References of "Fettweis, Xavier"
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See detailFuture climate and surface mass balance of Svalbard glaciers in an RCP8.5 climate scenario: a study with the regional climate model MAR forced by MIROC5
Lang, Charlotte ULg; Fettweis, Xavier ULg; Erpicum, Michel ULg

in Cryosphere (The) (2015), 9

We simulated the 21st century Svalbard SMB with the regional model MAR (RCP8.5 scenario). Melt is projected to increase gently up to 2050 and then dramatically increase, with a larger increase in the ... [more ▼]

We simulated the 21st century Svalbard SMB with the regional model MAR (RCP8.5 scenario). Melt is projected to increase gently up to 2050 and then dramatically increase, with a larger increase in the south of the archipelago. This difference is due to larger ice albedo decrease in the south causing larger increase of absorbed solar radiation. The ablation area is projected to disappear over the entire Svalbard by 2085. The SMB decrease compared to present is projected to contribute 7mm to SLR. [less ▲]

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See detailGlobal, diffuse and direct irradiances modelling over northwestern Europe using regional climate model MAR : validation and construction of a 30-year climatology
Beaumet, Julien ULg; Doutreloup, Sébastien ULg; Fettweis, Xavier ULg et al

Poster (2015, April 17)

Incoming solar global irradiances are modelled using MAR regional climate model forced by ERA-Interim reanalysis. Global irradiances are decomposed into direct and diffuse using sigmoid model from Ruiz ... [more ▼]

Incoming solar global irradiances are modelled using MAR regional climate model forced by ERA-Interim reanalysis. Global irradiances are decomposed into direct and diffuse using sigmoid model from Ruiz-Arias et al. (2010). Results are validated using data from the European Solar Radiation Atlas for Uccle and Braunschweig weather stations. A 30-year climatology has been built and trends and variability have been analyzed. [less ▲]

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See detailSnow cover evolution during the last fifty years in the Hautes Fagnes (Belgium) using the regional climate MAR model
Wyard, Coraline ULg; Fettweis, Xavier ULg; Erpicum, Michel ULg

Conference (2015, April 16)

The MAR model is a regional climate model originally developped for the polar regions to study the surface mass balance. In this study, the MAR model has been adapted to Belgium in order to study the snow ... [more ▼]

The MAR model is a regional climate model originally developped for the polar regions to study the surface mass balance. In this study, the MAR model has been adapted to Belgium in order to study the snow cover evolution of the Hautes Fagnes (south-east of Belgium), a region covered by snow one to two months per year. As validation, we have sucessfully compared MAR based daily snow heights with snowcam-based observations. Then, the model has been forced by ERA-Interim since 1958 to study the snow cover evolution during the last fifty years at the summit of Belgium. The results show non-significant trend. [less ▲]

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See detailFuture projections of the Greenland ice sheet mass balance using the regional climate MAR model coupled with the GRISLI ice sheet model
Wyard, Coraline ULg; Fettweis, Xavier ULg; Ritz, Catherine

Poster (2015, April 14)

During the two last decades, the Greenland ice sheet (GrIS) contribution to the global mean sea level rise has significantly increased. But, difficulties remain to assess GrIS future contribution because ... [more ▼]

During the two last decades, the Greenland ice sheet (GrIS) contribution to the global mean sea level rise has significantly increased. But, difficulties remain to assess GrIS future contribution because of large uncertainties linked to the feedback between the surface mass balance (SMB) and GrIS topography changes. The regional climate MAR model has been coupled with the GRISLI ice sheet model, in order to account of this feedback in the future projections. The aim of this study is to assess the pertinence of the MAR-GRISLI coupling which requires long computation time. In order to identify GRISLI sensitivity to MAR forcing, GRISLI has been forced with various non-coupled (i.e. using a fixed topography), coupled and modified non-coupled MAR outputs. To adapt the non-coupled MAR outputs to the GRISLI topography changes, we use an interpolation technique based on SMB vs elevation vertical gradient. These experiences evaluate the performances/limits of this interpolation technique used to avoid a RCM-ice sheet model coupling. [less ▲]

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See detailEGU2015 - ENSO forecast using a wavelet-based mode decomposition
Deliège, Adrien ULg; Nicolay, Samuel ULg; Fettweis, Xavier ULg

Conference (2015, April 13)

The aim of this work is to introduce a new method for forecasting major El Niño/ La Niña events with the use of a wavelet-based mode decomposition. These major events are related to sea surface ... [more ▼]

The aim of this work is to introduce a new method for forecasting major El Niño/ La Niña events with the use of a wavelet-based mode decomposition. These major events are related to sea surface temperature anomalies in the tropical Pacific Ocean: anomalous warmings are known as El Niño events, while excessive coolings are referred as La Niña episodes. These climatological phenomena are of primary importance since they are involved in many teleconnections ; predicting them long before they occur is therefore a crucial concern. First, we perform a wavelet transform (WT) of the monthly sampled El Niño Southern Oscillation 3.4 index (from 1950 to present) and compute the associated scale spectrum, which can be seen as the energy carried in the WT as a function of the scale. It can be observed that the spectrum reaches five peaks, corresponding to time scales of about 7, 20, 31, 43 and 61 months respectively. Therefore, the Niño 3.4 signal can be decomposed into five dominant oscillating components with time-varying amplitudes, these latter being given by the modulus of the WT at the associated pseudo-periods. The reconstruction of the index based on these five components is accurate since more than 93% of the El Niño/ La Niña events of the last 60 years are recovered and no major event is erroneously predicted. Then, the components are smoothly extrapolated using polynomials and added together, giving so several years forecasts of the Niño 3.4 index. In order to increase the reliability of the forecasts, we perform several months hindcasts (i.e. retroactive probing forecasts) which can be validated with the existing data. It turns out that most of the major events can be accurately predicted up to three years in advance, which makes our methodology competitive for such forecasts. Finally, we discuss the El Niño conditions currently undergone and give indications about the next La Niña event. [less ▲]

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See detailGreenland high-elevation mass balance: inference and implication of reference period (1961–90) imbalance
Colgan, W.; Box, J.; Andersen, M. et al

in Annals of Glaciology (2015), 56(70), 105117

We revisit the input–output mass budget of the high-elevation region of the Greenland ice sheet evaluated by the Program for Arctic Regional Climate Assessment (PARCA). Our revised reference period ... [more ▼]

We revisit the input–output mass budget of the high-elevation region of the Greenland ice sheet evaluated by the Program for Arctic Regional Climate Assessment (PARCA). Our revised reference period (1961–90) mass balance of 54 48 Gt a–1 is substantially greater than the 0 21 Gt a–1 assessed by PARCA, but consistent with a recent, fully independent, input–output estimate of high-elevation mass balance (41 61 Gt a–1). Together these estimates infer a reference period high-elevation specific mass balance of 4.8 5.4 cm w.e. a–1. The probability density function (PDF) associated with this combined input–output estimate infers an 81% likelihood of high-elevation specific mass balance being positive (>0 cm w.e. a–1) during the reference period, and a 70% likelihood that specific balance was >2 cm w.e. a–1. Given that reference period accumulation is characteristic of centurial and millennial means, and that in situ mass-balance observations exhibit a dependence on surface slope rather than surface mass balance, we suggest that millennial-scale ice dynamics are the primary driver of subtle reference period high-elevation mass gain. Failure to acknowledge subtle reference period dynamic mass gain can result in underestimating recent dynamic mass loss by 17%, and recent total Greenland mass loss by 7%. [less ▲]

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See detailThe summer 2012 Greenland heat wave: in situ and remote sensing observations of water vapour isotopic composition during an atmospheric river event†
Bonne, JL; Steen-Larsen, HC; Risi, C. et al

in Journal of Geophysical Research. Atmospheres (2015)

During July 7-12, 2012, extreme moist and warm conditions occurred over Greenland, leading to widespread surface melt. To investigate the physical processes during the atmospheric moisture transport of ... [more ▼]

During July 7-12, 2012, extreme moist and warm conditions occurred over Greenland, leading to widespread surface melt. To investigate the physical processes during the atmospheric moisture transport of this event, we study the water vapour isotopic composition using surface in situ observations in Bermuda Island, South Greenland coast (Ivittuut) and Northwest Greenland ice sheet (NEEM), as well as remote sensing observations (IASI instrument on-board MetOp-A), depicting propagation of similar surface and mid-tropospheric humidity and δD signals. Simulations using Lagrangian moisture source diagnostic and water tagging in a regional model showed that Greenland was affected by an atmospheric river transporting moisture from the western subtropical North Atlantic Ocean, which is coherent with observations of snow pit impurities deposited at NEEM. At Ivittuut, surface air temperature, humidity and δD increases are observed. At NEEM, similar temperature increase is associated with a large and long-lasting ~100 δD enrichment and ~15 deuterium excess decrease, thereby reaching Ivittuut level. We assess the simulation of this event in two isotope-enabled atmospheric general circulation models (LMDz-iso and ECHAM5-wiso). LMDz-iso correctly captures the timing of propagation for this event identified in IASI data but depict too gradual variations when compared to surface data. Both models reproduce the surface meteorological and isotopic values during the event but underestimate the background deuterium excess at NEEM. Cloud liquid water content parametrization in LMDz-iso poorly impacts the vapour isotopic composition. Our data demonstrate that during this atmospheric river event the deuterium excess signal is conserved from the moisture source to Northwest Greenland. [less ▲]

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See detailRecent summer Arctic atmospheric circulation anomalies in a historical perspective
Belleflamme, Alexandre ULg; Fettweis, Xavier ULg; Erpicum, Michel ULg

in Cryosphere (The) (2015), 9

A significant increase in the summertime occurrence of a high pressure area over the Beaufort Sea, the Canadian Arctic Archipelago, and Greenland has been observed since the beginning of the 2000s, and ... [more ▼]

A significant increase in the summertime occurrence of a high pressure area over the Beaufort Sea, the Canadian Arctic Archipelago, and Greenland has been observed since the beginning of the 2000s, and particularly between 2007 and 2012. These circulation anomalies are likely partly responsible for the enhanced Greenland ice sheet melt as well as the Arctic sea ice loss observed since 2007. Therefore, it is interesting to analyse whether similar conditions might have happened since the late 19th century over the Arctic region. We have used an atmospheric circulation type classification based on daily mean sea level pressure and 500 hPa geopotential height data from five reanalysis data sets (ERA-Interim, ERA-40, NCEP/NCAR, ERA-20C, and 20CRv2) to put the recent circulation anomalies in perspective with the atmospheric circulation variability since 1871. We found that circulation conditions similar to 2007–2012 have occurred in the past, despite a higher uncertainty of the reconstructed circulation before 1940. For example, only ERA-20C shows circulation anomalies that could explain the 1920–1930 summertime Greenland warming, in contrast to 20CRv2. While the recent anomalies exceed by a factor of 2 the interannual variability of the atmospheric circulation of the Arctic region, their origin (natural variability or global warming) remains debatable. [less ▲]

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See detailStable climate and surface mass balance in Svalbard over 1979–2013 despite the Arctic warming
Lang, Charlotte ULg; Fettweis, Xavier ULg; Erpicum, Michel ULg

in Cryosphere (The) (2015), 9

With the help of the regional climate model MAR (Modèle Atmosphérique Régional) forced by the ERA-Interim reanalysis (MARERA) and the MIROC5 (Model for Interdisciplinary Research on Climate) global model ... [more ▼]

With the help of the regional climate model MAR (Modèle Atmosphérique Régional) forced by the ERA-Interim reanalysis (MARERA) and the MIROC5 (Model for Interdisciplinary Research on Climate) global model (MARMIROC5) from the CMIP5 (Coupled Model Intercomparison Project) database, we have modelled the climate and surface mass balance of Svalbard at a 10 km resolution over 1979–2013. The integrated total surface mass balance (SMB) over Svalbard modelled by MARERA is negative (−1.6 Gt yr−1) with a large interannual variability (7.1 Gt) but, unlike over Greenland, there has been no acceleration of the surface melt over the past 35 years because of the recent change in atmospheric circulation bringing northwesterly flows in summer over Svalbard, contrasting the recent observed Arctic warming. However, in 2013, the atmospheric circulation changed to a south–southwesterly flow over Svalbard causing record melt, SMB (−20.4 Gt yr−1) and summer temperature. MIROC5 is significantly colder than ERA-Interim over 1980–2005 but MARMIROC5 is able to improve the near-surface MIROC5 results by simulating not significant SMB differences with MARERA over 1980–2005. On the other hand, MIROC5 does not represent the recent atmospheric circulation shift in summer and induces in MARMIROC5 a significant trend of decreasing SMB (−0.6 Gt yr−2) over 1980–2005. [less ▲]

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See detailSupraglacial lakes on the Greenland ice sheet advance inland under warming climate
Leeson, A.; Shepherd, A.; Briggs, K. et al

in Nature Climate Change (2015), 5

Supraglacial lakes (SGLs) form annually on the Greenland ice sheet and, when they drain, their discharge enhances ice-sheet flow by lubricating the base and potentially by warming the ice. Today, SGLs ... [more ▼]

Supraglacial lakes (SGLs) form annually on the Greenland ice sheet and, when they drain, their discharge enhances ice-sheet flow by lubricating the base and potentially by warming the ice. Today, SGLs tend to form within the ablation zone, where enhanced lubrication is offset by efficient subglacial drainage. However, it is not clear what impact a warming climate will have on this arrangement. Here, we use an SGL initiation and growth model to show that lakes form at higher altitudes as temperatures rise, consistent with satellite observations. Our simulations show that in southwest Greenland, SGLs spread 103 and 110 km further inland by the year 2060 under moderate (RCP 4.5) and extreme (RCP 8.5) climate change scenarios, respectively, leading to an estimated 48–53% increase in the area over which they are distributed across the ice sheet as a whole. Up to half of these new lakes may be large enough to drain, potentially delivering water and heat to the ice-sheet base in regions where subglacial drainage is inefficient. In such places, ice flow responds positively to increases in surface water delivered to the bed through enhanced basal lubrication and warming of the ice, and so the inland advance of SGLs should be considered in projections of ice-sheet change. [less ▲]

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See detailBasin-scale partitioning of Greenland ice sheet mass balance components (2007–2011)
Andersen, M.L.; Stenseng, L.; Skourup, H. et al

in Earth and Planetary Science Letters (2015), 409

The current deficit in Greenland ice sheet mass balance is due to both a decrease in surface mass balance (SMB ) input and an increase in ice discharge (D ) output. While SMB processes are beginning to be ... [more ▼]

The current deficit in Greenland ice sheet mass balance is due to both a decrease in surface mass balance (SMB ) input and an increase in ice discharge (D ) output. While SMB processes are beginning to be well captured by observationally-constrained climate modeling, insight into D is relatively limited. We use InSAR-derived velocities, in combination with ice thickness observations, to quantify the mass flux (F ) across a flux perimeter around the ice sheet at ∼1700 m elevation. To quantify D , we correct F for SMB , as well as changes in volume due to ice dynamics, in the area downstream of the gate. Using a 1961–1990 reference climatology SMB field from the MAR regional climate model, we quantify ice sheet mass balance within eighteen basins. We find a 2007–2011 mean D of View the MathML source. We find a 2007–2011 mean total mass balance of View the MathML source, which is equal to a 0.73 mm yr−1 global sea level rise contribution. This mass loss is dominated by SMB, which accounts for 61% of mass loss in the basins where partitioning is possible. [less ▲]

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See detailRapid dynamic activation of a marine-based Arctic ice cap
McMillan, M; Shepherd, A; Gourmelen, N et al

in Geophysical Research Letters (2014), 41(24), 89028909

We use satellite observations to document rapid acceleration and ice loss from a formerly slow-flowing, marine-based sector of Austfonna, the largest ice cap in the Eurasian Arctic. During the past two ... [more ▼]

We use satellite observations to document rapid acceleration and ice loss from a formerly slow-flowing, marine-based sector of Austfonna, the largest ice cap in the Eurasian Arctic. During the past two decades, the sector ice discharge has increased 45-fold, the velocity regime has switched from predominantly slow (~ 101 m/yr) to fast (~ 103 m/yr) flow, and rates of ice thinning have exceeded 25 m/yr. At the time of widespread dynamic activation, parts of the terminus may have been near floatation. Subsequently, the imbalance has propagated 50 km inland to within 8 km of the ice cap summit. Our observations demonstrate the ability of slow-flowing ice to mobilize and quickly transmit the dynamic imbalance inland; a process that we show has initiated rapid ice loss to the ocean and redistribution of ice mass to locations more susceptible to melt, yet which remains poorly understood. [less ▲]

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See detailAssessing spatio-temporal variability and trends in modelled and measured Greenland Ice Sheet albedo (2000–2013)
Alexander, P.; Tedesco, M.; Fettweis, Xavier ULg et al

in Cryosphere (The) (2014), 8

Accurate measurements and simulations of Greenland Ice Sheet (GrIS) surface albedo are essential, given the role of surface albedo in modulating the amount of absorbed solar radiation and meltwater ... [more ▼]

Accurate measurements and simulations of Greenland Ice Sheet (GrIS) surface albedo are essential, given the role of surface albedo in modulating the amount of absorbed solar radiation and meltwater production. In this study, we assess the spatio-temporal variability of GrIS albedo during June, July, and August (JJA) for the period 2000–2013. We use two remote sensing products derived from data collected by the Moderate Resolution Imaging Spectroradiometer (MODIS), as well as outputs from the Modèle Atmosphérique Régionale (MAR) regional climate model (RCM) and data from in situ automatic weather stations. Our results point to an overall consistency in spatio-temporal variability between remote sensing and RCM albedo, but reveal a difference in mean albedo of up to ~0.08 between the two remote sensing products north of 70° N. At low elevations, albedo values simulated by the RCM are positively biased with respect to remote sensing products by up to ~0.1 and exhibit low variability compared with observations. We infer that these differences are the result of a positive bias in simulated bare ice albedo. MODIS albedo, RCM outputs, and in situ observations consistently indicate a decrease in albedo of −0.03 to −0.06 per decade over the period 2003–2013 for the GrIS ablation area. Nevertheless, satellite products show a decline in JJA albedo of −0.03 to −0.04 per decade for regions within the accumulation area that is not confirmed by either the model or in situ observations. These findings appear to contradict a previous study that found an agreement between in situ and MODIS trends for individual months. The results indicate a need for further evaluation of high elevation albedo trends, a reconciliation of MODIS mean albedo at high latitudes, and the importance of accurately simulating bare ice albedo in RCMs. [less ▲]

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See detailENSO forecast using a wavelet-based mode decomposition
Deliège, Adrien ULg; Nicolay, Samuel ULg; Fettweis, Xavier ULg

Poster (2014, December)

We introduce a new method for forecasting major El Niño/ La Niña events based on a wavelet mode decomposition. This methodology allows us to approximate the ENSO time series with a superposition of three ... [more ▼]

We introduce a new method for forecasting major El Niño/ La Niña events based on a wavelet mode decomposition. This methodology allows us to approximate the ENSO time series with a superposition of three periodic signals corresponding to periods of about 31, 43 and 61 months respectively with time-varying amplitudes. This pseudo-periodic approximation is then extrapolated to give forecasts. While this last one only resolves the large variations in the ENSO time series, three years hindcast as retroactive prediction allows to recover most of the El Niño/ La Niña events of the last 60 years. [less ▲]

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See detailSensitivity of Greenland Ice Sheet surface mass balance to perturbations in sea surface temperature and sea ice cover: a study with the regional climate model MAR
Noel, Brice; Fettweis, Xavier ULg; van de Berg, W.J. et al

in Cryosphere (The) (2014), 8

During recent summers (2007–2012), several surface melt records were broken over the Greenland Ice Sheet (GrIS). The extreme summer melt resulted in part from a persistent negative phase of the North ... [more ▼]

During recent summers (2007–2012), several surface melt records were broken over the Greenland Ice Sheet (GrIS). The extreme summer melt resulted in part from a persistent negative phase of the North Atlantic Oscillation (NAO), favoring warmer atmospheric conditions than normal over the GrIS. Simultaneously, large anomalies in sea ice cover (SIC) and sea surface temperature (SST) were observed in the North Atlantic, suggesting a possible connection. To assess the direct impact of 2007–2012 SIC and SST anomalies on GrIS surface mass balance (SMB), a set of sensitivity experiments was carried out with the regional climate model MAR forced by ERA-Interim. These simulations suggest that perturbations in SST and SIC in the seas surrounding Greenland do not considerably impact GrIS SMB, as a result of the katabatic wind blocking effect. These offshore-directed winds prevent oceanic near-surface air, influenced by SIC and SST anomalies, from penetrating far inland. Therefore, the ice sheet SMB response is restricted to coastal regions, where katabatic winds cease. A topic for further investigation is how anomalies in SIC and SST might have indirectly affected the surface melt by changing the general circulation in the North Atlantic region, hence favoring more frequent warm air advection towards the GrIS. [less ▲]

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See detailSolar irradiance modelling over Belgium using Regional Climate Models within the frame of a day-ahead photovoltaic production forecasting system
Beaumet, Julien ULg; Doutreloup, Sébastien ULg; Fettweis, Xavier ULg et al

Poster (2014, October 06)

WRF-ARW and MAR climate models performances for the modelling of solar irradiances over Belgium are evaluated using in-situ measurements at Sart-Tilman and Daussoulx. Different WRF-ARW settings are tested ... [more ▼]

WRF-ARW and MAR climate models performances for the modelling of solar irradiances over Belgium are evaluated using in-situ measurements at Sart-Tilman and Daussoulx. Different WRF-ARW settings are tested. Sigmoid model proposed by Ruis-Ariaz etal. (2010) is used to decompose solar irradiance into direct and diffuse fraction. The performance of this model using measured and modelled global irradiances is also evaluated. [less ▲]

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See detailMICROPHYSIQUE DES NUAGES ET RAYONNEMENT SOLAIRE : COMPARAISON DES MESURES IN SITU AU MONT RIGI EN HAUTE BELGIQUE ET DES DONNÉES CLOUD PHYSICAL PROPERTIES (CPP) OBTENUES À PARTIR DES IMAGES METEOSAT-9
Beaumet, Julien ULg; Clerbaux, Nicolas; Cornet, Yves ULg et al

in Camberlin, Pierre; Richard, Yves (Eds.) Actes du XXVIIe Colloque de l'Association Internationale de Climatologie : CLIMAT : SYSTÈME & INTERACTIONS (2014, July 02)

Le rayonnement solaire global mesuré au mont Rigi a été comparé à l'épaisseur optique des nuages (COT) estimée à l'aide des données SEVIRI. Une relation logarithmique avec un coefficient de détermination ... [more ▼]

Le rayonnement solaire global mesuré au mont Rigi a été comparé à l'épaisseur optique des nuages (COT) estimée à l'aide des données SEVIRI. Une relation logarithmique avec un coefficient de détermination d'environ 0,5 a été trouvée. Ce résultat plutôt faible peut en grande partie s'expliquer par un nombre limité de cas où subsistent des erreurs de positionnement ou par des interactions plus complexes entre nébulosité et rayonnement. De plus, l'incertitude sur l'estimation de l'épaisseur optique des nuages à l'aide des données SEVIRI pour les nuages optiquement plus épais n'est pas négligeable. [less ▲]

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See detailComparaison entre le profil vertical de la vitesse du vent observé dans les basses couches de la troposphère et celui simulé par le modèle WRF en Belgique
Doutreloup, Sébastien ULg; Fettweis, Xavier ULg; Beaumet, Julien ULg et al

in Camberlin, Pierre; Richard, Yves (Eds.) Actes du XXVIIe Colloque de l'Association Internationale de Climatologie : CLIMAT : SYSTÈME & INTERACTIONS (2014, July 02)

In the framework of FLEXIPAC project funded by the "RELIABLE" program of Walloon Region (Belgium), the Laboratory of Climatology Topoclimatology (LCT) of the University of Liège (Belgium) aims to adjust ... [more ▼]

In the framework of FLEXIPAC project funded by the "RELIABLE" program of Walloon Region (Belgium), the Laboratory of Climatology Topoclimatology (LCT) of the University of Liège (Belgium) aims to adjust the WRF regional model (v.3.4.) forced by the ERA-Interim reanalysis for Belgium. Our analysis shows that wind speeds at 100m simulated by WRF are systematically overestimated compared to wind speeds extracted from wind productions of two wind farms. In order to solve this problem, four ways are considered in this contribution. The first way is to compare the WRF model with the reanalysis data. The second way is to test the influence of the spatial resolution by running WRF with a finer resolution. The third way is to smooth WRF outputs, where in order to analyze the variability created by the model. And finally, the fourth way is to compare the WRF model with the MAR (v3.3.) regional model. This last way seems to confirm that the MAR model better simulates wind speeds at 10m and at 100m than the WRF model. [less ▲]

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See detailSolar irradiance modelling over Belgium using WRF-ARW : A sensitivity analysis of Mellor-Yamada-Nakanishi-Niino (BYNN) boundary layer scheme parameters
Beaumet, Julien ULg; Doutreloup, Sébastien ULg; Fettweis, Xavier ULg et al

Conference (2014, June 06)

Global solar irradiances at ground level are modelled over Belgium using latest version of WRF-ARW regional climate model (RCM). The model set-up used has a resolution of 5 kilometres. The boundary layer ... [more ▼]

Global solar irradiances at ground level are modelled over Belgium using latest version of WRF-ARW regional climate model (RCM). The model set-up used has a resolution of 5 kilometres. The boundary layer scheme chosen is the Mellor-Yamada-Nakanishi-Niino (MYNN) 2.5 scheme with the Turbulent Kinetic Energy (TKE) closure proposed by Canuto et al., (2008) and Kitamura (2010). In this scheme, the modification of some parameters allows to change the determinant mixing length (surface layer, planet boundary layer, top of boundary layer/entrainment) which then modifies heat and moistures fluxes produced by turbulent mixing. Such modifications have significant influences on modelled cloudiness and therefore on modelled global solar irradiance incoming at the surface. The present study proposes a sensitivity analysis of the different parameters that influence the mixing length ('alp1' to 'alp5') and the TKE diffusion ('Sqfac') in order to find the most suitable constant values of these parameters for the modelling of cloudiness over Belgium. Results of different simulations are compared with global solar irradiance measurements performed by the Centre Spatial de Liège at Sart-Tilman in 2013 and 2014. Firsts results show that the dry bias frequently found when using WRF-ARW with standard set-ups can be greatly reduced thanks to an increased modelled cloudiness. The quantitative and qualitative effects of these modifications over cloudiness are also analysed by displaying 2D representation of modelled clouds over Sart-Tilman and confronting them with on-site observations. [less ▲]

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See detailComparison between wind speed observed at 100m height and wind speeds simulated by the WRF and MAR models
Doutreloup, Sébastien ULg; Fettweis, Xavier ULg; Erpicum, Michel ULg et al

Poster (2014, June 06)

In the context of FLEXIPAC project funded by "RELIABLE" program of Walloon Region (Belgium), the Laboratory of Climatology and Topoclimatology (LCT) of the University of Liège (Belgium) aims to adjust the ... [more ▼]

In the context of FLEXIPAC project funded by "RELIABLE" program of Walloon Region (Belgium), the Laboratory of Climatology and Topoclimatology (LCT) of the University of Liège (Belgium) aims to adjust the WRF regional model (v.3.4.) forced by ERA-Interim model. Our analysis shows that wind speeds at 100m height simulated by WRF are systematically overestimated compared to wind speeds extracted from wind productions of two wind farms. In order to identify this problem, four comparisons were performed in this contribution. Firstly, we compare WRF model with reanalysis based forcing model. Secondly, we compare two WRF simulations, where one of them has a more precise spatial resolution. Thirdly, we smooth WRF outputs in time (6-hr running mean) in order to study the accuracy of the 30-min variability generated by WRF model. Finally, we comp compare the WRF model with the MAR (v3.3.) regional model using the same forcing at its lateral boundaries. This last one seems to suggest that the MAR model better simulates wind speeds at 10m and at 100m than WRF model and then that wind speed underestimation by WRF is well linked to the WRF physics itself. [less ▲]

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