An improved firn densification model by integrating the Bucket scheme and Darcy’s law over the Greenland Ice Sheet

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

Modelling firn densification is conducive to enhancing the accuracy of monitoring glacier mass changes from satellite altimetry and extracting climate records from ice cores. As snowmelt is increasing in a warming climate on the Greenland Ice Sheet (GrIS), quantifying the role of liquid water within the firn layer becomes critical for simulating firn properties. Nevertheless, previously published firn densification models do not accurarely capture the extensive density fluctuations caused by liquid water refreezing in observations. In this study, an improved firn densification model is developed by integrating the Bucket scheme and Darcy’s law to assess the capillary retention, refreezing, and runoff of liquid water within the firn layer. Moreover, the improved model is employed for two study sites, KAN_U and Dye-2, over the GrIS to evaluate its performance. At the KAN_U site, characterized by high snowfall and snowmelt rates, the model captures high-density peaks (~917 kg · m -3) caused by the refreezing of liquid water, which corresponds to the formation of ice lenses or ice layers. At Dye-2 with comparatively limited liquid water, the model also captures the features of high-density layers resulting from refreezing. In general, the modelled firn depth-density profiles at the two study sites agree well with the in situ measurements obtained from 12 firn cores drilled between 2012 and 2019. For the regions with limited liquid water, low-density peaks are probably overestimated due to excess refreezing or limited knowledge of ice lenses or ice layers. Future work is expected to enhance the understanding and further improve numerical simulation of the mechanisms involved in firn densification, and subsequently integrate data-driven and physical mechanisms into firn densification modelling.

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Zhang, Xueyu / Liu, Lin / Noël, Brice / et al: An improved firn densification model by integrating the Bucket scheme and Darcy’s law over the Greenland Ice Sheet. 2024. Copernicus Publications.

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