Physical conditions in eruptive prominences at several solar radii     

Rainer M. E. Illing  R. Grant Athay 《Solar physics》1986,105(1):173-190

SMM data from the Corograph/Polarimeter experiment giving intensities of H and continuum emission in eight erupting prominences are analyzed to obtain the physical conditions in the regions of H emission. Since the H intensity depends upon three unknowns whereas only two independent observations are available, it is necessary to assume one additional condition in order to obtain unique solutions. Solutions are chosen that give the maximum expansion of the prominence volume as reflected by minimum values of the electron density. These solutions correspond closely with those giving the best agreement between the gas pressure in the prominence and the ambient coronal pressure. Electron densities are found to be of the order of 10⁸ cm^-3 at temperatures near 2 × 10⁴ K.The National Center for Atmospheric Research is operated by the University Corporation for Atmospheric Research under sponsorship of the National Science Foundation.  相似文献   

A THEORETICAL APPROACH TO RURAL LAND-USE PATTERNS     

A. Grant  Anderson 《New Zealand geographer》1973,29(2):198-199

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Towards the general circulation of the North Atlantic ocean     

Carl Wunsch  Barbara Grant 《Progress in Oceanography》1982,11(1):1-59

After reviewing the inverse method, we apply it to deducing the general circulation of the North Atlantic ocean. We argue that the method is purely classical in nature, being nothing more than a mathematical statement of the principles upon which nearly all previous circulation schemes have been based. The ‘smoothed’ solution is shown to represent the components of the flow field that are determinable independently of the initial reference level. We then produce two circulation schemes based upon two different initial reference levels — 2000 decibars and the bottom — called North Atlantic-1A and North Atlantic-1B respectively. The models share many features in common and are strikingly similar to several previous schemes, most notably those of Jacobsen and Defant in the region west of Bermuda. No simple level-of-no-motion emerges in the flow fields; rather the velocity sections exhibit a complex cellular structure. Zonally integrated meridional cells of models and of the uniquely determined components are very similar, showing a poleward movement of warm saline water compensated at depth by a return flow of cold, fresher water. The magnitudes of the implied polar sea overflows and the heat fluxes are in good agreement with previous estimates. Finally, it is argued that neither these model circulations nor any other circulation pattern based upon the existing data can be regarded as actually representing the true time average ocean circulation because the data are aliased in time; the frequency/wavenumber spectrum of the ocean is inadequately known to determine the resulting errors.  相似文献   

张八岭地区岩群出露年代研究     

徐孝彬  王建  Francoise Yiou  Grant Raisbeck  朱捷  姜洪涛  杨亦青 《海洋地质与第四纪地质》2003,23(1):77-79

暴露岩石中宇生核素的浓度与暴露年代、侵蚀速率相关,暴露年代和侵蚀速率可相互求证,但两者均为未知数时,可求算出最大侵蚀速率和最小暴露年代。据此得出张八岭地区的最大侵蚀速率为7 12m/Ma,最小暴露年代为(85700±1500)a,这一年代远小于统一夷平面的形成年代(7～3 6Ma),造成这种差距的主要原因是:①张八岭地区侵蚀速率大,岩石中宇生核素的浓度较早达到平衡,即达到该地区的测年上限;②采样地区曾被土壤覆盖,造成计算年代值过于年轻。  相似文献   

Groundwater amphipods alter aquifer sediment structure          下载免费PDF全文

Christine Stumpp  Grant C. Hose 《水文研究》2017,31(19):3452-3454

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Burial and preservation of a 30,000 year old perennial snowbank in Red Creek valley,Ogilvie Mountains,central Yukon,Canada     

Denis Lacelle  Melanie St-Jean  Bernard Lauriol  Ian D. Clark  Antoni Lewkowicz  Duane G. Froese  Stephen C. Kuehn  Grant Zazula 《Quaternary Science Reviews》2009,28(27-28):3401-3413

This study describes the origin and age of a body of massive ground ice exposed in the headwall of a thaw slump in the Red Creek valley, central Yukon, Canada. The site is located beyond the limits of Pleistocene glaciation in central Yukon and within the southern limit of the modern continuous permafrost zone. The origin of the massive ground ice, which is preserved under a fine-grained diamicton containing thin layers of tephra, was determined through ice petrography, stable O-H isotope composition of the ice, and gas composition of occluded air entrapped in the ice. The age of the massive ground ice was established by identifying the overlying tephra and radiocarbon dating of a “muck” deposit preserved within the ice. Collectively, the results indicate that the massive ground ice formed by snow densification with limited melting-refreezing and is interpreted as being a buried perennial snowbank. The muck deposit within the ice, which yielded an age of 30,720 ± 340 ¹⁴C a BP, and the Dawson tephra (25,300 ¹⁴C a BP) overlying the perennial snowbank, indicates that the snowbank accumulated at roughly the transition between marine isotope stages 3 and 2. Dry climatic conditions at this time and possibly high winds enabled the snowbank to accumulate in the absence of extensive local valley glaciation as occurred in the mountains to the south. In addition to documenting the persistence of relict permafrost and ground ice to warming climate in regions where they are predicted to disappear by numerical models, this study presents evidence of an isotopic biosignature preserved in a body of massive ground ice.  相似文献   

Hit or miss: Glacial incisions of snowball Earth     

Ross N. Mitchell  Thomas M. Gernon  Adam Nordsvan  Grant M. Cox  Zheng‐Xiang Li  Paul F. Hoffman 《地学学报》2019,31(4):381-389

Estimated at ~58 Ma in duration, the Sturtian snowball Earth (ca. 717–659 Ma) is one of the longest‐known glaciations in Earth history. Surprisingly few uncontroversial lines of evidence for glacial incisions associated with such a protracted event exist. We report here multiple lines of geological field evidence for deep but variable glacial erosion during the Sturtian glaciation. One incision, on the scale of several kilometres, represents the deepest incision documented for snowball Earth; another much more modest glacial valley, however, suggests an erosion rate similar to sluggish Quaternary glaciers. The heterogeneity in snowball glacial incisions reported here and elsewhere was likely influenced by actively extending horst‐and‐graben topography associated with the breakup of supercontinent Rodinia.  相似文献   

Exploring the extent to which fluctuations in ice-rafted debris reflect mass changes in the source ice sheet: a model–observation comparison using the last British–Irish Ice Sheet     

David J. Wilton  Grant R. Bigg  James D. Scourse  Jeremy C. Ely  Chris D. Clark 《第四纪科学杂志》2021,36(5):934-945

The British and Irish Ice Sheet (BIIS) was highly dynamic during the Late Quaternary, with considerable regional differences in the timing and extent of its change. This was reflected in equally variable offshore ice-rafted debris (IRD) records. Here we reconcile these two records using the FRUGAL intermediate complexity iceberg–climate model, with varying BIIS catchment-level iceberg fluxes, to simulate change in IRD origin and magnitude along the western European margin at 1000-year time steps during the height of the last BIIS glaciation (31–6 ka bp ). This modelled IRD variability is compared with existing IRD records from the deep ocean at five cores along this margin. There is general agreement of the temporal and spatial IRD variability between observations and model through this period. The Porcupine Bank off northwestern Ireland was confirmed by the modelling as a major dividing line between sites possessing exclusively northern or southern source regions for offshore IRD. During Heinrich events 1 and 2, the cores show evidence of a proportion of North American IRD, more particularly to the south of the British Isles. Modelling supports this southern bias for likely Heinrich impact, but also suggests North American IRD will only reach the British margin in unusual circumstances.  相似文献   

Technology transfer in the CDM: an updated analysis     

Kevin Murphy  Grant A. Kirkman  Stephen Seres 《Climate Policy》2015,15(1):127-145

The prevalence of technology transfer (TT) for Clean Development Mechanism (CDM) projects is analysed, based on information in the project design documents (PDDs) of 3949 projects registered as of 31 March 2012. Responses to a follow-up survey indicate that the PDD statements that concern TT are reasonably accurate and at least 39% of the related projects are expected to involve it. Technology transfer is very heterogeneous across project types and is more common for larger projects. It also usually involves both knowledge and equipment and differs significantly by host country. Technology transfer has declined over time in China, India, and Brazil, the countries that host most of the CDM projects, but it has remained high for other host countries. A host country's existing capacity specific to the technology, the scope for economic deployment of the technology, and complementary policies to build capacity and promote TT, increase the frequency of TT by CDM projects. The technology used by CDM projects originates mostly from Germany, the US, Japan, Denmark, and China, with multiple suppliers of the technology for all project types.  相似文献   

Iron in plagioclase in the Bushveld and Skaergaard intrusions: implications for iron contents in evolving basic magmas   总被引：1，自引：0，他引：1  

Christian Tegner  R. Grant Cawthorn 《Contributions to Mineralogy and Petrology》2010,159(5):719-730

The evolved, iron-rich rocks of the tholeiitic Bushveld and Skaergaard intrusions are similar in containing cumulus magnetite, ilmenite, plagioclase, clinopyroxene, apatite and olivine, and also orthopyroxenes/pigeonite in Bushveld. Here, we evaluate their liquid evolution trends using the total iron content in plagioclase determined by electron microprobe analyses. To aid this analysis a revised mass balance model for the liquid evolution of Skaergaard is presented. For plagioclase in the Upper Zone of Skaergaard it was previously demonstrated that total FeO increases from ~0.25 to ~0.45 wt% with differentiation and correlates inversely with An% [100 × Ca/(Na + Ca)]. The reverse trend is observed in two recently published datasets for Bushveld, showing that total FeO in plagioclase decreases upward through the magnetite-bearing Upper Zone from ~0.30 to ~0.15% and from ~0.40 to ~0.25% in the western and northern limbs, respectively, and correlates positively with An%. The partition coefficient of total iron between plagioclase and magma increases with oxidation and polymerisation in the liquid. Although Bushveld formed under slightly more oxidizing conditions than Skaergaard, differences in the partition coefficients cannot explain the two observed trends. We therefore conclude that the differentiation trends of the liquids subsequent to magnetite saturation were fundamentally different. The inferred liquid composition for Bushveld contained about 15 wt% total FeO at the level of magnetite-in, which is slightly less than the total FeO content of the subsequent cumulates. In contrast, the Skaergaard liquid contained more total FeO than the ensuing cumulates. As a result, in Bushveld residual liquids total FeO decreased after magnetite saturation, whereas in Skaergaard the residual liquids continued to become enriched in iron. This conclusion is corroborated by simple mass balance calculations between modelled residual liquids and extracted cumulate rocks. Despite the mineralogical similarities of evolved iron-rich rocks of Skaergaard and Bushveld, their liquid evolution trends were very different, and generalizations about the extent of iron enrichment in tholeiitic magmas should be avoided.  相似文献