Is the North Atlantic Oscillation reflected in Scandinavian glacier mass balance records?

The North Atlantic Oscillation (NAO) is one of the modes of climate variability in the North Atlantic region. The atmospheric circulation during the winter season in this region commonly displays a strong meridional (north–south) pressure contrast, with low air pressure (cyclone) centred close to Iceland and high air pressure (anticyclone) near the Azores. This pressure gradient drives the mean surface winds and the mid‐latitude winter storms from west to east across the North Atlantic, bringing mild moist air to northwest Europe. The NAO index is based on the difference of normalised sea‐level pressures (SLP) between Ponta Delgada, Azores and Stykkisholmur, Iceland. The SLP anomalies at these stations are normalised by division of each monthly pressure by the long‐term (1865–1984) standard deviation. Interannual atmospheric climate variability in northwest Europe, especially over Great Britain and western Scandinavia has, during the last decades, been attributed mainly to the NAO, causing variations in the winter weather over the northeast North Atlantic and the adjacent land areas. A comparison between the NAO index and the winter (December–March) precipitation between ad 1864 and 1995 in western Norway shows that these are strongly linked (correlation coefficient 0.77). Variations in the NAO index are also reflected in the mass balance records of glaciers in western Scandinavia. The NAO index is best correlated with mass balance data from maritime glaciers in southern Norway (e.g. Ålfotbreen R² = 0.51). The record of Holocene (last ca. 11 500 cal. yr) glacier variations of maritime glaciers in western Scandinavia is thus a proxy of pre‐instrumental NAO variations. Copyright © 2000 John Wiley & Sons, Ltd.     

冰川动力学模式模型进展及研究

冰冻圈是气候系统中的一个重要圈层, 其中冰川又是冰冻圈的重要组成部分, 冰川、 尤其是山地冰川的本构方程和建模一直是冰川动力学的核心任务。首先, 简要回顾冰川模型的研究和发展, 简要介绍了基于Navier-Stokes方程耦合温度场的三维冰川模型。然后, 介绍了冰川建模过程中的常用的静水压力近似、 一阶近似、 浅冰近似等的基本概念, 总结了冰川的动力数值模式建立的主要方法, 对于常用的GLIMMER冰盖模式的物理框架及其应用进行了介绍。最后, 针对目前的简化模型难以准确地描述山地冰川的物理过程及其变化的问题, 提出了一个基于全Navier-Stokes方程的山地冰川模型及其动力框架、 边界条件处理的设想。本文可为建立、 发展冰川及冰架模型, 尤其建立和发展山地冰川模型提供基础知识和参考。     

基于GF-1卫星遥感的冰川边界识别

高分一号（GF-1）卫星的成功发射开启了国产高分辨率对地观测的新时代, 为探讨国产高分卫星在冰川边界识别中的有效性, 在缺少短波红外和热红外波段的情况下, 将GF-1影像、 建立的波段比值Band1/Band4, 数字高程模型和坡度相结合, 采用面向对象的分析方法, 经过反复试验, 确定影像分割和合并尺度, 进而确定冰川边界的知识规则, 最终实现冰川边界的识别。以研究区第二次冰川编目数据集作为参考数据, 采用混淆矩阵的方法对识别结果进行验证, 总体精度和Kappa系数为90.05%和0.79。同时将识别结果与人工修订冰川边界进行对比, 可以发现除少量冰舌末端冰川外, 该方法可以有效地对冰川进行识别。建立的知识规则显示仅仅利用蓝色波段和DEM就可以有效地提取裸冰区, 波段比值、 坡度和纹理特征更有助于冰舌的提取。该研究表明GF-1卫星数据可以有效识别冰川范围, 为冰川研究提供可靠的数据和研究基础。     

Debris transport by Loch Lomond Readvance glaciers in Northern Scotland: Basin form and the within-valley asymmetry of lateral moraines

Moraines in six cirques in Northern Scotland are shown to be asymmetrically developed, being larger below north- or east-facing valley sides. Moraine asymmetry is strongly correlated with the distribution of free faces in the valleys, a relationship that is interpreted as the result of variation in slope retreat rates. Analysis of clast form and roundness demonstrates that following initial release from bedrock, debris entered both passive high-level glacial transport and tractive transport at the ice-bed interface. The importance of glacier velocities and medial moraines on debris flux is discussed. Consideration is also given to the implications of process asymmetry to long term landform development.     

Borehole drainage and its implications for the investigation of glacier hydrology: experiences from Haut Glacier d'Arolla,Switzerland

Studies of glacier hydrology rely increasingly on measurements made in boreholes as a basis for reconstructing the character and behaviour of subglacial drainage systems. In temperate glaciers, in which boreholes remain open to the atmosphere following drilling, the interpretation of such data may be complicated by supraglacial or englacial water flows to and from boreholes. We report on a suite of techniques used to identify borehole water sources and to reconstruct patterns of water circulation within boreholes at Haut Glacier d'Arolla, Switzerland. Results are used to define a number of borehole ‘drainage’ types. Examples of each drainage type are presented, along with the manner in which they influence interpretations of borehole water‐levels, borehole water‐quality data, and borehole dye traces. The analysis indicates that a full understanding of possible borehole drainage modes is required for the correct interpretation of many borehole observations, and that those observations provide an accurate indication of subglacial conditions only under relatively restricted circumstances. Copyright © 2001 John Wiley & Sons, Ltd.     

THE 'LITTLE ICE AGE': RE-EVALUATION OF AN EVOLVING CONCEPT

ABSTRACT. This review focuses on the development of the ‘Little Ice Age’ as a glaciological and climatic concept, and evaluates its current usefulness in the light of new data on the glacier and climatic variations of the last millennium and of the Holocene. ‘Little Ice Age’ glacierization occurred over about 650 years and can be defined most precisely in the European Alps (c. AD 1300–1950) when extended glaciers were larger than before or since. ‘Little Ice Age’ climate is defined as a shorter time interval of about 330 years (c. AD 1570–1900) when Northern Hemisphere summer temperatures (land areas north of 20°N) fell significantly below the AD 1961–1990 mean. This climatic definition overlaps the times when the Alpine glaciers attained their latest two highstands (AD 1650 and 1850). It is emphasized, however, that ‘Little Ice Age’ glacierization was highly dependent on winter precipitation and that ‘Little Ice Age’ climate was not simply a matter of summer temperatures. Both the glacier‐centred and the climate‐centred concepts necessarily encompass considerable spatial and temporal variability, which are investigated using maps of mean summer temperature variations over the Northern Hemisphere at 30‐year intervals from AD 1571 to 1900. ‘Little Ice Age’‐type events occurred earlier in the Holocene as exemplified by at least seven glacier expansion episodes that have been identified in southern Norway. Such events provide a broader context and renewed relevance for the ‘Little Ice Age’, which may be viewed as a ‘modern analogue’ for the earlier events; and the likelihood that similar events will occur in the future has implications for climatic change in the twenty‐first century. It is concluded that the concept of a ‘Little Ice Age’ will remain useful only by (1) continuing to incorporate the temporal and spatial complexities of glacier and climatic variations as they become better known, and (2) by reflecting improved understanding of the Earth‐atmosphere‐ocean system and its forcing factors through the interaction of palaeoclimatic reconstruction with climate modelling.     

度日模型在冰川与积雪研究中的应用进展

度日模型是基于冰川与积雪消融和气温,尤其是冰雪表面的正积温之间的线性关系建立的.度日模型已广泛应用于北欧、阿尔卑斯山、格陵兰冰盖、青藏高原等地区的冰雪消融、冰川物质平衡及对气候敏感性响应、冰川动力模型以及冰雪融水径流模拟等的研究中.度日模型尽管是对冰雪表面消融能量平衡这一复杂过程的简化描述,但在流域尺度上,通常可以获取类似于能量平衡模型的输出结果.度日模型也有其不足之处,仍需进一步的改进与完善.     

A joint analysis of river runoff and meteorological forcing in the Karakoram,upper Indus Basin

Satellite‐geodetic altimetry investigations in the Karakoram have indicated slight mass gain or loss of the glaciers during the early part of 21st century. Equivalent discharge in the upper Indus Basin due to these mass changes has been estimated at 5 to 10% of mean annual flow. However, satellite altimetry and geodetic glacier mass estimates in the extreme topography of the Karakoram have not yet been counter‐validated by hydrological analysis. Therefore, we present a first cross validation of three to five decades of river flow data from the three major watersheds in the Karakoram, with matching series of monthly precipitation, temperature, and evaporation provided by six atmospheric reanalysis products for 1979–2014. The analyses suggest that in most cases river flows have been increasing steadily from the end of the 1960s and 1970s to the middle of the 1990s and have stabilized or are in decline since then. Hunza watershed in Karakoram West shows consistently declining flows over the first half of the analysis period and stable flows during the second half for most of the summer melting season, suggesting mass accumulation. Rising river flows in the Shyok and Shigar watersheds, followed by stabilizing or slightly declining flows from 1995 onward, can be explained by consistently increasing precipitation during the first half of the analysis period, and successive stabilization or minor decline thereof. Flow data do not necessarily suggest considerable loss or gain of glacial mass in the Karakoram during the late 90s and early 2000s as suggested by satellite‐based altimetry studies.     

On the sensitivity of Holocene talus-derived rock glaciers to climate change in the Ben Ohau Range,New Zealand

The morphology and surface ages of talus-derived rock glaciers are investigated to establish the timing of rock glacier formation in the central Southern Alps. Samples of rock weathering rinds show that all rock glaciers studied were formed during the Neoglacial period, but differences exist between sites in the number of new rock glacier lobes formed by Holocene climatic fluctuations. A qualitative conceptual model is proposed to explain rock glacier formation in terms of two thresholds. An external threshold relates to the presence of a cool climate capable of allowing internal ice to form within talus slopes. An internal threshold relates to the presence of sufficiently thick talus at a site to generate a shear stress capable of overcoming internal friction within the talus/ice mass. The model produces a non-steady-state response to explain why unmodified talus, single-lobed and double-lobed rock glaciers developed at adjacent sites under the same climatic regime. Individual landforms have different sensitivities to formation, which depend partly on the previous history of talus accumulation and rock glacier activity at a site. The model demonstrates how successive cool climate periods may be fully represented by rock glacier lobes at sensitive sites but under-represented at insensitive sites. Sensitivity (and therefore climatic representativeness) is favoured by high rates of debris supply. By implication, the timing of formation of rock glacier lobes in regions of prolonged cool climate and low debris production is less likely to correspond to the timing of climatic cooling and more likely to follow the ‘rules’ of deterministic chaos.