Earth hummocks (thúfur): new insights to their thermal characteristics and development in eastern Lesotho,southern Africa     

Stefan W. Grab 《地球表面变化过程与地形》2005,30(5):541-555

The aspect‐controlled variations in soil freezing within earth hummocks of eastern Lesotho (southern Africa) are analysed. Ground thermal data were measured for an earth hummock from late autumn to early spring in 1995 and 1996, using Tinytalk? data loggers. During 1995, ground temperatures were recorded at 15 and 20 cm depth on the hummock north, east, south and west aspects, whilst in 1996 temperatures were recorded at 1 cm, 5 cm and 10 cm on the north and south aspects. The data from 1995 indicate that soil freezing commences on the hummock southern aspects and gradually progresses towards the western and northern aspects, whilst the eastern aspect remained unfrozen throughout winter. The data from 1996 indicate that a thick snow cover almost nullifies the temperature differences between the hummock northern and southern aspects. However, given the relative absence of snow during contemporary winters, freeze intensity and duration is longest on the hummock southern and western aspects, which helps explain earth hummock deformation (elongation and coalescence) in a southwesterly direction on slope gradients ≤3°. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Sensitivity Analysis of Snow Cover to Climate Change Scenarios and Their Impact on Plant Habitats in Alpine Terrain   总被引：2，自引：1，他引：2  

Franziska Keller  Stéphane Goyette  Martin Beniston 《Climatic change》2005,72(3):299-319

In high altitude areas snow cover duration largely determines the length of the growing season of the vegetation. A sensitivity study of snow cover to various scenarios of temperature and precipitation has been conducted to assess how snow cover and vegetation may respond for a very localized area of the high Swiss Alps (2050–2500 m above sea level). A surface energy balance model has been upgraded to compute snow depth and duration, taking into account solar radiation geometry over complex topography. Plant habitat zones have been defined and 23 species, whose photoperiodic preferences were documented in an earlier study, were grouped into each zone. The sensitivity of snowmelt to a change in mean, minimum and maximum temperature alone and a change in mean temperature combined with a precipitation change of +10% in winter and −10% in summer is investigated. A seasonal increase in the mean temperature of 3 to 5 K reduces snow cover depth and duration by more than a month on average. Snow melts two months earlier in the rock habitat zone with the mean temperature scenario than under current climate conditions. This allows the species in this habitat to flower earlier in a warmer climate, but not all plants are able to adapt to such changes.  相似文献   

North Atlantic Oscillation – Concepts And Studies     

Heinz Wanner  Stefan Brönnimann  Carlo Casty  Dimitrios Gyalistras  Jürg Luterbacher  Christoph Schmutz  David B. Stephenson  Eleni Xoplaki 《Surveys in Geophysics》2001,22(4):321-381

This paper aims to provide a comprehensive review of previous studies and concepts concerning the North Atlantic Oscillation. The North Atlantic Oscillation (NAO) and its recent homologue, the Arctic Oscillation/Northern Hemisphere annular mode (AO/NAM), are the most prominent modes of variability in the Northern Hemisphere winter climate. The NAO teleconnection is characterised by a meridional displacement of atmospheric mass over the North Atlantic area. Its state is usually expressed by the standardised air pressure difference between the Azores High and the Iceland Low. ThisNAO index is a measure of the strength of the westerly flow (positive with strong westerlies, and vice versa). Together with the El Niño/Southern Oscillation (ENSO) phenomenon, the NAO is a major source of seasonal to interdecadal variability in the global atmosphere. On interannual and shorter time scales, the NAO dynamics can be explained as a purely internal mode of variability of the atmospheric circulation. Interdecadal variability maybe influenced, however, by ocean and sea-ice processes.  相似文献   

SENSOR: a tool for the simulation of hyperspectral remote sensing systems   总被引：1，自引：0，他引：1  

Anko Brner  Lorenz Wiest  Peter Keller  Ralf Reulke  Rolf Richter  Michael Schaepman  Daniel Schlpfer 《ISPRS Journal of Photogrammetry and Remote Sensing》2001,55(5-6)

The consistent end-to-end simulation of airborne and spaceborne earth remote sensing systems is an important task, and sometimes the only way for the adaptation and optimisation of a sensor and its observation conditions, the choice and test of algorithms for data processing, error estimation and the evaluation of the capabilities of the whole sensor system.The presented software simulator SENSOR (Software Environment for the Simulation of Optical Remote sensing systems) includes a full model of the sensor hardware, the observed scene, and the atmosphere in between. The simulator consists of three parts. The first part describes the geometrical relations between scene, sun, and the remote sensing system using a ray-tracing algorithm. The second part of the simulation environment considers the radiometry. It calculates the at-sensor radiance using a pre-calculated multidimensional lookup-table taking the atmospheric influence on the radiation into account. The third part consists of an optical and an electronic sensor model for the generation of digital images. Using SENSOR for an optimisation requires the additional application of task-specific data processing algorithms.The principle of the end-to-end-simulation approach is explained, all relevant concepts of SENSOR are discussed, and first examples of its use are given. The verification of SENSOR is demonstrated. This work is closely related to the Airborne PRISM Experiment (APEX), an airborne imaging spectrometer funded by the European Space Agency.  相似文献   

Local environmental action plans and the `glocalisation' of post-socialist governance: The Macedonian experience   总被引：1，自引：0，他引：1  

Stefan Buzarovski 《GeoJournal》2001,55(2-4):557-568

Local Environmental Action Plans (LEAPs) are a useful starting point for the theoretical and empirical unravelling of the global post-Fordist socio-economic drive, within the framework of environmental policy devolution in Transition. Accordingly, this paper aims to identify the interconnected economic, social and political specifities involved in the formulation and institutionalisation of such projects in the Republic of Macedonia. Seven LEAPs - broadly representative of the immense micro-scale physical and social diversity of the country - have been selected for detailed review, so as to provide more fine-tuned insights that should be relevant for the wider LEAP process in Macedonia and beyond. Preliminary evidence about the realisation of these initiatives indicates that comprehensive implementation is highly dependent upon the realistic political and economic abilities (and interests) of local and national elites, plus international organisations. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

A diatomaceous origin for long-chain diols and mid-chain hydroxy methyl alkanoates widely occurring in quaternary marine sediments: indicators for high-nutrient conditions     

Jaap S. Sinninghe Damsté  Sebastiaan Rampen  C. Rijpstra  Gerard Muyzer  Stefan Schouten 《Geochimica et cosmochimica acta》2003,67(7):1339-1348

For the first time a biological source for the long-chain alkyl 1,14-diols and 12-hydroxy methyl alkanoates, lipids widely occurring in the marine water column and sediments, has been identified. Cultures of Proboscia indica and Proboscia alata, rhizosolenoid diatoms belonging to the widespread diatom genus Proboscia, contain C₂₈, C_28:1, C₃₀, and C_30:1 alkyl 1,14-diols, and C₂₇ and C₂₉ 12-hydroxy methyl alkanoates as major neutral lipids. These components form a substantial fraction of lipid fractions from sediment traps or sediments, especially in areas with an elevated primary production such as upwelling regions. Examination of literature data reveals that as much as 20 to 35% of the total lipid flux in the Arabian Sea is derived from Proboscia diatoms during the start of the upwelling season. Their rapid transfer to the water-sediment interface may explain why corresponding 1,14-keto-ols, inferred oxidation products of diols, are hardly formed. These interpretations are supported by compound-specific carbon isotopic analysis of long-chain keto-ols and diols in surface sediments of the Arabian Sea. The data indicate that long-chain alkyl 1,14-diols and 12-hydroxy methyl alkanoates can be applied as indicators for high-nutrient conditions in the photic zone.  相似文献   

Assessment of the atmospheric nitrogen and sulphur inputs into the North Sea using a Lagrangian model     

O. Hertel  C. Ambelas Skjøth  L.M. Frohn  E. Vignati  J. Frydendall  G. de Leeuw  Uwe Schwarz  Stefan Reis 《Physics and Chemistry of the Earth》2002,27(35):1507-1515

The atmospheric chemistry and deposition model has been applied for calculation of nitrogen and sulphur depositions to the entire North Sea area for the year 1999. The total atmospheric nitrogen and sulphur depositions to the North Sea area were determined to 709 kton (kt) N and 551 kt S, respectively. Since the North Sea area was calculated to be 747,988 km², this is equivalent to an average deposition of 0.9 ton N km^?2 and 0.7 ton S km^?2, respectively. The depositions decrease strongly from the south end (about 2–3 kt N km^?2) to the north end (about 0.2 kt N km^?2) of the North Sea, due to increasing distance to the large source areas in the northern part of the European continent. The territorial waters of Belgium, the Netherlands and Germany receive about 50% higher deposition densities than the average value for the entire North Sea area. For the remaining territorial waters of the North Sea the depositions follow more or less the fraction of the area. The results furthermore show that about 60% of the total nitrogen deposition is related to emissions from combustion sources (nitrogen oxides) and about 40% from emissions related to agricultural activities (ammonia).  相似文献   

Global environmental consequences of tourism   总被引：15，自引：0，他引：15  

Stefan Gssling 《Global Environmental Change》2002,12(4):629

In 2000, almost 700 million international tourist arrivals were counted worldwide. Even though a global activity of this scale can be assumed to have a substantial impact on the environment, its consequences have never been assessed and quantified. In this contribution, five major aspects of the leisure-related alteration of the environment are investigated: (1) the change of land cover and land use, (2) the use of energy and its associated impacts, (3) the exchange of biota over geographical barriers and the extinction of wild species, (4) the exchange and dispersion of diseases, and (5), a psychological consequence of travel, the changes in the perception and the understanding of the environment initiated by travel.  相似文献   

A Late Glacial–Holocene Tephrochronology for Glacial Lakes in Southern Ecuador     

Donald T. Rodbell  Stefan Bagnato  Jeffrey C. Nebolini  Geoffrey O. Seltzer  Mark B. Abbott 《Quaternary Research》2002,57(3):343

Despite the presence of numerous active volcanoes in the northern half of Ecuador, few, if any, distal tephras have been previously recognized in the southern one third of the country. In this article, we document the presence of thin (0.1–1.0-cm-thick) distal tephras comprising glass and/or phenocrysts of hornblende and feldspar in sediment cores from five glacial lakes and one bog in Las Cajas National Park (2°40′–3°00′S, 79°00′–79°25′W). The lake cores contain from 5 to 7 tephras, and each has a diagnostic major element geochemistry as determined from electron microprobe analysis of 710 glass shards and 440 phenocrysts of feldspar and hornblende. The loss of sodium with exposure to the electron microbeam causes a 10±7 wt.% (±1σ) reduction in Na content, which we empirically determined and corrected for before correlating tephras among the sediment cores. We use a similarity coefficient to correlate among the sediment cores; pair-wise comparison of all tephras generally yields an unambiguous correlation among the cores. Six tephras can be traced among all or most of the cores, and several tephras are present in only one or two of the cores. Twenty-six accelerator mass spectrometry ¹⁴C dates on macrofossils preserved in the sediment cores provide the basis for establishing a regional tephrochronology. The widespread tephras were deposited 9900, 8800, 7300, 5300, 2500, and 2200 cal yr B.P. The oldest tephras were deposited 15,500 and 15,100 cal yr B.P., but these are not found in all cores. Two of the tephras appear correlative with volcaniclastic strata on the flanks of Volcán Cotopaxi and one tephra may correlate with strata on the flanks of Volcán Ninahuilca; both volcanoes are in central Ecuador. The absence of tephras in sediment cores correlative with the numerous eruptions of active volcanoes of the past two millennia implies that the earlier eruptions, which did deposit tephras in the lakes, must have been either especially voluminous, or southerly winds must have prevailed at the time of the eruption, or both.  相似文献   

Correlations of Climate and Streamflow in Three Minnesota Streams     

Laura L. Kletti  Heinz G. Stefan 《Climatic change》1997,37(4):575-600

Correlations between four climate parameters and streamflow in three Minnesota streams were investigated. Runoff values measured over periods of up to 37 years were correlated with precipitation, air temperature, wind, and dew point temperature. The overall objective was to examine if relationships can be obtained which require only readily available input parameters without calibration. Such relationships would be of great use, e.g. to compute future lake water budgets without recourse to more detailed and complex hydrologic runoff models. Monthly, seasonal, and annual time frames were investigated. A seasonal time frame using 3 month averages gave the closest fit for the linear regressions without time lag. Although the watershed sizes varied from 360 to 49,600 square kilometers, the 3 month period seemed sufficiently long to average long term hydrologic processes such as infiltration, evaporation, and groundwater flow. An equation was found for each season (3 months) for each of the rivers. Winter (December, January, February) regressions required only precipitation data; spring regressions required air temperature and precipitation; summer and fall regressions were found with precipitation, air temperature, dew point temperature, and wind speed. The coefficients in the regression equations were related to the watershed characteristics. The r² values were highest for the Zumbro River in spring (0.69) and lowest for the Baptism River in winter (0.14). Root mean square error values ranged from 2.8 mm/mo for the Mississippi River in winter to 18 mm/mo for the Baptism River in spring. The coefficients of variability (CV) ranged from 0.24 to 0.52. Overall the results were disappointing but not all bad. Climate parameters without watershed parameters can characterize runoff only within limits. To project possible future runoff averages the GISS GCM-values for the 2 × CO₂ climate scenario were applied to the seasonal runoff regression equations. The projections were that the spring runoff values would decrease by up to 35% while in the other seasons streamflows would increase by up to 50%. Annual runoff would not change significantly enough to be predictable. The results were in the range of changes predicted by other investigations using very different techniques. Since predictions were based on equations found with past records, it was implied that the land cover would remain unchanged in the 2 × CO₂ environment. This may be unrealistic and needs further investigation.  相似文献