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See detailComparison Between Surface Melt Days Estimation from a Regional Climate Model and Near-Daily Synthetic Aperture Radar Backscattering
Glaude, Quentin ULiege; Glaude, Quentin; Kittel, Christoph ULiege

Conference (2020, May 05)

Remote sensing has long been used as a powerful tool for the observation in cryospheric sciences. With the advances brought by the ESA Copernicus program, Earth observation goes a step further in its ... [more ▼]

Remote sensing has long been used as a powerful tool for the observation in cryospheric sciences. With the advances brought by the ESA Copernicus program, Earth observation goes a step further in its ability to get acquisitions at very high temporal rate. This is even amplified in polar regions due to heliosynchronism of satellites’ orbits. Earth observation shifts from sporadic observations to Earth monitoring. Observations are a critical aspect for the assessment of geophysical models. The ability of a model to replicate observations is crucial as a benchmark. It also allows to refine our comprehension of Earth systems, such as in cryospheric sciences. In this work, we are using the regional climate model MAR to compute the surface melt on a domain focusing on the Roi Baudouin Ice Shelf, Queen Maud Land, East Antarctica. From the results, we extract the number of days with surface melt in a region. In parallel, we employ remote sensing to obtain comparison data. Synthetic aperture radar appears as a solution of choice thanks to its day-and-night (critical in polar regions) and atmospheric-free capabilities. Radar backscattering anomalies between different dates are witnesses of substantial increase of soil moisture. Using Sentinel-1 in its wide-swath modes (namely Interferometric Wide Swath and Extra Wide Swath modes) and multiple satellite paths, near-daily acquisitions can be obtained. By comparing the two independent results, we better constraint model’s outputs while also better interpret SAR acquisitions. [less ▲]

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See detailBrief communication: Evaluation of the near-surface climate in ERA5 over the Greenland Ice Sheet
Delhasse, Alison ULiege; Kittel, Christoph ULiege; Amory, Charles ULiege et al

in The Cryosphere (2020), 14

The ERA5 reanalysis, recently made available by the European Centre for Medium-Range Weather Forecasts (ECMWF), is a new reanalysis product at a high resolution replacing ERA-Interim and is considered to ... [more ▼]

The ERA5 reanalysis, recently made available by the European Centre for Medium-Range Weather Forecasts (ECMWF), is a new reanalysis product at a high resolution replacing ERA-Interim and is considered to provide the best climate reanalysis over Greenland to date. However, so far little is known about the performance of ERA5 over the Greenland Ice Sheet (GrIS). In this study, we compare the near-surface climate from the new ERA5 reanalysis to ERAInterim, the Arctic System Reanalysis (ASR) as well as to a state-of-the-art polar regional climate model (MAR). The results show (1) that ERA5 does not outperform ERA-Interim significantly when compared with near-surface climate observations over GrIS, but ASR better models the near-surface temperature than both ERA reanalyses. (2) Polar regional climate models (e.g., MAR) are still a useful tool to downscale the GrIS climate compared to ERA5, as in particular the near-surface temperature in summer has a key role for representing snow and ice processes such as the surface melt. However, assimilating satellite data and using a more recent radiative scheme enable both ERA and ASR reanalyses to represent more satisfactorily than MAR the downward solar and infrared fluxes. (3) MAR near-surface climate is not affected when forced at its lateral boundaries by either ERA5 or ERA-Interim. Therefore, forcing polar regional climate models with ERA5 starting from 1950 will enable long and homogeneous surface mass balance reconstructions. [less ▲]

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See detailInterannual variability of summer surface mass balance and surface melting in the Amundsen sector, West Antarctica
Donat-Magnin, Marion; Jourdain, Nicolas C.; Gallée, Hubert et al

in Cryosphere (2020)

Understanding the interannual variability of surface mass balance (SMB) and surface melting in Antarctica is key to quantify the signal-to-noise ratio in climate trends, identify opportunities for multi ... [more ▼]

Understanding the interannual variability of surface mass balance (SMB) and surface melting in Antarctica is key to quantify the signal-to-noise ratio in climate trends, identify opportunities for multi-year climate predictions and assess the ability of climate models to respond to climate variability. Here we simulate summer SMB and surface melting from 1979 to 2017 using the Regional Atmosphere Model (MAR) at 10 km resolution over the drainage basins of the Amundsen Sea glaciers in West Antarctica. Our simulations reproduce the mean present-day climate in terms of near-surface temperature (mean overestimation of 0.10 ∘C), near-surface wind speed (mean underestimation of 0.42 m s−1), and SMB (relative bias <20 % over Thwaites glacier). The simulated interannual variability of SMB and melting is also close to observation-based estimates. For all the Amundsen glacial drainage basins, the interannual variability of summer SMB and surface melting is driven by two distinct mechanisms: high summer SMB tends to occur when the Amundsen Sea Low (ASL) is shifted southward and westward, while high summer melt rates tend to occur when ASL is shallower (i.e. anticyclonic anomaly). Both mechanisms create a northerly flow anomaly that increases moisture convergence and cloud cover over the Amundsen Sea and therefore favors snowfall and downward longwave radiation over the ice sheet. The part of interannual summer SMB variance explained by the ASL longitudinal migrations increases westward and reaches 40 % for Getz. Interannual variation in the ASL relative central pressure is the largest driver of melt rate variability, with 11 % to 21 % of explained variance (increasing westward). While high summer SMB and melt rates are both favored by positive phases of El Niño–Southern Oscillation (ENSO), the Southern Oscillation Index (SOI) only explains 5 % to 16 % of SMB or melt rate interannual variance in our simulations, with moderate statistical significance. However, the part explained by SOI in the previous austral winter is greater, suggesting that at least a part of the ENSO–SMB and ENSO–melt relationships in summer is inherited from the previous austral winter. Possible mechanisms involve sea ice advection from the Ross Sea and intrusions of circumpolar deep water combined with melt-induced ocean overturning circulation in ice shelf cavities. Finally, we do not find any correlation with the Southern Annular Mode (SAM) in summer. [less ▲]

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See detailProjection of the Antarctic surface mass balance by 2100 using MAR
Kittel, Christoph ULiege

Poster (2019, December)

The surface mass balance of the Antarctic ice sheet is often considered as a negative contributor to the sea level rise as snowfall accumulation largely overestimates ablation through wind erosion ... [more ▼]

The surface mass balance of the Antarctic ice sheet is often considered as a negative contributor to the sea level rise as snowfall accumulation largely overestimates ablation through wind erosion, sublimation and runoff. Contrary to the Greenland ice sheet, current surface melting is limited to relatively scarce events over the Antarctic peninsula, ice shelves and more generally peripheral areas. However, surface melting can significantly affect the stability of ice shelves through hydrofracturing, potentially leading to their disintegration, acceleration of grounded ice and increased sea level rise. Although a large increase in snowfall is expected in a warmer climate, more numerous and stronger melting events could conversely lead to a larger risk of ice shelf collapse. In this study, we provide an estimation of the surface mass balance of the Antarctic ice sheet for the end of the 21st century by forcing the state-of-the-art regional climate model MAR with three different global climate models. We chose the models (from both the Coupled Model Intercomparison Project Phase 5 and 6 - CMIP5 and CMIP6) providing the best metrics for representing the present Antarctic climate. Our results show that the increase in snowfall compensates snow ablation though sublimation and runoff over the margins except over the Larsen and Amery ice shelves. However, melt rates over the other ice shelves are higher than those that led to the collapse of Larsen A and B ice shelves, suggesting a high probability of ice shelf collapses by 2100. [less ▲]

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See detailSpatial and temporal variability of Glacier surface velocities and outlet areas on James Ross island, northern Antarctic Peninsula
Lippl, Stefan; Friedl, Peter; Kittel, Christoph ULiege et al

in Geosciences (2019)

The northern Antarctic Peninsula was affected by a significant warming over the second half of the 20th century and the collapse of several ice shelves. Local climate conditions on James Ross Island on ... [more ▼]

The northern Antarctic Peninsula was affected by a significant warming over the second half of the 20th century and the collapse of several ice shelves. Local climate conditions on James Ross Island on the northeastern coast can differ strongly from the main part of the Antarctic Peninsula. This paper reports the spatial and temporal variability of glacier surface velocities and the area of their outlets throughout James Ross Island, and evaluates potential relationships with atmospheric and oceanic conditions. Velocity estimates were retrieved from intensity feature tracking of scenes from satellite synthetic aperture radar sensors TerraSAR-X and TanDEM-X between 2014 and 2018, which were validated against ground observations. Calving front positions back to 1945 were used to calculate outlet area changes for the glaciers by using a common-box approach. The annual recession rates of almost all investigated glacier calving fronts decelerated for the time periods 2009–2014 and 2014–2018 in comparison to the period 1988–2009, but their velocity patterns differed. Analysis of atmospheric conditions failed to explain the different patterns in velocity and area changes. We suggest a strong influence from local bathymetric conditions. Future investigations of the oceanic conditions would be necessary for a profound understanding of the super-position of different influencing factors. [less ▲]

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See detailPrecipitation Evolution over Belgium by 2100 and Sensitivity to Convective Schemes Using the Regional Climate Model MAR
Doutreloup, Sébastien ULiege; Kittel, Christoph ULiege; Wyard, Coraline et al

in Atmosphere (2019), 10(321),

The first aim of this study is to determine if changes in precipitation and more specifically in convective precipitation are projected in a warmer climate over Belgium. The second aim is to evaluate if ... [more ▼]

The first aim of this study is to determine if changes in precipitation and more specifically in convective precipitation are projected in a warmer climate over Belgium. The second aim is to evaluate if these changes are dependent on the convective scheme used. For this purpose, the regional climate model Modèle Atmosphérique Régional (MAR) was forced by two general circulation models (NorESM1-M and MIROC5) with five convective schemes (namely: two versions of the Bechtold schemes, the Betts–Miller–Janjić scheme, the Kain–Fritsch scheme, and the modified Tiedtke scheme) in order to assess changes in future precipitation quantities/distributions and associated uncertainties. In a warmer climate (using RCP8.5), our model simulates a small increase of convective precipitation, but lower than the anomalies and the interannual variability over the current climate, since all MAR experiments simulate a stronger warming in the upper troposphere than in the lower atmospheric layers, favoring more stable conditions. No change is also projected in extreme precipitation nor in the ratio of convective precipitation. While MAR is more sensitive to the convective scheme when forced by GCMs than when forced by ERA-Interim over the current climate, projected changes from all MAR experiments compare well. [less ▲]

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See detailAdded value of a regional climate model (MAR) for simulating the current surface mass balance of the Antarctic ice sheet compared to a general circulation model (ACCESS1.3)
Kittel, Christoph ULiege

Conference (2019, May 10)

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 ▲]

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See detailEvaluation of the near-surface climate of the Greenland ice sheet as modelled by the climate model MAR and the ERA-Interim, ERA5 and Arctic System reanalyses
Delhasse, Alison ULiege; Kittel, Christoph ULiege; Amory, Charles ULiege et al

Conference (2019, April 12)

The new reanalysis produced by the ECMWF, ERA5, is currently available over the period 2000-2017. Ultimately, it will cover the period 1950 to the present-time and will replace the ERA-Interim, which is ... [more ▼]

The new reanalysis produced by the ECMWF, ERA5, is currently available over the period 2000-2017. Ultimately, it will cover the period 1950 to the present-time and will replace the ERA-Interim, which is by many considered as one of the best reanalyses over the Greenland ice sheet (GrIS). We first compare the ERA5 reanalysis to ERA-Interim and ASR (Arctic System Reanalysis), which is a regional reanalysis specifically developed for the Arctic area at a finer resolution. We evaluate them against a set of near-surface climate observations from the AWS of the PROMICE network covering the GrIS. This observation data set is not assimilated in these reanalyses. We furthermore assess the ability of the state-of-the-art regional climate model (RCM) MAR, forced by the ECMWF reanalyses, ERA-Interim and ERA5, to represent the AWS observations. Finally, we demonstrate the advantages of using MAR compared to the forcing reanalyses alone. ERA5 improves ERA-Interim almost for radiative fluxes, but not significantly. ASR, which is more specific for Arctic region and has a finer spatial resolution, outclasses other reanalyses for wind speed and near-surface temperature. The comparison of results from MAR simulations forced by ERA-Interim and ERA5 reanalysis shows that the near-surface climate variables are closed to each other and then not significantly different according to the forcing used. ERA5 which should replace ERA-Interim after 2018, can be used to force a RCM such as MAR in the same way than ERA-Interim now. Although the reanalyses seem to be sufficient to study the surface climate of Greenland, the RCM MAR has the best representation of the near-surface temperature even without any data assimilation. This is mainly due to a better representation of the snowpack and interactions between surface and atmosphere by MAR, resulting in a better representation of the surface melt and the GrIS surface mass balance (SMB). Near-surface temperature and SMB are both very useful for constraining glacial dynamics models in order to represent the current and future evolution of the ice dynamics of the GrIS. [less ▲]

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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 ▲]

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See detailSensitivity to Convective Schemes on Precipitation Simulated by the Regional Climate Model MAR over Belgium (1987–2017)
Doutreloup, Sébastien ULiege; Wyard, Coraline ULiege; Amory, Charles ULiege et al

in Atmosphere (2019), 10(1), 34

The aim of this study is to assess the sensitivity of convective precipitation modelled by the regional climate model MAR (Modèle Atmosphérique Régional) over 1987–2017 to four newly implemented ... [more ▼]

The aim of this study is to assess the sensitivity of convective precipitation modelled by the regional climate model MAR (Modèle Atmosphérique Régional) over 1987–2017 to four newly implemented convective schemes: the Bechtold scheme coming from the MESO-NH regional model and the Betts-Miller-Janjić, Kain-Fritsch and modified Tiedtke schemes coming from the WRF regional model. MAR version 3.9 is used here at a resolution of 10 km over a domain covering Belgium using the ERA-Interim reanalysis as forcing. The simulated precipitation is compared against SYNOP and E-OBS gridded precipitation data. Trends in total and convective precipitation over 1987–2017 are discussed. None of the MAR experiments compares better with observations than the others and they all show the same trends in (extreme) precipitation. Over the period 1987–2017, MAR suggests a significant increase in the mean annual precipitation amount over the North Sea but a significant decrease over High Belgium. [less ▲]

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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 ▲]

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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 ▲]

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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 ▲]

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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 ▲]

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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 ▲]

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See detailInfluence of the recent circulation change in summer on future surface mass balance of Greenland ice sheet
Delhasse, Alison ULiege; Fettweis, Xavier ULiege; Kittel, Christoph ULiege et al

Conference (2018, April 11)

Regional Climate Models (RCM) driven by General Circulation Models (GCM) are often used to produce future projections of the surface climate and surface mass balance (SMB) of polar ice sheets. However ... [more ▼]

Regional Climate Models (RCM) driven by General Circulation Models (GCM) are often used to produce future projections of the surface climate and surface mass balance (SMB) of polar ice sheets. However, GCM do not represent the recent circulation change observed in summer over the Greenland Ice Sheet (GrIS) since the 2000’s and do not predict any circulation changes for the next century. The goal of this study is to evaluate the impact of an atmospheric circulation change (as currently observed) combined with a temperature increase on the future GrIS SMB. We compare here SMB results from the RCM MAR (Modèle atmosphérique régional) forced by warmer reanalyses (ERA-Interim with a temperature correction of +1, +1,5 and +2 C at the lateral boundaries) to SMB results from MAR future simulations forced with GCM during a period where there is a temperature increase of +1, +1,5 and +2 C compared to 1980-1999. Mean SMB produced with warmer reanalyses over 1980-1999 is similar to that obtained when forcing with GCM over a period characterized by a similarly warmer climate. During last years (2000-2016) when a circulation change has been observed in summer, MAR forced with warmer reanalyses shows a significant amplified SMB decrease compared to future simulations forced by GCM for the same temperature increase. [less ▲]

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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 ▲]

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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)

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