Transport de la neige par le vent en Terre Adélie (Antarctique) : observation et modélisation avec le Modèle Atmosphérique Régional (MAR).

peer reviewe

Influence of particles shape on the vertical profile of blowing snow concentration

International audienceIn alpine regions, blowing snow events strongly influence the temporal and spatial evolution of the snow cover throughout the winter season. In Antarctica, blowing snow is an essential surface mass balance process and plays a non-negligible role in the annual accumulation. The vertical profile of blowing snow concentration determines the quantity of snow transported in turbulent suspension. A power law is often used to represent this vertical profile. It serves as an analytical solution representing an equilibrium between vertical turbulent diffusion and gravitational settling. In this work, we study how the exponent of the power law depends on the type of transported particles. Vertical profiles of blowing snow concentration have been collected at the experimental site of Col du Lac Blanc (French Alps) in 2011 and 2012 and near the research station of Cap Prud’homme (Antarctica) in 2010 and 2011.We used mechanical gauges (butterfly nets) and optical devices (Snow Particles Counters). Profiles collected during blowing snow events with precipitation have been corrected to account for the contribution of snowfall. Results show that profiles collected during blowing snow without snowfall differ from the corrected profiles collected during snowfall. At a given wind speed, particles transported during snowfall have a lower settling velocity than particles transported without snowfall. This difference confirms earlier observations (Takahashi, 1985) and can be explained by the change of drag coefficient between dendritic and rounded particles. This difference pertains several hours after the end of the snowfall illustrating the fragmentation of snow grains during blowing snow events

Blowing snow in coastal Adelie Land, Antarctica: three atmospheric-moisture issues

International audienceA total of 3 years of blowing-snow observations and associated meteorology along a 7 m mast at site D17 in coastal Adelie Land are presented. The observations are used to address three atmospheric-moisture issues related to the occurrence of blowing snow, a feature which largely affects many regions of Antarctica: ( 1) blowing-snow sublimation raises the moisture content of the surface atmosphere close to saturation, and atmospheric models and meteorological analyses that do not carry blowing-snow parameterizations are affected by a systematic dry bias; ( 2) while snowpack modelling with a parameterization of surface-snow erosion by wind can reproduce the variability of snow accumulation and ablation, ignoring the high levels of atmospheric-moisture content associated with blowing snow results in overestimating surface sublimation, affecting the energy budget of the snowpack; ( 3) the well-known profile method of calculating turbulent moisture fluxes is not applicable when blowing snow occurs, because moisture gradients are weak due to blowing-snow sublimation, and the impact of measurement uncertainties are strongly amplified in the case of strong winds

Transport de la neige par le vent, observations et modélisation en Terre Adélie, Antarctique

National audienceLe Bilan de Masse de Surface (BMS) de la calotte antarctique est probablement la seule importante contribution négative à la hausse du niveau moyen des mers. La contribution de la neige soufflée semble jouer un rôle important dans le BMS à la côte antarctique, particulièrement aux endroits où les vents sont violents. Le Modèle Atmosphérique Régional est un modèle développé au LGGE possédant un module de neige soufflée. Pour valider ce module, des instruments spécifiques à la mesure de neige soufflée, des FlowCapts, ont été installés près du camp d'été de Cap Prud'homme, en Terre Adélie, en ajout aux mesures météorologiques classiques. Une comparaison des évènements de neige soufflée observés par les FlowCapts et modélisés par le MAR est faite. La comparaison porte sur le mois de janvier 2010. La météorologie générale de la région tout comme les évènements de neige soufflée semblent bien reproduits par le modèle

Transport de la neige par le vent en Terre Adélie (Antarctique) : observation et modélisation avec le Modèle Atmosphérique Régional (MAR)

International audienceLe modèle climatique à aire limitée MAR a été utilisé pour simuler la détection du transport de neige par le vent en Terre Adélie, Antarctique, sur un petit domaine (500 x 500 km2) et une résolution horizontale fine (5 km). Le mois de janvier 2010 est simulé et l'accord avec l'observation est excellent, comme en témoignent les tests statistiques appliqués aux résultats. Même si MAR sous-estime légèrement la détection des évènements de transport, la mise en ½uvre du modèle sur tout l'Antarctique à 40 km de résolution met en évidence une contribution du processus de transport au bilan de masse en surface bien plus importante qu'estimée auparavant

Present weather-sensor tests for measuring drifting snow

International audienceIn Antarctica, blowing snow accounts for a major component of the surface mass balance near the coast. Measurements of precipitation and blowing snow are scarce, and therefore collected data would allow testing of numerical models of mass flux over this region. A present weather station (PWS), Biral VPF730, was set up on the coast at Cap Prud'homme station, 5 km from Dumont d'Urville (DDU), principally to quantify precipitation. Since we expected to be able to determine blowing-snow fluxes from the PWS data, we tested this device first on our experimental site, the Lac Blanc pass. An empirical calibration was made with a snow particle counter. Although the physics of the phenomenon was not well captured, the flux outputs were better than those from FlowCapts. The first data from Antarctica were reanalyzed. The new calibration seems to be accurate for estimating the high blowingsnow flux with an interrogation of the precipitation effects

Transport of snow by the wind in Adélie Land (Antarctica). Observation and modeling by the Modèle Atmosphérique Régional (MAR)

International audiencePrésentation orale lors du séminaire Ice2sea

New blowing snow observations in Adélie Land, East Antarctica

[Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGEInternational audiencePrésentation orale faite lors de la conférence Davos Atmosphere and Cryosphere Assembly DACA-13

Determination of the surface roughness length for momentum over a coastal region of Adélie Land, Antarctica

[Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGEInternational audiencePrésentation orale faite lors de la conférence Davos Atmosphere and Cryosphere Assembly DACA-13