Publications of Xavier Fettweis
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See detailRemapping of Greenland ice sheet surface mass balance anomalies for large ensemble sea-level change projections
Goelzer, H.; Noël, B.; Edwards, T. et al

in Cryosphere (2020), 14

Future sea-level change projections with process-based stand-alone ice sheet models are typically driven with surface mass balance (SMB) forcing derived from climate models. In this work we address the ... [more ▼]

Future sea-level change projections with process-based stand-alone ice sheet models are typically driven with surface mass balance (SMB) forcing derived from climate models. In this work we address the problems arising from a mismatch of the modelled ice sheet geometry with the geometry used by the climate model. We present a method for applying SMB forcing from climate models to a wide range of Greenland ice sheet models with varying and temporally evolving geometries. In order to achieve that, we translate a given SMB anomaly field as a function of absolute location to a function of surface elevation for 25 regional drainage basins, which can then be applied to different modelled ice sheet geometries. The key feature of the approach is the non-locality of this remapping process. The method reproduces the original forcing data closely when remapped to the original geometry. When remapped to different modelled geometries it produces a physically meaningful forcing with smooth and continuous SMB anomalies across basin divides. The method considerably reduces non-physical biases that would arise by applying the SMB anomaly derived for the climate model geometry directly to a large range of modelled ice sheet model geometries. [less ▲]

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See detailFuture evolution of the hydroclimatic conditions favouring floods in the south‐east of Belgium by 2100 using a regional climate model
Wyard, C; Scholzen, C.; Doutreloup, Sébastien ULiege et al

in International Journal of Climatology (2020)

In Belgium, most flood events occur in winter as a result of intense precipitation events but also through the abrupt melting of the snowpack that covers the Ardennes summits. These conditions favourable ... [more ▼]

In Belgium, most flood events occur in winter as a result of intense precipitation events but also through the abrupt melting of the snowpack that covers the Ardennes summits. These conditions favourable to floods exhibit a decreasing trend over 1959–2010 resulting from the reduction in snow accumulation, although extreme precipitation events show a positive, albeit non‐significant signal. In this study, the evolution of these trends in warmer climates is investigated by using future projections performed with the regional climate model MAR (“Modèle Atmosphérique Régional”) forced by two global models NorESM1‐M and MIROC5 under the RCP8.5 scenario. These models were selected from the CMIP5 archive after evaluation of their ability to represent the current (1976–2005) mean climate over Europe. By the end of the century, the results show an acceleration of the snow depletion resulting in fewer snowmelt‐associated flood risk days depending on the warming rate from the AOGCM forcing MAR. Regarding the impact of the evolution of extreme precipitation events on hydroclimatic conditions favouring floods, no significant change was found although these trends are subject to uncertainties due to model physics and natural variability. [less ▲]

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See detailUnprecedented atmospheric conditions (1948–2019) drive the 2019 exceptional melting season over the Greenland ice sheet
Tedesco, Marco; Fettweis, Xavier ULiege

in Cryosphere (2020), 14

Understanding the role of atmospheric circulation anomalies on the surface mass balance of the Greenland ice sheet (GrIS) is fundamental for improving estimates of its current and future contributions to ... [more ▼]

Understanding the role of atmospheric circulation anomalies on the surface mass balance of the Greenland ice sheet (GrIS) is fundamental for improving estimates of its current and future contributions to sea level rise. Here, we show, using a combination of remote sensing observations, regional climate model outputs, reanalysis data, and artificial neural networks, that unprecedented atmospheric conditions (1948–2019) occurring in the summer of 2019 over Greenland promoted new record or close-to-record values of surface mass balance (SMB), runoff, and snowfall. Specifically, runoff in 2019 ranked second within the 1948–2019 period (after 2012) and first in terms of surface mass balance negative anomaly for the hydrological year 1 September 2018–31 August 2019. The summer of 2019 was characterized by an exceptional persistence of anticyclonic conditions that, in conjunction with low albedo associated with reduced snowfall in summer, enhanced the melt–albedo feedback by promoting the absorption of solar radiation and favored advection of warm, moist air along the western portion of the ice sheet towards the north, where the surface melt has been the highest since 1948. The analysis of the frequency of daily 500 hPa geopotential heights obtained from artificial neural networks shows that the total number of days with the five most frequent atmospheric patterns that characterized the summer of 2019 was 5 standard deviations above the 1981–2010 mean, confirming the exceptional nature of the 2019 season over Greenland. [less ▲]

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See detailTwenty-first century ocean forcing of the Greenland ice sheet for modelling of sea level contribution
Slater, Donald; Felikson, Denis; Straneo, Fiamma et al

in Cryosphere (2020), 14

Changes in ocean temperature and salinity are expected to be an important determinant of the Greenland ice sheet's future sea level contribution. Yet, simulating the impact of these changes in continental ... [more ▼]

Changes in ocean temperature and salinity are expected to be an important determinant of the Greenland ice sheet's future sea level contribution. Yet, simulating the impact of these changes in continental-scale ice sheet models remains challenging due to the small scale of key physics, such as fjord circulation and plume dynamics, and poor understanding of critical processes, such as calving and submarine melting. Here we present the ocean forcing strategy for Greenland ice sheet models taking part in the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6), the primary community effort to provide 21st century sea level projections for the Intergovernmental Panel on Climate Change Sixth Assessment Report. Beginning from global atmosphere–ocean general circulation models, we describe two complementary approaches to provide ocean boundary conditions for Greenland ice sheet models, termed the “retreat” and “submarine melt” implementations. The retreat implementation parameterises glacier retreat as a function of projected subglacial discharge and ocean thermal forcing, is designed to be implementable by all ice sheet models and results in retreat of around 1 and 15 km by 2100 in RCP2.6 and 8.5 scenarios, respectively. The submarine melt implementation provides estimated submarine melting only, leaving the ice sheet model to solve for the resulting calving and glacier retreat and suggests submarine melt rates will change little under RCP2.6 but will approximately triple by 2100 under RCP8.5. Both implementations have necessarily made use of simplifying assumptions and poorly constrained parameterisations and, as such, further research on submarine melting, calving and fjord–shelf exchange should remain a priority. Nevertheless, the presented framework will allow an ensemble of Greenland ice sheet models to be systematically and consistently forced by the ocean for the first time and should result in a significant improvement in projections of the Greenland ice sheet's contribution to future sea level change. [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 detailConfronting Arctic Troposphere, Clouds, and Surface Energy Budget Representations in Regional Climate Models With Observations
Sedlar, Joseph; Tjernström, Michael; Rinke, Annette et al

in Journal of Geophysical Research. Atmospheres (2020), 125

A coordinated regional climate model (RCM) evaluation and intercomparison project based on observations from a July–October 2014 trans‐Arctic Ocean field experiment (ACSE‐Arctic Clouds during Summer ... [more ▼]

A coordinated regional climate model (RCM) evaluation and intercomparison project based on observations from a July–October 2014 trans‐Arctic Ocean field experiment (ACSE‐Arctic Clouds during Summer Experiment) is presented. Six state‐of‐the‐art RCMs were constrained with common reanalysis lateral boundary forcing and upper troposphere nudging techniques to explore how the RCMs represented the evolution of the surface energy budget (SEB) components and their relation to cloud properties. We find that the main reasons for the modeled differences in the SEB components are a direct consequence of the RCM treatment of cloud and cloud‐radiative interactions. The RCMs could be separated into groups by their overestimation or underestimation of cloud liquid. While radiative and turbulent heat flux errors were relatively large, they often invoke compensating errors. In addition, having the surface sea‐ice concentrations constrained by the reanalysis or satellite observations limited how errors in the modeled radiative fluxes could affect the SEB and ultimately the surface evolution and its coupling with lower tropospheric mixing and cloud properties. Many of these results are consistent with RCM biases reported in studies over a decade ago. One of the six models was a fully coupled ocean‐ice‐atmosphere model. Despite the biases in overestimating cloud liquid, and associated SEB errors due to too optically thick clouds, its simulations were useful in understanding how the fully coupled system is forced by, and responds to, the SEB evolution. Moving forward, we suggest that development of RCM studies need to consider the fully coupled climate system. [less ▲]

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See detailCritical Time Windows for Renewable Resource Complementarity Assessment
Berger, Mathias ULiege; Radu, David-Constantin ULiege; Fonteneau, Raphaël ULiege et al

in Energy (2020)

This paper proposes a framework to assess the complementarity between geographically dispersed variable renewable energy resources over arbitrary time scales. More precisely, the framework relies on the ... [more ▼]

This paper proposes a framework to assess the complementarity between geographically dispersed variable renewable energy resources over arbitrary time scales. More precisely, the framework relies on the concept of critical time windows, which offers an accurate, time-domain description of low-probability power production events impacting power system operation and planning. A scalar criticality indicator is also derived to quantify the spatiotemporal complementarity that renewable generation sites may exhibit, and it is leveraged to propose optimisation models seeking to identify deployment patterns with maximum complementarity. The usefulness of the framework is shown in a case study investigating the complementarity between wind regimes in continental western Europe and southern Greenland, using roughly 300 candidate locations and 10 years of reanalysis and simulated data with hourly resolution. Besides showing that the occurrence of low wind power production events can be reduced on a regional scale by exploiting diversity in local wind patterns, results highlight the fact that aggregating wind power production sites located on different continents may result in a lower occurrence of system-wide low wind power production events and point to potential bene ts of intercontinental electrical interconnections. [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 detailMass balance of the Greenland Ice Sheet from 1992 to 2018
Shepherd, A.; Ivins, E.; Rignot, E. et al

in Nature (2019)

In recent decades, the Greenland Ice Sheet has been a major contributor to global sea-level rise1,2, and it is expected to be so in the future3. Although increases in glacier flow4–6 and surface ... [more ▼]

In recent decades, the Greenland Ice Sheet has been a major contributor to global sea-level rise1,2, and it is expected to be so in the future3. Although increases in glacier flow4–6 and surface melting7–9 have been driven by oceanic10–12 and atmospheric13,14 warming, the degree and trajectory of today’s imbalance remain uncertain. Here we compare and combine 26 individual satellite measurements of changes in the ice sheet’s volume, flow and gravitational potential to produce a reconciled estimate of its mass balance. Although the ice sheet was close to a state of balance in the 1990s, annual losses have risen since then, peaking at 335 ± 62 billion tonnes per year in 2011. In all, Greenland lost 3,800 ± 339 billion tonnes of ice between 1992 and 2018, causing the mean sea level to rise by 10.6 ± 0.9 millimetres. Using three regional climate models, we show that reduced surface mass balance has driven 1,971 ± 555 billion tonnes (52%) of the ice loss owing to increased meltwater runoff. The remaining 1,827 ± 538 billion tonnes (48%) of ice loss was due to increased glacier discharge, which rose from 41 ± 37 billion tonnes per year in the 1990s to 87 ± 25 billion tonnes per year since then. Between 2013 and 2017, the total rate of ice loss slowed to 217 ± 32 billion tonnes per year, on average, as atmospheric circulation favoured cooler conditions15 and as ocean temperatures fell at the terminus of Jakobshavn Isbræ16. Cumulative ice losses from Greenland as a whole have been close to the IPCC’s predicted rates for their high-end climate warming scenario17, which forecast an additional 50 to 120 millimetres of global sea-level rise by 2100 when compared to their central estimate. [less ▲]

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See detailSurface meltwater runoff on the Greenland ice sheet estimated from remotely sensed supraglacial lake infilling rate
Yang, K.; Smith, L.; Fettweis, Xavier ULiege et al

in Remote Sensing of Environment (2019)

Surface runoff constitutes a large percentage of Greenland Ice Sheet (GrIS) mass loss at present but is difficult to measure directly. This study provides a novel method to estimate surface runoff through ... [more ▼]

Surface runoff constitutes a large percentage of Greenland Ice Sheet (GrIS) mass loss at present but is difficult to measure directly. This study provides a novel method to estimate surface runoff through remote sensing of supraglacial lake volumes. Because terminal, non-draining (consistently expanding during the melt season) lakes impound runoff from their surrounding contributing catchments, such changes reflect runoff produced within the catchment. To estimate supraglacial lake volumes, multi-temporal lake maps derived from Landsat-8 images are intersected with dry lake-bed topographic depressions (showing lake bathymetry) identified for two supraglacial catchments (~10 km2) in southwestern GrIS, using high-resolution (2 m) ArcticDEMs. Intersecting remotely sensed lake shorelines with their underlying ice surface topography yields multi-temporal lake volume changes, which are then compared with cumulative runoff as simulated by four Surface Mass Balance (SMB) models (HIRHAM5, MAR3.6, RACMO2.3, and MERRA-2). Comparison of cumulative lake infilling with SMB simulations for these two lakes over the period 8–31 July 2015 indicates that SMB models overestimated surface runoff by 106 – 123%. These large offsets improved after early July, overestimating runoff by 40 – 55%. The runoff delay function incorporated into the MAR3.6 model improves simulation of early melt season runoff, signifying the importance of integrating meltwater routing schemes into SMB models for improved understanding of Greenland supraglacial hydrology and surface mass balance. [less ▲]

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See detailEvaluating a regional climate model simulation of Greenland ice sheet snow and firn density for improved surface mass balance estimates
Alexander, P.; Tedesco, M.; Koening, L. et al

in Geophysical Research Letters (2019)

Modeling vertical profiles of snow and firn density near the surface of the Greenland ice sheet (GrIS) is key to estimating GrIS mass balance, and by extension, global sea level change. To understand ... [more ▼]

Modeling vertical profiles of snow and firn density near the surface of the Greenland ice sheet (GrIS) is key to estimating GrIS mass balance, and by extension, global sea level change. To understand sources of error in simulated GrIS density, we compare GrIS density profiles from a leading regional climate model with coincident in situ measurements. We identify key contributors to model density and mass balance biases, including underestimated simulated fresh snow density (which leads to underestimation of density in the top 1 m of snow by ~10%). In areas undergoing frequent melting, positive density biases (of 7% in the top 1 m, and 10% between 1 and 10 m) are likely associated with errors in representing meltwater production, retention and refreezing. The results highlight the importance of accurately capturing fresh snow density and meltwater processes in models used to estimate GrIS mass balance change. [less ▲]

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See detailEstimating Greenland tidewater glacier retreat driven by submarine melting
Slater, D.; Straneo, F.; Felikson, D. et al

in Cryosphere (2019), (13), 24892509

The effect of the North Atlantic Ocean on the Greenland Ice Sheet through submarine melting of Greenland's tidewater glacier calving fronts is thought to be a key driver of widespread glacier retreat ... [more ▼]

The effect of the North Atlantic Ocean on the Greenland Ice Sheet through submarine melting of Greenland's tidewater glacier calving fronts is thought to be a key driver of widespread glacier retreat, dynamic mass loss and sea level contribution from the ice sheet. Despite its critical importance, problems of process complexity and scale hinder efforts to represent the influence of submarine melting in ice-sheet-scale models. Here we propose parameterizing tidewater glacier terminus position as a simple linear function of submarine melting, with submarine melting in turn estimated as a function of subglacial discharge and ocean temperature. The relationship is tested, calibrated and validated using datasets of terminus position, subglacial discharge and ocean temperature covering the full ice sheet and surrounding ocean from the period 1960–2018. We demonstrate a statistically significant link between multi-decadal tidewater glacier terminus position change and submarine melting and show that the proposed parameterization has predictive power when considering a population of glaciers. An illustrative 21st century projection is considered, suggesting that tidewater glaciers in Greenland will undergo little further retreat in a low-emission RCP2.6 scenario. In contrast, a high-emission RCP8.5 scenario results in a median retreat of 4.2 km, with a quarter of tidewater glaciers experiencing retreat exceeding 10 km. Our study provides a long-term and ice-sheet-wide assessment of the sensitivity of tidewater glaciers to submarine melting and proposes a practical and empirically validated means of incorporating ocean forcing into models of the Greenland ice sheet. [less ▲]

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See detailRapid expansion of Greenland’s low-permeability ice slabs
MacFerrin, Michael; Machguth, Horst; van As, D. et al

in Nature (2019), 573

In recent decades, meltwater runoff has accelerated to become the dominant mechanism for mass loss in the Greenland ice sheet1,2,3. In Greenland’s high-elevation interior, porous snow and firn accumulate ... [more ▼]

In recent decades, meltwater runoff has accelerated to become the dominant mechanism for mass loss in the Greenland ice sheet1,2,3. In Greenland’s high-elevation interior, porous snow and firn accumulate; these can absorb surface meltwater and inhibit runoff4, but this buffering effect is limited if enough water refreezes near the surface to restrict percolation5,6. However, the influence of refreezing on runoff from Greenland remains largely unquantified. Here we use firn cores, radar observations and regional climate models to show that recent increases in meltwater have resulted in the formation of metres-thick, low-permeability ‘ice slabs’ that have expanded the Greenland ice sheet’s total runoff area by 26 ± 3 per cent since 2001. Although runoff from the top of ice slabs has added less than one millimetre to global sea-level rise so far, this contribution will grow substantially as ice slabs expand inland in a warming climate. Runoff over ice slabs is set to contribute 7 to 33 millimetres and 17 to 74 millimetres to global sea-level rise by 2100 under moderate- and high-emissions scenarios, respectively—approximately double the estimated runoff from Greenland’s high-elevation interior, as predicted by surface mass balance models without ice slabs. Ice slabs will have an important role in enhancing surface meltwater feedback processes, fundamentally altering the ice sheet’s present and future hydrology. [less ▲]

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See detailRepresentation of the rain shadow effect in Patagonia using an orographic‐derived regional climate model
Damseaux, Adrien ULiege; Fettweis, Xavier ULiege; Lambert, Marius ULiege et al

in International Journal of Climatology (2019)

This study focuses on Patagonia, where Foehn events observed in the lee of the Andes mountains are not yet well simulated by state‐of‐the‐art climate models. It has been agreed that one source of this ... [more ▼]

This study focuses on Patagonia, where Foehn events observed in the lee of the Andes mountains are not yet well simulated by state‐of‐the‐art climate models. It has been agreed that one source of this shortcoming is related to the poor relief representation in models. To resolve this need, a common method used is to enhance the spatial resolution of the model to retrieve a more complex surface elevation, at the expense of calculation time or surface area covered. This paper tackles the problem from a different angle by addressing the Digital Elevation Model (DEM) generalization, .i.e. the altitudes generalization from a high‐resolution DEM to a coarser resolution grid model. Most current climate models use DEM generalization methods that smooth the relief, a key controlling factor in Foehn events modeling. The aim of this study is to compare three original methods of DEM generalization (percentile 90 (P90), envelope maximum (EM), and thalweg and crests (TC)) and to evaluate their impact on simulated precipitation and temperature fields on the eastern part of Patagonia, where warm and dry air masses are expected. Thanks to MAR, a Regional Climate Model, we validate the models at 10 and 5 km resolutions against the Climate Research Unit and perform three sensitivity experiments involving a change in the DEM generalization. Our results show that (i) a finer spatial resolution can slightly improve the temperature biases, however, it cannot resolve the precipitation biases and (ii) a more appropriate use of DEM generalization induces a significant decrease in precipitation for the P90 and EM methods and an increase in mean temperature for all three methods in the study area. This study serves as a recommendation for a better use of DEM generalization in climate models performing in Patagonia, but also regions sharing the same orographic features as the Patagonian relief. [less ▲]

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See detailGreenland Ice Sheet late-season melt: investigating multiscale drivers of K-transect events
Ballinger, T.; Mote, T.; Mattingly, K. et al

in Cryosphere (2019), 13

One consequence of recent Arctic warming is an increased occurrence and longer seasonality of above-freezing air temperature episodes. There is significant disagreement in the literature concerning ... [more ▼]

One consequence of recent Arctic warming is an increased occurrence and longer seasonality of above-freezing air temperature episodes. There is significant disagreement in the literature concerning potential physical connectivity between high-latitude open water duration proximate to the Greenland Ice Sheet (GrIS) and late-season (i.e., end-of-summer and autumn) GrIS melt events. Here, a new date of sea ice advance (DOA) product is used to determine the occurrence of Baffin Bay sea ice growth along Greenland's west coast for the 2011–2015 period. Over the 2-month period preceding the DOA, northwest Atlantic Ocean and atmospheric conditions are analyzed and linked to late-season melt events observed at a series of on-ice automatic weather stations (AWSs) along the K-transect in southwestern Greenland. Surrounding ice sheet, tundra, and coastal winds from the Modèle Atmosphérique Régional (MAR) and Regional Atmospheric Climate Model (RACMO) provide high-resolution spatial context to AWS observations and are analyzed along with ERA-Interim reanalysis fields to understand the meso-to-synoptic-scale (thermo)dynamic drivers of the melt events. Results suggest that late-season melt events, which primarily occur in the ablation area, are strongly affected by ridging atmospheric circulation patterns that transport warm, moist air from the subpolar North Atlantic toward west Greenland. Increasing concentrations of North Atlantic water vapor are shown to be necessary to produce melt conditions as autumn progresses. While thermal conduction and advection off south Baffin Bay open waters impact coastal air temperatures, local marine air incursions are obstructed by barrier flows and persistent katabatic winds along the western GrIS margin. [less ▲]

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See detailFuture projections of cyclone activity in the Arctic for the 21st century from regional climate models (Arctic-CORDEX)
Akperov, M.; Rinke, A.; Mokhov, I. et al

in Global and Planetary Change (2019)

Changes in the characteristics of cyclone activity (frequency, depth and size) in the Arctic are analyzed based on simulations with state-of-the-art regional climate models (RCMs) from the Arctic-CORDEX ... [more ▼]

Changes in the characteristics of cyclone activity (frequency, depth and size) in the Arctic are analyzed based on simulations with state-of-the-art regional climate models (RCMs) from the Arctic-CORDEX initiative and global climate models (GCMs) from CMIP5 under the Representative Concentration Pathway (RCP) 8.5 scenario. Most of RCMs show an increase of cyclone frequency in winter (DJF) and a decrease in summer (JJA) to the end of the 21st century. However, in one half of the RCMs, cyclones become weaker and substantially smaller in winter and deeper and larger in summer. RCMs as well as GCMs show an increase of cyclone frequency over the Baffin Bay, Barents Sea, north of Greenland, Canadian Archipelago, and a decrease over the Nordic Seas, Kara and Beaufort Seas and over the sub-arctic continental regions in winter. In summer, the models simulate an increase of cyclone frequency over the Central Arctic and Greenland Sea and a decrease over the Norwegian and Kara Seas by the end of the 21st century. The decrease is also found over the high-latitude continental areas, in particular, over east Siberia and Alaska. The sensitivity of the RCMs' projections to the boundary conditions and model physics is estimated. In general, different lateral boundary conditions from the GCMs have larger effects on the simulated RCM projections than the differences in RCMs' setup and/or physics. [less ▲]

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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 ▲]

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See detailGreenland ice sheet mass balance assessed by PROMICE (1995–2015)
Colgan, W.; Mankoff; Kjeldsen, K. et al

in GEUS Bulletin (2019), 43

The Programme for Monitoring of the Greenland Ice Sheet (PROMICE) has measured ice-sheet elevation and thickness via repeat airborne surveys circumscribing the ice sheet at an average elevation of 1708 ± ... [more ▼]

The Programme for Monitoring of the Greenland Ice Sheet (PROMICE) has measured ice-sheet elevation and thickness via repeat airborne surveys circumscribing the ice sheet at an average elevation of 1708 ± 5 m (Sørensen et al. 2018). We refer to this 5415 km survey as the ‘PROMICE perimeter’. Here, we assess ice-sheet mass balance following the input-output approach of Andersen et al. (2015). We estimate ice-sheet output, or the ice discharge across the ice-sheet grounding line, by applying downstream corrections to the ice flux across the PROMICE perimeter. We subtract this ice discharge from ice-sheet input, or the area-integrated, ice sheet surface mass balance, estimated by a regional climate model. While Andersen et al. (2015) assessed ice-sheet mass balance in 2007 and 2011, this updated input-output assessment now estimates the annual sea-level rise contribution from eighteen sub-sectors of the Greenland ice sheet over the 1995–2015 period. [less ▲]

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See detailCloud microphysics and circulation anomalies control differences in future Greenland melt
Hofer, Stefan ULiege; Tedstone, A.; Fettweis, Xavier ULiege et al

in Nature Climate Change (2019), 9

Recently, the Greenland Ice Sheet (GrIS) has become the main source of barystatic sea-level rise. The increase in the GrIS melt is linked to anticyclonic circulation anomalies, a reduction in cloud cover ... [more ▼]

Recently, the Greenland Ice Sheet (GrIS) has become the main source of barystatic sea-level rise. The increase in the GrIS melt is linked to anticyclonic circulation anomalies, a reduction in cloud cover and enhanced warm-air advection. The Climate Model Intercomparison Project fifth phase (CMIP5) General Circulation Models (GCMs) do not capture recent circulation dynamics; therefore, regional climate models (RCMs) driven by GCMs still show significant uncertainties in future GrIS sea-level contribution, even within one emission scenario. Here, we use the RCM Modèle Atmosphèrique Règional to show that the modelled cloud water phase is the main source of disagreement among future GrIS melt projections. We show that, in the current climate, anticyclonic circulation results in more melting than under a neutral-circulation regime. However, we find that the GrIS longwave cloud radiative effect is extremely sensitive to the modelled cloud liquid-water path, which explains melt anomalies of +378 Gt yr–1 (+1.04 mm yr–1 global sea level equivalent) in a +2 °C-warmer climate with a neutral-circulation regime (equivalent to 21% more melt than under anticyclonic circulation). The discrepancies between modelled cloud properties within a high-emission scenario introduce larger uncertainties in projected melt volumes than the difference in melt between low- and high-emission scenarios. [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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