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See detailImportant role of the mid-tropospheric atmospheric circulation in the recent surface melt increase over the Greenland ice sheet
Fettweis, Xavier ULg; Hanna, Edward; Lang, Charlotte ULg et al

in Cryosphere (The) (2013), 7

Since 2007, there has been a series of surface melt records over the Greenland ice sheet (GrIS), continuing the trend towards increased melt observed since the end of the 1990's. The last two decades are ... [more ▼]

Since 2007, there has been a series of surface melt records over the Greenland ice sheet (GrIS), continuing the trend towards increased melt observed since the end of the 1990's. The last two decades are characterized by an increase of negative phases of the North Atlantic Oscillation (NAO) favouring warmer and drier summers than normal over GrIS. In this context, we use a circulation type classification based on daily 500 hPa geopotential height to evaluate the role of atmospheric dynamics in this surface melt acceleration for the last two decades. Due to the lack of direct observations, the interannual melt variability is gauged here by the summer (June–July–August) mean temperature from reanalyses at 700 hPa over Greenland; analogous atmospheric circulations in the past show that ~70% of the 1993–2012 warming at 700 hPa over Greenland has been driven by changes in the atmospheric flow frequencies. Indeed, the occurrence of anticyclones centred over the GrIS at the surface and at 500 hPa has doubled since the end of 1990's, which induces more frequent southerly warm air advection along the western Greenland coast and over the neighbouring Canadian Arctic Archipelago (CAA). These changes in the NAO modes explain also why no significant warming has been observed these last summers over Svalbard, where northerly atmospheric flows are twice as frequent as before. Therefore, the recent warmer summers over GrIS and CAA cannot be considered as a long-term climate warming but are more a consequence of NAO variability affecting atmospheric heat transport. Although no global model from the CMIP5 database projects subsequent significant changes in NAO through this century, we cannot exclude the possibility that the observed NAO changes are due to global warming. [less ▲]

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See detailCurrent and future atmospheric circulation at 500 hPa over Greenland simulated by the CMIP3 and CMIP5 global models
Belleflamme, Alexandre ULg; Fettweis, Xavier ULg; Lang, Charlotte ULg et al

in Climate Dynamics (2013), 41(7-8),

The Greenland ice sheet is projected to be strongly affected by global warming. These projections are either issued from downscaling methods (such as Regional Climate Models) or they come directly from ... [more ▼]

The Greenland ice sheet is projected to be strongly affected by global warming. These projections are either issued from downscaling methods (such as Regional Climate Models) or they come directly from General Circulation Models (GCMs). In this context, it is necessary to evaluate the accuracy of the daily atmospheric circulation simulated by the GCMs, since it is used as forcing for downscaling methods. Thus, we use an automatic circulation type classification based on two indices (Euclidean distance and Spearman rank correlation using the daily 500 hPa geopotential height) to evaluate the ability of the GCMs from both CMIP3 and CMIP5 databases to simulate the main circulation types over Greenland during summer. For each circulation type, the GCMs are compared to three reanalysis datasets on the basis of their frequency and persistence differences. For the current climate (1961–1990), we show that most of the GCMs do not reproduce the expected frequency and the persistence of the circulation types and that they simulate poorly the observed daily variability of the general circulation. Only a few GCMs can be used as reliable forcings for downscaling methods over Greenland. Finally, when applying the same approach to the future projections of the GCMs, no significant change in the atmospheric circulation over Greenland is detected, besides a generalised increase of the geopotential height due to a uniform warming of the atmosphere. [less ▲]

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See detailFuture projections of the Greenland ice sheet surface mass balance simulated by the regional climate model MAR forced by three CMIP5 global models.
Fettweis, Xavier ULg; Franco, Bruno ULg; Lang, Charlotte ULg et al

Conference (2012, September 11)

As part of the ICE2SEA project, the regional climate model MAR was forced by the global models HadCM3 and ECHAM5 for making future projections of the Greenland Ice Sheet (GrIS) Surface Mass Balance (SMB ... [more ▼]

As part of the ICE2SEA project, the regional climate model MAR was forced by the global models HadCM3 and ECHAM5 for making future projections of the Greenland Ice Sheet (GrIS) Surface Mass Balance (SMB) over 1980-2099 at a resolution of 25km. However, the comparison with MAR forced by the ERA-40 reanalysis over 1980-1999 shows that MAR forced by these GCMs is not able to represent reliably the current SMB due to biases in the general circulation and in the free atmosphere summer temperature modelled by these GCMs around the GrIS. That is why, we present here first results of MAR forced by the next generation of GCMs from the CMIP5 data base (CanESM2, NorESM1 and MIROC5 here). The comparison with the ERA-INTERIM forced MAR simulations over current climate is a lot of better, which increases the reliability and the interest of these new MAR projections. In addition, the new scenarios (RCP 2.6, 4.5, 6.0 and 8.5) of the next IPCC Assessment Report (AR5) are used here. These new simulations show notably that the response of SMB to rising temperature is not a linear function of the temperature anomalies due to the positive albedo feedback which enhances the surface melt. For 2100, in case of extreme rising temperature (RCP 8.5 scenario), MAR simulates a surface GrIS mass loss corresponding to a cumulated sea level rise (SLR) of about 15 cm since 2000! Mainly the changes in SMB and in surface energy balance will be discussed here and estimations of the GrIS surface melt contribution to the SLR using all the CMIP5 outputs will be given. [less ▲]

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See detailEvaluation des modèles climatiques régionaux MAR et WRF sur le Svalbard
Lang, Charlotte ULg; Fettweis, Xavier ULg; Erpicum, Michel ULg

Poster (2012, September)

: Il est bien connu que les zones de hautes latitudes sont très sensibles aux changements climatiques. A cause du réchauffement global, la fonte des calottes a augmenté, ce qui à son tour a une influence ... [more ▼]

: Il est bien connu que les zones de hautes latitudes sont très sensibles aux changements climatiques. A cause du réchauffement global, la fonte des calottes a augmenté, ce qui à son tour a une influence sur le climat via des modifications de la circulation thermohaline, la rétroaction de l’albédo de la glace, l’augmentation du niveau des mers… Nous avons comparé le climat du Svalbard modélisé par deux modèles régionaux (MAR et WRF) à une résolution de 10 km sur la période 2000-2010 à des mesures provenant de plusieurs stations météorologiques localisées dans différentes régions de l’archipel afin d'évaluer lequel de ces modèles pouvait représenter au mieux le climat du Svalbard. [less ▲]

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See detailEvaluation of the MAR and WRF regional climate models over Svalbard
Lang, Charlotte ULg; Fettweis, Xavier ULg; Doutreloup, Sébastien ULg et al

Conference (2012, June 01)

It is well known that high latitude zones are very sensitive to climate change. As a result of global warming, ice sheet melting has increased which in turn has an influence on climate through ... [more ▼]

It is well known that high latitude zones are very sensitive to climate change. As a result of global warming, ice sheet melting has increased which in turn has an influence on climate through modifications of the thermohaline circulation, feedback of ice albedo, sea level rise... Svalbard is an archipelago between 74 and 81°lat N and 60 percent of its area (62 248 km2) is covered with glaciers and ice sheets. The impact of global warming on the Svalbard cryosphere can be estimated with climate models. However, we need to use regional climate models as they offer the possibility of a higher resolution than general circulation models. We have ran two regional climate models (MAR and WRF) at a 10-kilometre resolution between 2006 and 2010 over Svalbard and compared their simulated climate to near surface measurements at several weather stations through the archipelago in order to determine which one of them could best represent the Svalbard climate. [less ▲]

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See detailEvaluation of the regional climate model WRF over Svalbard
Lang, Charlotte ULg; Fettweis, Xavier ULg; Doutreloup, Sébastien ULg et al

Poster (2012, April 24)

It is well known that high latitude zones are very sensitive to climate change. As a result of global warming, ice sheet melting has increased which in turn has an influence on climate through ... [more ▼]

It is well known that high latitude zones are very sensitive to climate change. As a result of global warming, ice sheet melting has increased which in turn has an influence on climate through modifications of the thermohaline circulation, feedback of ice albedo, sea level rise, … Svalbard is an archipelago between 74 and 81°lat N and 60 percent of its area (62 248 km2) is covered with glaciers and ice sheets. The impact of global warming on the Svalbard cryosphere can be estimated with climate models. However, we need to use regional climate models as they offer the possibility of a higher resolution than general circulation models. We have ran two regional climate models (MAR and WRF) at a 10-kilometre resolution between 2006 and 2010 over Svalbard and compared their simulated climate to near surface measurements at several weather stations through the archipelago in order to determine which one of them could best represent the Svalbard climate. [less ▲]

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See detailModélisation du bilan de masse en surface du Svalbard avec le modèle régional MAR entre 1958 et 2010
Lang, Charlotte ULg

Conference (2012, March 07)

It is well known that high latitude zones are very sensitive to climate change. As a result of global warming, ice sheet melting has increased which in turn has an influence on climate through modifications ... [more ▼]

It is well known that high latitude zones are very sensitive to climate change. As a result of global warming, ice sheet melting has increased which in turn has an influence on climate through modifications of the thermohaline circulation, feedback of ice albedo, sea level rise,. . . Svalbard is an archipelago located between 74 and 81◦ lat N and 60 percent of its area (62 248 km2 ) is covered with glaciers and ice sheets. The impact of global warming on the Svalbard cryosphere can be estimated with climate models. However, we need to use regional climate models as they offer the possibility of a higher resolution than general circulation models. We have carried out a simulation of the Svalbard climate over the last 50 years (from 1958 to 2010) with the regional climate MAR model (tuned for the Greenland ice sheet) at a 10 km resolution forced with the ECMWF reanalysis. As validation, the modeled climate has been compared to near surface measurements at several weather stations through the archipelago. The results show a large interannual variability of the surface mass balance over Svalbard along with an increasing melting. The increase in temperature is responsible for the melting rate and the interannual variability is due to the variations of the mean summer temperature. [less ▲]

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See detailModeling of the surface mass balance in Svalbard with the regional climate model MAR over 1958-2010
Lang, Charlotte ULg

Master's dissertation (2011)

It is well known that high latitude zones are very sensitive to climate change. As a result of global warming, ice sheet melting has increased which in turn has an influence on climate through ... [more ▼]

It is well known that high latitude zones are very sensitive to climate change. As a result of global warming, ice sheet melting has increased which in turn has an influence on climate through modifications of the thermohaline circulation, feedback of ice albedo, sea level rise,. . . Svalbard is an archipelago located between 74 and 81 ◦lat N and 60 percent of its area (62 248 km2 ) is covered with glaciers and ice sheets. The impact of global warming on the Svalbard cryosphere can be estimated with climate models. However, we need to use regional climate models as they offer the possibility of a higher resolution than general circulation models. We have carried out a simulation of the Svalbard climate over the last 50 years (from 1958 to 2010) with the regional climate MAR model (tuned for the Greenland ice sheet) at a 10 km resolution forced with the ECMWF reanalysis. As validation, the modeled climate has been compared to near surface measurements at several weather stations through the archipelago. The results show a large interannual variability of the surface mass balance over Svalbard along with an increasing melting. The increase in temperature is responsible for the melting rate and the interannual variability is due to the variations of the mean summer temperature. [less ▲]

Detailed reference viewed: 17 (2 ULg)