Eine Methode zur Registrierung der räumlichen Verteilung der Globalstrahlung in einem Pflanzenbestand     

Niels Rodskjer  Alois Kornher 《Theoretical and Applied Climatology》1967,15(1-2):186-190

Zusammenfassung Mit zwei Pyranometern wird gleichzeitig und auf gleichem Papier die Globalstrahlung über und in einem Pflanzenbestand registriert. Im Laufe der Registrierung bewegt sich der Strahlungsempf?nger im Bestand mit konstanter Geschwindigkeit entlang einer horizontalen Bahn. Die Apparatur und die Durchführung der Messung werden beschrieben.

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Summary Global radiation above and within a stand of plants is recorded simultaneous and on the same strip of paper. While the record is effectuated the receiver of the radiation is moved horizontally through the stand with constant speed. The equipment and the practical measuring are described.

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Résumé On a enregistré simultanément et sur la même bande d'enregistrement le rayonnement global au moyen de deux pyranomètres placés l'un au-dessus. l'autre à l'intérieur d'une culture. Durant l'enregistrement, l'appareil situé entre les plantes se dépla?ait de long d'une trajectoire horizontale et à une vitesse constante. On décrit ici l'appareillage et l'exécution des mesures.

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Mit 3 Textabbildungen  相似文献   

From smallholders to transnationals: The impact of changing consumer preferences in the EU on Ghana’s pineapple sector     

Niels Fold  Katherine V. Gough   《Geoforum》2008,39(5):1687-1697

This paper explores the impact that a new type of pineapple, and subsequent changing consumer preferences in the Global North, has had on the livelihoods of pineapple growers in Ghana. The paper starts by tracing how research and development in Costa Rica by the world’s largest producers of pineapple, Del Monte and Dole, have resulted in a new variety MD2. This new pineapple type has been marketed in the EU through campaigns carried out by plantation companies via supermarkets. Consumer preferences have subsequently switched to MD2 away from the varieties which previously dominated the market, including the Ghanaian grown Smooth Cayenne. Ghanaian smallholders have experienced a dramatic drop in the demand for Smooth Cayenne and are unable to switch to growing MD2. The Ghanaian pineapple sector is consequently being restructured with large-scale pineapple farms, principally run by transnational companies, growing large quantities of MD2 for export. Through a detailed empirical study of the changing livelihoods of pineapple growers in two settlements in Ghana, we show how smallholders have been affected in differing ways as transnational companies have increasingly entered the market. Recent attempts to incorporate smallholders as producers of niche pineapple products are discussed. The paper illustrates the mutual benefits of linking global value chain analysis with livelihood analysis.  相似文献   

Direct evidence of the feedback between climate and weathering   总被引：1，自引：0，他引：1  

Sigurdur R. Gislason  Eric H. Oelkers  Eydis S. Eiriksdottir  Marin I. Kardjilov  Gudrun Gisladottir  Bergur Sigfusson  Arni Snorrason  Sverrir Elefsen  Jorunn Hardardottir  Peter Torssander  Niels Oskarsson 《Earth and Planetary Science Letters》2009,277(1-2):213-222

Long-term climate moderation is commonly attributed to chemical weathering; the higher the temperature and precipitation the faster the weathering rate. Weathering releases divalent cations to the ocean via riverine transport where they promote the drawdown of CO₂ from the atmosphere by the precipitation and subsequent burial of carbonate minerals. To test this widely-held hypothesis, we performed a field study determining the weathering rates of 8 nearly pristine north-eastern Iceland river catchments with varying glacial cover over 44 years. The mean annual temperature and annual precipitation of these catchments varied by 3.2 to 4.5 °C and 80 to 530%, respectively during the study period. Statistically significant linear positive correlations were found between mean annual temperature and chemical weathering in all 8 catchments and between mean annual temperature and both mechanical weathering and runoff in 7 of the 8 catchments. For each degree of temperature increase, the runoff, mechanical weathering flux, and chemical weathering fluxes in these catchments are found to increase from 6 to 16%, 8 to 30%, and 4 to 14% respectively, depending on the catchment. In contrast, annual precipitation is less related to the measured fluxes; statistically significant correlations between annual precipitation and runoff, mechanical weathering, and chemical weathering were found for 3 of the least glaciated catchments. Mechanical and chemical weathering increased with time in all catchments over the 44 year period. These correlations were statistically significant for only 2 of the 8 catchments due to scatter in corresponding annual runoff and average annual temperature versus time plots. Taken together, these results 1) demonstrate a significant feedback between climate and Earth surface weathering, and 2) suggest that weathering rates are currently increasing with time due to global warming.  相似文献   

A lateral model parameter correlation procedure for one-dimensional inverse modelling     

Niels B. Christensen  Rasmus J. Tølbøll 《Geophysical Prospecting》2009,57(5):919-929

We present a new, fast and versatile method, the lateral parameter correlation method, of invoking lateral smoothness in model sections of one-dimensional (1D) models. Modern, continuous electrical and electromagnetic methods are capable of recording very large data sets and except for a few cases, standard inversion methodology still relies on 1D models. In environments where the lateral rate of change of resistivity is small, 1D inversion can be justified but model sections of concatenated 1D models do not necessarily display the expected lateral smoothness.
The lateral parameter correlation method has three steps. First, all sounding data are inverted individually. Next, a laterally smooth version of each model parameter, one at a time, is found by solving a simple constrained inversion problem. Identity is postulated between the uncorrelated and correlated parameters and the equations are solved including a model covariance matrix. As a last step, all sounding data are inverted again to produce models that better fit the data, now subject to constraints by including the correlated parameter values as a priori values. Because the method separates the inversion from the correlation it is much faster than methods where the inversion and correlation are solved simultaneously, typically with a factor of 200–500.
Theoretical examples show that the method produces laterally smooth model sections where the main influence comes from the well-determined parameters in such a way that problems with equivalence and poor resolution are alleviated. A field example is presented, demonstrating the improved resolution obtained with the lateral parameter correlation method. The method is very flexible and is capable of coupling models from inversion of different data types and information from boreholes.  相似文献   

Distribution of erosion across bedrock channels     

Jens M. Turowski  Niels Hovius  Hsieh Meng‐Long  Dimitri Lague  Chen Men‐Chiang 《地球表面变化过程与地形》2008,33(3):353-363

Lateral erosion in bedrock rivers is an important control on the shape of channel cross‐sections, and the coupling of channels and hillslopes. Recent observations link lateral erosion to the variability of flow. We propose two mechanisms to explain this. One is based on changing shear stress distributions within the channel with varying flood level, the other on the competition between cover and tool effects in fluvial bedrock erosion. We assess these processes for the Liwu River, Taiwan, and conclude that cover and tool effects dominate the partitioning of lateral and vertical erosion in this case. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Tectonic,sedimentary and diagenetic controls on sediment maturity of lower Cambrian quartz arenite from southwestern Baltica     

Sanne Lorentzen  Carita Augustsson  Jens Jahren  Johan P. Nystuen  Niels H. Schovsbo 《Basin Research》2019,31(6):1098-1120

Lower Cambrian quartz arenitic deposits have a worldwide occurrence. In this study, petrographic and mineralogical analyses were carried out on samples from the quartz‐rich Ringsaker Member of the Vangsås Formation from southern Norway and the corresponding Hardeberga Formation from southern Sweden and on the Danish island of Bornholm. The quartz arenite is almost completely quartz cemented and has an average intergranular volume of 30%. The quartz cement is the dominating cause for porosity loss. Dissolution along stylolites and microstylolites is suggested to be the primary and secondary source for the quartz cement respectively. The quartzose sandstone from southern Norway was severely cemented prior to the Caledonian Orogeny, thus limiting the tectonic influence on diagenesis during thrusting. For most samples, authigenic clay minerals and detrital phyllosilicates represent ca. 5% of the present‐day composition. This, together with a low feldspar content, of on average 4%, indicates that the sediment was extremely quartz‐rich already during deposition. The low amount of feldspar prior to burial and the formation of early diagenetic kaolinite point to weathering, sediment reworking and early diagenesis act as important controls on sediment maturity. The large variation in clay‐mineral and feldspar content between the localities, as well as within the sandstone successions, can be explained by different palaeogeography on the shelf during deposition and subsequently dissimilar subjection to reworking and early diagenetic processes. Weathering in the provenance area, reworking in the depositional shallow‐marine environment and meteoric flushing during the burial stage are suggested to explain the high mineralogical maturity of the lower Cambrian sandstone from southwestern Baltica. These processes may generally account for similar quartz‐rich shallow‐marine sandstone units, deposited as a result of intensive continental denudation and during temperate to subtropical and moderately humid conditions.  相似文献   

Optimal planning and operation of irrigation systems under water resource constraints in Oman considering climatic uncertainty     

Niels Schütze  Sebastian Kloss  Franz Lennartz  Ahmed Al Bakri  Gerd H. Schmitz 《Environmental Earth Sciences》2012,65(5):1511-1521

In this contribution, we introduce a stochastic framework for decision support for optimal planning and operation of water supply in irrigation. This consists of (1) a weather generator for simulating regional impacts of climate change on the basis of IPCC scenarios, (2) a tailor-made evolutionary optimization algorithm for optimal irrigation scheduling with limited water supply, (3) a mechanistic model for simulating water transport and crop growth in a sound manner, and (4) a kernel density estimator for estimating stochastic productivity, profit, and demand functions by a nonparametric method. As a result of several simulation/optimization runs within the framework, we present stochastic crop-water production functions (SCWPF) for different crops which can be used as a basic tool for assessing the impact of climate variability on the risk for the potential yield for specific crops and specific agricultural areas. A case study for an agricultural area in the Al Batinah region of the Sultanate of Oman is used to illustrate these methodologies. In addition, microeconomic impacts of climate change and the vulnerability of the agro-ecological system are discussed.  相似文献   

Meteorological observations 1998 at the arctic station,Qeqertarsuaq (69°15'N), Central West Greenland/Active layer monitoring in two Greenlandic permafrost areas: Zackenberg and Disko Island     

Ole Humlum  Birger Ulf Hansen  Niels Nielsen  Hanne H. Christiansen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):113-121

An automatic meteorological station has been operating at the Arctic Station (69°15'N, 53°31'W) in West Greenland since 1990. This paper summarises meteorological parameters during 1998, including snow cover, ground temperatures and active layer development, and presents comments on the local permafrost thickness.

Abstract

Active layer monitoring in Greenland was started in 1996 and 1997, and forms part of the Circumpolar Active Layer Monitoring (CALM) Network of the International Permafrost Association (IPA). The results of the first years of this monitoring of thaw progression and maximum active layer thickness in two Greenlandic permafrost areas are presented. Two sites are in the continuous permafrost zone at Zackenberg in NE Greenland (74 °N), and one at Disko Island in W Greenland (69 °N), at the border between discontinuous and continuous permafrost.

The data collected at Zackenberg demonstrate interannual variation in the timing of thaw progression in the monitoring grid holding a seasonal snowpatch, while there is less variation in the horizontal grid without a snowpatch. The maximum active layer thickness for the two Zackenberg grids is more or less consistent for the first three years with averages from 58 to 66 cm in mid and late August. At Disko the active layer reached 71 cm in mid August 1998. Spatially the distribution of the maximum, annual active layer thickness within the grids is concordant.  相似文献   

Total sediment budget of a transgressive barrier-spit,Skallingen, SW Denmark: A review     

Christian Christiansen  Troels Aagaard  Jesper Bartholdy  Merete Christiansen  Jørgen Nielsen  Niels Nielsen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):107-126

Average sea-level rise in the northern part of the Danish Wadden Sea has been 1.3 mm a^?1 during the last 100 years but during the last 25 years a rise of 4.2 mm a^?1 was observed. Concurrent with the recent sea-level rise the Skallingen barrier spit has migrated landward by 3–5 m a^?1. Long term sediment budgets for each of the morphological units involved in the migration are reviewed (e.g. onshore in the shore face +90.000 m³ a^?1, longshore -641.000 m³ a^?1, foredunes +65,000 m³ a^?1, overwash fan including shorenormal dunes +11,000 m³ a^?1, spit terminus -96,000 m³ a^?1, tidal flat + 10,000 m³ a^?1 and backbarrier salt marsh +33,000 m³ a^?1) and used to establish the relative importance of sediment transport processes involved in barrier migration. Strong interannual variations exist in the long term budget making evaluation of barrier behaviour based on short term measurements doubtful. In a cross shore sense the barrier spit is accreting in spite of the sea level rise. This is specially pronounced at an active overwash fan. However, due to substantial sediment losses to longshore transport the barrier, gets narrower and shorter during its transgressive behaviour. This may indicate that preservation of barriers in the geological record during rapid sea level rise is promoted when sediment loss to longshore transport is insignificant.  相似文献   

Role of landscape parameters in riverine run-off,and sediment and organic matter yield on Disko Island,West Greenland     

Morten Rasch  Niels Nielsen  Christian Christiansen  Thomas Balstrøm  Robert Gilbert  Joseph Desloges 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(2):1-11

Measurements of discharge and suspended sediment and organic matter yield from nine different drainage basins on the island Disko in central West Greenland were carried out in the period 19–30 July 1997. A series of landscape properties (glacier cover, altitude, slope, aspect and vegetation cover) were measured for each drainage basin from a digital elevation model and a satellite image. Principal Component Analysis and regression statistics have been used to examine which landscape parameters dominate the measured discharges and yields. It is concluded that differences in suspended sediment and organic matter yield between the drainage basins can be explained by the measured morphometric properties while differences in water run-off can not. Glacier cover percentage and percent area above 800 m a.s.l. were the most important parameters influencing suspended sediment and organic matter yield in the drainage basins on Disko during the study period.  相似文献