Publications of ???
Bookmark and Share    
Full Text
See detailRegional modeling of surface mass balance on the Cook Ice Cap, Kerguelen Islands
Verfaillie, D.; Favier, V.; Gallée, H. et al

in Climate Dynamics (2019)

We assess the ability of the regional circulation model MAR to represent the recent negative surface mass balance (SMB) observed over the Kerguelen Islands ( 49∘S , 69∘E ) and evaluate the uncertainties ... [more ▼]

We assess the ability of the regional circulation model MAR to represent the recent negative surface mass balance (SMB) observed over the Kerguelen Islands ( 49∘S , 69∘E ) and evaluate the uncertainties in SMB projections until the end of the century. The MAR model forced by ERA-Interim reanalysis shows a good agreement with meteorological observations at Kerguelen, particularly after slight adjustment of the forcing fields (+ 10% humidity, +0.8∘C , all year round) to improve precipitation occurrence and intensity. The modeled SMB and surface energy balance (SEB) are also successfully evaluated with observations, and spatial distributions are explained as being largely driven by the elevation gradient and by the strong west to east foehn effect occurring on the ice cap. We select five general circulation models (GCMs) from the Coupled Model Intercomparison Project phase 5 (CMIP5) by evaluating their ability to represent temperature and humidity in the southern mid-latitudes over 1980–1999 with respect to ERA-Interim and use them to force the MAR model. These simulations fail to replicate SMB observations even when outputs from the best CMIP5 model (ACCESS1-3) are used as forcing because all GCMs fail in accurately reproducing the circulation changes observed at Kerguelen since the mid-1970s. Global models chosen to represent extreme values of SMB drivers also fail in producing extreme values of SMB, suggesting that more rigorous modeling of present and future circulation changes with GCMs is still needed to accurately assess future changes of the cryosphere in this area. [less ▲]

Detailed reference viewed: 36 (3 ULiège)
Full Text
See detailThe Effect of Foehn‐Induced Surface Melt on Firn Evolution Over the Northeast Antarctic Peninsula
Datta, R.T.; Tedesco, M.; Fettweis, Xavier ULiege et al

in Geophysical Research Letters (2019), 46

Surface meltwater ponding has been implicated as a major driver for recent ice shelf collapse as well as the speedup of tributary glaciers in the northeast Antarctic Peninsula. Surface melt on the NAP is ... [more ▼]

Surface meltwater ponding has been implicated as a major driver for recent ice shelf collapse as well as the speedup of tributary glaciers in the northeast Antarctic Peninsula. Surface melt on the NAP is impacted by the strength and frequency of westerly winds, which result in sporadic foehn flow. We estimate changes in the frequency of foehn flow and the associated impact on snow melt, density, and the percolation depth of meltwater over the period 1982–2017 using a regional climate model and passive microwave data. The first of two methods extracts spatial patterns of melt occurrence using empirical orthogonal function analysis. The second method applies the Foehn Index, introduced here to capture foehn occurrence over the full study domain. Both methods show substantial foehn‐induced melt late in the melt season since 2015, resulting in compounded densification of the near‐surface snow, with potential implications for future ice shelf stability. [less ▲]

Detailed reference viewed: 169 (14 ULiège)
Full Text
See detailEstimation of the Antarctic surface mass balance using the regional climate model MAR (1979–2015) and identification of dominant processes
Agosta, Cécile ULiege; Amory, Charles ULiege; Kittel, Christoph ULiege et al

in Cryosphere (2019)

The Antarctic ice sheet mass balance is a major component of the sea level budget and results from the difference of two fluxes of a similar magnitude: ice flow discharging in the ocean and net snow ... [more ▼]

The Antarctic ice sheet mass balance is a major component of the sea level budget and results from the difference of two fluxes of a similar magnitude: ice flow discharging in the ocean and net snow accumulation on the ice sheet surface, i.e. the surface mass balance (SMB). Separately modelling ice dynamics and SMB is the only way to project future trends. In addition, mass balance studies frequently use regional climate models (RCMs) outputs as an alternative to observed fields because SMB observations are particularly scarce on the ice sheet. Here we evaluate new simulations of the polar RCM MAR forced by three reanalyses, ERA-Interim, JRA-55, and MERRA-2, for the period 1979–2015, and we compare MAR results to the last outputs of the RCM RACMO2 forced by ERA-Interim. We show that MAR and RACMO2 perform similarly well in simulating coast-to-plateau SMB gradients, and we find no significant differences in their simulated SMB when integrated over the ice sheet or its major basins. More importantly, we outline and quantify missing or underestimated processes in both RCMs. Along stake transects, we show that both models accumulate too much snow on crests, and not enough snow in valleys, as a result of drifting snow transport fluxes not included in MAR and probably underestimated in RACMO2 by a factor of 3. Our results tend to confirm that drifting snow transport and sublimation fluxes are much larger than previous model-based estimates and need to be better resolved and constrained in climate models. Sublimation of precipitating particles in low-level atmospheric layers is responsible for the significantly lower snowfall rates in MAR than in RACMO2 in katabatic channels at the ice sheet margins. Atmospheric sublimation in MAR represents 363 Gt yr−1 over the grounded ice sheet for the year 2015, which is 16 % of the simulated snowfall loaded at the ground. This estimate is consistent with a recent study based on precipitation radar observations and is more than twice as much as simulated in RACMO2 because of different time residence of precipitating particles in the atmosphere. The remaining spatial differences in snowfall between MAR and RACMO2 are attributed to differences in advection of precipitation with snowfall particles being likely advected too far inland in MAR. [less ▲]

Detailed reference viewed: 77 (19 ULiège)
Full Text
See detailAdded value of the regional climate model MAR for simulating the surface mass balance of the Antarctic ice sheet compared to a global climate model (ACCESS1.3)
Kittel, Christoph ULiege; Amory, Charles ULiege; Agosta, Cécile ULiege et al

Poster (2019)

Due to their ability to produce climate projections, General circulation models (GCM) are often used to provide estimates of the surface mass balance (SMB) of the Antarctic ice sheet that can be used to ... [more ▼]

Due to their ability to produce climate projections, General circulation models (GCM) are often used to provide estimates of the surface mass balance (SMB) of the Antarctic ice sheet that can be used to constrain ice sheet models. However, GCM still benefit from a poor representation of polar climate specificities such as stable boundary layers, polar clouds or interactions between snow-covered surfaces and the atmosphere. In this study, we highlight the importance of downscaling GCM outputs from the Fifth Climate Model Intercomparison Project (CMIP5) with a regional climate model to provide accurate estimates of the Antarctic SMB. For that purpose, the regional climate model MAR is forced by 6-hourly outputs from ACCESS1.3 that is currently considered as one of the best GCM from CMIP5 over the Antarctic ice sheet. Estimates of the SMB computed by MAR and ACCESS1.3 are evaluated against SMB observations. Even if the temporal variability of the SMB is forced by the driving GCM, the comparison shows that MAR improves the spatial variability of the Antarctic SMB, emphasizing the added value of using a polar RCM for downscaling GCM outputs at high latitudes. [less ▲]

Detailed reference viewed: 82 (7 ULiège)
Full Text
See detailSensitivity of the current Antarctic surface mass balance to sea surface conditions using MAR
Kittel, Christoph ULiege; Amory, Charles ULiege; Agosta, Cécile ULiege et al

in Cryosphere (2018), 12

Estimates for the recent period and projections of the Antarctic surface mass balance (SMB) often rely on high-resolution polar-oriented regional climate models (RCMs). However, RCMs require large-scale ... [more ▼]

Estimates for the recent period and projections of the Antarctic surface mass balance (SMB) often rely on high-resolution polar-oriented regional climate models (RCMs). However, RCMs require large-scale boundary forcing fields prescribed by reanalyses or general circulation models (GCMs). Since the recent variability of sea surface conditions (SSCs, namely sea ice concentration, SIC, and sea surface temperature, SST) over the Southern Ocean is not reproduced by most GCMs from the 5th phase of the Coupled Model Intercomparison Project (CMIP5), RCMs are then subject to potential biases. We investigate here the direct sensitivity of the Antarctic SMB to SSC perturbations around the Antarctic. With the RCM “Modèle Atmosphérique Régional” (MAR), different sensitivity experiments are performed over 1979–2015 by modifying the ERA-Interim SSCs with (i) homogeneous perturbations and (ii) mean anomalies estimated from all CMIP5 models and two extreme ones, while atmospheric lateral boundary conditions remained unchanged. Results show increased (decreased) precipitation due to perturbations inducing warmer, i.e. higher SST and lower SIC (colder, i.e. lower SST and higher SIC), SSCs than ERA-Interim, significantly affecting the SMB of coastal areas, as precipitation is mainly related to cyclones that do not penetrate far into the continent. At the continental scale, significant SMB anomalies (i.e greater than the interannual variability) are found for the largest combined SST/SIC perturbations. This is notably due to moisture anomalies above the ocean, reaching sufficiently high atmospheric levels to influence accumulation rates further inland. Sensitivity experiments with warmer SSCs based on the CMIP5 biases reveal integrated SMB anomalies (+5 % to +13 %) over the present climate (1979–2015) in the lower range of the SMB increase projected for the end of the 21st century. [less ▲]

Detailed reference viewed: 144 (34 ULiège)
Full Text
See detailBrief communication: Impact of the recent atmospheric circulation change in summer on the future surface mass balance of the Greenland Ice Sheet
Delhasse, Alison ULiege; Fettweis, Xavier ULiege; Kittel, Christoph ULiege et al

in Cryosphere (2018)

Since the 2000s, a change in the atmospheric circulation over the North Atlantic resulting in more frequent blocking events has favoured warmer and sunnier weather conditions over the Greenland Ice Sheet ... [more ▼]

Since the 2000s, a change in the atmospheric circulation over the North Atlantic resulting in more frequent blocking events has favoured warmer and sunnier weather conditions over the Greenland Ice Sheet (GrIS) in summer, enhancing the melt increase. This circulation change is not represented by general circulation models (GCMs) of the Coupled Model Intercomparison Project Phase 5 (CMIP5), which do not predict any circulation change for the next century over the North Atlantic. The goal of this study is to evaluate the impact of an atmospheric circulation change (as currently observed) on projections of the future GrIS surface mass balance (SMB). We compare GrIS SMB estimates simulated by the regional climate model MAR forced by perturbed reanalysis (ERA-Interim with a temperature correction of +1, +1.5, and +2°C at the MAR lateral boundaries) over 1980–2016 to projections of the future GrIS SMB from MAR simulations forced by three GCMs over selected periods for which a similar temperature increase of +1, +1.5, and +2°C is projected by the GCMs in comparison to 1980–1999. Mean SMB anomalies produced with perturbed reanalysis over the climatologically stable period 1980–1999 are similar to those produced with MAR forced by GCMs over future periods characterised by a similar warming over Greenland. However, over the 2 last decades (2000–2016) when an increase in the frequency of blocking events has been observed in summer, MAR forced by perturbed reanalysis suggests that the SMB decrease could be amplified by a factor of 2 if such atmospheric conditions persist compared to projections forced by GCMs for the same temperature increase but without any circulation change. [less ▲]

Detailed reference viewed: 366 (19 ULiège)
Full Text
See detailMelting over the northeast Antarctic Peninsula (1999–2009): evaluation of a high-resolution regional climate model
Datta, R.T.; Tedesco, M.; Agosta, Cécile ULiege et al

in Cryosphere (2018), 12

Surface melting over the Antarctic Peninsula (AP) may impact the stability of ice shelves and thus the rate at which grounded ice is discharged into the ocean. Energy and mass balance models are needed to ... [more ▼]

Surface melting over the Antarctic Peninsula (AP) may impact the stability of ice shelves and thus the rate at which grounded ice is discharged into the ocean. Energy and mass balance models are needed to understand how climatic change and atmospheric circulation variability drive current and future melting. In this study, we evaluate the regional climate model MAR over the AP at a 10km spatial resolution between 1999 and 2009, a period when active microwave data from the QuikSCAT mission is available. This model has been validated extensively over Greenland, has is applied here to the AP at a high resolution and for a relatively long time period (full outputs are available to 2014). We find that melting in the northeastern AP, the focus area of this study, can be initiated both by sporadic westerly föhn flow over the AP mountains and by northerly winds advecting warm air from lower latitudes. A comparison of MAR with satellite and automatic weather station (AWS) data reveals that satellite estimates show greater melt frequency, a larger melt extent, and a quicker expansion to peak melt extent than MAR in the centre and east of the Larsen C ice shelf. These differences are reduced in the north and west of the ice shelf, where the comparison with satellite data suggests that MAR is accurately capturing melt produced by warm westerly winds. MAR shows an overall warm bias and a cool bias at temperatures above 0°C as well as fewer warm, strong westerly winds than reported by AWS stations located on the eastern edge of the Larsen C ice shelf, suggesting that the underestimation of melt in this region may be the product of limited eastward flow. At higher resolutions (5km), MAR shows a further increase in wind biases and a decrease in meltwater production. We conclude that non-hydrostatic models at spatial resolutions better than 5km are needed to better-resolve the effects of föhn winds on the eastern edges of the Larsen C ice shelf. [less ▲]

Detailed reference viewed: 79 (6 ULiège)
Full Text
See detailInterest of a Regional Climate Model for doing future projections over the Greenland Ice Sheet
Fettweis, Xavier ULiege; Delhasse, Alison ULiege; Agosta, Cécile ULiege et al

Conference (2018, June 22)

With the aim of evaluating the added value of a regional climate model in downscaled future projections over the Greenland Ice Sheet, we have compared the surface fields (snowfall and summer near-surface ... [more ▼]

With the aim of evaluating the added value of a regional climate model in downscaled future projections over the Greenland Ice Sheet, we have compared the surface fields (snowfall and summer near-surface temperature) coming from the “best” CMIP5 and CMIP6 global models (GCMs) with these fields simulated by the MAR model forced by the same GCMs. These "best" GCMS were selected according to their ability to simulate the summer temperature at 700 hPa and the general circulation at 500 hPa over Greenland with respect to ERA-Interim over 1980-1999. However, despite their ability to correctly represent the free atmosphere, the selected GCMs present significant biases at the surface of the ice sheet. The comparison shows that MAR is however able to strongly reduce these GCM surface biases. We then forced the lateral boundaries of MAR with ERA-Interim to which we applied temperature corrections of +1°C and +2°C. The outputs were compared to MAR forced by GCM future projections corresponding to a climate about 1 and 2°C warmer than the current climate. The results of the different GCM-forced runs and sensitivity experiments are very similar to each other as the GCMs do not project general circulation changes. Moreover, the sensitivity experiments forced by modified ERA-Interim reveal that the projected SMB decrease is exponentially amplified if the increased occurrence of blocking events over Greenland in summer that has been observed since the 2000´s continues in the future. [less ▲]

Detailed reference viewed: 80 (3 ULiège)
Full Text
See detailModelling the impact of drifting snow on the surface mass balance
Kittel, Christoph ULiege; Amory, Charles ULiege; Agosta, Cécile ULiege et al

Conference (2018, June 20)

The transport of snow by the wind is an important component of the Antarctic surface mass balance (SMB) as drifting snow counts up for a large amount of snow ablation over the ice sheet. However, this ... [more ▼]

The transport of snow by the wind is an important component of the Antarctic surface mass balance (SMB) as drifting snow counts up for a large amount of snow ablation over the ice sheet. However, this process is frequently neglected in atmospheric models. Two simulations (one with drifting snow and one without) were performed at a resolution of 8 km with the regional climate model MAR forced by ERA-Interim, in order to assess the impact of drifting snow on the SMB of Adelie Land (East Antarctica) during the period 2002 - 2016. We evaluated results against field observations (including meteorological and snow skate measurements). Besides to better represent climate surface as airborne snow particles can sublimate and interact with the lowest atmospheric levels, the drifting snow simulation improves the modelled spatial distribution of the SMB and reduces the overestimation of the accumulation in comparison with MAR results without drifting snow. [less ▲]

Detailed reference viewed: 78 (14 ULiège)
Full Text
See detailEstimation des températures au début du dernier millénaire dans l’ouest du Groenland : résultats préliminaires issus de l’application d’un modèle glaciologique de type degré‑jour sur le glacier du Lyngmarksbræen
Biette, M.; Jomelli, V.; Favier, V. et al

in Géomorphologie: Relief, Processus, Environnement (2018), 24

The last millennium is defined as a “stable” climatic period with anomalies such as the Little Ice Age (LIA: ~1450 AD to 1850 AD), a period marked by low temperatures and associated with a glacier advance ... [more ▼]

The last millennium is defined as a “stable” climatic period with anomalies such as the Little Ice Age (LIA: ~1450 AD to 1850 AD), a period marked by low temperatures and associated with a glacier advance. Also the Medieval Climate Anomaly (MCA: ~950 AD to 1250 AD), considered as a period at least as warm as nowadays and associated with glacier retreat in the northern hemisphere. However, several studies have shown that glacial advances have occurred during the MCA period in the Baffin Land and western Greenland, in contradiction with hemispheric‑scale temperature reconstructions. In this study we propose temperature conditions for the last millennium determined from a recent study on the glacial fluctuations of the Lyngmarksbræen glacier and the application of an empirical positive degree‑day model (PDD) constrained by the outputs of the regional climate MAR atmospheric model. This simulation was conducted on the Lyngmarksbræen glacier, which shows an original succession of nested moraines dated from the last millennium. The results show that the most likely scenarios are based on air temperatures in the range of ‑1.3°C to ‑1.6°C lower during the MCA than at the end of the 20th century if we consider a variation of about ± 10% in precipitation. Sensitivity tests are then made on different parameters of the glaciological model to better constrain the uncertainty of the temperature estimations. [less ▲]

Detailed reference viewed: 30 (6 ULiège)
Full Text
See detailSensitivity of the Antarctic surface mass balance to oceanic perturbations
Kittel, Christoph ULiege; Amory, Charles ULiege; Agosta, Cécile ULiege et al

Poster (2017, December 15)

Regional climate models (RCMs) are suitable numerical tools to study the surface mass balance (SMB) of the wide polar ice sheets due to their high spatial resolution and polar-adapted physics. Nonetheless ... [more ▼]

Regional climate models (RCMs) are suitable numerical tools to study the surface mass balance (SMB) of the wide polar ice sheets due to their high spatial resolution and polar-adapted physics. Nonetheless, RCMs are driven at their boundaries and over the ocean by reanalysis or global climate model (GCM) products and are thus influenced by potential biases in these large-scale fields. These biases can be significant for both the atmosphere and the sea surface conditions (i.e. sea ice concentration and sea surface temperature). With the RCM MAR, a set of sensitivity experiments has been realized to assess the direct response of the SMB of the Antarctic ice sheet to oceanic perturbations. MAR is forced by ERA-Interim and anomalies based on mean GCM biases are introduced in sea surface conditions. Results show significant increases (decreases) of liquid and solid precipitation due to biases related to warm (cold) oceans. As precipitation is mainly caused by low-pressure systems that intrude into the continent and do not penetrate far inland, coastal areas are more sensitive than inland regions. Furthermore, warm ocean representative biases lead to anomalies as large as anomalies simulated by other RCMs or GCMs for the end of the 21st century. [less ▲]

Detailed reference viewed: 71 (17 ULiège)
Full Text
See detailInterests of using the RCM MAR to downscale CMIP6 outputs
Amory, Charles ULiege; Kittel, Christoph ULiege; Delhasse, Alison ULiege et al

Conference (2017, December 10)

Detailed reference viewed: 39 (6 ULiège)
Full Text
See detailAntarctica-Regional Climate and Surface Mass Budget
Favier, Vincent; Krinner, Gerhard; Amory, Charles ULiege et al

in Current Climate Change Reports (2017)

Detailed reference viewed: 53 (5 ULiège)
Full Text
See detailEvaluating Model Simulations of Twentieth-Century Sea Level Rise. Part 2: Regional Sea-Level Changes
Meyssignac, B.; Slangen, A.; Melet, A. et al

in Journal of Climate (2017), in press

Twentieth century regional sea-level changes are estimated from 12 climate models from the 5th phase of the Climate Model Intercomparison Project (CMIP5). The output of the CMIP5 climate model simulations ... [more ▼]

Twentieth century regional sea-level changes are estimated from 12 climate models from the 5th phase of the Climate Model Intercomparison Project (CMIP5). The output of the CMIP5 climate model simulations were used to calculate the global and regional sea-level changes associated with dynamic sea level, atmospheric loading, glacier mass changes and ice sheet surface mass balance contributions. The contribution from groundwater depletion, reservoir storage and dynamic ice sheet mass changes are estimated from observations as they are not simulated by climate models. All contributions are summed, including the GIA contribution, and compared to observational estimates from 27 tide gauge records over the twentieth century (1900-2015). We find a general agreement between the simulated sea level and tide gauge records in terms of inter-annual to multi-decadal variability over 1900-2015. But climate models tend to systematically underestimate the observed sea-level trends, particularly in the first half of the 20th century. The corrections based on attributable biases between observations and models that have been identified in the part-1-paper, result in an improved explanation of the spatial variability in observed sea-level trends by climate models. Climate models show that the spatial variability in sea-level trends observed by tide-gauge records is dominated by the GIA contribution and the steric contribution over 1900-2015. Climate models also show that it is important to include all contributions to sea-level changes as they cause significant local deviations; for example, the groundwater depletion around India which is responsible for the low 20th century sea-level rise in the region. [less ▲]

Detailed reference viewed: 40 (4 ULiège)
Full Text
See detailEvaluating model simulations of 20th century sea-level rise. Part 1: Global mean sea-level change
Slangen, A.; Meyssignac, B.; Agosta, Cécile ULiege et al

in Journal of Climate (2017)

Sea-level change is one of the major consequences of climate change and is projected to affect coastal communities around the world. Here, we compare Global Mean Sea-Level (GMSL) change estimated by 12 ... [more ▼]

Sea-level change is one of the major consequences of climate change and is projected to affect coastal communities around the world. Here, we compare Global Mean Sea-Level (GMSL) change estimated by 12 climate models from the 5th phase of the World Climate Research Programme’s Climate Model Intercomparison Project (CMIP5) to observational estimates for the period 1900-2015. We analyse observed and simulated individual contributions to GMSL change (thermal expansion, glacier mass change, ice sheet mass change, landwater storage change) and compare the summed simulated contributions to observed GMSL change over the period 1900-2007 using tide gauge reconstructions, and over the period 1993-2015 using satellite altimetry estimates. The model-simulated contributions allow us to explain 50 ± 30% (uncertainties 1.65σ unless indicated otherwise) of the mean observed change from 1901-1920 to 1988-2007. Based on attributable biases between observations and models, we propose to add a number of corrections, which result in an improved explanation of 75 ± 38% of the observed change. For the satellite era (1993-1997 to 2011-2015) we find an improved budget closure of 102 ± 33% (105 ± 35% when including the proposed bias corrections). Simulated decadal trends over the 20th century increase, both in the thermal expansion and the combined mass contributions (glaciers, ice sheets and landwater storage). The mass components explain the majority of sea-level rise over the 20th century, but the thermal expansion has increasingly contributed to sea-level rise, starting from 1910 onwards and in 2015 accounting for 46% of the total simulated sea-level change. [less ▲]

Detailed reference viewed: 52 (4 ULiège)
Full Text
See detailReconstructions of the 1900–2015 Greenland ice sheet surface mass balance using the regional climate MAR model
Fettweis, Xavier ULiege; Box, Jason; Agosta, Cécile ULiege et al

in Cryosphere (2017), 11

With the aim of studying the recent Greenland ice sheet (GrIS) surface mass balance (SMB) decrease relative to the last century, we have forced the regional climate MAR (Modèle Atmosphérique Régional ... [more ▼]

With the aim of studying the recent Greenland ice sheet (GrIS) surface mass balance (SMB) decrease relative to the last century, we have forced the regional climate MAR (Modèle Atmosphérique Régional; version 3.5.2) model with the ERA-Interim (ECMWF Interim Re-Analysis; 1979–2015), ERA-40 (1958–2001), NCEP–NCARv1 (National Centers for Environmental Prediction–National Center for Atmospheric Research Reanalysis version 1; 1948–2015), NCEP–NCARv2 (1979–2015), JRA-55 (Japanese 55-year Reanalysis; 1958–2014), 20CRv2(c) (Twentieth Century Reanalysis version 2; 1900–2014) and ERA-20C (1900–2010) reanalyses. While all these forcing products are reanalyses that are assumed to represent the same climate, they produce significant differences in the MAR-simulated SMB over their common period. A temperature adjustment of +1 °C (respectively −1 °C) was, for example, needed at the MAR boundaries with ERA-20C (20CRv2) reanalysis, given that ERA-20C (20CRv2) is ∼ 1 °C colder (warmer) than ERA-Interim over Greenland during the period 1980–2010. Comparisons with daily PROMICE (Programme for Monitoring of the Greenland Ice Sheet) near-surface observations support these adjustments. Comparisons with SMB measurements, ice cores and satellite-derived melt extent reveal the most accurate forcing datasets for the simulation of the GrIS SMB to be ERA-Interim and NCEP–NCARv1. However, some biases remain in MAR, suggesting that some improvements are still needed in its cloudiness and radiative schemes as well as in the representation of the bare ice albedo. Results from all MAR simulations indicate that (i) the period 1961–1990, commonly chosen as a stable reference period for Greenland SMB and ice dynamics, is actually a period of anomalously positive SMB (∼ +40 Gt yr−1) compared to 1900–2010; (ii) SMB has decreased significantly after this reference period due to increasing and unprecedented melt reaching the highest rates in the 120-year common period; (iii) before 1960, both ERA-20C and 20CRv2-forced MAR simulations suggest a significant precipitation increase over 1900–1950, but this increase could be the result of an artefact in the reanalyses that are not well-enough constrained by observations during this period and (iv) since the 1980s, snowfall is quite stable after having reached a maximum in the 1970s. These MAR-based SMB and accumulation reconstructions are, however, quite similar to those from Box (2013) after 1930 and confirm that SMB was quite stable from the 1940s to the 1990s. Finally, only the ERA-20C-forced simulation suggests that SMB during the 1920–1930 warm period over Greenland was comparable to the SMB of the 2000s, due to both higher melt and lower precipitation than normal. [less ▲]

Detailed reference viewed: 789 (40 ULiège)
Full Text
See detailReconstruction of the Greenland ice sheet surface mass balance over 1900-2015 with the help of the regional climate MARv3.6 model
Fettweis, Xavier ULiege; Agosta, Cécile ULiege; Hubert, Gallée

Speech/Talk (2016)

With the aim of studying the recent Greenland ice sheet Surface Mass Balance (SMB) decrease with respect to the last century, we have forced the regional climate MAR model (version 3.6) with the ERA ... [more ▼]

With the aim of studying the recent Greenland ice sheet Surface Mass Balance (SMB) decrease with respect to the last century, we have forced the regional climate MAR model (version 3.6) with the ERA-Interim (1979-2015), ERA-40 (1958-2001), NCEP1 (1948-2015), NCEP2 (1979-2015), JRA-55 (1958-2015), 20CRv2(c) (1880-2012) and ERA-20C (1900-2010) reanalysis. While all of these forcing products are reanalyses, MAR simulates differences in SMB over the common period. A temperature correction of +1°C (resp. -1°C) had notably to be applied to the MAR boundary conditions given that ERA-20C (resp. 20CRv2) is ~1° colder (resp. warmer) over Greenland than ERA-Interim data over 1980-2010. Comparisons with PROMICE daily temperature measurements valid these corrections. In most of regions, the SMB discrepancies between the different simulations are not significant except in the South-East where the maximum of precipitation occurs and where SMB measurements are missing. This suggests that uncertainties in the current SMB reconstruction remain and that observations are still needed. Comparisons with SMB measurements from the PROMICE data set, ice cores and satellite derived melt extent allows to select the best reanalysis forced data set. All of these simulations show that i) the period 1961-1990 usually chosen as reference for SMB and ice dynamics (stable ice sheet) over Greenland is a period when the SMB was abnormally high in respect to the last 120 years; ii) SMB has been significantly decreasing after this reference period due to increasing melt. Both ERA-20C and 20CRv2 forced simulations suggest a precipitation increase since the beginning of the last century and the ERA-20C forced simulation only suggests that SMB during the 1920-1930 warm period over Greenland was comparable with the SMB of the 2000's. Finally, the sensitivity of switching on the erosion of the snow by the wind in MARv3.6 will be discussed. [less ▲]

Detailed reference viewed: 85 (2 ULiège)
Full Text
See detailVery high resolution surface mass balance over Greenland modeled by the regional climate model MAR with a downscaling technique
Kittel, Christoph ULiege; Lang, Charlotte; Agosta, Cécile ULiege et al

Poster (2016, April 20)

This study presents surface mass balance (SMB) results at 10 km resolution with the regional climate MAR model over the Greenland ice sheet. Here, we use the last MAR version (v3.6) where the land-ice ... [more ▼]

This study presents surface mass balance (SMB) results at 10 km resolution with the regional climate MAR model over the Greenland ice sheet. Here, we use the last MAR version (v3.6) where the land-ice module (SISVAT) using a high resolution grid (10km) for surface variables is fully coupled while the MAR atmospheric module running at a lower resolution of 20km. This online downscaling technique enables to correct near-surface temperature and humidity from MAR by a gradient based on elevation before forcing SISVAT. The 20 km precipitations are not corrected. Corrections are stronger over the ablation zone where topography presents more variations. The model has been force by ERA-Interim between 1979 and 2014. We will show the advantages of using an online SMB downscaling technique in respect to an offline downscaling extrapolation based on local SMB vertical gradients. Results at 10 km show a better agreement with the PROMICE surface mass balance data base than the extrapolated 20 km MAR SMB results. [less ▲]

Detailed reference viewed: 274 (41 ULiège)
Full Text
See detailAnthropogenic forcing dominates global mean sea-level rise since 1970
Slagen, A.; Church, J.; Agosta, Cécile ULiege et al

in Nature Climate Change (2016)

Sea-level change is an important consequence of anthropogenic climate change, as higher sea levels increase the frequency of sea-level extremes and the impact of coastal flooding and erosion on the ... [more ▼]

Sea-level change is an important consequence of anthropogenic climate change, as higher sea levels increase the frequency of sea-level extremes and the impact of coastal flooding and erosion on the coastal environment, infrastructure and coastal communities1, 2. Although individual attribution studies have been done for ocean thermal expansion3, 4 and glacier mass loss5, two of the largest contributors to twentieth-century sea-level rise, this has not been done for the other contributors or total global mean sea-level change (GMSLC). Here, we evaluate the influence of greenhouse gases (GHGs), anthropogenic aerosols, natural radiative forcings and internal climate variability on sea-level contributions of ocean thermal expansion, glaciers, ice-sheet surface mass balance and total GMSLC. For each contribution, dedicated models are forced with results from the Coupled Model Intercomparison Project Phase 5 (CMIP5) climate model archive6. The sum of all included contributions explains 74 ± 22% (±2σ) of the observed GMSLC over the period 1900–2005. The natural radiative forcing makes essentially zero contribution over the twentieth century (2 ± 15% over the period 1900–2005), but combined with the response to past climatic variations explains 67 ± 23% of the observed rise before 1950 and only 9 ± 18% after 1970 (38 ± 12% over the period 1900–2005). In contrast, the anthropogenic forcing (primarily a balance between a positive sea-level contribution from GHGs and a partially offsetting component from anthropogenic aerosols) explains only 15 ± 55% of the observations before 1950, but increases to become the dominant contribution to sea-level rise after 1970 (69 ± 31%), reaching 72 ± 39% in 2000 (37 ± 38% over the period 1900–2005). [less ▲]

Detailed reference viewed: 70 (3 ULiège)
Full Text
See detailCentury-scale simulations of the response of the West Antarctic Ice Sheet to a warming climate
Cornford, S.L.; Martin, D.F.; Payne, A.J. et al

in Cryosphere (2015), 9

We use the BISICLES adaptive mesh ice sheet model to carry out one, two, and three century simulations of the fast-flowing ice streams of the West Antarctic Ice Sheet, deploying sub-kilometer resolution ... [more ▼]

We use the BISICLES adaptive mesh ice sheet model to carry out one, two, and three century simulations of the fast-flowing ice streams of the West Antarctic Ice Sheet, deploying sub-kilometer resolution around the grounding line since coarser resolution results in substantial underestimation of the response. Each of the simulations begins with a geometry and velocity close to present-day observations, and evolves according to variation in meteoric ice accumulation rates and oceanic ice shelf melt rates. Future changes in accumulation and melt rates range from no change, through anomalies computed by atmosphere and ocean models driven by the E1 and A1B emissions scenarios, to spatially uniform melt rate anomalies that remove most of the ice shelves over a few centuries. We find that variation in the resulting ice dynamics is dominated by the choice of initial conditions and ice shelf melt rate and mesh resolution, although ice accumulation affects the net change in volume above flotation to a similar degree. Given sufficient melt rates, we compute grounding line retreat over hundreds of kilometers in every major ice stream, but the ocean models do not predict such melt rates outside of the Amundsen Sea Embayment until after 2100. Within the Amundsen Sea Embayment the largest single source of variability is the onset of sustained retreat in Thwaites Glacier, which can triple the rate of eustatic sea level rise. [less ▲]

Detailed reference viewed: 114 (4 ULiège)