Preprints
https://doi.org/10.5194/egusphere-2024-1726
https://doi.org/10.5194/egusphere-2024-1726
21 Jun 2024
 | 21 Jun 2024
Status: this preprint is open for discussion.

Modelling firn density at Dye-2 and KAN_U, two sites in the percolation zone of the Greenland ice sheet

Xueyu Zhang, Lin Liu, Brice Noël, and Zhicai Luo

Abstract. Modelling firn density is crucial for understanding the current mass balance of the Greenland ice sheet (GrIS) and predicting its future. As snowmelt increases in a warming climate on the GrIS, accurate information about firn density and its variability over time and space becomes increasingly important in the percolation zone. Previous research indicates that none of the existing models accurately simulate firn properties at sites with varying snowmelt rates due to the limited knowledge of liquid water percolation and the complexity of firn densification. Here, we enhance the representation of the firn densification model based on the Community Firn Model (CFM) by (i) using the stressed-based dry-firn densification scheme and recently published parametrizations for firn characteristics, (ii) modifying the expression of irreducible water in the Darcy-flow scheme, and (iii) allowing the time step to be adaptive. The improved model is employed at two climatologically distinct sites, Dye-2 and KAN_U, two sites in the southwest percolation zone of the GrIS, to evaluate its performance. The modelled firn depth-density profiles at the two study sites generally agree well with the in situ measurements obtained from 16 firn cores drilled between 2012 and 2019. At Dye-2, with comparatively high accumulation and low snowmelt rates, the model simulates thin ice lenses and/or ice layers in the top 10 m of the firn column. The modelled firn density aligns with the average level of observations, with the relative bias in density ranging from 0.36 % to 6 %. At the KAN_U site, characterized by relatively low accumulation and high snowmelt rates, the model captures high-density layers (~917 kg · m-3) caused by the refreezing of liquid water. The observed ice slabs are partly reproduced, and the relative bias in density between simulations and observations at all 8 cores is within ±5 %.

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Xueyu Zhang, Lin Liu, Brice Noël, and Zhicai Luo

Status: open (until 21 Aug 2024)

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  • RC1: 'Comment on egusphere-2024-1726', Baptiste Vandecrux, 25 Jul 2024 reply
Xueyu Zhang, Lin Liu, Brice Noël, and Zhicai Luo
Xueyu Zhang, Lin Liu, Brice Noël, and Zhicai Luo

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Short summary
This study indicates that the overall characteristics of the upper firn density in the percolation zone could be captured by the choice of appropriate model configurations and climatic forcing, which is necessary for understanding the current mass balance of the GrIS and predicting its future. The modelled firn density in this study generally aligns well with observations from 16 cores, with the relative bias in density ranging from 0.36 % to 6 % at Dye-2 and being within ±5 % at KAN_U.