Preprints
https://doi.org/10.5194/egusphere-2022-745
https://doi.org/10.5194/egusphere-2022-745
 
22 Aug 2022
22 Aug 2022

Improving modelled albedo over the Greenland ice sheet through parameter optimisation and MODIS retrievals

Nina Raoult1, Sylvie Charbit1, Christophe Dumas1, Fabienne Maignan1, Catherine Ottlé1, and Vladislav Bastrikov2 Nina Raoult et al.
  • 1Laboratoire des Sciences du Climat et de l’Environnement, LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay, Gif-sur-Yvette, France
  • 2Science Partners, Paris, France

Abstract. Greenland ice sheet mass loss continues to accelerate as global temperatures increase. The surface albedo of the ice sheet determines the amount of absorbed solar energy, which is a key factor in driving surface snow and ice melting. Satellite retrieved albedo allows us to compare and optimise modelled albedo over the entirety of the ice sheet. We optimise the parameters of the albedo scheme in the ORCHIDEE land surface model for three random years taken over the 2000–2017 period and validate over the remaining years. In particular, we want to improve the albedo at the edges of the ice sheet since they correspond to ablation areas and show the greatest variations in runoff and surface mass balance. By giving a larger weight to points at the ice sheet's edge, we improve the model-data fit by reducing the RMSD by over 25 % for the whole ice sheet for the summer months. This improvement is consistent for all years, even those not used in the calibration step. We conclude by showing which additional model outputs are impacted by changes to the albedo parameters encouraging future work using multiple data streams for optimisation.

Nina Raoult et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-745', Anonymous Referee #1, 17 Oct 2022
    • AC1: 'Reply on RC1', Nina Raoult, 02 Dec 2022
  • RC2: 'Comment on egusphere-2022-745', Anonymous Referee #2, 22 Oct 2022
    • AC2: 'Reply on RC2', Nina Raoult, 02 Dec 2022
  • EC1: 'Comment on egusphere-2022-745', Patricia de Rosnay, 04 Nov 2022

Nina Raoult et al.

Nina Raoult et al.

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Short summary
Greenland ice sheet melting due to global warming could significantly impact the global sea-level rise. The ice sheet's albedo, i.e., how reflective the surface is, affects the melting speed. The ORCHIDEE computer model is used to simulate albedo and snow melt to make predictions. However, the albedo in ORCHIDEE is lower than that observed using satellites. To correct this, we change model parameters (e.g., the rate of snow decay) to reduce the difference between simulated and observed values.