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Dynamics of the MAP IOP 15 severe Mistral event: Observations and high-resolution numerical simulations

机译:MAP IOP 15严重Mistral事件的动力学:观测和高分辨率数值模拟

摘要

This paper investigates the fundamental processes involved in a severe Mistral event that occurred during the Mesoscale Alpine Program (from 6 to 9 November 1999). The Mistral refers to a violent north/north-westerly wind blowing in south-eastern France from the Rhône valley to the French Riviera. The study is based on measurements from radiosoundings launched from Lyon and Nîmes and from two UHF wind profilers located near Marseille and Toulon allowing a good description of the flow in the complex terrain formed by the south-western Alps. Observational results are compared with RAMS non-hydrostatic numerical simulations performed with 27 km, 9 km and 3 km nested grids. The numerical simulations capture the flow complexity both upstream of the Alps and in the coastal area affected by the Mistral. They correctly reproduce horizontal wind speeds and directions, vertical velocities, virtual potential temperature and relative humidity documented by the observational network. The simulations are used to point out the main dynamical processes generating the Mistral. It is found that flow splitting around the Alps and around the isolated peaks bordering the south-eastern part of the Rhône valley (Mont Ventoux 1909 m, Massif du Lubéron 1425 m) induces the low-level jet observed near Marseille that lasts for 36 hours. The high-resolution simulation indicates that the transient low-level jet lasting for only 9 hours observed at Toulon is due to a gravity wave breaking over local topography (the Sainte Baume 1147 m) where hydraulic jumps are involved. A mountain wake with two opposite-sign potential-vorticity banners is generated. The mesoscale wake explains the westward progression of the large-scale Alpine wake.
机译:本文调查了中尺度高山计划(1999年11月6日至9日)期间发生的严重Mistral事件所涉及的基本过程。米斯特拉尔是指在法国东南部从罗纳河谷到法国里维埃拉的猛烈的北/西北风。这项研究基于对里昂和尼姆发射的无线电声音以及位于马赛和土伦附近的两个UHF风廓线仪进行的测量,从而很好地描述了西南阿尔卑斯山形成的复杂地形中的水流。将观测结果与使用27 km,9 km和3 km嵌套网格进行的RAMS非静水数值模拟进行比较。数值模拟捕获了阿尔卑斯山上游和受Mistral影响的沿海地区的水流复杂性。它们正确地再现了观测网络记录的水平风速和方向,垂直速度,虚拟潜在温度和相对湿度。仿真用于指出产生Mistral的主要动力学过程。发现在阿尔卑斯山和与罗纳河谷东南部接壤的孤立峰周围的水流分裂(Mont Ventoux 1909 m,Massif duLubéron1425 m)引起了在马赛附近观测到的持续36小时的低空急流。高分辨率模拟表明,在土伦仅观测到9个小时的瞬态低空急流的原因是重力波突破了涉及液压跃变的局部地形(Sainte Baume 1147 m)。生成带有两个相反符号的势涡横幅的山尾。中尺度苏醒解释了大型阿尔卑斯苏醒向西发展的过程。

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