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RANS and LES face to face for forecasting extreme precipitation events in the Liguria region (northwestern Italy)

机译:rans和les面对面地面对预测利古里亚地区(意大利西北部)的极端降水事件

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In the present work, seven different extreme precipitation events, that affected Liguria region (Italy) in the past ten years, were analysed in depth by means of sub-km resolution numerical simulations with the state-of-the-art non-hydrostatic Weather Research and Forecasting (WRF) mesoscale model. The study aims at evaluating the impact on quantitative precipitation forecast of an explicit description of atmospheric boundary layer turbulence through a Large-Eddy Simulation (LES) approach versus the classical Reynolds-Averaged Navier & ndash;Stokes (RANS) modelling framework. To this purpose, three different sets of simulations were carried out. In the first set, reaching a resolution of 1.1 km through three nested domains, the best performing planetary boundary layer (PBL) parameterization scheme identified in a preliminary sensitivity analysis, was imposed on each domain. This modelling setup was chosen as the reference one. Then, a further nested domain was introduced with horizontal resolution of 367 m, on which both RANS and LES simulations were performed. Quantitative precipitation forecasts were compared with observed data coming from the regional rain gauge network, composed of about 200 professional stations. In four out of the seven considered events, results show an evident LES contribution to improve model performances, regarding both intensity and/or location of precipitation. This improvement is observed both in cases of underestimation and overestimation by the reference simulations and is mostly associated to a better description of low-level dynamics as well as convection triggering and intensity. In other cases, the effect of LES is not remarkable and simulations closely resemble the reference ones. Further investigation is necessary to strengthen these conclusions, but the results of this study can suggest the possibility to integrate LES in operational simulations.
机译:在目前的工作中,通过具有最先进的非静液压天气的亚克分辨率数值模拟,深入分析了七种不同的极端降水事件,影响了Liguria地区(意大利)的影响,这些事件影响了Liguria地区(意大利)。研究与预测(WRF)Messcale模型。该研究旨在通过大涡模拟(LES)方法来评估大气边界层湍流明确描述的定量降水预测的影响与古典雷诺平均Navier&Ndash; Stokes(Rans)建模框架。为此目的,进行了三组不同的模拟。在第一个集合中,通过三个嵌套域达到1.1 km的分辨率,在每个域上施加在初步灵敏度分析中识别的最佳性行星边界层(PBL)参数化方案。选择该建模设置作为参考。然后,通过367μm的水平分辨率引入了另一个嵌套域,其中进行了rans和les模拟。将定量降水预测与来自区域雨量网络的观察数据进行比较,由约200个专业站组成。在七种所考虑的事件中,结果表明,提高模型性能的结果表明,关于降水的强度和/或位置的贡献。在参考仿真低估和高估的情况下,观察到这种改进,并且大多数与更好地描述低级动力学以及对流触发和强度相关联。在其他情况下,LES的效果不是显着的,并且仿真非常类似于参考值。进一步调查是加强这些结论所必需的,但本研究的结果可以建议将LES整合在运营模拟中的可能性。

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