References of "van den Broeke, Michiel"
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See detailGreenland climate change: from the past to the future
Masson‐Delmotte, Valérie; Swingedouw, Didier; Landais, Amaëlle et al

in Wiley Interdisciplinary Reviews. RNA (2012), 3(5), 427-449

Climate archives available from deep sea and marine shelf sediments, glaciers, lakes, and ice cores in and around Greenland allow us to place the current trends in regional climate, ice sheet dynamics ... [more ▼]

Climate archives available from deep sea and marine shelf sediments, glaciers, lakes, and ice cores in and around Greenland allow us to place the current trends in regional climate, ice sheet dynamics, and land surface changes in a broader perspective. We show that, during the last decade (2000s), atmospheric and sea surface temperatures are reaching levels last encountered millennia ago, when northern high latitude summer insolation was higher due to a different orbital configuration. Records from lake sediments in southern Greenland document major environmental and climatic conditions during the last 10,000 years, highlighting the role of soil dynamics in past vegetation changes, and stressing the growing anthropogenic impacts on soil erosion during the recent decades. Furthermore, past and present changes in atmospheric and oceanic heat advection appear to strongly influence both regional climate and ice sheet dynamics. Projections from climate models are investigated to quantify the magnitude and rates of future changes in Greenland temperature, which may be faster than past abrupt events occurring under interglacial conditions. Within one century, in response to increasing greenhouse gas emissions, Greenland may reach temperatures last time encountered during the last interglacial period, approximately 125,000 years ago. We review and discuss whether analogies between the last interglacial and future changes are reasonable, because of the different seasonal impacts of orbital and greenhouse gas forcings. Over several decades to centuries, future Greenland melt may act as a negative feedback, limiting regional warming albeit with global sea level and climatic impacts. [less ▲]

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See detailMelting trends over the Greenland ice sheet (1958–2009) from spaceborne microwave data and regional climate models
Fettweis, Xavier ULg; Tedesco, Marco; van den Broeke, Michiel et al

in The Cryosphere [=TC] (2011), 5

To study near-surface melt changes over the Greenland ice sheet (GrIS) since 1979, melt extent estimates from two regional climate models were compared with those obtained from spaceborne microwave ... [more ▼]

To study near-surface melt changes over the Greenland ice sheet (GrIS) since 1979, melt extent estimates from two regional climate models were compared with those obtained from spaceborne microwave brightness temperatures using two different remote sensing algorithms. The results from the two models were consistent with those obtained with the remote sensing algorithms at both daily and yearly time scales, encouraging the use of the models for analyzing melting trends before the satellite era (1958–1979), when forcing data is available. Differences between satellite-derived and model-simulated results still occur and are used here to identify (i) biases in the snow models (notably in the albedo parametrization, in the thickness of a snow layer, in the maximum liquid water content within the snowpack and in the snowfall impacting the bare ice appearance in summer) and (ii) limitations in the use of passive microwave data for snowmelt detection at the edge of the ice sheet due to mixed pixel effect (e.g., tundra or rock nearby the ice sheet). The results from models and spaceborne microwave sensors confirm a significant (p-value = 0.01) increase in GrIS surface melting since 1979. The melt extent recorded over the last years (1998, 2003, 2005 and 2007) is unprecedented in the last 50 yr with the cumulated melt area in the 2000's being, on the average, twice that of the 1980's. [less ▲]

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See detailExplanation of the extreme low surface mass balance over the Greenland ice sheet in 2010 with the help of a regional climate model and a circulation type classification.
Fettweis, Xavier ULg; van den Broeke, Michiel; van de Berg, Willem Jan et al

Conference (2011, April 06)

The regional climate models MAR and RCMO show that the surface mass balance (SMB) rate of the whole Greenland ice sheet (GrIS) is the lowest in 2010 since 50 years. This record is a combination of an ... [more ▼]

The regional climate models MAR and RCMO show that the surface mass balance (SMB) rate of the whole Greenland ice sheet (GrIS) is the lowest in 2010 since 50 years. This record is a combination of an abnormal dry year and an exceptional melt in summer confirmed by ground measurements and satellite-derived observations. An automated circulation type classification (CTC) is used for detecting anomalies in the daily atmospheric circulation at 500hPa over the Greenland ice sheet during 2010. The CTC reveals that the low snow accumulation is due to the general circulation (negative NAO index) while the record melt in summer is rather a consequence of the well known surface albedo-temperature feedback induced by - a warmer and thinner than normal snowpack above the bare ice at the end of the spring. - an earlier beginning of the melt season. - a drier summer. - an exceptional persistence of atmospheric circulations inducing warm and dry conditions over the GrIS. All these anomalies induced in summer 2010 an exceptional time exposure of bare ice areas (with a lower albedo than snow) over the GrIS which impacts the surface melt. Sensitivity experiments carried out by the MAR model allow to estimate the importance of each anomaly in the record simulated melt of summer 2010. [less ▲]

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See detailEvaluation of the Greenland ice sheet surface mass balance simulated by a regional climate model forced by some selected IPCC AR5/CMIP5 AOGCMs over the current climate.
Fettweis, Xavier ULg; van den Broeke, Michiel; van de Berg, Willem Jan et al

Conference (2011, April 05)

Abstract. As part of the ICE2SEA project, the regional climate model MAR was forced by the general circulation model ECHAM5 for making future projections of the Greenland Ice Sheet (GrIS) Surface Mass ... [more ▼]

Abstract. As part of the ICE2SEA project, the regional climate model MAR was forced by the general circulation model ECHAM5 for making future projections of the Greenland Ice Sheet (GrIS) Surface Mass Balance (SMB) over 1980-2099 at a resolution of 25km. For the A1B scenario, MAR projects a highly negative (-500 GT/yr) SMB rate at the end of this century and a induced mass loss corresponding to a sea level rise of ~7 cm over 2000-2100. However, the comparison with MAR forced by the ERA-40 reanalysis over 1980-1999 shows that MAR forced by the 20C3M scenario is not able to represent reliably the current SMB due to biases in the general circulation and in the free atmosphere summer temperature modeled by ECHAM5 around the GrIS. These biases induce in MAR an underestimation of the snow accumulation and an overestimation of the surface melt. Therefore, this questions the reliability of these ECHAM5-forced future projections, knowing that i) these biases could be amplified in future and that ii) the MAR outputs are used to force ice sheets models for the ICE2SEA project. That is why, by waiting the outputs from the next generation of GCMs (CMIP5), we investigate the impacts of current climate biases over the future projections and we suggest corrections of ECHAM5 forcing files for having a better agreement with the ERA-40 forced simulation. This is useful for the ice sheet model wanting to use the absolute values of MAR future projections instead of anomalies. [less ▲]

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See detailAssimilation of the 1979-2009 microwave satellite data into the regional climate MAR model for studying the Greenland ice sheet melt extent
Fettweis, Xavier ULg; Tedesco, Marco; van den Broeke, Michiel

Conference (2011, April 05)

The 1979-2009 melt extent derived from the amount of produced meltwater by day simulated by the regional climate model MAR and derived from the spaceborne microwave 19GHz horizontal polarizated (T19H ... [more ▼]

The 1979-2009 melt extent derived from the amount of produced meltwater by day simulated by the regional climate model MAR and derived from the spaceborne microwave 19GHz horizontal polarizated (T19H) brightness temperature compares well over the Greenland ice sheet (GrIS). However, some disagreements still occur in some pixels for any days. Therefore, we run the MAR model in an assimilation mode, constrained by the daily SMMR-SSM/I derived melt extent over 1979-2009. As assimilation, we change the MAR near-surface snowpack temperature for the pixels where MAR and satellite disagree. This correction allows to conserve the water equivalent of the snowpack mass in MAR while having a full agreement between model and satellite derived melt extent. The assimilation helps to improve the meltwater production simulation as well as the matching with other satellite data sets (MODIS, GRACE, ...), with the objective to reduce the uncertainties of the current SMB model-based estimates over the GrIS. [less ▲]

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See detailRecord Summer Melt in Greenland in 2010
Tedesco, Marco; Fettweis, Xavier ULg; van den Broeke, Michiel et al

in EOS : Transactions, American Geophysical Union (2011), 92(15), 126

As Arctic temperatures increase, there is growing concern about the melting of the Greenland ice sheet, which reached a new record during the summer of 2010. Understanding the changing surface mass ... [more ▼]

As Arctic temperatures increase, there is growing concern about the melting of the Greenland ice sheet, which reached a new record during the summer of 2010. Understanding the changing surface mass balance of the Greenland ice sheet requires appreciation of the close links among changes in surface air temperature, surface melting, albedo, and snow accumulation. Increased melting accelerates surface snow grain growth, leading to a decrease in surface albedo, which then fosters further melt. In turn, winter accumulation contributes to determining how much snow is required before a dark (e.g., lower albedo), bare ice surface is exposed in spring (Figure 1). [less ▲]

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See detailSurface Energy Balance
van den Broeke, Michiel; Fettweis, Xavier ULg; Molg, Thomas

in Encyclopedia of Snow, Ice and Glaciers (2011)

Definition of surface energy balance over a snowpack

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See detailThe role of albedo and accumulation in the 2010 melting record in Greenland
Tedesco, Marco; Fettweis, Xavier ULg; van den Broeke, Michiel et al

in Environmental Research Letters (2011), 6(1),

Analyses of remote sensing data, surface observations and output from a regional atmosphere model point to new records in 2010 for surface melt and albedo, runoff, the number of days when bare ice is ... [more ▼]

Analyses of remote sensing data, surface observations and output from a regional atmosphere model point to new records in 2010 for surface melt and albedo, runoff, the number of days when bare ice is exposed and surface mass balance of the Greenland ice sheet, especially over its west and southwest regions. Early melt onset in spring, triggered by above-normal near-surface air temperatures, contributed to accelerated snowpack metamorphism and premature bare ice exposure, rapidly reducing the surface albedo. Warm conditions persisted through summer, with the positive albedo feedback mechanism being a major contributor to large negative surface mass balance anomalies. Summer snowfall was below average. This helped to maintain low albedo through the 2010 melting season, which also lasted longer than usual. [less ▲]

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See detailEvaluation over Greenland of WRF with GC-NET observations (1995-2005) by comparison with 2 other RCMs
Sacré, Bernard ULg; Fettweis, Xavier ULg; Doutreloup, Sébastien ULg et al

Conference (2011)

In the context of climate change, the Greenland Ice Sheet (GrIS) plays an important role in sea level variation and oceanic thermohaline circulation changes. Unfortunately, Global Climate Models do not ... [more ▼]

In the context of climate change, the Greenland Ice Sheet (GrIS) plays an important role in sea level variation and oceanic thermohaline circulation changes. Unfortunately, Global Climate Models do not illustrate enough the characteristics of Greenland. To solve that, specific RCMs have been developed to take into account the features of polar regions. In this project, we compare three RCMs : the MAR model, the RACMO model and the Weather Research and Forecasting (WRF) model. WRF is an open source model developed by the Mesoscale and Microscale Meteorology Division of NCAR. We use here the standard WRF (version 3.2.1) and its polar optimization (called polar WRF). The MAR version tuned for the GrIS and coupled with a 1D surface scheme called SISVAT (for Soil Ice Snow Vegetation Atmosphere Transfer) is compared here. The version of RACMO is a specific version for the Greenland climate, RACMO2/GR. This model contains a special surface module for snow-ice treatment and other modifications concerning, for example, the surface turbulence heat flux or the surface roughness. The comparison is made on a domain centered on Greenland at a 25-km horizontal resolution over the 1995-2005 period when Automatic Weather Station (AWS) measurements are available from the Greenland Climate NETwork (GC-NET). Statistics (mean, bias, RMSE, correlation coefficient) are calculated for the near-surface temperature, surface pressure, 10m-wind speed and specific humidity for winter (October to April) and summer (May to September). In addition, the modeled snowfall are evaluated with ice core-based snow accumulation climatologies. Comparison shows a significant improvement from RCMs compared to the reanalyses (NCEP2 and ERA-INTERIM) in respect to the AWS measurements. RACMO and MAR seem to compare better with observations than WRF. [less ▲]

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See detailThe 1958–2009 Greenland ice sheet surface melt and the mid-tropospheric atmospheric circulation
Fettweis, Xavier ULg; Mabille, Georges; Erpicum, Michel ULg et al

in Climate Dynamics (2011), 36(1 (2011)), 139-159

In order to assess the impact of the mid-tropospheric circulation over the Greenland ice sheet (GrIS) on surface melt, as simulated by the regional climate model MAR, an automatic Circulation type ... [more ▼]

In order to assess the impact of the mid-tropospheric circulation over the Greenland ice sheet (GrIS) on surface melt, as simulated by the regional climate model MAR, an automatic Circulation type classification (CTC) based on 500 hPa geopotential height from reanalyses is developed. General circulation correlates significantly with the surface melt anomalies for the summers in the period 1958–2009. The record surface melt events observed during the summers of 2007–2009 are linked to the exceptional persistence of atmospheric circulations favouring warm air advection. The CTC emphasizes that summer 500 hPa circulation patterns have changed since the beginning of the 2000s; this process is partly responsible for the recent warming observed over the GrIS. [less ▲]

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See detailExtreme snowmelt in Northern Greenland during summer 2008
Tedesco, Marco; Fettweis, Xavier ULg; van den Broeke, Michiel et al

in EOS : Transactions, American Geophysical Union (2008), 89(41), 391

Extreme snowmelt occurred during summer 2008 over the northern part of the Greenland ice sheet, according to the analysis of microwave data recorded by the Special Sensor Microwave Imager (SSM/I) on board ... [more ▼]

Extreme snowmelt occurred during summer 2008 over the northern part of the Greenland ice sheet, according to the analysis of microwave data recorded by the Special Sensor Microwave Imager (SSM/I) on board the F13 satellite of the U.S. Defense Meteorological Satellite Program (DMSP). New records of the number of melting days were also observed over large portions of the same areas (letters A and B in Figure 1). [less ▲]

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