Brouillard

Résumé

Le brouillard est le phénomène météorologique constitué d’un amas de fines gouttelettes ou de fins cristaux de glace, accompagné de fines particules hygroscopiques saturées d'eau, souvent de taille microscopique, réduisant la visibilité en surface. Sa composition est donc identique à celle d'un nuage dont la base toucherait le sol. Par convention, les météorologistes parlent de brume lorsque la visibilité horizontale est supérieure à un kilomètre et de brouillard si la visibilité est inférieure à un kilomètre. Les marins utilisent souvent le terme de brume quelle que soit la visibilité horizontale et le nomment également fumée de mer quand il s'agit de brouillard d'évaporation. Lorsque la température de l'air, du sol et des objets baignés par la nappe de brouillard est inférieure à le brouillard peut être givrant. Les gouttelettes en suspension sont alors en surfusion (à l'état liquide par température négative) et gèlent au contact, formant du givre (ou de la glace noire sur une ch

Source officielle

https://fr.wikipedia.org/wiki/Brouillard

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 (61)

Concepts associés

Chargement

Cours associés (19)

Cours associés

Chargement

Séances de cours associées (32)

Séances de cours associées

Chargement

Modeling Extreme Warm-Air Advection in the Arctic During Summer: The Effect of Mid-Latitude Pollution Inflow on Cloud Properties

Georgia Sotiropoulou

Usually the Arctic is relatively free of anthropogenic influence in summer, which means that particles from natural sources can be the most significant nuclei for cloud droplets. However, this is not the case during anomalously warm-air intrusions when the air origin comes from lower latitudes. In this modeling study, we investigate the effect of mid-latitude pollution inflow (anthropogenic and biomass burning [BB]) on the aerosol-cloud-radiation interactions during an episode of extreme warm-air advection. This particular episode resulted in anomalously high air temperatures over the East Siberian Sea and has accelerated sea-ice melting. The impact of different emission sources on aerosol vertical distribution, chemical composition, cloud formation, and radiation budget is examined using the Weather Research and Forecasting model, fully coupled with chemistry. Elevated turbulent clouds that occurred at the beginning of the episode are found to be more sensitive to aerosol variations and their negative feedback on supersaturation, compared to stably stratified fog layers that were dominant during the core period. Omission of either anthropogenic or BB source results in decreased cloud liquid water and cloud droplet concentrations; however, these changes are not substantially large to significantly modify the net surface radiation budget. Significant reduction of the net surface radiation is only observed if both anthropogenic and BB transported pollution reaches the area of interest.

2021

Chargement

Acidity, defined as pH, is a central component of aqueous chemistry. In the atmosphere, the acidity of condensed phases (aerosol particles, cloud water, and fog droplets) governs the phase partitioning of semivolatile gases such as HNO3, NH3, HCl, and organic acids and bases as well as chemical reaction rates. It has implications for the atmospheric lifetime of pollutants, deposition, and human health. Despite its fundamental role in atmospheric processes, only recently has this field seen a growth in the number of studies on particle acidity. Even with this growth, many fine-particle pH estimates must be based on thermodynamic model calculations since no operational techniques exist for direct measurements. Current information indicates acidic fine particles are ubiquitous, but observationally constrained pH estimates are limited in spatial and temporal coverage. Clouds and fogs are also generally acidic, but to a lesser degree than particles, and have a range of pH that is quite sensitive to anthropogenic emissions of sulfur and nitrogen oxides, as well as ambient ammonia. Historical measurements indicate that cloud and fog droplet pH has changed in recent decades in response to controls on anthropogenic emissions, while the limited trend data for aerosol particles indicate acidity may be relatively constant due to the semivolatile nature of the key acids and bases and buffering in particles. This paper reviews and synthesizes the current state of knowledge on the acidity of atmospheric condensed phases, specifically particles and cloud droplets. It includes recommendations for estimating acidity and pH, standard nomenclature, a synthesis of current pH estimates based on observations, and new model calculations on the local and global scale.

2020

Chargement

Size distribution of interstitial and total particles between 18 and 660 nm collected during the Arctic Ocean 2018 expedition

Andrea Baccarini, Julia Schmale

The aerosol size distribution was measured with a custom made scanning mobility particle sizer (SMPS), range 18⁠ – ⁠660 nm. Aerosols are important for a variety of reasons, one of the most prominent is that a sub-set of the aerosol population can act as cloud condensation nuclei (CCN) influencing cloud formation and the Earth radiative budget. The measurements reported here can be used to investigate aerosol sources and processes. Moreover, an interstitial inlet was used to characterize the interstitial aerosol population during fog events. Measurements were performed on the 4th deck of icebreaker Oden during August and September 2018 along the track of the expedition. The concentration is reported as dN/dlog(Dp) per cubic centimeter with a 3 minutes time resolution.

2020

Chargement