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The Cryosphere An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/tc-2019-109
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/tc-2019-109
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 24 May 2019

Research article | 24 May 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal The Cryosphere (TC).

Interannual Variability of Summer Surface Mass Balance and Surface Melting in the Amundsen Sector, West Antarctica

Marion Donat-Magnin1, Nicolas C. Jourdain1, Hubert Gallée1, Charles Amory3, Christoph Kittel3, Xavier Fettweis3, Jonathan D. Wille1, Vincent Favier1, Amine Drira1, and Cécile Agosta2 Marion Donat-Magnin et al.
  • 1Université Grenoble Alpes/CNRS/IRD/G-INP, IGE, 38000, Grenoble, France
  • 2Laboratoire des Sciences du Climat et de l'Environnement, IPSL/CEA-CNRS-UVSQ UMR 8212, CEA Saclay, F-91190, Gif-sur-Yvette, France
  • 3F.R.S.-FNRS, Laboratory of Climatology, Department of Geography, University of Liège, B-4000 Liège, Belgium

Abstract. 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 to 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 atmospheric model MAR at 10 km resolution over the drainage basins of the Amundsen 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 are 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 of 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 NINO34 index only explains 2 to 8 % of SMB or melt rates interannual variance in our simulations, with moderate statistical significance. However, the part explained by NINO34 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.

Marion Donat-Magnin et al.
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MAR Amundsen simulation M. Donat-Magnin and N. C. Jourdain https://doi.org/10.5281/zenodo.2815907

Marion Donat-Magnin et al.
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Short summary
Modelling the interannual variability of the surface conditions over Antarctic glaciers is important for the identification of climate trends, for climate predictions and to assess models. We simulate snow accumulation and surface melting in the Amundsen sector (West Antarctica) over 1979–2017. For all the glaciers, the interannual variability of summer snow accumulation and surface melting are driven by two distinct mechanisms related to variations of the Amundsen Sea Low strength and position.
Modelling the interannual variability of the surface conditions over Antarctic glaciers is...
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