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Page de résumé pour ULgetd-11122012-132730

Auteur : Franco, Bruno
E-mail de l'auteur : Bruno.Franco@ulg.ac.be
URN : ULgetd-11122012-132730
Langue : Anglais/English
Titre : Present and future Greenland ice sheet surface energy balances with the help of the regional climate MAR model
Intitulé du diplôme : Doctorat en sciences
Département : FS - Département des sciences géographiques
Jury :
Nom : Titre :
Agosta, Cécile Membre du jury/Committee Member
François, Louis Membre du jury/Committee Member
Gallée, Hubert Membre du jury/Committee Member
Schneider, Christoph Membre du jury/Committee Member
Petit, François Président du jury/Committee Chair
Erpicum, Michel Promoteur/Director
Fettweis, Xavier Promoteur/Director
Mots-clés :
  • surface energy balance
  • future projections
  • regional modelling
  • spatial resolution
  • surface mass balance
Date de soutenance : 2012-10-19
Type d'accès : Public/Internet
Résumé :

The Greenland ice sheet (GrIS) surface mass balance (SMB) was modelled at different spatial resolutions (15-50 km), using the regional climate model MAR (Modèle Atmosphérique Régional) forced by the ERA-INTERIM reanalysis over the 1990-2010 period. The comparison of these simulations revealed that (i) the inter-annual variability of the SMB components is consistent within the different resolutions investigated when they are integrated over the whole ice sheet, (ii) the MAR model simulates heavier precipitation on average over the GrIS with decreasing resolution, and (iii) the SMB components (except precipitation) can be derived from a lower-resolution simulation with an enhanced interpolation. This interpolation can also be used to approximate the SMB components over another topography/ice sheet mask of the GrIS. These results are valuable for the forcing of an ice dynamical model, needed to enable full projections of the GrIS mass balance contribution to sea-level rise (SLR) over the coming centuries. Moreover, this work showed that 25 km-resolution MAR simulation is a good compromise between computing time and results precision in the aim to perform afterwards 21st-century projections of the GrIS melt.

The most suited atmosphere-ocean general circulation models (AOGCMs) for the GrIS current climate modelling were selected on the basis of comparison between the 1970-1999 outputs and reanalyses, showing that the representation quality of surface parameters (temperature, precipitation) are highly correlated to the atmospheric circulation and its inter-annual variability (North Atlantic oscillation). Future atmospheric circulation changes according to greenhouse gas (GHG) emissions scenarios were projected to dampen the zonal flow, enhance the meridional fluxes and provide additional heat and moisture to the GrIS, increasing temperature over the whole ice sheet and precipitation over its northeastern area. Moreover, future projections performed with the selected AOGCMs showed consistent anomalies to the present-day climate. The GrIS SMB anomalies from the A1B scenario amount to -300 Gt/yr with respect to 1970-1999, leading to a SLR of 5 cm by the end of the 21st century. This work helped to select the AOGCMs used as forcing fields in the MAR model to carry out future projections of the GrIS.

20th and 21st centuries MAR simulations at 25km resolution forced by previously selected GCMs according to GHG scenarios were performed over the GrIS in order to investigate the projected changes of the surface energy balance (SEB) components driving the surface melt. Analysis of 2000-2100 melt anomalies to 1980–1999 results revealed an exponential relationship of the surface melt to the near-surface temperature anomalies, mainly due to the surface albedo positive feedback associated with the extension of bare ice areas in summer. On the GrIS margins, the future melt anomalies are driven by stronger sensible heat fluxes, induced by enhanced warm air advections. Over the central dry snow zone, the increase of melt surpasses the negative feedback from heavier snowfall inducing a decrease of the summer surface albedo. In addition to the incoming longwave flux increase associated to the atmosphere warming, MAR projected an increase of the cloud cover decreasing the ratio of the incoming shortwave versus longwave radiation and dampening the albedo feedback. This trend of cloud cover is contrary to that simulated by reanalyses-forced MAR over current climate, where the observed melt increase since the 1990’s is rather a consequence of more anticyclonic atmospheric conditions. No significant change was projected in the length of the melt season, highlighting the importance of solar radiation in the melt SEB.

Autre version : http://hdl.handle.net/2268/132087
Fichiers :
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[Public/Internet] abstract-and-contents.pdf 77.28 Kb 00:00:11 < 00:00:01
[Public/Internet] papers.pdf 43.68 Kb 00:00:06 < 00:00:01

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