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Multi-model convection-resolving simulations of the October 2018 Vaia storm over Northeastern Italy
Atmospheric Research ( IF 5.5 ) Pub Date : 2021-01-07 , DOI: 10.1016/j.atmosres.2021.105455
Lorenzo Giovannini , Silvio Davolio , Mattia Zaramella , Dino Zardi , Marco Borga

The aim of this study is to identify the main mesoscale features and mechanisms responsible for the generation of a very intense precipitation and wind storm event, named “Vaia”, that affected the eastern Italian Alps on 27–29 October 2018. The event was characterized by extreme accumulated precipitation (up to 850 mm in three days) and exceptionally strong winds, causing severe and widespread impacts, such as floods, landslides, and extensive damages to forests and growing stock. The synoptic situation was characterized by a trough, which deepened over the eastern Atlantic, extending to France and Spain, driving a strong moist flow towards the Alpine region. At the surface, a wide cyclonic area developed over the western Mediterranean, east of the trough axis, and moved, deepening, towards northwestern Italy. The storm is investigated using a comprehensive dataset composed of both observations and numerical simulations by means of two models, namely WRF and MOLOCH, at convection-permitting resolution. The analysis highlights that the storm was characterized by two consecutive phases with strong precipitations, both fed by an intense moist southerly flow. In particular, the second phase was also marked by strong wind gusts in the Alpine area, exceeding 50 m s−1 at some weather stations. It is found that these extreme wind gusts were connected to the presence of an intense southerly low-level jet immediately ahead of a cold front, displaying an average wind speed of 35 m s−1 at 1500 m MSL. The comparison between observations and numerical results shows that the main characteristics of the storm are well simulated by both models, confirming the high predictability of this kind of events, typically associated with well-defined large-scale forcing. Also local scale features are reasonably captured by the simulations, despite the high complexity of the Alpine orography. However, WRF significantly underestimates total precipitation amounts over the most affected areas, while wind speed is overestimated by both models in the inner Alpine sectors.



中文翻译:

2018年10月意大利东北部Vaia风暴的多模型对流解析模拟

这项研究的目的是确定造成2018年10月27日至29日影响意大利东部阿尔卑斯山的非常强烈的降水和暴风雨事件(称为“ Vaia”)的主要中尺度特征和机理。极端的累积降水量(三天内可达850毫米)和异常强的风,造成了严重而广泛的影响,例如洪水,山体滑坡以及对森林和林木的广泛破坏。天气情况的特征是低谷,该深谷在东大西洋上空加深,延伸到法国和西班牙,驱使大量湿润的水流流向高山地区。在地表,一个宽的气旋区在海槽轴以东的地中海西部发展,并向意大利西北部移动并加深。利用对流分辨率下的WRF和MOLOCH这两个模型,使用由观测和数值模拟组成的综合数据集对风暴进行了研究。分析强调,暴风雨的特征是连续两个阶段都具有强降水,这两个阶段都由强烈的潮湿南风引起。特别是,第二阶段的特征还在于高山地区的阵风超过50毫秒-1在某些气象站。发现这些极端阵风与紧接冷锋前存在强烈的向南低空急流有关,在1500 m MSL处显示出35 ms -1的平均风速。观测结果和数值结果之间的比较表明,两个模型都很好地模拟了风暴的主要特征,证实了这种事件的高度可预测性,通常与定义明确的大规模强迫有关。尽管高山地形的复杂性很高,但模拟仍能合理地捕获局部尺度特征。但是,WRF大大低估了受影响最严重地区的总降水量,而风速却被两个内部阿尔卑斯地区的模型高估了。

更新日期:2021-01-22
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