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排序方式: 共有1475条查询结果,搜索用时 356 毫秒
701.
Miguel Rodríguez‐Rodríguez Enrique Moreno‐Ostos Inmaculada De Vicente Luis Cruz‐Pizarro Sergio Luiz Rodrigues Da Silva 《新西兰海洋与淡水研究杂志》2013,47(5):879-894
This work examines the diel change of energy storage and its associated patterns of thermal stratification during the ice‐free period in a high mountain lake (La Caldera Lake, Sierra Nevada, Spain), in response to meteorological conditions. Bihourly data have been implemented to a standard methodology of surface heat exchange calculations in lakes. Strong variations have been observed on the diverse components of the energy budget at different time scales, ranging from diel to seasonal. Additionally, time‐series analyses have been applied to reveal the underlying periodicities involved in relation to the different variables studied. The results obtained from this study provided realistic conditions for the environmental modelling of such processes, which are very sensitive in time scale. 相似文献
702.
《Norsk geografisk tidsskrift. Norwegian journal of geography》2012,66(2):76-91
The cumulative net mass balances of maritime glaciers in Norway display a net surplus during the period 1963–2000. The article seeks to establish the causal mechanisms that resulted in the positive net balances occurring on Norwegian maritime glaciers. To achieve this, a Temporal Synoptic Index (TSI) was derived for a 30-year period for a number of synoptic meteorological stations in Norway. The TSI is derived using Principal Components Analysis (PCA) and subsequent clustering of component scores to classify days for both winter and summer seasons. Findings indicate that the occurrence of ‘warm’ type air masses during the summer months have increased in frequency, particularly since the late 1980s. A reduction in the frequency of ‘cold’ cluster types during the winter months is evident after this period, while the frequency of ‘warm’ types, with an increased moisture carrying capacity, has increased in frequency. The frequency occurrence of these key air mass types is shown to be significantly related to glacier mass balance during both the accumulation and ablation season. Winter air mass types from maritime source regions act to enhance accumulation and suppress ablation, while summer continental source types suppress accumulation and enhance ablation. 相似文献
703.
萨拉乌苏河流域MGS2层段粒度与CaCO3记录的千年尺度气候变化 总被引:2,自引:0,他引:2
测定、分析毛乌素沙漠东南缘萨拉乌苏河流域米浪沟湾剖面MGS2层段的粒度与CaCO3,发现该层段不同沉积相粒度Mz和σ呈现峰谷变化,CaCO3含量在沙丘砂及其上覆的河流相和湖沼相中依次变化于0-2.94%(平均值0.39%)、0.14%-2.68%(1.43%)和0.39%-15.57%(8.82%),并与Mz呈显著相关,构成与沉积旋回波动韵律相同的5.5个峰谷交替的粒度与CaCO3旋回。研究表明,毛乌素沙漠冬季风盛行时期沙丘砂强烈堆积,CaCO3发生迁移;夏季风盛行时期河流相和湖沼相发育,粉砂和粘土含量增加,CaCO3相对聚集。这些旋回代表东亚冬夏季风千年尺度交替变化的气候旋回。 相似文献
704.
何永彬 《亚热带资源与环境学报》2012,7(2)
阐述了云南降雪形成的山地环境因子.同时运用统计方法对云南1980-2000年降雪的时间与地域空间的格局变化进行分析,初步把云南降雪区域划分为滇西北高山常年-长期降雪区、滇中-滇东北山原季节降雪区、滇西-滇东南山地少降雪区和滇南-滇西南无降雪区. 相似文献
705.
Influence of glacial isostatic adjustment upon current sea level variations in the Mediterranean 总被引:1,自引:0,他引:1
Present-day sea level variations in the Mediterranean depend on various factors, including recent climatic forcing, tectonic activity, anthropogenic effects, and glacio-isostatic adjustment. The latter is governed by mantle rheology and the spatio–temporal distribution of the late-Pleistocene ice sheets and it is expected to produce a long-wavelength pattern of sea level variations across the Mediterranean, mostly determined by the response of the solid earth and of the geoid to loading effects of melt water since the end of deglaciation. Modeling glacio-isostatic effects in this region is necessary for a correct interpretation of tide gauge and GPS time-series, and thereby to constrain both the present-day climate-related sea level rise and regional or local geological, tectonic and human-driven displacements. By an exhaustive exploration of the parameter space of mantle rheology and ice sheet chronologies, in this work we outline upper and lower bounds on the current rate of sea level variation associated with glacial isostatic adjustment in the Mediterranean. This may contribute to a full assessment of coastal vulnerability by sea level rise on a regional and local scale. 相似文献
706.
Cr, Cu, Fe, K, Mg, Mn, N, Ni, Pb, S, V and Zn concentrations were determined during a whole seasonal cycle in leaves and in water and sediment roots of the aquatic macrophyte Phragmites australis (Cav.) Trin. ex Steudel from three sites in the Lake Averno (Naples, Italy), a volcanic lake contaminated by trace elements. At the beginning of the research, elemental analysis was also performed on lake sediments, that showed different trace-element concentrations depending on the sites. 相似文献
707.
Rashid Umar Izrar Ahmed Fakhre Alam Mohammad Muqtada Khan 《Environmental Geology》2009,58(6):1295-1300
The present study was undertaken to assess major ion chemistry of groundwater in parts of the Central Ganga Plain and observe
seasonal variations in its chemical quality. Systematic sampling was carried out during November 2005 and June 2006. The major
ion chemistry of groundwater shows large variations, so much so that at times the meteoric signature seems to be completely
obliterated. In many samples the concentrations of SO4, NO3 and F are above the permissible limit for human consumption. The graphical treatment of major ion chemistry helps in identifying
four types of groundwater. All possible ionic species such as NaCl, KCl, NaHCO3, NaSO4, KNO3, NaNO3, CaHCO3, MgHCO3, MgSO4 are likely to occur in groundwater system. The observed chemical variations may be attributed to sediment water interaction,
ion exchange, dissolution mechanisms and anthropogenic influences such as application of fertilizers and effluents from sugar
factories and paper mills. A general increase in TDS is observed in samples during June 2006. The increase in salinity is
attributed to evaporation from water table, irrigation return flows, anthropogenic activities and below average rainfall in
2005 and 2006.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
708.
Spatial and temporal knowledge representation 总被引:1,自引:1,他引:0
Antony Galton 《Earth Science Informatics》2009,2(3):169-187
Knowledge Representation (KR) originated as a discipline within Artificial Intelligence, and is concerned with the representation
of knowledge in symbolic form so that it can be stored and manipulated on a computer. This article surveys that part of KR
that is concerned with the representation of space and time, with particular reference to the use of such representations
in geographical information science.
相似文献
Antony GaltonEmail: |
709.
Temporal and spatial variations in water discharge and sediment load in the Alaknanda and Bhagirathi Rivers in Himalaya, India 总被引:2,自引:0,他引:2
The Alaknanda and Bhagirathi Rivers originate in the mountainous regions of the Himalayas (Garhwal) and result in high sediment yields causing flood hazards downstream of the Ganga River and high sediment flux to the Bay of Bengal. The rivers are perennial, since runoff in these rivers is controlled by both precipitation and glacial melt. In the present study, three locations in the upper reaches of the Ganga River were monitored for 1 yr (daily observations of, more than >1000 samples) for suspended sediment concentrations. In addition, more than one hundred samples were collected from various locations of the Alaknanda and Bhagirathi Rivers at different periods to observe spatial and temporal variations in river suspensions. Further, multi-annual data (up to 40 yrs) of water flow and sediment concentrations were used for inferring the variations in water flow and sediment loads on longer time scales. In most previous studies of Himalayan Rivers, there has been a general lack of long term water flow and sediment load data. In the present study, we carried out high frequency sampling, considered long term discharge data and based on these information, discussed the temporal and spatial variations in water discharge and sediment loads in the rivers in the Himalayan region. The results show that, >75% of annual sediment loads are transported during the monsoon season (June through September). The annual physical weathering rates in the Alaknanda and Bhagirathi River basins at Devprayag are estimated to be 863 tons km−2 yr−1 (3.25 mm yr−1) and 907 tons km−2 yr−1 (3.42 mm yr−1) respectively, which are far in excess of the global average of 156 tons km−2 yr−1 (0.58 mm yr−1). 相似文献
710.
白云机场低空风切变的时空特点及其大气环流形势分析 总被引:6,自引:4,他引:2
本文通过对白云机场附近近年多起低空风切变的大气环流形势进行了统计分析,发现风切变的发生与高压脊、脊后槽前、锋面低槽和热带气旋环流4种主要天气形势密切相关。预报业务中利用这4种分型对提前发布低空风切变预警趋势,确保飞行安全有一定的参考价值。 相似文献