Understanding Temporal Changes of Glacial Dynamics with Numerical Modeling: A Case Study of Upernavik Isstrm, Greenland
冰川（又稱冰河）的動力特性在空間及時間上有所變化。近數十年，格陵蘭冰川運動轉變加劇融冰，以致全球平均海平面上升，但現時對很多重要影響冰川動力的因素均了解不深。衛星遙感觀測顯示，二零一零年七月間，格陵蘭西部烏佩納凡克地區其中一條冰川的流速，由每年四公里急劇加速至每年六公里。由此觀測結果推動，本項目旨在利用數值模型以探索可導致短期冰川運動變化的潛在因素。利用冰川數值模型「CISM」，我們進行了一系列高空間（一百米）、高時間（一天）解析度的地區性模擬，以研究不同冰川温度、表面質量平衡、以及大型冰山崩解活動對冰川流速的影響。模擬顯示，當冰層温度愈高，冰川速度、和速度變化均較高。 同時模擬結果亦顯示，更...
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| Format: | Text |
| Language: | English Chinese |
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2016
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| Subjects: | |
| Online Access: | https://repository.lib.cuhk.edu.hk/en/item/cuhk-1292284 |
| Summary: | 冰川（又稱冰河）的動力特性在空間及時間上有所變化。近數十年，格陵蘭冰川運動轉變加劇融冰，以致全球平均海平面上升，但現時對很多重要影響冰川動力的因素均了解不深。衛星遙感觀測顯示，二零一零年七月間，格陵蘭西部烏佩納凡克地區其中一條冰川的流速，由每年四公里急劇加速至每年六公里。由此觀測結果推動，本項目旨在利用數值模型以探索可導致短期冰川運動變化的潛在因素。利用冰川數值模型「CISM」，我們進行了一系列高空間（一百米）、高時間（一天）解析度的地區性模擬，以研究不同冰川温度、表面質量平衡、以及大型冰山崩解活動對冰川流速的影響。模擬顯示，當冰層温度愈高，冰川速度、和速度變化均較高。 同時模擬結果亦顯示，更強的冰川表面融化未有導致更高的速度，與常識相反，這因為模型未有考慮冰川對融化導致的水文變化和其於底部滑行之作用。更重要的結果為模擬顯示，大型冰山崩解可引致冰川速度大幅提升，而加速的幅度與崩離冰山的大小有關。然而，因模擬中加入的冰山崩解現象非模型中所包含的物理過程之結果，此結果未能反映冰山崩解所致的加速屬於突變或緩慢過程。下一版本的「CISM」將配備基於實際的冰川崩解物理，有望作為更佳的模型以解決上述問題。 Glaciers, moving ‘ice rivers’, are known to vary their dynamic behaviors across a wide range of spatial and temporal scales. Changes in glacier dynamics in Greenland in recent decades have caused significant ice loss, contributing to global sea level rise. Nonetheless, many key processes in glacier dynamics remain poorly understood or quantified. Satellite observations revealed that one of the outlet glaciers in Upernavik Isstrøm in western Greenland sped up abruptly from about 4 kilometres/year to 6 kilometres/year during July 2010. Motivated by these observations, this study aims to investigate the potential factors and mechanisms that control temporal variations in outlet glacier dynamics through numerical modeling. Using the Community Ice Sheet Model (CISM), we designed and conducted a series of numerical simulations with high spatial (100 metres) and temporal (1 day) resolutions. The numerical experiments have been performed with varying ice temperatures and surface mass balance rates, as well as user-defined large-scale calving events. We found that increasing ice temperatures can lead to higher glacial velocities with greater fluctuations in magnitude. A more negative surface mass balance rate leads to slower velocity. This contradicts a common hypothesis that melting can promote glacial speed-up. This is because the consequential hydrological response after surface melting is not included in the model. Thus, more negative surface mass in CISM only leads to a thinning of glaciers but not an enhancement of ... |
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