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See detailEvolution of the Antarctic surface mass balance by high-resolution downscaling and impact on sea-level change for the next centuries
Agosta, Cécile ULiege; Favier, Vincent; Krinner, Gerhard et al

Conference (2012, July)

Most of the IPCC-AR4 Atmospheric Global Circulation Models (AGCM) predict an increase of the Antarctic Surface Mass Balance (SMB) during the 21st century that would mitigate global sea level rise. Present ... [more ▼]

Most of the IPCC-AR4 Atmospheric Global Circulation Models (AGCM) predict an increase of the Antarctic Surface Mass Balance (SMB) during the 21st century that would mitigate global sea level rise. Present accumulation and predicted change are largest at the ice sheet margins because they are driven by snowfall, which mostly comes from warm, moist air arising over the land slopes. The coastal belt is also where complex processes of sublimation, melt and refreezing occur. Thus, high-resolution modelling is necessary to adequately capture the effects of small-scale variations in topography on the atmospheric variables in this area, but limitations in computing resources prevent such resolution at the scale of Antarctica in full climate models. We present here a downscaling method leading to 15-km SMB resolution for century time-scales over Antarctica. We compute the effect of the fine topography on orographic precipitation and on boundary layer processes that lead to sublimation, melt and refreezing. We first display the SMB downscaled from ERA-Interim and show that the downscaling improves the agreement between modelled and observed SMB for the end of the 20th century. We then present hi-resolution features of the Antarctic SMB evolution during the 21st century downscaled from LMDZ4 for different scenarios. We show that a higher resolution induce at the same time more run-off but a significantly higher mitigation of sea level rise. [less ▲]

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See detailA 40-year accumulation dataset for Adelie Land, Antarctica and its application for model validation
Agosta, Cécile ULiege; Favier, Vincent; Genthon, Christophe et al

Poster (2012, July)

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See detailÉvolution du bilan de masse de surface Antarctique par régionalisation physique et conséquences sur les variations du niveau des mers
Agosta, Cécile ULiege

Doctoral thesis (2012)

The Antarctic surface mass balance (SMB, i.e. the snow accumulation from which we sub- tract ablation by sublimation, run-off or erosion) is a major yet poorly known contribution to changes in the present ... [more ▼]

The Antarctic surface mass balance (SMB, i.e. the snow accumulation from which we sub- tract ablation by sublimation, run-off or erosion) is a major yet poorly known contribution to changes in the present-day sea level. Water storage by snow accumulation at the top of the ice- sheet is expected to increase during the 21st century, which would moderate the rise in sea level. Three-quarters of the Antarctic SMB are concentrated below 2000 m above sea level whereas this area represents only 40% of the grounded ice sheet area. Orographic precipitation is a major contributor to snow accumulation in this region, which is why a better estimation of this term is important. The representation of this process by models depends to a great extent on the resolu- tion of the model, since precipitation amounts depend on the ice sheet slopes. Sublimation and snowmelt also depend on elevation. Global and regional atmospheric climate models are unable to achieve a 40-km resolution over Antarctica at a century time scale, due to their computing cost. At this resolution, ice-sheet margins are still badly resolved. <br />That is why we developed the downscaling model SMHiL (surface mass balance high-resolution downscaling), which estimates the Antarctic SMB components at a high resolution (∼15 km) from large-scale atmospheric forcings. We compute the impact of the high-resolution topography on orographic precipitation amounts and on the boundary-layer processes that lead to sublima- tion, melting and refreezing. To validate SMHiL, we compare our results with more than 2700 field data recently updated and quality-controlled. However, we exhibit that field data below 2000 m above sea level are too scarce to settle SMHiL efficiency. In light of this, we show that the GLACIOCLIM-SAMBA stake lines located on the ice sheet coast-to-plateau area is an ap- propriate reference to evaluate model performance. Finally, we downscale the atmospheric global climate model LMDZ4 to estimate the SMB changes during the 21st and 22nd centuries. The high-resolution SMB is significantly different from the SMB given by LMDZ4. Our results sug- gest that running LMDZ4 at a finer resolution may give a future increase in SMB in Antarctica between 15% to 30% higher than at its standard resolution. Future changes in the Antarctic SMB at low elevations will result from the conflict between higher snow accumulation and ru- noff. The downscaling model is a powerful tool that can be applied to climate models for a better assessment of a future rise in sea level. [less ▲]

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See detailImpact of model resolution on simulated wind, drifting snow and surface mass balance in Terre Adelie, East Antarctica
Lenaerts, J. T. M.; van den Broeke, Michiel R.; Scarchilli, Claudio et al

in Journal of Glaciology (2012), 58(211), 821

This paper presents the impact of model resolution on the simulated wind speed, drifting snow climate and surface mass balance (SMB) of Terre Ade ́lie and its surroundings, East Antarctica. We compare ... [more ▼]

This paper presents the impact of model resolution on the simulated wind speed, drifting snow climate and surface mass balance (SMB) of Terre Ade ́lie and its surroundings, East Antarctica. We compare regional climate model simulations at 27 and 5.5 km resolution for the year 2009. The wind speed maxima in Terre Ade ́lie and the narrow glacial valleys of Victoria Land are better represented at 5.5 km resolution, because the topography is better resolved. Drifting snow sublimation is >100 mm a−1 in regions with high wind speeds. Our results indicate a strong feedback between topography, wind gradients and drifting snow erosion. As a result, SMB shows much more local spatial variability at 5.5 km resolution that is controlled by drifting snow erosion, whereas the large-scale SMB gradient is largely determined by precipitation. Drifting snow processes lead to ablation in the narrow glacial valleys of Victoria Land. The integrated SMB equals 86 Gt. Although wind climate, drifting snow processes and SMB variability are better represented at 5.5 km, the area-integrated SMB is not significantly different between the simulations at 27 and 5.5 km. A horizontal resolution of 27 km is sufficient to realistically simulate ice-sheet wide SMB. [less ▲]

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See detailA 40-year accumulation dataset for Adelie Land, Antarctica and its application for model validation
Agosta, Cécile ULiege; Favier, Vincent; Genthon, Christophe et al

in Climate Dynamics (2012), 38(1-2), 75-8686

The GLACIOCLIM-SAMBA (GS) Antarctic accumulation monitoring network, which extends from the coast of Adelie Land to the Antarctic plateau, has been surveyed annually since 2004. The network includes a 156 ... [more ▼]

The GLACIOCLIM-SAMBA (GS) Antarctic accumulation monitoring network, which extends from the coast of Adelie Land to the Antarctic plateau, has been surveyed annually since 2004. The network includes a 156-km stake-line from the coast inland, along which accumulation shows high spatial and interannual variability with a mean value of 362 mm water equivalent a -1. In this paper, this accumulation is compared with older accumulation reports from between 1971 and 1991. The mean and annual standard deviation and the km-scale spatial pattern of accumulation were seen to be very similar in the older and more recent data. The data did not reveal any significant accumulation trend over the last 40 years. The ECMWF analysis-based forecasts (ERA-40 and ERA-Interim), a stretched-grid global general circulation model (LMDZ4) and three regional circulation models (PMM5, MAR and RACMO2), all with high resolution over Antarctica (27-125 km), were tested against the GS reports. They qualitatively reproduced the meso-scale spatial pattern of the annual-mean accumulation except MAR. MAR significantly underestimated mean accumulation, while LMDZ4 and RACMO2 overestimated it. ERA-40 and the regional models that use ERA-40 as lateral boundary condition qualitatively reproduced the chronology of interannual variability but underestimated the magnitude of interannual variations. Two widely used climatologies for Antarctic accumulation agreed well with the mean GS data. The model-based climatology was also able to reproduce the observed spatial pattern. These data thus provide new stringent constraints on models and other large-scale evaluations of the Antarctic accumulation. [less ▲]

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See detail21st century Antarctic surface mass balance downscaling from global circulation models
Agosta, Cécile ULiege; Favier, Vincent; Genthon, Christophe et al

Poster (2011, October)

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See detail21st century high-resolution downscaling of the Antarctic surface mass balance from global circulation models
Agosta, Cécile ULiege; Favier, Vincent; Genthon, Christophe et al

Conference (2011, April)

Most of the IPCC-AR4 Atmospheric Global Circulation Models (AGCM) predict an increase of the Antarctic Surface Mass Balance (SMB) during the 21st century that would mitigate global sea level rise. Present ... [more ▼]

Most of the IPCC-AR4 Atmospheric Global Circulation Models (AGCM) predict an increase of the Antarctic Surface Mass Balance (SMB) during the 21st century that would mitigate global sea level rise. Present accumulation and predicted change are largest at the ice sheet margins because they are driven by snowfall, which mostly comes from warm, moist air arising over the land slopes. The coastal belt is also where complex processes of sublimation, melt and redistribution by the wind occur. Thus, high-resolution modelling (5 to 10 km) is necessary to adequately capture the effects of small-scale variations in topography on the atmospheric variables in this area, but limitations in computing resources prevent such resolution at the scale of Antarctica in full climate models. We present here a downscaling method leading to 10-km SMB resolution for century time-scales over Antarctica. We compute the effect of the fine topography on orographic precipitation and on boundary layer processes that lead to melt and sublimation. We show that the accumulation downscaled from ERA-Interim is in good agreement with field measurements for the last 40 years. We then display the SMB downscaled from LMDZ4 AGCM outputs (~60-km resolution), and show that the downscaling improves the agreement between present modelled and observed SMB. Finally, we present hi-resolution features of the Antarctic SMB evolution during the 21st century downscaled from LMDZ4 and discuss the effect of the resolution on the Antarctic SMB contribution to sea level change. The downscaling model is a powerful tool that will be applied to others climate models for a better assessment of future sea level rise. [less ▲]

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See detailEvolution of Antarctic Surface Mass Balance by high-resolution downscaling of LMDZ4 AGCM and contribution to sea-level change
Agosta, Cécile ULiege; Favier, Vincent; Krinner, Gerhard et al

Conference (2011, March)

Most of the IPCC-AR4 Atmospheric Global Circulation Models (AGCM) predict an increase of the Antarctic Surface Mass Balance (SMB) during the 21st century that would mitigate global sea level rise. Present ... [more ▼]

Most of the IPCC-AR4 Atmospheric Global Circulation Models (AGCM) predict an increase of the Antarctic Surface Mass Balance (SMB) during the 21st century that would mitigate global sea level rise. Present accumulation and predicted change are largest at the ice sheet margins because they are driven by snowfall, which mostly comes from warm, moist air arising over the land slopes. The coastal belt is also where complex processes of sublimation, melt and redistribution by the wind occur. Thus, high-resolution modelling (5 to 15 km) is necessary to adequately capture the effects of small-scale variations in topography on the atmospheric variables in this area, but limitations in computing resources prevent such resolution at the scale of Antarctica in full climate models. We present here a downscaling method leading to 15-km SMB resolution for century time-scales over Antarctica. We compute precipitation fields by considering orographic processes induced by the broad-scale and the fine-scale topography, and we estimate sublimation, melting and refreezing with a surface scheme validated for snow and ice-covered land surface. We display the SMB downscaled from LMDZ4 AGCM outputs (~60-km resolution), and compare the agreement of the broad-scale SMB and the downscaled SMB with 20th century observations. Then, we present hi-resolution features of the Antarctic SMB evolution during the 21st century downscaled from LMDZ4 and discuss the effect of the resolution on the Antarctic SMB contribution to sea level change. The downscaling model is a powerful tool that will be applied to others climate models for a better assessment of future sea level rise. [less ▲]

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See detailDésagrégation du Bilan de Masse et du Bilan d’Energie en Surface de la calotte polaire Antarctique, application pour le 21ème siècle
Agosta, Cécile ULiege; Favier, Vincent; Krinner, Gerhard et al

Conference (2011, February)

Most of the IPCC-AR4 Atmospheric Global Circulation Models (AGCM) predict an increase of the Antarctic Surface Mass Balance (SMB) during the 21st century, driven by an increase of snow falls, which would ... [more ▼]

Most of the IPCC-AR4 Atmospheric Global Circulation Models (AGCM) predict an increase of the Antarctic Surface Mass Balance (SMB) during the 21st century, driven by an increase of snow falls, which would mitigate the sea level rise. Much of the SMB change is expected to happen in the Antarctic coastal area, which concentrates the major part of the snow falls. This area is also were we find complex processes of precipitation, sublimation, melt and redistribution by the wind. High-resolution modeling (5 to 10 km) is necessary to accurately capture the effects of the fine topography on the atmospheric variables but limitations in computing resources prevent such resolution at the scale of Antarctica in full climate models. We present here a downscaling method yielding to a 10-km resolution of the SMB for the 21st century, from ~60-km resolution LMDZ4 AGCM outputs. We compute orographic precipitation induced by the finer topography, as well as the boundary layer processes leading to melt and sublimation. It shows a clear improvement of the SMB distribution in coastal regions with consequences on the grounded ice sheet SMB estimation. [less ▲]

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See detailA Downscaling Approach Toward High-resolution Surface Mass Balance Over Antarctica
Gallée, Hubert; Agosta, Cécile ULiege; Gential, Luc et al

in Surveys in Geophysics (2011), 32(4-5), 507-518518

The Antarctic ice sheet surface mass balance shows high spatial variability over the coastal area. As state-of-the-art climate models usually require coarse resolutions to keep computational costs to a ... [more ▼]

The Antarctic ice sheet surface mass balance shows high spatial variability over the coastal area. As state-of-the-art climate models usually require coarse resolutions to keep computational costs to a moderate level, they miss some local features that can be captured by field measurements. The downscaling approach adopted here consists of using a cascade of atmospheric models from large scale to meso-gamma scale. A regional climate model (Modegravele Atmospheacuterique Reacutegional) forced by meteorological reanalyses provides a diagnostic physically-based rain- and snowfall downscaling model with meteorological fields at the regional scale. Although the parameterizations invoked by the downscaling model are fairly simple, the knowledge of small-scale topography significantly improves the representation of spatial variability of precipitation and therefore that of the surface mass balance. Model evaluation is carried out with the help of shallow firn cores and snow height measurements provided by automatic weather stations. Although downscaling of blowing snow still needs to be implemented in the model, the net accumulation gradient across Law Dome summit is shown to be induced mostly by orographic effects on precipitation. [less ▲]

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See detailModeling the mass and surface heat budgets in a coastal blue ice area of Adelie Land, Antarctica
Favier, Vincent; Agosta, Cécile ULiege; Genthon, Christophe et al

in Journal of Geophysical Research. Earth Surface (2011), 116

Meteorological data recorded from 12 December 2008 to 30 June 2010 were analyzed to assess the surface energy balance (SEB) in a blue ice area of Cap Prudhomme, Adelie Land (66 degrees 41'S, 139 degrees ... [more ▼]

Meteorological data recorded from 12 December 2008 to 30 June 2010 were analyzed to assess the surface energy balance (SEB) in a blue ice area of Cap Prudhomme, Adelie Land (66 degrees 41'S, 139 degrees 55'E). The SEB was computed with a newly developed model forced by direct measurements and with a voluntarily limited number of parameters to better assess model sensitivity. Incoming short-wave radiation was corrected for the slope and orientation of the local terrain assuming direct and diffuse radiation components. Turbulent heat fluxes were assessed using the bulk aerodynamic approach. Heat conduction in the ice was computed by solving the thermal diffusion equation. Snow accumulation was modeled using ERA interim total precipitation and a one-dimensional erosion model. The surface heat budget and accumulation/erosion model accurately reproduced field observations. The occurrence of blue ice is linked with higher rates of erosion than in the surrounding snow covered areas, which may be caused by local flow divergence or snow not being redistributed from higher elevations. Melting occurs between December and February when incoming short-wave radiation is high. However, the SEB was closely linked to air temperature through the incoming long-wave radiation and the turbulent sensible heat flux. Several warm events caused by cyclones intruding into the continent led to significant warming of the ice and high melting rates. Intruding cyclones were also associated with high precipitation that led to significant accumulation. Except in blue ice areas, modeling suggests that expected higher precipitation in a warmer climate will result in more accumulation. [less ▲]

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See detailDésagrégation du bilan de masse en surface de la calotte polaire Antarctique
Agosta, Cécile ULiege

Scientific conference (2009, November)

Le bilan de masse de surface (BMS) de la calotte polaire Antarctique est une composante majeure de l’évolution du niveau des mers. Le modèle de circulation général LMDZ4 et la grande majorité des modèles ... [more ▼]

Le bilan de masse de surface (BMS) de la calotte polaire Antarctique est une composante majeure de l’évolution du niveau des mers. Le modèle de circulation général LMDZ4 et la grande majorité des modèles atmosphériques utilisés dans l’IPCC-AR4 prévoient une augmentation du BMS en Antarctique au cours du siècle prochain, menée par une augmentation des précipitations neigeuses, qui contribuerait à une modération de l’élévation du niveau des mers. Les changements prévus sont particulièrement importants sur la zone côtière Antarctique, qui concentre la majorité des précipitations du continent. Il est donc crucial d’avoir une connaissance plus fine de l’évolution du BMS Antarctique, particulièrement en zone côtière. Les modèles actuels atteignent une résolution de 60 km à l’échelle de l’Antarctique pour des simulations longues (> 20 ans). L’objectif de ma thèse est d’estimer le BMS à une résolution inférieure à 15 km sur l’ensemble du continent, en désagrégeant les sorties des modèles de climat avec un modèle à temps de calcul réduit. La validation des modèles désagrégés est un point clé pour estimer la qualité des simulations futures. Or cette validation n’est pas aisée, du fait de l’impossibilité de mesurer directement les précipitations neigeuses et de la faible quantité de données d’accumulation à l’échelle du continent. Nous commencerons donc par une évaluation de la base de données Glacioclim-SAMBA et son utilisation pour valider différents modèles de climat en région côtière. Nous nous concentrerons ensuite sur la validation des modèles à l’échelle de l’Antarctique, en proposant une modification de la méthode utilisée par Arthern et al. (2006) pour fournir une climatologie du BMS à partir de données de terrain et de données satellite. Enfin, nous verrons le fonctionnement des modèles de désagrégation des précipitations et du bilan d’énergie en surface de la calotte polaire Antarctique. Je préciserai ma contribution au développement des modèles et présenterai des résultats préliminaires de désagrégation du BMS ainsi que les modifications que je prévoie d’apporter aux modèles. [less ▲]

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See detailSpatial distribution of accumulation in the Adélie Land - Comparison of the Antarctic GLACIOCLIM-SAMBA observation data with remote sensing techniques and high-resolution climate models
Agosta, Cécile ULiege; Genthon, Christophe; Favier, Vincent et al

Conference (2009, July)

The Surface Mass Balance (SMB) of Antarctica is typically much larger within the first 200 km from the coast than further inland. This is also likely where much of the SMB change is expected due to ... [more ▼]

The Surface Mass Balance (SMB) of Antarctica is typically much larger within the first 200 km from the coast than further inland. This is also likely where much of the SMB change is expected due to climate warming. That is why since 2004 the GLACIOCLIM- SAMBA French observatory monitors the SMB in this region with spatial scales resolving those of climate models. A stakes line made of 91 stakes was deployed along a 150 km transect from the coast of Adélie Land towards Dome C on the plateau. This transect is surveyed each year and 3 complete records are now available. We first compare recent SMB measurements with older reports from the 1972-1992 period. We show that a significant fraction of the observed kilometer-scale spatial variability is stationary with time. Moreover the large spatial and inter-annual variabilities of recent measurements are consistent with the historical ones. The lateral spatial significance of the transect is then evaluated using the background remote-sensing- based model of Arthern et al. (2006). Finally, results from 3 high-resolution climate models are presented and compared with the field reports: the global atmosphere-surface climate model LMDZ4 zoomed to reach a 35 km resolution over Antarctica, the regional atmospheric climate model MAR developed for polar regions (20 km resolution) and the ECMWF analysis (50 km resolution). We show large differences between the 3 models, which don’t have the same ability to reproduce the meso-scale characteristics of the distribution of the observed SMB in the critical coast-to-plateau area. [less ▲]

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See detailTransect GLACIOCLIM-SAMBA : observation et modélisation du Bilan de Masse de Surface sur la zone de transition côte-plateau Antarctique
Agosta, Cécile ULiege; Genthon, Christophe; Favier, Vincent et al

Conference (2008, October)

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See detailSensibilité aux variations climatiques d'un bassin à forts enjeux - Le cas de la Garonne
Dupeyrat, Anne; Agosta, Cécile ULiege; Sauquet, Eric et al

in IWRA 13th World Water Congress (2008, September)

Detailed reference viewed: 20 (2 ULiège)