长过程的随机性和雪颗粒的不规则形状而引起的雪颗粒微物理和偏振散射特性方面的不确定性。单次散射特性将被用来取代EMVORADO中目前基于T矩阵近似的云冰和雪的散射模块。更新后的散射模拟的性能将根据多频率、多普勒分辨率、极化雷达观测进行评估。将向PROM项目伙伴和更大的科学界提供EMVORADO和DDA散布数据的连续更新版本。

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.