CHANGING SPATIAL CHARACTERISTICS OF WILLAMETTE VALLEY FARMS     

George A. van Otten 《The Professional geographer》1980,32(1):63-71

In the post-World War II era the need to achieve satisfactory economies of scale has led to fever but larger farms in the Willamette Valley. Vigorous demand for farm land by the nonfarm sector has served to inflate land values. As a result, farmers have turned to leasing and renting as alternatives to land purchase. Difficulty in finding suitable land with which to enlarge farm operations has led to the use of noncontiguous fields.  相似文献   

A Magnetometer Array Study in Southern Africa     

D. I. Gough  J. H. de  Beer J. S. V. van  Zijl 《Geophysical Journal International》1973,34(4):421-433

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Length Scales of Scalar Diffusion in the Convective Boundary Layer: Laboratory Observations   总被引：1，自引：1，他引：0  

Han?van?DopEmail author  Dirk?van?As  Alec?van?Herwijnen  Mark?F.?Hibberd  Harm?Jonker 《Boundary-Layer Meteorology》2005,116(1):1-35

A laboratory study of scalar diffusion in the convective boundary layer has found results that are consistent with a 1999 large-eddy simulation (LES) study by Jonker, Duynkerke and Cuijpers. For bottom-up and top-down scalars (introduced as ‘infinite’ area sources of passive tracer at the surface and inversion, respectively) the dominant length scale was found to be much larger than the length scale for density fluctuations, the latter being equal to the boundary-layer depth h. The variance of the normalized passive scalar grew continuously with time and its magnitude was about 3–5 times larger for the top-down case than for the bottom-up case. The vertical profiles of the normalized passive scalar variance were found to be approximately constant through the convective boundary layer (CBL) with a value of about 3–8c_*² for bottom-up and 10–50c_*² for top-down diffusion. Finally, there was some evidence of a minimum in the variance and dominant length scale for scalar flux ratios (top-down to bottom-up flux) close to −0.5. All these convection tank results confirm the LES results and support the hypothesis that there is a distinct difference in behaviour between the dynamic and passive variables in the CBL.  相似文献   

A new method to estimate ice age temperatures     

Richard Bintanja  Roderik S. W. van de Wal  Johannes Oerlemans 《Climate Dynamics》2005,24(2-3):197-211

On glacial time scales, the waxing and waning of the Eurasian and North American ice sheets depend largely on variations in atmospheric temperature. As global sea level is primarily determined by the volume of these ice sheets, there is a direct (yet complex) relation between global sea level and the northern hemispheric (NH) temperature. This relation is essentially represented by a model of the NH ice sheets. We use a thermomechanical ice-sheet–ice shelf–bedrock model in conjunction with an inverse method to deduce a time series of NH temperature (from 120 kyr BP until present) that is consistent with the observed global sea level record. The advantage of this method is that it provides the annual mean surface air temperature averaged over the NH continents north of 40°N. The results reveal that ice age temperatures were 4–10°C lower than today, which agrees with other temperature reconstructions. However, reconstructed temperatures are comparitively low during the early stages of the glacial, a feature that is consistent with the rapid growth of the ice sheets. The sensitivity of the results for uncertainties in precipitation rate, in observed sea level and in some other model parameters is examined to quantify the error in reconstructed temperature. During the glacial period (120–15 kyr BP), surface air temperatures in the NH (north of 40°N) were 7.2±1.5°C lower than todays (interglacial) temperatures.  相似文献   

An obliquity-controlled Early Pleistocene river terrace record from Western Turkey?     

Darrel Maddy  Tuncer Demir  David R. Bridgland  Antonie Veldkamp  Chris Stemerdink  Tim van der Schriek  Rob Westaway 《Quaternary Research》2005,63(3):66-346

Investigation of the Pleistocene sequence of the Gediz River, Western Turkey, has revealed a record of Early Pleistocene river terraces. Eleven terraces spanning the interval from 1.67 to 1.245 million years ago (MIS 59–37) are preserved beneath basaltic lava flows. The high number of terraces over this short time period reflects high-frequency sedimentation/incision cycles preserved due to the fortuitous combination of relatively high uplift rates (0.16 mm yr⁻¹) and progressive southwards valley migration. Comparison of this record with ODP967 from the Eastern Mediterranean Basin suggests a link between the production of terraces and obliquity-driven 41,000 year climate cycles in the Early Pleistocene.  相似文献   

Geochemistry of the acid Kawah Putih lake, Patuha Volcano, West Java, Indonesia     

T. Sriwana  M. J. van Bergen  J. C. Varekamp  S. Sumarti  B. Takano  B. J. H. van Os  M. J. Leng 《Journal of Volcanology and Geothermal Research》2000,97(1-4)

Kawah Putih is a summit crater of Patuha volcano, West Java, Indonesia, which contains a shallow, 300 m-wide lake with strongly mineralized acid–sulfate–chloride water. The lake water has a temperature of 26–34°C, pH=<0.5–1.3, S^tot=2500–4600 ppm and Cl=5300–12 600 ppm, and floating sulfur globules with sulfide inclusions are common. Sulfur oxyanion concentrations are unusually high, with S₄O₆²⁻+S₅O₆²⁻+S₆O₆²⁻=2400 – 4200 ppm. Subaerial fumaroles (<93°C) on the lake shore have low molar SO₂/H₂S ratios (<2), which is a favorable condition to produce the observed distribution of sulfur oxyanion species. Sulfur isotope data of dissolved sulfate and native sulfur show a significant ³⁴S fractionation (ΔSO₄–S_e of 20‰), probably the result of SO₂ disproportionation in or below the lake. The lake waters show strong enrichments in ¹⁸O and D relative to local meteoric waters, a result of the combined effects of mixing between isotopically heavy fluids of deep origin and meteoric water, and evaporation-induced fractionation at the lake surface. The stable-isotope systematics combined with energy-balance considerations support very rapid fluid cycling through the lake system. Lake levels and element concentrations show strong seasonal fluctuations, indicative of a short water residence time in the lake as well.Thermodynamic modeling of the lake fluids indicates that the lake water is saturated with silica phases, barite, pyrite and various Pb, Sb, Cu, As, Bi-bearing sulfides when sulfur saturation is assumed. Precipitating phases predicted by the model calculations are consistent with the bulk chemistry of the sulfur-rich bottom sediments and their identified mineral phases. Much of the lake water chemistry can be explained by congruent rock dissolution in combination with preferential enrichments from entering fumarolic gases or brines and element removal by precipitating mineral phases, as indicated by a comparison of the fluids, volcanic rocks and lake bed sediment.Flank springs on the mountain at different elevations vary in composition, and are consistent with local rock dissolution as a dominant factor and pH-dependent element mobility. Discharges of warm sulfate- and chloride-rich water at the highest elevation and a near-neutral spring at lower level may contain a small contribution of crater-lake water. The acid fluid-induced processes at Patuha have led to the accumulation of elements that are commonly associated with volcano-hosted epithermal ore deposits. The dispersal of heavy metals and other potentially toxic elements from the volcano via the local drainage system is a matter of serious environmental concern.  相似文献   

Ground clutter cancellation in incoherent radars: solutions for EISCAT Svalbard radar     

T. Turunen  J. Markkanen  A. P. van Eyken 《Annales Geophysicae》2000,18(9):1242-1247

Incoherent scatter radars measure ionosphere parameters using modified Thomson scatter from free electrons in the target (see e.g. Hagfors, 1997). The integrated cross section of the ionospheric scatterers is extremely small and the measurements can easily be disturbed by signals returned by unwanted targets. Ground clutter signals, entering via the antenna side lobes, can render measurements at the nearest target ranges totally impossible. The EISCAT Svalbard Radar (ESR), which started measurements in 1996, suffers from severe ground clutter and the ionosphere cannot be measured in any simple manner at ranges less than about 120–150 km, depending on the modulation employed. If the target and clutter signals have different, and clearly identifiable, properties then, in principle, there are always ways to eliminate the clutter. In incoherent scatter measurements, differences in the coherence times of the wanted and unwanted signals can be used for clutter cancellation. The clutter cancellation must be applied to all modulations, usually alternating codes in modern experiments, used for shorter ranges. Excellent results have been obtained at the ESR using a simple pulse-to-pulse clutter subtraction method, but there are also other possibilities.  相似文献   

Moscow and St. Petersburg, a sequence of capitals, a tale of two cities     

Olga Gritsai  Herman van der Wusten 《GeoJournal》2000,51(1-2):33-45

From early modern times until the present, Russia (temporarily extended to the USSR) had two capital cities: Moscow and Petersburg. Moscow was the original capital, it was succeeded by Petersburg from the beginning of the 18th century. From the early 20th century onward Moscow again became the capital, but it became a different kind of capital at the end of the 20th century. The paper describes the evolution of the representation of the state function in the appearance of the capital cities by way of the state buildings, the monuments, the street names. In addition it analyses the fate of the former capitals (first Moscow, then Petersburg) in terms of their symbolic functions. Petersburg originated as a capital turned to the outside emphasizing Russia's European vocation, while Moscow was at first the inward looking capital city representing the distinctive spiritual values of Russia. Changes had to do with the changes in the nature of the successive political regimes and with the changing roles of the two cities within those regimes.  相似文献   

Dictators and their capital cities: Moscow and Berlin in the 1930s     

Herman van der Wusten 《GeoJournal》2000,52(2):339-344

Stalin and Hitler planned major changes in the townscapes of their capital cities. These plans were part of their effort to install highly mobilized despotic regimes that needed a wide-ranging set of symbols to focus allegiance and to impress awe. These plans remained to some extent paper exercises but part of it left significant traces in the contemporary cities, particularly in Moscow. The intended changes showed similarities in their megalomania expressed in plans for a gigantic dome surrounded by a huge public square in the core of the city. There were also differences as regards the type of symbols used due to both dictotors' different roles within their regimes, the degree of didactic intent due to the nature of the commanding ideologies and the level of modernization of both countries, and the diverging versions of antimodernist building style (which they shared with many others elsewhere at the time).  相似文献   

Fluid history of UHP metamorphism in Dabie Shan, China: a fluid inclusion and oxygen isotope study on the coesite-bearing eclogite from Bixiling   总被引：32，自引：1，他引：31  

Yilin Xiao  Jochen Hoefs  Alfons M. van den Kerkhof  Jens Fiebig  Yongfei Zheng 《Contributions to Mineralogy and Petrology》2000,139(1):1-16

This paper characterizes late Holocene basalts and basaltic andesites at Medicine Lake volcano that contain high pre-eruptive H₂O contents inherited from a subduction related hydrous component in the mantle. The basaltic andesite of Paint Pot Crater and the compositionally zoned basaltic to andesitic lavas of the Callahan flow erupted approximately 1000 ¹⁴C years Before Present (¹⁴C years b.p.). Petrologic, geochemical and isotopic evidence indicates that this late Holocene mafic magmatism was characterized by H₂O contents of 3 to 6 wt% H₂O and elevated abundances of large ion lithophile elements (LILE). These hydrous mafic inputs contrast with the preceding episodes of mafic magmatism (from 10,600 to ∼3000 ¹⁴C years b.p.) that was characterized by the eruption of primitive high alumina olivine tholeiite (HAOT) with low H₂O (<0.2 wt%), lower LILE abundance and different isotopic characteristics. Thus, the mantle-derived inputs into the Medicine Lake system have not always been low H₂O, primitive HAOT, but have alternated between HAOT and hydrous subduction related, calc-alkaline basalt. This influx of hydrous mafic magma coincides temporally and spatially with rhyolite eruption at Glass Mountain and Little Glass Mountain. The rhyolites contain quenched magmatic inclusions similar in character to the mafic lavas at Callahan and Paint Pot Crater. The influence of H₂O on fractional crystallization of hydrous mafic magma and melting of pre-existing granite crust beneath the volcano combined to produce the rhyolite. Fractionation under hydrous conditions at upper crustal pressures leads to the early crystallization of Fe-Mg silicates and the suppression of plagioclase as an early crystallizing phase. In addition, H₂O lowers the saturation temperature of Fe and Mg silicates, and brings the temperature of oxide crystallization closer to the liquidus. These combined effects generate SiO₂-enrichment that leads to rhyodacitic differentiated lavas. In contrast, low H₂O HAOT magmas at Medicine Lake differentiate to iron-rich basaltic liquids. When these Fe-enriched basalts mix with melted granitic crust, the result is an andesitic magma. Since mid-Holocene time, mafic volcanism has been dominated primarily by hydrous basaltic andesite and andesite at Medicine Lake Volcano. However, during the late Holocene, H₂O-poor mafic magmas continued to be erupted along with hydrous mafic magmas, although in significantly smaller volumes. Received: 4 January 1999 / Accepted: 30 August 1999  相似文献