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

in Encyclopedia of Snow, Ice and Glaciers (2011)

Definition of surface energy balance over a snowpack

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See detailUnderstanding the climatic signal in the water stable isotope records from the NEEM shallow firn/ice cores in northwest Greenland
Steen-Larsen; Masson-Delmotte; Sjolte et al

in Journal of Geophysical Research. Atmospheres (2011), 116

Samples of precipitation and atmospheric water vapor were collected together with shallow firn/ice cores as part of the new deep drilling project in northwest Greenland: the NEEM project. These samples ... [more ▼]

Samples of precipitation and atmospheric water vapor were collected together with shallow firn/ice cores as part of the new deep drilling project in northwest Greenland: the NEEM project. These samples were analyzed for their isotope composition to understand the processes affecting the climatic signal archived in the water stable isotope records from the NEEM deep ice core. The dominant moisture source for the snow deposited at the NEEM-site may be originating as far south as 35°N from the western part of the Atlantic Ocean. The surface atmospheric water vapor appears in isotopic equilibrium with the snow surface indicating a large water exchange between the atmosphere and snowpack. The interannual variability of NEEM shallow firn/ice cores stable isotope data covering the last ∼40 years shows an unexpectedly weak NAO signal. Regional to global atmospheric models simulate a dominant summer precipitation in the NEEM area, suggesting that the intermittency of modern winter precipitation is responsible for the lack of a strong NAO imprint. The interannual variability of NEEM isotope data however shows a strong correlation with interannual variations of Baffin Bay sea ice cover, a relationship consistent with air mass trajectories. NEEM deep ice core isotopic records may therefore provide detailed information on past Baffin Bay sea ice extent. NEEM stable water isotope content increasing trend points to a local warming trend of ∼3.0°C over the last 40 years. [less ▲]

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

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

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

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

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See detailPresent and future climates of the Greenland ice sheet according to the IPCC AR4 models
Franco, Bruno ULg; Fettweis, Xavier ULg; Erpicum, Michel ULg et al

in Climate Dynamics (2011), 36

The atmosphere–ocean general circulation models (AOGCMs) used for the IPCC 4th Assessment Report (IPCC AR4) are evaluated for the Greenland ice sheet (GrIS) current climate modelling. The most suited ... [more ▼]

The atmosphere–ocean general circulation models (AOGCMs) used for the IPCC 4th Assessment Report (IPCC AR4) are evaluated for the Greenland ice sheet (GrIS) current climate modelling. The most suited AOGCMs for Greenland climate simulation are then selected on the basis of comparison between the 1970–1999 outputs of the Climate of the twentieth Century experiment (20C3M) and reanalyses (ECMWF, NCEP/NCAR). This comparison indicates that the representation quality of surface parameters such as temperature and precipitation are highly correlated to the atmospheric circulation (500 hPa geopotential height) and its interannual variability (North Atlantic oscillation). The outputs of the three most suitable AOGCMs for present-day climate simulation are then used to assess the changes estimated by three IPCC greenhouse gas emissions scenarios (SRES) over the GrIS for the 2070–2099 period. Future atmospheric circulation changes are projected to dampen the zonal flow, enhance the meridional fluxes and therefore provide additional heat and moisture to the GrIS, increasing temperature over the whole ice sheet and precipitation over its northeastern area. We also show that the GrIS surface mass balance anomalies from the SRES A1B scenario amount to −300 km3/year with respect to the 1970–1999 period, leading to a global sea-level rise of 5 cm by the end of the 21st century. This work can help to select the boundaries conditions for AOGCMs-based downscaled future projections. [less ▲]

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

Conference (2011)

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

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

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

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

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

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

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See detailUsing a circulation type classification to analyse the general circulation over Greenland simulated by GCMs
Belleflamme, Alexandre ULg; Fettweis, Xavier ULg; Erpicum, Michel ULg

Conference (2010, November 23)

Future projections of the Greenland ice sheet melt are mainly based on General Circulation Model (GCM) outputs. The atmospheric circulation type classification offers a unique opportunity for validating ... [more ▼]

Future projections of the Greenland ice sheet melt are mainly based on General Circulation Model (GCM) outputs. The atmospheric circulation type classification offers a unique opportunity for validating the GCM-based circulations. Six GCMs used in the last IPCC report are analysed here. A correlation-based classification is constructed for each model using daily geopotential height at 500 hPa over Greenland. It is applied to a dataset combining the GCM-based outputs (20C3M scenario) for the current climate and the NCEP-NCAR 1 reanalysis data over the period 1961-1990 allowing a direct comparison for each circulation type. Most of the analysed models are able to reproduce the main circulation types, but they fail to reproduce their frequencies because they underestimate the climate variability. In addition, some biases in the mean geopotential height remain. However, we use our atmospheric circulation type classification for analysing future projections made by GCMs. As for the 20th century climate, a combined classification is made integrating reanalysis data over 1971-1990, GCM-based outputs over 1971-1990 (using 20C3M scenario) and GCM-based outputs over 2046-2065 and 2081-2100 (using A1B scenario). No new circulation types are individualised knowing that the main changes are just a general increase of the geopotential height. Furthermore, the changes in frequency observed between the 20th century climate and the first future period (2046-2065) are of the same order than the uncertainties of the models for simulating the current climate by comparison with the reanalysis data. Therefore, the circulation type classification is a useful tool to give a precise analysis of the atmospheric circulation simulated by GCMs knowing that most of downscaling techniques are dependent on the general circulation simulated by the GCMs. [less ▲]

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See detailHigh resolution modelling of the Greenland ice sheet surface mass balance using the regional climate model MAR coupled with a downscaling interface
Franco, Bruno ULg; Fettweis, Xavier ULg; Erpicum, Michel ULg

Poster (2010, November 05)

We are developing a coupling interface downscaling the 25km-atmosphere fields simulated by the regional climate MAR (Modèle Atmosphérique Régional) model onto a 5km-grid in order to resolve the surface ... [more ▼]

We are developing a coupling interface downscaling the 25km-atmosphere fields simulated by the regional climate MAR (Modèle Atmosphérique Régional) model onto a 5km-grid in order to resolve the surface processes at high resolution with the SISVAT (Sea Ice Soil Vegetation Atmosphere Transfer) snow-ice module. This coupling interface improves the representation of the topography and ablation zone of the Greenland ice sheet (GrIS) in the MAR model, and therefore will provide higher resolution estimations of the GrIS surface mass balance (SMB) without additional computing time. By using outputs from previously-gauged global circulation models (GCM) as forcing fields, the MAR model coupled with the downscaling interface will then perform 5km future simulations of the GrIS SMB for different IPCC greenhouse gas emissions scenarios for the 21st century. [less ▲]

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See detailAnalysis of the atmospheric circulation simulated by GCMs over Greenland
Belleflamme, Alexandre ULg; Fettweis, Xavier ULg; Erpicum, Michel ULg

Conference (2010, November 05)

The variability of the geopotential height at 500 hPa simulated by General Circulation Models (GCMs) over Greenland is evaluated using an atmospheric circulation type classification. The GCM outputs for ... [more ▼]

The variability of the geopotential height at 500 hPa simulated by General Circulation Models (GCMs) over Greenland is evaluated using an atmospheric circulation type classification. The GCM outputs for the current climate (20C3M) are first compared to reanalysis data over 1961-1990. The comparison shows that most of them simulate well the main circulation types but fail to reproduce their frequencies because of underestimations of circulation variability and biases in the mean geopotential height. GCM-based future projections do not individualise new circulation types but show a general increase of the geopotential height. Based on this approach, the correlation between surface temperature and atmospheric circulation offers a new way for estimating the Greenland ice sheet melt. [less ▲]

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See detailInterests of regional modelisation for wind power forecasting
Doutreloup, Sébastien ULg; Fettweis, Xavier ULg; Erpicum, Michel ULg

Conference (2010, October 22)

European policies have decided to reduce the greenhouse gas emissions of 20% and to reach 20% of renewable power production by 2020. Increasing wind power is one of the numerous solutions to reach these ... [more ▼]

European policies have decided to reduce the greenhouse gas emissions of 20% and to reach 20% of renewable power production by 2020. Increasing wind power is one of the numerous solutions to reach these goals. However, this kind of energy production depends on the meteorological conditions and gives it an intermittent behaviour. The wind speed variations cause voltage and frequency fluctuations that are unacceptable for the power grid. Therefore, forecasting production will become essential with the aim of integrating this kind of energy production into the power grid. We have developed and compared two forecasting models which give as outputs the wind power production every 15 minutes over the Belgian territory: the first one uses the outputs from the global model GFS (available at a horizontal resolution of 0.5° every 3h) and the second one uses the regional climate model WRF-NMM (using a horizontal resolution of 4km). Both of these models predict the wind speed and transform wind speed into wind power production, using a power curve which depends on the wind turbines and their characteristics. The first model using the GFS outputs is not precise enough in space and time to correctly forecast the wind speed in punctual wind farms. That is why we apply some specific tunings on these forecasts. These tunings depend on the air density, the wind direction and the stability of the air mass. The second model using the WRF-NMM outputs runs over the Belgian territory. Initial conditions are forced by the GFS outputs at 0.5° and WRF computes a physical based spatio-temporal downscaling of the meteorological variables. The outputs have a spatial resolution of 4 km and a time resolution of 15 minutes. Some tunings are also needed to adjust the wind power forecasts by comparison to the wind power observations. We present here some results of both models and the interest of using a regional model for more precise wind power forecasting. [less ▲]

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See detailGreenland [in Arctic Report Card 2010]
Box, J.; Cappelen, J.; Decker, D. et al

Report (2010)

Record warm air temperatures were observed over Greenland in 2010. This included the warmest year on record for Greenland's capital, Nuuk, in at least 138 years. The duration of the melt period on ... [more ▼]

Record warm air temperatures were observed over Greenland in 2010. This included the warmest year on record for Greenland's capital, Nuuk, in at least 138 years. The duration of the melt period on Greenland’s inland ice sheet was exceptional, being 1 month longer than the average over the past 30 years, and led to an extended period of amplified summer melt. All of the additional melt water very likely contributing to a faster rate of crevasse widening. Glacier loss along the Greenland margins was also exceptional in 2010, with the largest single glacier area loss (110 square miles, at Petermann glacier) equivalent to an area four times that of Manhattan Island. There is now no doubt that Greenland ice losses have not just increased above past decades, but have accelerated. The implication is that sea level rise projections will again need to be revised upward. [less ▲]

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See detailAnalysis of the evolution of the climate parameters, especially precipitations and temperatures, in the province of Binh Thuan in Southern Vietnam based on IPCC models
Doutreloup, Sébastien ULg; Fettweis, Xavier ULg; Ozer, Pierre ULg

Report (2010)

This research is implied into the BELSPO / Vietnamese desertification project and the aim of this work is to analyse the future evolution of the temperatures and precipitations in the region of Binh Thuan ... [more ▼]

This research is implied into the BELSPO / Vietnamese desertification project and the aim of this work is to analyse the future evolution of the temperatures and precipitations in the region of Binh Thuan thanks to the IPCC models (CMIP3). [less ▲]

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See detailGreenland [in "State of the Climate in 2009"]
Box, J.; Bhattacharya, I.; Cappelen, J. et al

in Bulletin of the American Meteorological Society [= BAMS] (2010), 91(6), 121-124

The summer minimum ice extent in the Arctic was the third-lowest recorded since 1979. The 2008/09 boreal snow cover season marked a continuation of relatively shorter snow seasons, due primarily to an ... [more ▼]

The summer minimum ice extent in the Arctic was the third-lowest recorded since 1979. The 2008/09 boreal snow cover season marked a continuation of relatively shorter snow seasons, due primarily to an early disappearance of snow cover in spring. Preliminary data indicate a high probability that 2009 will be the 19th consecutive year that glaciers have lost mass. Below normal precipitation led the 34 widest marine terminating glaciers in Greenland to lose 101 km2 ice area in 2009, within an annual loss rate of 106 km2 over the past decade. Observations show a general increase in permafrost temperatures during the last several decades in Alaska, northwest Canada, Siberia, and Northern Europe. Changes in the timing of tundra green-up and senescence are also occurring, with earlier green-up in the High Arctic and a shift to a longer green season in fall in the Low Arctic. [less ▲]

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See detailMicrowave data and a regional climate model for studying the Greenland ice sheet surface mass balance over 1979-2009
Fettweis, Xavier ULg; Marco, Tedesco

Poster (2010, May 03)

Results (melt extent and winter accumulation) from an atmosphere-snow coupled regional climate model are compared with microwave brightness temperatures-derived estimates to study the surface mass balance ... [more ▼]

Results (melt extent and winter accumulation) from an atmosphere-snow coupled regional climate model are compared with microwave brightness temperatures-derived estimates to study the surface mass balance (SMB) changes over the Greenland ice sheet (GrIS) since 1979. Two simple algorithms are selected to retrieve the melt extent from the brightness temperatures. The first one is sensible to the production of surface meltwater as suggests the regional model and the second one is rather sensible to the presence of liquid water content into the snowpack. Both algorithms compare very well with model outputs and they are unanimous to show a significant increase of the surface melt over 1979-2009.We found also a good correlation between the March-April mean brightness temperatures and the simulated winter snow accumulation although no significant changes are found in both simulated and microwave-derived snow accumulation. The interannual variability of the brightness temperature-derived SMB components compare very well with the model results. This suggests that the variability of the model is reliable and that the model can be used to detect SMB changes over longer periods where no satellite data is available. Finally, both model and satellite agree to confirm the acceleration of the GrIS surface melting since 30 years. [less ▲]

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See detailA statistical validation for the cycles found in air temperature data using a Morlet wavelet-based method
Nicolay, Samuel ULg; Mabille, Georges ULg; Fettweis, Xavier ULg et al

in Nonlinear Processes in Geophysics (2010), 17

Recently, new cycles, associated with periods of 30 and 43 months, respectively, have been observed by the authors in surface air temperature time series, using a wavelet-based methodology. Although many ... [more ▼]

Recently, new cycles, associated with periods of 30 and 43 months, respectively, have been observed by the authors in surface air temperature time series, using a wavelet-based methodology. Although many evidences attest the validity of this method applied to climatic data, no systematic study of its efficiency has been carried out. Here, we estimate confidence levels for this approach and show that the observed cycles are significant. Taking these cycles into consideration should prove helpful in increasing the accuracy of the climate model projections of climate change and weather forecast. [less ▲]

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See detailMulti-Months Cycles Observed in Climatic Data
Nicolay, Samuel ULg; Mabille, Georges ULg; Fettweis, Xavier ULg et al

in Simard, Suzanne (Ed.) Climate Change and Variability (2010)

Climatic variations happen at all time scales and since the origins of these variations are usually of very complex nature, climatic signals are indeed chaotic data. The identification of the cycles ... [more ▼]

Climatic variations happen at all time scales and since the origins of these variations are usually of very complex nature, climatic signals are indeed chaotic data. The identification of the cycles induced by the natural climatic variability is therefore a knotty problem, yet the knowing of these cycles is crucial to better understand and explain the climate (with interests for weather forecasting and climate change projections). Due to the non-stationary nature of the climatic time series, the simplest Fourier-based methods are inefficient for such applications (see e.g. Titchmarsh (1948)). This maybe explains why so few systematic spectral studies have been performed on the numerous datasets allowing to describe some aspects of the climate variability (e.g. climatic indices, temperature data). However, some recent studies (e.g. Matyasovszky (2009); Paluš & Novotná (2006)) show the existence of multi-year cycles in some specific climatic data. This shows that the emergence of new tools issued from signal analysis allows to extract sharper information from time series. Here, we use a wavelet-based methodology to detect cycles in air-surface temperatures obtained from worldwide weather stations, NCEP/NCAR reanalysis data, climatic indices and some paleoclimatic data. This technique reveals the existence of universal rhythms associated with the periods of 30 and 43 months. However, these cycles do not affect the temperature of the globe uniformly. The regions under the influence of the AO/NAO indices are influenced by a 30 months period cycle, while the areas related to the ENSO index are affected by a 43 months period cycle; as expected, the corresponding indices display the same cycle. We next show that the observed periods are statistically relevant. Finally, we consider some mechanisms that could induce such cycles. This chapter is based on the results obtained in Mabille & Nicolay (2009); Nicolay et al. (2009; 2010). [less ▲]

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See detailCOST733CAT - a database of weather and circulation
Philipp, Andreas; Bartholy, Judit; Beck, Christoph et al

in Physics & Chemistry of the Earth - Parts A/B/C (2010), 35(9-12), 360-373

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See detailThe 1958-2008 Greenland ice sheet surface mass balance variability simulated by the regional climate model MAR
Fettweis, Xavier ULg

Poster (2009, April 24)

Results made with the regional climate model MAR over 1958-2008 show a very high interannual variability of the Greenland ice sheet (GrIS) surface mass balance (SMB) modelled in average to be 330 +/- 130 ... [more ▼]

Results made with the regional climate model MAR over 1958-2008 show a very high interannual variability of the Greenland ice sheet (GrIS) surface mass balance (SMB) modelled in average to be 330 +/- 130 km^3/yr. To a first approximation, the SMB variability is driven by the annual precipitation anomaly minus the meltwater run-off rate variability. Sensitivity experiments carried out by the MAR model evaluate the impacts on the surface melt of (i) the summer SST around the Greenland, (ii) the snow pack temperature at the beginning of the spring, (iii) the winter snow accumulation, (iv) the solid and liquid summer precipitations and (v) the summer atmospheric circulation. This last one, by forcing the summer air temperature above the ice sheet, explains mainly the surface melt anomalies. [less ▲]

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