Front (météorologie)

Résumé

Un front météorologique est une surface de discontinuité étendue, qui sépare deux masses d’air ayant des propriétés physiques différentes (ex : température, humidité, pression). Le concept a été développé au début du par les météorologues norvégiens pour expliquer le comportement de l'atmosphère dans les latitudes moyennes terrestres : la formation des nuages, des précipitations, des dépressions et des anticyclones ainsi que leur déplacement. Le développement de la météorologie depuis cette époque a permis de démontrer que les fronts sont une conséquence des forces en jeu plutôt que leur cause mais la représentation est maintenant tellement répandue qu'ils sont toujours largement utilisés dans les présentations météo. Histoire de l'analyse des fronts Météorologie L'histoire de l'analyse moderne des cartes de surface en météorologie débute au . L'invention du télégraphe en 1845 a permis de diffuser des observations prises à des endroits très éloignés les uns des autres dan

Source officielle

https://fr.wikipedia.org/wiki/Front_(m%C3%A9t%C3%A9orologie)

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 (5)

Publications associées

Chargement

Personnes associées

Chargement

Unités associées

Chargement

Concepts associés (36)

Concepts associés

Chargement

Cours associés (2)

This course covers principles of snow physics, snow hydrology, snow-atmosphere interaction and snow modeling. It transmits sound understanding of physical processes within the snow and at its interfaces with the atmosphere and the ground, including field, laboratory, and modeling techniques.

This course provides an introduction to particle-based methods for the numerical resolution of partial differential equations describing continuum phenomena or for the simulation of particulate flows. Details are given for the Material Point Method (MPM) and the Discrete Element Method (DEM).

Cours associés

Chargement

Séances de cours associées (3)

Séances de cours associées

Chargement

Clustering of winter precipitations in Valais

Clémence Marie Anne Le Cornec

This master thesis provides an extended study of winter precipitations in Valais (Switzerland). It was rst tried to relate local conditions in Valais, as measured at gauges, to the Hess-Brezowski classication for Europe. It was not possible to clearly relate this classication to local precipitation events in Winter in this region. Self-organizing maps were used to try to distinguish between sub-regions only based on the precipitation regime in Valais. The obtained results present coherence with the existing literature. ERA-Interim (global atmospheric reanalysis) data were then used to develop a new classication to link European meteorological conditions to local events. Three unsupervised clustering techniques were used for this purpose: k-means, k-medoids, hierachical clustering. The optimal number of cluster was determined using a com- bination four commonly used internal clusters indices (Dunn index, Davies-Bouldin index, silhouette index and Calinski-Harabasz index). Two clusters appeared to be optimal compared to the various parameters of the problem. The outputs of the three classication techniques were compared in term of robustness and results. A physical interpretation was then made. It was found that the two classes were associated respectively with small or large precipitation events. The associated synoptic conditions at the European scale reveal that the small precipitation class is associated with a North-East ux over Switzerland whereas the large precipitation class is linked to a South-West ux linked to a stationary front over Switzerland.

2017

Chargement

Quantifying evaporation drying front dynamics using neutron radiography

Dani Or, Nima Shokri

Soil evaporation plays an important role in the hydrologic cycle and affects near surface energy balance. Changes in evaporative drying rates reflect complex interplay between soil pore space and transport properties and atmospheric conditions. Typically, initial drying rate from the wet soil surface is high and is limited by atmospheric conditions. Subsequently, when hydraulic connection between the receding drying front and atmosphere can no longer be maintained, the drying rate becomes dominated by vapor diffusion through the air-filled pores. We show that the depth of drying front where a transition from atmospheric (high) to diffusion controlled (slow) evaporation takes place, is related to air entry value of the medium (or to a critical pore size). Fine textured soils with small pores sustain higher drying rates than coarser ones. We delineated drying front position and morphology of sand-filled Hele-Shaw cells using neutron transmission technique. Insights on water content distribution and dynamics of drying front in sands of different textures will be presented and compared with theoretical predictions.

2006

Chargement

Evaporative drying of porous media is jointly controlled by external ( atmospheric) conditions and by media internal transport properties. Effects of different atmospheric potential evaporative demand on observed drying rates were studied in a series of laboratory experiments using sand-filled Hele-Shaw cells. We examined two potential evaporation rates of about 8 and 40 mm per day. The evolution and geometry of the drying front (marking the interface between saturated and partially dry regions) and water content distribution above the drying front were measured every 5 min at 0.1 mm spatial resolution using neutron radiography. Water loss rates decreased with time for both rates, but the decrease was more pronounced for high evaporative demand. External evaporative demand had no effect on drying front geometry or spatial water content distribution for depths below 2 mm. Cycles of roughening and smoothing of drying fronts due to interfacial pinning and unpinning were observed. The water content above the front showed irregular patterns due to formation of isolated liquid clusters with the general profile showing a decrease in mean water content with deepening drying front. Measured water content profiles support the hypothesis that liquid flow supply surface evaporation during stage 1 and water content distribution were not affected by external drying rates. Additionally, observed saturation profiles indicate that the corresponding hydraulic conductivity supports fluxes larger than the highest drying rate measured for sand, suggesting that decreasing drying rate was limited by vapor exchange between progressively drying surface and the viscous boundary layer above.

2008

Chargement