土壤的冷生构造及其对阿拉斯加土地利用的意义     

C. L Ping  M.T. Jorgeson  Y.L. Shur 《冰川冻土》2004,26(Z1):1-7

Cryogenic structure (patterns made by ice inclusions) in seasonally frozen and permafrost-af-fected soils result from ice formation during freezing. Analysis of cryogenic structures in soils is essential to our understanding of the cryogenic processes in soils and to formulating land use management interpretations. When soils freeze, the freezing front moves downward and attracts water moving upward resulting in mainly horizontal lenticular ice formation. Platy and lenticular soil structures form between ice lenses in upper active layer. The reticular soil structure usually forms above the permafrost table caused by freeze-back of the permafrost. The upward freeze-back resulted in platy soil structure and the volume changes following the annual freeze-thaw cycle resulted in vertical cracks. The combined result is an ice-net formation with mineral soils embedded in the ice net. The upper permafrost layer that used to be a part of the active layer has an ice content exceeding 50% due to repeated freeze-thaw cycles over time. The mineral soils appear in blocks embedded in an ice matrix. The permafrost layer that never experienced the freeze-thaw cycle often consists of alternate layers of thin ice lens and frozen soils with extreme hard consistence and has relatively lower ice content than the ice-rich layer of the upper permafrost. Ice contents and thaw settling potentials associated with each cryogenic structure should be considered in engineering and land use interpretations.  相似文献   

用混合和扩散云室对大气冰核浓度的观测分析   总被引：3，自引：0，他引：3  

杨绍忠  王祥国  游来光  皮家雄 《气象》2004,30(12):39-43

继1963年用混合云室对春季冰核浓度观测之后，1994～1996年，在同季节、同地点用混合和静力扩散云室又做了同步观测。对取得的资料进行整理分析，得出了凝华核浓度在不同天气背景下占总冰核浓度的百分比，两种云室测值的对应关系；分析了扩散云室的容积效应及冰核浓度随气压、能见度等气象因子的变化。  相似文献   

北半球海冰强迫作用下大气可预报性研究   总被引：2，自引：0，他引：2       下载免费PDF全文

王嘉  郭裕福 《应用气象学报》2004,15(3):291-300

使用LASG/IAP GOALS耦合模式中的全球大气环流模式分量AGCMR15L9的计算结果，在其他外强迫维持气候值不变的情况下，用方差分析的方法，以外部方差与总方差之比R_e作为衡量标准，考察该模式关于海冰的季节和跨季节潜在可预报性的大小。结果发现，从总体上看，北半球海冰变化所造成的潜在可预报性较小，只有在大气低层的一些气候要素，如温度、湿度的结果中，才存在R_e＞0.5的现象。潜在可预报性结果的局地特征比较明显，高值往往发生在海冰年际变率大的区域里。与中低纬海温在中高纬地区的影响相比，不排除海冰的作用更大的可能性。另外，如果分区域看，北半球某些区域的海冰，在若干挑选出的其区域海冰面积发生大异常年份中的潜在可预报性可能会比不做挑选的总体结果要大。这说明北半球某些区域海冰在面积发生较大异常的时候，可能对同期或（及）后期环流有着比较重要的影响。  相似文献   

L'archivage des activités humaines par les neiges et glaces polaires : le cas du plomb     

Claude Boutron  Kevin Rosman  Carlo Barbante  Michael Bolshov  Freddy Adams  Sungmin Hong  Christophe Ferrari 《Comptes Rendus Geoscience》2004,336(10):847-867

The investigation of the occurrence of lead in dated snow and ice from Greenland and Antarctica has played a major role in our understanding of the history of the pollution of the atmosphere of our planet by this metal. Such studies have however proved to be very demanding, mainly because of the extreme purity of polar snow and ice. Reliable measurements can be obtained only if ultra-clean and highly sensitive procedures are used, as pioneered by Clair Patterson. The Greenland data show evidence of large-scale pollution of the atmosphere of the Northern Hemisphere for lead as early as two millennia ago during Greco–Roman times, especially because of mining and smelting activities in southern Spain. It peaked at the end of the 1960s, with lead concentrations in snow about 200 times higher than natural values, before declining during recent times because of the fall in the use of leaded gasoline. Lead pollution in Antarctica was already significant at the end of the 19th century as a consequence of whaling activities, the traffic of coal-powered ships crossing the Cape Horn, and mining activities in South America, South Africa and Australia. After declining because of the opening of the Panama Canal, the great economic depression and World War II, it reached a maximum during the 1980s, with lead concentrations 20 times higher than natural values. Other studies focus on past natural variations of lead in ancient ice dated from the last climatic cycles. To cite this article: C. Boutron et al., C. R. Geoscience 336 (2004).  相似文献   

Recent progress of glaciological studies in China     

LIU Shiyin  WANG Ninglian  DUAN Keqin  XIAO Cunde  DING Yongjian  HAN Haidong 《地理学报(英文版)》2004,14(4):401-410

1IntroductionIn the early 1960s, glaciers in western China were classified into maritime- and continental-types by different glacial environment and physical characteristics (Shi and Xie, 1964). With extensive glaciological investigations in the western regions (Lanzhou Institute of Glaciology and Geocryology of CAS, 1988), Lai and Huang (1990) suggested a new classification of temperate, subpolar and quasipolar glaciers, corresponding to the maritime-, subcontinental- and extremely contin…  相似文献   

合理设计岩屑规程保证正常钻进条件——金刚石钻进技术专题之一          下载免费PDF全文

汤凤林  段隆臣  В.Ф.Чихоткин  刘晓阳 《探矿工程》2004,31(6):45-48

论述了正常钻进的条件，提出了合理岩屑规程是保证正常钻进的关键和设计钻头的主要依据之一，讨论了岩屑规程与金刚石钻头唇面工作状态、孔底表面粗糙度和岩屑粒度的关系，提出了相应的建议。  相似文献   

MODIS数据在黄河凌汛监测中的应用   总被引：11，自引：0，他引：11  

鄢俊洁  刘良明  马浩录  许志辉 《武汉大学学报(信息科学版)》2004,29(8):679-681

对MODIS数据的特性及其在黄河凌汛监测中的应用情况进行了探讨和总结。试验结果表明 ,MODIS数据在冰雪检测方面具有很大的潜力  相似文献   

Recent progress of glaciological studies in China     

LIU Shiyin  WANG Ninglian  DUAN Keqin  XIAO Cunde  DING Yongjian  HAN Haidong 《地理学报》2004,14(4):401-410

Glacier inventory compilation during the past 20 years and modifications of that for the Eastern Pamir and Banggong Lake indicate that there are 46,342 modern glaciers with a total area and volume of 59415 km2 and 5601 km3 respectively in China. These glaciers can be classified into maritime and continental (including sub-continental and extremely continental) types. Researches show that glaciers in China have been retreating since the Little Ice Age and the mass wastage was accelerated during the past 30 to 40 years. Being an important part of glaciological studies in China, ice core climatic and environmental studies on Tibetan Plateau and in the Antarctica have provided abundant, high resolution information about past climatic and environmental evolution over the Tibetan Plateau and Antarctica. Except for different parameters recorded in ice cores relating to climate and environment changes on Tibetan Plateau, records from ice cores extracted from different glaciers show that the discrepancies in climatic and environmental changes on the north and south parts of the plateau may be the consequence of different influencing effects from terrestrial and solar sources. Glaciological and meteorological phenomena imply that Lambert Glacier valley is an important boundary of climate in the east Antarctica, which is thought to be connected with cyclonic activities and Circum-polar Waves over the Antarctica.  相似文献   

Spatial Dimensions of Urban Commuting: A Review of Major Issues and Their Implications for Future Geographic Research*   总被引：3，自引：0，他引：3  

Mark W. Horner 《The Professional geographer》2004,56(2):160-173

Modern urban transportation systems continuously challenge, and are challenged by, the changing nature of 21st‐century travel demand. Today, congestion is the norm in cities of the United States, and researchers and practitioners are seeking solutions to these problems. Urban commuting is identified as contributing to the suboptimal performance of transportation systems. This paper offers a review and critique of recent research on urban commuting, emphasizing geographical dimensions of this topic. Three broad areas of research related to urban commuting are discussed. These include (1) urban sustainability, (2) land use, and (3) geographic information systems (GIS). Major themes are examined in an effort to elicit thought on future geographic research. At the conclusion of the paper, summary remarks are provided and avenues for research are outlined.  相似文献   

Experimental and theoretical study of stability of dense hydrous magnesium silicates in the deep upper mantle     

Tetsuya Komabayashi  Soichi Omori  Shigenori Maruyama 《Physics of the Earth and Planetary Interiors》2005,153(4):191-209

Fluid-undersaturated experiments were conducted to determine the phase relations in the simplified peridotite system MgO-SiO₂-H₂O (MSH) at 11.0-14.5 GPa and 800-1400 °C. Stability relations of dense hydrous magnesium silicates (DHMSs) under fluid-undersaturated conditions were experimentally examined. From the fluid-absent experimental results, we retrieved thermodynamic data for clinohumite, phase A, phase E, and hydrous wadsleyite, consistent with the published data set for dry mantle minerals. With this new data set, we have calculated phase equilibria in the MSH system including dehydration reactions. The dehydration reactions calculated with lower water activities of 0.68-0.60 match the fluid-present experiments of this study above 11.0 GPa and 1000 °C, indicating that considerable amounts of silicate component were dissolved into the fluid phase. The calculated phase equilibria illustrate the stability of the post-antigorite phase A-bearing assemblages. In the cold subducting slab peridotite, phase A + enstatite assemblage survives into the transition zone, whereas phase A + forsterite + enstatite assemblage forms hydrous wadsleyite at a much shallower depth of about 360-km. The slab is subducted with no dehydration reactions occurring when entering the transition zone. The phase equilibria also show the high temperature stability of phase E. Phase E is stable up to 1200 °C at 13.5 GPa, a plausible condition in the mantle of relatively low temperature, i.e., beneath subduction zones. Phase E is a possible water reservoir in the mantle as well as wadsleyite and ringwoodite.  相似文献