Grêle

Résumé

La grêle est un des types solides de précipitations atmosphériques. Elle est constituée de billes disjointes de glace (grêlons) dont le diamètre peut varier de quelques millimètres à une vingtaine de centimètres, mais il est en général de . Le code METAR de la grêle est GR. Elle se forme spécifiquement dans les cumulonimbus ; un nuage de forte extension verticale dû à l'instabilité de l'air où les puissants courants ascendants soulèvent rapidement en altitude de l'air très humide qui se condense puis gèle en montant à la suite du refroidissement rapide. Les grêlons redescendent ensuite en périphérie du cumulonimbus et commencent à fondre quand ils repassent sous l'altitude de l'isotherme zéro degré. Les averses de grêle durent peu de temps, ne touchent qu'une superficie limitée le long d'un corridor sous l'orage. À l'intérieur des précipitations de grêle, le diamètre des grêlons n'est pas uniforme car la vitesse ascensionnelle et la densité d'humidité dans un nuage convectif varient

Source officielle

https://fr.wikipedia.org/wiki/Gr%C3%AAle

À propos de ce résultat

Cette page est générée automatiquement et peut contenir des informations qui ne sont pas correctes, complètes, à jour ou pertinentes par rapport à votre recherche. Il en va de même pour toutes les autres pages de ce site. Veillez à vérifier les informations auprès des sources officielles de l'EPFL.

Publications associées (4)

Publications associées

Chargement

Personnes associées

Chargement

Unités associées

Chargement

Concepts associés (27)

Concepts associés

Chargement

Cours associés (2)

Cours associés

Chargement

Séances de cours associées (2)

Séances de cours associées

Chargement

This project aims to investigate the possibility of exploiting the polarimetric radar measurements to improve the discrimination between hail stones of different size, by involving machine learning techniques.

2018

Chargement

Robust glass-free lightweight photovoltaic modules with improved resistance to mechanical loads and impact

Ana Cristina Oliveira Martins

In several countries, building-integrated photovoltaics (PV) solutions could contribute to the growth of total installed PV capacity. However, in some circumstances, the relative high weight (10–15 kg/m2) and lack of aesthetics of PV may constitute a barrier to its diffusion. In this work, we propose a glass-free lightweight solution (6 kg/m2) compliant with hail and mechanical load tests as prescribed by the IEC 61215-2:2016. The low weight is achieved by substituting the conventional glass cover with a polymer multi-layer resistant to hail impacts and the conventional polymer/glass backsheet by an innovative composite backsheet. A total of two module design contributions to impact resistance are highlighted: a global energy dissipation, mostly related to the backsheet properties; and a local energy dissipation, mainly related to the frontsheet properties. These results clearly show that a balance between frontsheet design and backsheet stiffness have to be found in order to maximize hail resistance and mechanical rigidity while minimizing the module’s weight.

2018

Chargement

This paper studies a damaging hail storm that occurred on 6 June 2015 in the complex topography of Switzerland. The storm persisted for several hours and produced large hail resulting in significant damage. Storms of comparable severity occur on average only three times per year within the entire Swiss radar domain, but are rare events at this exact location, according to a set of over 400,000 automatically identified storms. A multitude of datasets, partly novel for central Europe, is now available to study the storm in great detail capturing its impacts, severity and development. The data we use include radar-based hail products, crowd-sourced hail reports, and insurance loss data. These independent datasets permitted a verification of both hail occurrence and hail size estimations by radar. The crowd-sourced reports agree well with radar-based hail observations and insurance data. Model data (ERA-Interim reanalysis, regional COSMO-2 analysis and WRF simulations) and radio-sounding data showed, that conditions were favourable for thunderstorm development due to an unstable and moist atmosphere over Switzerland, brought about by an interplay of large-scale pattern and local processes. Advection ahead of a cold front west of Switzerland and local evapotranspiration lead to high lower-tropospheric moisture. The large-scale flow and topographically induced Alpine pumping resulted in strong directional wind shear, and contributed to the longevity and severity of this storm. The cold front was not relevant for the vertical lifting. Using model simulations with very high resolution, we identified mountain wind systems and cold-air outflow as possible triggering and propagation mechanisms of this hail storm.

ELSEVIER SCIENCE INC2018

Chargement