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Widespread slowdown in thinning rates of West Antarctic ice shelves 南极西部冰架减薄速度普遍放缓
IF 5.2 2区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2023-08-23 DOI: 10.5194/tc-17-3409-2023
F. Paolo, A. Gardner, C. Greene, J. Nilsson, M. Schodlok, N. Schlegel, H. Fricker
Abstract. Antarctica's floating ice shelves modulate discharge ofgrounded ice into the ocean by providing a backstress. Ice shelf thinningand grounding line retreat have reduced this backstress, driving rapiddrawdown of key unstable areas of the Antarctic Ice Sheet, leading to sea-level rise. If ice shelf loss continues, it may initiate irreversibleglacier retreat through the marine ice sheet instability. Identification ofareas undergoing significant change requires knowledge of spatial andtemporal patterns in recent ice shelf loss. We used 26 years (1992–2017)of satellite-derived Antarctic ice shelf thickness, flow, and basal meltrates to construct a time-dependent dataset of ice shelf thickness and basalmelt on a 3 km grid every 3 months. We used a novel data fusion approach,state-of-the-art satellite-derived velocities, and a new surface massbalance model. Our data revealed an overall pattern of thinning all aroundAntarctica, with a thinning slowdown starting around 2008 widespread acrossthe Amundsen, Bellingshausen, and Wilkes sectors. We attribute this slowdownpartly to modulation in external ocean forcing, altered in West Antarcticaby negative feedbacks between ice shelf thinning rates and grounded iceflow, and sub-ice-shelf cavity geometry and basal melting. In agreement withearlier studies, the highest rates of ice shelf thinning are found for those iceshelves located in the Amundsen and Bellingshausen sectors. Our studyreveals that over the 1992–2017 observational period the Amundsen andBellingshausen ice shelves experienced a slight reduction in rates of basalmelting, suggesting that high rates of thinning are largely a response tochanges in ocean conditions that predate our satellite altimetry record,with shorter-term variability only resulting in small deviations from thelong-term trend. Our work demonstrates that causal inference drawn from iceshelf thinning and basal melt rates must take into account complex feedbacksbetween thinning and ice advection and between ice shelf draft and basalmelt rates.
摘要南极洲的浮动冰架通过提供一个反向压力来调节向海洋排放的结冰。冰架变薄和接地线退缩减少了这种背景压力,导致南极冰盖关键不稳定区域的快速下降,导致海平面上升。如果冰架的消失持续下去,它可能会通过海洋冰盖的不稳定性引发不可逆转的冰川退缩。识别正在发生重大变化的原因需要了解最近冰架损失的空间和时间模式。我们使用了26年(1992-2017)的卫星得出的南极冰架厚度、流量和基底熔体,构建了一个3 km电网每3个月。我们使用了一种新的数据融合方法、最先进的卫星速度和新的表面质量平衡模型。我们的数据揭示了整个南极洲的总体减薄模式,从2008年左右开始,减薄放缓在阿蒙森、贝灵山和威尔克斯板块普遍存在。我们将这种缓慢归因于外部海洋强迫的调节,在西南极洲,冰架变薄率和搁浅冰流之间的负反馈、亚冰架空腔几何形状和基底融化改变了这种调节。与早期的研究一致,位于阿蒙森和别林斯豪森地区的冰架减薄率最高。我们的研究表明,在1992-2017年的观测期内,阿蒙森冰架和别林斯豪森冰架的基底融化率略有下降,这表明高减薄率在很大程度上是对我们的卫星测高记录之前海洋条件变化的反应,短期变化只会导致与长期趋势的微小偏差。我们的工作表明,从冰架变薄和基底融化速率得出的因果推断必须考虑到变薄和冰平流之间以及冰架吃水深度和基底融化率之间的复杂反馈。
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引用次数: 4
Spatially continuous snow depth mapping by aeroplane photogrammetry for annual peak of winter from 2017 to 2021 in open areas 开放地区2017 - 2021年冬季年高峰的飞机摄影测量空间连续雪深制图
IF 5.2 2区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2023-08-22 DOI: 10.5194/tc-17-3383-2023
Leon J. Bührle, M. Marty, Lucie A. Eberhard, A. Stoffel, Elisabeth D. Hafner, Y. Bühler
Abstract. Information on snow depth and its spatial distribution is important fornumerous applications, including natural hazard management, snow waterequivalent estimation for hydropower, the study of the distribution andevolution of flora and fauna, and the validation of snow hydrologicalmodels. Due to its heterogeneity and complexity, specific remote sensingtools are required to accurately map the snow depth distribution in Alpineterrain. To cover large areas (>100 km2),airborne laser scanning (ALS) or aerial photogrammetry with large-formatcameras is needed. While both systems require piloted aircraft for dataacquisition, ALS is typically more expensive than photogrammetry but yieldsbetter results in forested terrain. While photogrammetry is slightlycheaper, it is limited due to its dependency on favourable acquisitionconditions (weather, light conditions). In this study, we presentphotogrammetrically processed high-spatial-resolution (0.5 m) annual snowdepth maps, recorded during the peak of winter over a 5-year period underdifferent acquisition conditions over a study area around Davos,Switzerland. Compared to previously carried out studies, using the VexcelUltraCam Eagle Mark 3 (M3) sensor improves the average ground sampling distance to0.1 m at similar flight altitudes above ground. This allows for verydetailed snow depth maps in open areas, calculated by subtracting a snow-offdigital terrain model (DTM, acquired with ALS) from the snow-on digitalsurface models (DSMs) processed from the airborne imagery. Despitechallenging acquisition conditions during the recording of the UltraCamimages (clouds, shaded areas and fresh snow), 99 % of unforested areaswere successfully photogrammetrically reconstructed. We applied masks (highvegetation, settlements, water, glaciers) to increase the reliability of thesnow depth calculations. An extensive accuracy assessment was carried outusing check points, the comparison to DSMs derived from unpiloted aerialsystems and the comparison of snow-free DSM pixels to the ALS DTM. Theresults show a root mean square error of approximately 0.25 m for theUltraCam X and 0.15 m for the successor, the UltraCam Eagle M3. We developeda consistent and reliable photogrammetric workflow for accurate snow depthdistribution mapping over large regions, capable of analysing snowdistribution in complex terrain. This enables more detailed investigationson seasonal snow dynamics and can be used for numerous applications relatedto snow depth distribution, as well as serving as a ground reference for newmodelling approaches and satellite-based snow depth mapping.
摘要雪深及其空间分布信息在许多应用中都很重要,包括自然灾害管理、水电站雪水当量估计、动植物分布和进化研究以及雪水文模型的验证。由于其异质性和复杂性,需要特定的遥感工具来准确绘制Alpineterrain的雪深分布图。覆盖大面积(>100 km2)、机载激光扫描(ALS)或具有大格式相机的航空摄影测量。虽然这两个系统都需要有人驾驶的飞机进行数据采集,但ALS通常比摄影测量更昂贵,但在森林地形中效果更好。虽然摄影测量有点小,但由于它依赖于有利的获取条件(天气、光照条件),所以它是有限的。在这项研究中,我们提出了经过摄影测量处理的高空间分辨率(0.5 m) 在瑞士达沃斯周围的一个研究区域,在不同的采集条件下,在5年的冬季高峰期记录的年度积雪深度图。与之前进行的研究相比,使用VexcelUltraCam Eagle Mark 3(M3)传感器将平均地面采样距离提高到0.1 m,在地面以上类似的飞行高度。这允许在开阔地区绘制非常详细的雪深图,通过从航空图像处理的数字地面上的雪模型(DSM)中减去数字地形模型外的雪(DTM,用ALS获取)来计算。UltraCam图像记录过程中极具挑战性的采集条件(云层、阴影区域和新鲜雪),99 % 成功地对未受挤压的区域进行了摄影测量重建。我们应用了遮罩(高植被、定居点、水、冰川)来提高现在深度计算的可靠性。使用检查点进行了广泛的精度评估,与无人驾驶航空系统得出的DSM进行了比较,并将无雪DSM像素与ALS DTM进行了比较。结果显示均方根误差约为0.25 m用于UltraCam X和0.15 m代表继任者UltraCam Eagle M3。我们开发了一个一致可靠的摄影测量工作流程,用于大面积精确的积雪深度分布测绘,能够分析复杂地形中的积雪分布。这使得能够对季节性雪动力学进行更详细的研究,并可用于与雪深度分布相关的许多应用,以及作为新建模方法和基于卫星的雪深度测绘的地面参考。
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引用次数: 0
A model for the Arctic mixed layer circulation under a summertime lead: implications for the near-surface temperature maximum formation 夏季主导下的北极混合层环流模型:对近地表温度最高值形成的影响
IF 5.2 2区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2023-08-21 DOI: 10.5194/tc-17-3343-2023
A. Alvarez
Abstract. Leads in sea ice cover have been studied extensively because of the climatic relevance of the intense ocean–atmosphere heat exchange that occursduring winter. Leads are also preferential locations of heat exchange and melting in early summer, but their oceanography and climate relevance, ifany, remains largely unexplored during summertime. In particular, the development of a near-surface temperature maximum (NSTM) layer typically10–30 m deep under different Arctic basins has been observationally related to the penetration of solar radiation through the leads. Theseobservations reveal that the concatenation of calm and wind events in the leads could facilitate the development of the NSTM layer. Using numericalmodeling and an idealized framework, this study investigates the formation of the NSTM layer under a summer lead exposed to a combination of calmand moderate wind periods. During the calm period, solar heat accumulates in the upper layers under the lead. Near-surface convection cells aregenerated daily, extending from the lead sides to its center. Convection cells affect the heat storage in the mixed layer under the lead and theadjacent ice cap. A subsequent wind event (and corresponding ice drift) mixes and spreads fresh and cold meltwater into the warm layers near thesurface. Surface mixing results in temperatures in the near-surface layers that are lower than in the deeper layers, where the impact of the surfacestresses is weaker. Additionally, the warm waters initially located under the lead surface stretch and spread horizontally. Thus, an NSTM layer isformed. The study analyzes the sensitivity of the depth and temperature of the NSTM layer to buoyancy forcing, wind intensity, ice drift, stratification,and lead geometry. Numerical results suggest that the NSTM layer appears with moderate wind and ice drift and disappears when the wind intensity ishigher than 9 m s−1. Depending on the background stratification, the calm period reinforces or becomes critical in NSTM layerformation. According to the results, ice drift is key to the development of the NSTM layer.
摘要由于冬季发生的强烈海洋-大气热交换的气候相关性,海冰覆盖中的铅已被广泛研究。铅也是初夏热交换和融化的首选地点,但它们的海洋学和气候相关性,如果有的话,在夏季仍未得到很大程度的探索。特别是,在不同的北极盆地下,一个典型的10 - 30 m深的近地表最高温度(NSTM)层的发展,在观测上与太阳辐射穿过引线的穿透有关。这些观测结果表明,导联中的平静事件和风事件的串联可以促进NSTM层的发展。利用数值模拟和一个理想化的框架,本研究调查了夏季铅暴露在平静和温和风期的组合下NSTM层的形成。在平静期,太阳热量在铅下的上层积聚。近地表对流单元每天都在产生,从前边一直延伸到中心。对流细胞影响铅和邻近冰盖下的混合层中的热量储存。随后的风事件(以及相应的冰漂移)将新鲜和冷的融水混合并传播到靠近地表的温暖层中。表面混合导致近表层温度低于深层温度,而深层温度受表面应力的影响较弱。此外,最初位于铅表面下的温暖水域伸展并水平扩散。因此,形成了一个NSTM层。该研究分析了NSTM层的深度和温度对浮力强迫、风强度、冰漂移、分层和铅几何形状的敏感性。数值结果表明,NSTM层以中等风和冰漂移出现,当风强度大于9 m s−1时消失。根据背景分层的不同,平静期在NSTM层的形成中会加强或变得至关重要。结果表明,冰的漂移是NSTM层发育的关键。
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引用次数: 0
Permafrost saline water and Early to mid-Holocene permafrost aggradation in Svalbard 斯瓦尔巴群岛永久冻土咸水与全新世早期至中期永久冻土退化
IF 5.2 2区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2023-08-21 DOI: 10.5194/tc-17-3363-2023
Dotan Rotem, V. Lyakhovsky, H. Christiansen, Y. Harlavan, Y. Weinstein
Abstract. Deglaciation in Svalbard was followed by seawateringression and deposition of marine (deltaic) sediments in fjord valleys,while elastic rebound resulted in fast land uplift and the exposure of these sediments to the atmosphere, whereby the formation of epigenetic permafrost was initiated. This was then followed by the accumulation of aeolian sediments, with syngenetic permafrost formation. Permafrost was studied in the eastern Adventdalen valley, Svalbard, 3–4 km from the maximum up-valley reach ofpost-deglaciation seawater ingression, and its ground ice was analysed forits chemistry. While ground ice in the syngenetic part is basically fresh,the epigenetic part has a frozen freshwater–saline water interface (FSI), withchloride concentrations increasing from the top of the epigenetic part (at5.5 m depth) to about 15 % that of seawater at 11 m depth. We applied a one-dimensional freezing model to examine the rate of top-down permafrostformation, which could be accommodated by the observed frozen FSI. The modelexamined permafrost development under different scenarios of mean averageair temperature, water freezing temperature and degree of pore-waterfreezing. We found that even at the relatively high air temperatures of theEarly to mid-Holocene, permafrost could aggrade quite fast down to 20 to 37 m (the whole sediment fill of 25 m at this location) within 200 years. This, in turn, allowed freezing and preservation of the freshwater–saline waterinterface despite the relatively fast rebound rate, which apparentlyresulted in an increase in topographic gradients toward the sea. Thepermafrost aggradation rate could also be enhanced due to non-complete pore-water freezing. We conclude that freezing must have started immediatelyafter the exposure of the marine sediment to atmospheric conditions.
摘要斯瓦尔巴群岛的冰川消融之后,峡湾山谷中的海洋(三角洲)沉积物发生了海侵和沉积,而弹性反弹导致了快速的陆地抬升和这些沉积物暴露在大气中,从而开始了表观古冻土的形成。随后是风成沉积物的堆积,形成了同生的永久冻土。对斯瓦尔巴群岛Adventdalen山谷东部3-4年的永久冻土进行了研究 距冰川后期海水入侵的最大河谷上游km,并对其地面冰的化学性质进行了分析。虽然同生部分的地面冰基本上是新鲜的,但表观遗传部分有一个冻结的淡水-盐水界面(FSI),氯化物浓度从表观遗传顶部开始增加(5.5 m深度)至约15 % 海水在11 m深度。我们应用一维冻结模型来检查自上而下的永久冻结速率,这可以通过观察到的冻结FSI来调节。该模型考察了多年冻土在平均气温、水冻结温度和孔隙水冻结程度等不同情景下的发展。我们发现,即使在全新世早期至中期相对较高的气温下,永久冻土也会迅速沉积到20至37 m(25的整个沉积物填充 m)。这反过来又允许淡水-盐水界面的冻结和保存,尽管回弹率相对较快,这显然导致了向海洋的地形梯度增加。由于孔隙水的非完全冻结,永久冻土的沉积速率也可能提高。我们得出的结论是,海洋沉积物暴露在大气条件下后,一定立即开始结冰。
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引用次数: 1
Patterns of wintertime Arctic sea-ice leads and their relation to winds and ocean currents 冬季北极海冰的形态及其与风和洋流的关系
IF 5.2 2区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2023-08-17 DOI: 10.5194/tc-17-3291-2023
S. Willmes, G. Heinemann, F. Schnaase
Abstract. We use a novel sea-ice lead climatology for the winters of 2002/03 to 2020/21 based on satellite observations with 1 km2 spatial resolution to identify predominant patterns in Arctic wintertime sea-ice leads. The causes for the observed spatial and temporal variabilities are investigated using ocean surface current velocities and eddy kinetic energies from an ocean model (Finite Element Sea Ice–Ice-Shelf–Ocean Model, FESOM) and winds from a regional climate model (CCLM) and ERA5 reanalysis, respectively. The presented investigation provides evidence for an influence of ocean bathymetry and associated currents on the mechanic weakening of sea ice and the accompanying occurrence of sea-ice leads with their characteristic spatial patterns. While the driving mechanisms for this observation are not yet understood in detail, the presented results can contribute to opening new hypotheses on ocean–sea-ice interactions. The individual contribution of ocean and atmosphere to regional lead dynamics is complex, and a deeper insight requires detailed mechanistic investigations in combination with considerations of coastal geometries. While the ocean influence on lead dynamics seems to act on a rather long-term scale (seasonal to interannual), the influence of wind appears to trigger sea-ice lead dynamics on shorter timescales of weeks to months and is largely controlled by individual events causing increased divergence. No significant pan-Arctic trends in wintertime leads can be observed.
摘要基于卫星观测,我们对2002/03年至2020/21年冬季使用了一种新的海冰铅气候学 平方公里的空间分辨率,以确定北极冬季海冰导线的主要模式。分别使用海洋模型(有限元海冰-冰架-海洋模型,FESEM)的海面流速和涡动能以及区域气候模型(CCLM)和ERA5再分析的风,研究了观测到的空间和时间变化的原因。所提出的调查提供了证据,证明海洋测深和相关洋流对海冰的机械弱化以及伴随而来的海冰引线的出现及其特征空间模式的影响。虽然这一观测的驱动机制尚未得到详细了解,但所提供的结果有助于开启关于海洋-海冰相互作用的新假设。海洋和大气对区域铅动力学的单独贡献是复杂的,需要结合海岸几何形状的考虑进行详细的机制调查才能更深入地了解。虽然海洋对铅动力学的影响似乎是长期的(季节性到年际性),但风的影响似乎在几周到几个月的较短时间尺度上触发了海冰铅动力学,并且在很大程度上受到导致差异增加的个别事件的控制。没有观察到冬季铅的明显泛北极趋势。
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引用次数: 1
Modelling the development and decay of cryoconite holes in northwestern Greenland 格陵兰岛西北部冰锥洞的发育和衰变模型
IF 5.2 2区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2023-08-17 DOI: 10.5194/tc-17-3309-2023
Y. Onuma, Koji Fujita, N. Takeuchi, M. Niwano, T. Aoki
Abstract. Cryoconite holes (CHs) are water-filled cylindrical holes with cryoconite (dark-coloured sediment) deposited at their bottoms, forming on ablatingice surfaces of glaciers and ice sheets worldwide. Because the collapse of CHs may disperse cryoconite on the ice surface, thereby decreasing theice surface albedo, accurate simulation of the temporal changes in CH depth is essential for understanding ice surface melt. We established a novelmodel that simulates the temporal changes in CH depth using heat budgets calculated independently at the ice surface and CH bottom based onhole-shaped geometry. We evaluated the model with in situ observations of the CH depths on the Qaanaaq ice cap in northwestern Greenland during the2012, 2014, and 2017 melt seasons. The model reproduced the observed depth changes and timing of CH collapse well. Although earlier models haveshown that CH depth tends to be deeper when downward shortwave radiation is intense, our sensitivity tests suggest that deeper CH tends to form whenthe diffuse component of downward shortwave radiation is dominant, whereas CHs tend to be shallower when the direct component is dominant. Inaddition, the total heat flux to the CH bottom is dominated by shortwave radiation transmitted through ice rather than that directly from theCH mouths when the CH is deeper than 0.01 m. Because the shortwave radiation transmitted through ice can reach the CH bottom regardless ofCH diameter, CH depth is unlikely to be correlated with CH diameter. The relationship is consistent with previous observationalstudies. Furthermore, the simulations highlighted that the difference in albedo between ice surface and CH bottom was a key factor for reproducingthe timing of CH collapse. It implies that lower ice surface albedo could induce CH collapse and thus cause further lowering of the albedo. Heatcomponent analysis suggests that CH depth is governed by the balance between the intensity of the diffuse component of downward shortwave radiationand the turbulent heat transfer. Therefore, these meteorological conditions may be important factors contributing to the recent surface darkening ofthe Greenland ice sheet and other glaciers via the redistribution of CHs.
摘要冰晶石孔(CH)是一种充满水的圆柱形孔,底部沉积有冰晶石(深色沉积物),形成于世界各地冰川和冰盖的消融表面。由于CH的坍塌可能会将冰锥分散在冰面上,从而降低冰面反照率,因此准确模拟CH深度的时间变化对于理解冰面融化至关重要。我们建立了一个新颖的模型,该模型使用基于孔形几何形状在冰面和CH底部独立计算的热量预算来模拟CH深度的时间变化。我们通过在2012年、2014年和2017年融化季节对格陵兰西北部卡纳克冰盖CH深度的现场观测对该模型进行了评估。该模型再现了观测到的CH坍塌井的深度变化和时间。尽管早期的模型表明,当向下短波辐射强烈时,CH深度往往更深,但我们的灵敏度测试表明,当向下短波辐射的扩散分量占主导时,CH往往形成更深的CH,而当直接分量占主导权时,CH往往较浅。此外,当CH深度大于0.01时,到达CH底部的总热通量主要由通过冰传输的短波辐射控制,而不是直接来自CH口的短波辐射 m。由于通过冰传输的短波辐射可以到达CH底部,而与CH直径无关,因此CH深度不太可能与CH直径相关。这种关系与以前的观测研究一致。此外,模拟强调,冰面和CH底部反照率的差异是再现CH坍塌时间的关键因素。这意味着较低的冰面反照率可能导致CH崩塌,从而导致反照率的进一步降低。热分量分析表明,CH深度由向下短波辐射的扩散分量强度和湍流传热之间的平衡决定。因此,这些气象条件可能是通过甲烷的重新分布导致格陵兰冰盖和其他冰川最近表面变暗的重要因素。
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引用次数: 1
Exploring the potential of thermal infrared remote sensing to improve a snowpack model through an observing system simulation experiment 通过观测系统模拟实验探索热红外遥感技术改进积雪模型的潜力
IF 5.2 2区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2023-08-17 DOI: 10.5194/tc-17-3329-2023
E. Alonso‐González, S. Gascoin, Sara Arioli, G. Picard
Abstract. The assimilation of data from Earth observation satellites intonumerical models is considered to be the path forward to estimate snow coverdistribution in mountain catchments, providing accurate information on themountainous snow water equivalent (SWE). The land surface temperature (LST)can be observed from space, but its potential to improve SWE simulationsremains underexplored. This is likely due to the insufficient temporal orspatial resolution offered by the current thermal infrared (TIR) missions.However, three planned missions will provide global-scale TIR data at muchhigher spatiotemporal resolution in the coming years. To investigate the value of TIR data to improve SWE estimation, we developeda synthetic data assimilation (DA) experiment at five snow-dominated sitescovering a latitudinal gradient in the Northern Hemisphere. We generatedsynthetic true LST and SWE series by forcing an energy balance snowpackmodel with the ERA5-Land reanalysis. We used this synthetic true LST torecover the synthetic true SWE from a degraded version of ERA5-Land. Wedefined different observation scenarios to emulate the revisiting times ofLandsat 8 (16 d) and the Thermal infraRed Imaging Satellite forHigh-resolution Natural resource Assessment (TRISHNA) (3 d) whileaccounting for cloud cover. We replicated the experiments 100 times at eachexperimental site to assess the robustness of the assimilation process withrespect to cloud cover under both revisiting scenarios. We performed theassimilation using two different approaches: a sequential scheme (particlefilter) and a smoother (particle batch smoother). The results show that LST DA using the smoother reduced the normalized rootmean square error (nRMSE) of the SWE simulations from 61 % (open loop) to17 % and 13 % for 16 d revisit and 3 d revisit respectively in theabsence of clouds. We found similar but higher nRMSE values by removingobservations due to cloud cover but with a substantial increase in thestandard deviation of the nRMSE of the replicates, highlighting theimportance of revisiting times in the stability of the assimilationperformance. The smoother largely outperformed the particle filteralgorithm, suggesting that the capability of a smoother to propagate theinformation along the season is key to exploit LST information for snowmodelling. Finally, we have compared the benefit of assimilating LST withsynthetic observations of fractional snow cover area (FSCA). LST DAperformed better than FSCA DA in all the study sites, suggesting that theinformation provided by LST is not limited to the duration of the snowseason. These results suggest that the LST data assimilation has anunderappreciated potential to improve snowpack simulations and highlight thevalue of upcoming TIR missions to advance snow hydrology.
摘要将对地观测卫星数据同化到数值模式中被认为是估计山区集水区积雪分布的前进路径,提供了山区雪水当量(SWE)的准确信息。陆地表面温度(LST)可以从太空观测到,但其改善SWE模拟的潜力仍未得到充分探索。这可能是由于当前热红外(TIR)任务提供的时间或空间分辨率不足。然而,三个计划中的任务将在未来几年以更高的时空分辨率提供全球尺度的TIR数据。为了探讨TIR数据对提高SWE估计的价值,我们在北半球5个积雪覆盖的站点进行了综合数据同化(DA)实验。我们利用ERA5-Land再分析强迫能量平衡积雪模型生成了合成的真实地表温度和SWE序列。我们使用这种合成真LST来从退化版本的ERA5-Land中恢复合成真SWE。我们定义了不同的观测情景,以模拟landsat 8 (16 d)和用于高分辨率自然资源评估的热红外成像卫星(TRISHNA) (3 d)的重访时间,同时考虑云层覆盖。我们在每个实验地点重复了100次实验,以评估两种重访情景下同化过程相对于云覆盖的稳健性。我们使用两种不同的方法进行同化:顺序方案(粒子过滤器)和平滑(粒子批平滑)。结果表明,在无云条件下,LST DA在16 d重访和3 d重访时,将SWE模拟的归一化均方根误差(nRMSE)分别从61%(开环)降低到17%和13%。我们发现相似的,但更高的nRMSE值通过去除观测由于云层覆盖,但在重复的nRMSE的标准偏差大幅增加,突出重访时间在同化性能的稳定性的重要性。平滑器在很大程度上优于粒子滤波算法,这表明平滑器沿季节传播信息的能力是利用地表温度信息进行雪建模的关键。最后,我们比较了同化地表温度与合成积雪面积(FSCA)观测的效益。LST数据在所有研究点的表现都优于FSCA数据,这表明LST提供的信息并不局限于雪季的持续时间。这些结果表明,地表温度数据同化在改善积雪模拟方面具有未被充分认识的潜力,并突出了即将到来的TIR任务在推进积雪水文方面的价值。
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引用次数: 0
A long-term proxy for sea ice thickness in the Canadian Arctic: 1996–2020 加拿大北极海冰厚度的长期指标:1996-2020
IF 5.2 2区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2023-08-15 DOI: 10.5194/tc-17-3269-2023
I. Glissenaar, J. Landy, D. Babb, G. Dawson, S. Howell
Abstract. This study presents a long-term winter sea ice thickness proxy product for the Canadian Arctic based on a random forest regression model – applied to ice charts and scatterometer data, trained on CryoSat-2 observations, and applying an ice type–sea ice thickness correction using the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) – that provides 25 years of sea ice thickness in the Beaufort Sea, Baffin Bay, and, for the first time, the Canadian Arctic Archipelago. An evaluation of the product with in situ sea ice thickness measurements shows that the presented sea ice thickness proxy product correctly estimates the magnitudes of the ice thickness and accurately captures spatial and temporal variability. The product estimates sea ice thickness within 30 to 50 cm uncertainty from the model. The sea ice thickness proxy product shows that sea ice is thinning over most of the Canadian Arctic, with a mean trend of −0.82 cm yr−1 in April over the whole study area (corresponding to 21 cm thinning over the 25-year record), but that trends vary locally. The Beaufort Sea and Baffin Bay show significant negative trends during all months, though with peaks in November (−2.8 cm yr−1) and April (−1.5 cm yr−1), respectively. The Parry Channel, which is part of the Northwest Passage and relevant for shipping, shows significant thinning in autumn. The sea ice thickness proxy product provides, for the first time, the opportunity to study long-term trends and variability in sea ice thickness in the Canadian Arctic, including the narrow channels in the Canadian Arctic Archipelago.
摘要这项研究基于随机森林回归模型,提出了加拿大北极冬季海冰厚度的长期代理产品,该模型应用于冰图和散射仪数据,并在CryoSat-2观测上进行了训练,以及应用冰类型——使用泛北冰洋冰洋建模和同化系统(PIOMAS)进行海冰厚度校正——首次提供了波弗特海、巴芬湾和加拿大北极群岛25年的海冰厚度。通过现场海冰厚度测量对该产品进行的评估表明,所提出的海冰厚度代理产品正确地估计了冰厚度的大小,并准确地捕捉了空间和时间变化。该产品估计海冰厚度在30到50之间 cm模型的不确定性。海冰厚度代理产品显示,加拿大北极大部分地区的海冰正在变薄,平均趋势为-0.82 厘米 整个研究区域的4月1年(对应21年 在25年的记录中变薄了厘米),但这种趋势在当地有所不同。波弗特海和巴芬湾在所有月份都呈现出显著的负面趋势,尽管在11月达到峰值(-2.8 厘米 1年)和4月(-1.5 厘米 yr−1)。帕里海峡是西北航道的一部分,与航运有关,秋季明显变薄。海冰厚度代理产品首次为研究加拿大北极海冰厚度的长期趋势和变化提供了机会,包括加拿大北极群岛的狭窄航道。
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引用次数: 0
Everest South Col Glacier did not thin during the period 1984–2017 1984年至2017年期间,珠峰南冷冰川没有变薄
IF 5.2 2区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2023-08-11 DOI: 10.5194/tc-17-3251-2023
F. Brun, O. King, M. Réveillet, C. Amory, Anton Planchot, E. Berthier, A. Dehecq, T. Bolch, Kévin Fourteau, J. Brondex, M. Dumont, C. Mayer, S. Leinss, R. Hugonnet, P. Wagnon
Abstract. The South Col Glacier is a small body of ice and snow (approx. 0.2 km2) located at the very high elevation of 8000 m a.s.l. (above sea level) on the southern ridge of Mt. Everest. A recent study by Potocki et al. (2022) proposed that South Col Glacier is rapidly losing mass. This is in contradiction to our comparison of two digital elevation models derived from aerial photographs taken in December 1984 and a stereo Pléiades satellite acquisition from March 2017, from which we estimate a mean elevation change of 0.01 ± 0.05 m a−1. To reconcile these results, we investigate some aspects of the surface energy and mass balance of South Col Glacier. From satellite images and a simple model of snow compaction and erosion, we show that wind erosion has a major impact on the surface mass balance due to the strong seasonality in precipitation and wind and that it cannot be neglected. Additionally, we show that the melt amount predicted by a surface energy and mass balance model is very sensitive to the model structure and implementation. Contrary to previous findings, melt is likely not a dominant ablation process on this glacier, which remains mostly snow-covered during the monsoon.
摘要南科尔冰川(South Col Glacier)是一个小的冰雪体。0.2平方公里),位于海拔8000米的高海拔地区。(海拔以上)在珠穆朗玛峰的南山脊上。Potocki等人(2022)最近的一项研究提出,南冷冰川正在迅速失去质量。这与我们对1984年12月拍摄的航空照片和2017年3月获得的立体声placimiades卫星拍摄的两个数字高程模型的比较相矛盾,我们从中估计平均高程变化为0.01±0.05 ma - 1。为了调和这些结果,我们研究了南冷冰川表面能量和物质平衡的一些方面。从卫星图像和一个简单的雪压实和侵蚀模型中,我们表明,由于降水和风的强烈季节性,风蚀对地表物质平衡有重大影响,并且不可忽视。此外,我们还表明,表面能和质量平衡模型预测的熔体量对模型结构和实现非常敏感。与先前的发现相反,融化可能不是这个冰川的主要消融过程,在季风期间,它仍然大部分被雪覆盖。
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引用次数: 0
Atmospheric highs drive asymmetric sea ice drift during lead opening from Point Barrow 在巴罗角引线开通期间,大气高压驱动不对称海冰漂移
IF 5.2 2区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2023-08-09 DOI: 10.5194/tc-17-3229-2023
MacKenzie E. Jewell, J. Hutchings, C. Geiger
Abstract. Throughout winter, the winds of migrating weather systems drive the recurrent opening of sea ice leads from Alaska's northernmost headland, Point Barrow. As leads extend offshore into the Beaufort and Chukchi seas, they produce sea ice velocity discontinuities that are challenging to represent in models. We investigate how synoptic wind patterns form leads originating from Point Barrow and influence patterns of sea ice drift across the Pacific Arctic. We identify 135 leads from satellite thermal infrared imagery between January–April 2000–2020 and generate an ensemble of lead-opening sequences by averaging atmospheric conditions and ice velocity across events. On average, leads open as migrating atmospheric highs drive differing ice–coast interactions across Point Barrow. Northerly winds compress the Beaufort ice pack against the coast over several days, slowing ice drift. As winds west of Point Barrow shift offshore, the ice cover fractures and a lead extends from the headland into the pack interior. Ice west of the lead accelerates as it separates from the coast, drifting twice as fast (relative to winds) as ice east of the lead, which remains coastally bound. Consequently, sea ice drift and its contribution to climatological ice circulation becomes zonally asymmetric across Point Barrow. These findings highlight how coastal boundaries modify the response of the consolidated ice pack to wind forcing in winter, producing spatially varying regimes of ice stress and kinematics. Observed connections between winds, ice drift, and lead opening provide test cases for sea ice models aiming to capture realistic ice transport during these recurrent deformation events.
摘要整个冬天,迁徙的天气系统的风驱动着阿拉斯加最北端的巴罗角不断开放的海冰。当导线延伸到波弗特海和楚科奇海时,它们会产生海冰速度不连续性,这在模型中很难表示。我们研究了天气风模式如何形成源自巴罗角的导线,以及太平洋北极海冰漂移的影响模式。我们从2000年1月至2020年4月的卫星热红外图像中识别了135条铅,并通过平均大气条件和各事件的冰速生成了一组铅开放序列。平均而言,由于迁移的大气高压驱动了巴罗角不同的冰-海岸相互作用,导线打开。几天来,北风将波弗特冰袋吹向海岸,减缓了冰的漂移。当巴罗角以西的风转移到近海时,冰盖破裂,一根引线从岬延伸到了狼群内部。铅以西的冰在与海岸分离时加速,漂移的速度(相对于风)是铅以东的冰的两倍,铅仍沿海岸移动。因此,海冰漂移及其对气候冰循环的贡献在巴罗角呈带状不对称。这些发现突显了海岸边界如何改变冬季固结冰盖对风力的响应,从而产生空间变化的冰应力和运动学状态。观测到的风、冰漂移和铅开口之间的联系为海冰模型提供了测试案例,旨在捕捉这些反复发生的变形事件中真实的冰传输。
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引用次数: 1
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Cryosphere
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