An evaluation of a physics-based firn model and a semi-empirical firn model across the Greenland Ice Sheet (1980–2020)

IF 4.4 2区 地球科学 Q1 GEOGRAPHY, PHYSICAL Cryosphere Pub Date : 2023-05-25 DOI:10.5194/tc-17-2185-2023
M. Thompson-Munson, N. Wever, C. Stevens, J. Lenaerts, B. Medley
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引用次数: 3

Abstract

Abstract. The Greenland Ice Sheet's (GrIS) firn layer buffers the ice sheet's contribution to sea level rise by storing meltwater in its pore space. However, available pore space and meltwater retention capability is lost due to ablation of the firn layer and refreezing of meltwater as near-surface ice slabs in the firn. Understanding how firn properties respond to climate is important for constraining the GrIS's future contribution to sea level rise in a warming climate. Observations of firn density provide detailed information about firn properties, but they are spatially and temporally limited. Here we use two firn models, the physics-based SNOWPACK model and the Community Firn Model configured with a semi-empirical densification equation (CFM-GSFC), to quantify firn properties across the GrIS from 1980 through 2020. We use an identical forcing (Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2) atmospheric reanalysis) for SNOWPACK and the CFM-GSFC in order to isolate firn model differences. To evaluate the models, we compare simulated firn properties, including firn air content (FAC), to measurements from the Surface Mass Balance and Snow on Sea Ice Working Group (SUMup) dataset of snow and firn density. Both models perform well (mean absolute percentage errors of 14 % in SNOWPACK and 16 % in the CFM-GSFC), though their performance is hindered by the spatial resolution of the atmospheric forcing. In the ice-sheet-wide simulations, the 1980–1995 average spatially integrated FAC (i.e., air volume in the firn) for the upper 100 m is 34 645 km3 from SNOWPACK and 28 581 km3 from the CFM-GSFC. The discrepancy in the magnitude of the modeled FAC stems from differences in densification with depth and variations in the sensitivity of the models to atmospheric forcing. In more recent years (2005–2020), both models simulate substantial depletion of pore space. During this period, the spatially integrated FAC across the entire GrIS decreases by 3.2 % (−66.6 km3 yr−1) in SNOWPACK and 1.5 % (−17.4 km3 yr−1) in the CFM-GSFC. These differing magnitudes demonstrate how model differences propagate throughout the FAC record. Over the full modeled record (1980–2020), SNOWPACK simulates a loss of pore space equivalent to 3 mm of sea level rise buffering, while the CFM-GSFC simulates a loss of 1 mm. The greatest depletion in FAC is along the margins and especially along the western margin where observations and models show the formation of near-surface, low-permeability ice slabs that may inhibit meltwater storage.
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对格陵兰冰盖上基于物理的firn模型和半经验firn模型的评估(1980-2020)
摘要格陵兰冰盖(GrIS)的冷杉层通过将融水储存在其孔隙空间来缓冲冰盖对海平面上升的贡献。然而,由于firn层的消融和融水在firn中作为近表面冰盖的重新冻结,可用孔隙空间和融水保持能力丧失。了解冷杉的特性如何对气候做出反应,对于限制GrIS在气候变暖的情况下对海平面上升的未来贡献至关重要。冷杉密度的观测提供了有关冷杉特性的详细信息,但它们在空间和时间上都是有限的。在这里,我们使用两个firn模型,基于物理的SNOWPACK模型和配置有半经验致密化方程(CFM-GSFC)的社区firn模型来量化1980年至2020年GrIS的firn特性。我们对SNOWPACK和CFM-GSFC使用了相同的强迫(现代研究与应用回顾分析,第2版(MERRA-2)大气再分析),以隔离firn模型的差异。为了评估这些模型,我们将模拟的冷杉特性(包括冷杉空气含量(FAC))与地表质量平衡和海冰上雪工作组(SUMup)的雪和冷杉密度数据集的测量结果进行了比较。两个模型都表现良好(平均绝对百分比误差为14 % 在雪包和16 % 尽管它们的性能受到大气强迫的空间分辨率的阻碍。在整个冰盖的模拟中,1980–1995年的平均空间积分FAC(即firn中的空气体积)为100 m是34 645 距离雪包和28公里 581 km3。模拟FAC大小的差异源于随深度的致密化差异以及模型对大气强迫的敏感性变化。在最近几年(2005-2020),这两个模型都模拟了孔隙空间的大量消耗。在此期间,整个GrIS的空间积分FAC减少了3.2 % (−66.6 km3 yr−1)和1.5 % (−17.4 km3 yr−1)。这些不同的幅度说明了模型差异如何在FAC记录中传播。在完整的建模记录(1980-2020)中,SNOWPACK模拟了相当于3的孔隙空间损失 毫米的海平面上升缓冲,而CFM-GSFC模拟1的损失 FAC的最大损耗是沿边缘,尤其是沿西部边缘,在那里,观测和模型显示形成了可能抑制融水储存的近地表低渗透冰盖。
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来源期刊
Cryosphere
Cryosphere GEOGRAPHY, PHYSICAL-GEOSCIENCES, MULTIDISCIPLINARY
CiteScore
8.70
自引率
17.30%
发文量
240
审稿时长
4-8 weeks
期刊介绍: The Cryosphere (TC) is a not-for-profit international scientific journal dedicated to the publication and discussion of research articles, short communications, and review papers on all aspects of frozen water and ground on Earth and on other planetary bodies. The main subject areas are the following: ice sheets and glaciers; planetary ice bodies; permafrost and seasonally frozen ground; seasonal snow cover; sea ice; river and lake ice; remote sensing, numerical modelling, in situ and laboratory studies of the above and including studies of the interaction of the cryosphere with the rest of the climate system.
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