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121.
122.
Adrian DeHeer-Amissah Ulf Högström Ann-Sofi Smedman-Högström 《Boundary-Layer Meteorology》1981,20(1):35-49
A set of semi-continuous measurements of temperature, wind and moisture gradients as well as of net radiation and ground heat flux covering a period of about one and a half years has been analysed to give a corresponding set of complete surface energy balance data on an hourly basis. An analysis of the evaporation data so obtained is given.It is shown that surface resistance r
S exhibits a diurnal trend: values are smallest (ca. 150 s m-1) a few hours before noon and increase to as much as 800 s m-1 towards dusk. The minimum values tend to be higher during dry periods when the soil moisture is low. There is also some indication that r
S decreases rapidly soon after rainfall.An exponential relation is found between the fraction of available energy used as evaporative flux, , and r
S for values of r
I/rS <0.70, where r
I is the climatological resistance. On the other hand, the ratio of r
I to r
S is linearly correlated with , implying that an equilibrium state is established between the grass surface and the atmosphere, at least from mid-morning to mid-afternoon when the leaves are dry. Near-noon values calculated by Stewart and Thom for Thetford Forest also follow a linear trend.The above two regression results (In (r
S) versus r
I/rS versus ) are combined to obtain an empirical relation of the form r
I=m exp (a-b) which is used to estimate evaporative flux. The estimates are found to be within 20% of calculated values.Guest Scientist from Department of Physics, University of Cape Coast, Cape Coast, Ghana. 相似文献
123.
Large areas of acid sulfate (AS) soils are located along the coastal plains of Finland, and previous studies have shown that
after reclamation they release extreme quantities of metals to watercourses in mid-western and northern Finland. In this study
on streams of south-western Finland, where little information about AS soils is available, these soils were found to exhibit
the same pattern of elevated metal- and sulfate concentrations as in the notorious AS soil landscapes of mid-western Finland.
Meteorologically/hydrologically driven temporal variations of these elements were great in the most affected streams. There
were also significant positive implications regarding future environmental work; AS soils in the highlighted region were found
to cause sudden temporal influxes of acidic water only in the most affected streams, indicating that the overburden and soils
of the area discharge well buffered water. Moreover, it was indicated that the high (less toxic) metal concentrations are
largely caused by erosion of suspended phyllosilicates (<0.45 μm) from farmland rather than by AS soils. 相似文献
124.
Several intrusions of ultrabasic to basic composition occur in the Roslagen area of east‐central Sweden in close spatial and temporal association with the surrounding 1.90–1.87 Ga old early orogenic Svecofennian granitoids. An imprecise Sm‐Nd WR errorchron yields an age of 1895 ± 71 Ma. In spite of the penetrative deformation in the granitoids, the basic–ultrabasic rocks mostly appear undeformed and largely preserve magmatic textures with plagioclase, olivine (in some rock types), orthopyroxene and clinopyroxene, and amphibole as major constituents. The plagioclase is typically very anorthitic (ca. An90). The Roslagen intrusions range in composition from primitive to evolved (Mg# 80 to 49) but contain only 40–50 wt% SiO2. Many samples are highly elevated in Al2O3 (up to 30 wt%), CaO (up to 16 wt%) and Sr (up to 800 ppm), with strongly positive Eu and Sr anomalies, in line with being plagioclase cumulates. Although masked by cumulus effects, the relative trace element contents indicate a volcanic arc signature. The initial Nd isotope composition is homogeneously ‘mildly depleted’, with εNd of +0.3 to +1.1, and the initial Sr isotope composition ‘mildly enriched’, with εSr of +8 to +15. Non‐cumulus rocks with small Eu and Sr anomalies can be used to deduce the composition of the parental magma. This LILE‐ and LREE‐enriched and HFSE‐depleted high‐alumina basalt magma, with Mg# of ca. 50–60 and Ca# of ca. 80, most likely formed by partial melting of mantle material, enriched by fluids in a subduction environment, at 1.9 Ga. The cumulate rocks apparently crystallized from a somewhat more evolved water‐rich magma with Mg# of ca. 40. Crystallization was followed by the development of late‐magmatic to post‐magmatic coronas between olivine and plagioclase in the presence of H2O‐rich fluids. The subduction‐related setting would make these intrusions Palaeoproterozoic counterparts of Alaskan‐type ultramafic intrusions, but they differ from those in being plagioclase enriched, possibly reflecting different levels of exposure. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
125.
Jens Götze Hans-Peter Schertl Rolf D. Neuser Ulf Kempe John M. Hanchar 《Mineralogy and Petrology》2013,107(3):373-392
Optical microscope-cathodoluminescence (OM-CL) microscopy is a modern luminescence technique with widespread applications in geosciences. Many rock-forming and accessory minerals show specific CL properties that can be successfully used in geoscience and materials science research. One of the most spectacular applications is the visualization of growth textures, alteration, and other internal textures in minerals that are not discernible with other analytical techniques. These results provide information about the real structure of minerals and materials and can be used for the reconstruction of geological processes of mineral formation and subsequent alteration. The information obtained from CL imaging in combination with spectral measurements of the CL emission allows for a more thorough understanding of structural states of solids and/or trace-element incorporation. Additional information can be obtained when luminescence studies are combined with other analytical techniques with high sensitivity and high spatial resolution. 相似文献
126.
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
127.
Sebastian H. Mernild Bent Hasholt Birger Ulf Hansen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(2):49-56
Geografisk Tidsskrift, Danish Journal of Geography 105(2):49–56, 2005 Meteorological stations have been in operation since 1993 at Sermilik (65°40'N, 38°10'W), located in southeast Greenland. This note presents meteorological observations for the year 2003, including ground temperature, orographic effect (liquid precipitation) and air temperature lapse rates between two meteorological stations, Station Nunatak (515 m a.s.l.) and Station Coast (25 m a.s.l.). 相似文献
128.
Marius N. Müller Ba?ak K?sakürek Ruth Gutperlet Ulf Riebesell Anton Eisenhauer 《Geochimica et cosmochimica acta》2011,75(8):2088-5818
Calcium and magnesium concentrations in seawater have varied over geological time scales. On short time scales, variations in the major ion composition of seawater influences coccolithophorid physiology and the chemistry of biogenically produced coccoliths. Validation of those changes via controlled laboratory experiments is a crucial step in applying coccolithophorid based paleoproxies for the reconstruction of past environmental conditions. Therefore, we examined the response of two species of coccolithophores, Emiliania huxleyi and Coccolithus braarudii, to changes in the seawater Mg/Ca ratio (≈0.5 to 10 mol/mol) by either manipulating the magnesium or calcium concentration under controlled laboratory conditions. Concurrently, seawater Sr/Ca ratios were also modified (≈2 to 40 mmol/mol), while keeping salinity constant at 35. The physiological response was monitored by measurements of the cell growth rate as well as the production rates of particulate inorganic and organic carbon, and chlorophyll a. Additionally, coccolithophorid calcite was analyzed for its elemental composition (Sr/Ca and Mg/Ca) as well as isotope fractionation of calcium and magnesium (Δ44/40Ca and Δ26/24Mg). Our results reveal that physiological rates were substantially influenced by changes in seawater calcium rather than magnesium concentration within the range estimated to have occurred over the past 250 million years when coccolithophores appear in the fossil record. All physiological rates of E. huxleyi decreased at a calcium concentration above 25 mmol L−1, whereas C. braarudii displayed a higher tolerance to increased seawater calcium concentrations. Partition coefficient of Sr was calculated as 0.36 ± 0.04 (±2σ) independent of species. Partition coefficient of Mg2+ increased with increasing seawater Ca2+ concentrations in both coccolithophore species. Calcium isotope fractionation was constant at 1.1 ± 0.1‰ (±2σ) and not altered by changes in seawater Mg/Ca ratio. There is a well-defined inverse linear relationship between calcium isotope fractionation and partition coefficient of Sr2+ in all experiments, suggesting similar controls on both proxies in the investigated species. Magnesium isotope ratios were relatively stable for seawater Mg/Ca ratios ranging from 1 to 5, with a higher degree of fractionation in Emiliania huxleyi (by ≈0.2‰ in Δ26/24Mg). Although Mg/Ca ratios in the calcite of coccolithophores and foraminifera are similar, the former have considerably higher Δ26/24Mg (by >+3‰), presumably due to differences in calcification mechanisms between the two taxa. These observations suggest, a physiological control over magnesium elemental and isotopic fractionation during the process of calcification in coccolithophores. 相似文献
129.
Jan Esper Lara Klippel Paul J. Krusic Oliver Konter Christoph C. Raible Elena Xoplaki Jrg Luterbacher Ulf Bntgen 《Climate Dynamics》2020,54(3):1367-1382
The Mediterranean has been identified as particularly vulnerable to climate change, yet a high-resolution temperature reconstruction extending back into the Medieval Warm Period is still lacking. Here we present such a record from a high-elevation site on Mt. Smolikas in northern Greece, where some of Europe’s oldest trees provide evidence of warm season temperature variability back to 730 CE. The reconstruction is derived from 192 annually resolved, latewood density series from ancient living and relict Pinus heldreichii trees calibrating at r1911–2015 = 0.73 against regional July–September (JAS) temperatures. Although the recent 1985–2014 period was the warmest 30-year interval (JAS Twrt.1961–1990 = + 0.71 °C) since the eleventh century, temperatures during the ninth to tenth centuries were even warmer, including the warmest reconstructed 30-year period from 876–905 (+ 0.78 °C). These differences between warm periods are statistically insignificant though. Several distinct cold episodes punctuate the Little Ice Age, albeit the coldest 30-year period is centered during high medieval times from 997–1026 (− 1.63 °C). Comparison with reconstructions from the Alps and Scandinavia shows that a similar cold episode occurred in central Europe but was absent at northern latitudes. The reconstructions also reveal different millennial-scale temperature trends (NEur = − 0.73 °C/1000 years, CEur = − 0.13 °C, SEur = + 0.23 °C) potentially triggered by latitudinal changes in summer insolation due to orbital forcing. These features, the opposing millennial-scale temperature trends and the medieval multi-decadal cooling recorded in Central Europe and the Mediterranean, are not well captured in state-of-the-art climate model simulations. 相似文献
130.
Rana Arun Nikulin Grigory Kjellstrm Erik Strandberg Gustav Kupiainen Marco Hansson Ulf Kolax Michael 《Climate Dynamics》2020,54(5):2883-2901
Climate Dynamics - Two ensembles of climate simulations, one global and one regional, are used to investigate model errors and projected climate change in seasonal mean temperature and... 相似文献