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531.
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Ephemeral active regions attain maximum development within 1 day or less of their initial appearance and are typically observed for 1–2 days. They appear mostly as small bipolar regions having a typical dimension of about 30000 km and a maximum total flux of the order of 1020 Mx. The ephemeral regions generally do not produce sunspots and flares, though they are identified in H as small active centers.Our observations indicate that the ephemeral regions are frequently generated both near large active centers and in extensive quiet areas of the Sun. The location of emerging ephemeral regions does not appear to be associated with the distribution of the existing network fields. As many as 100 ephemeral regions may form per day. On the average, as much flux may erupt in the form of small ephemeral regions as erupts in larger active centers.The latitude distribution of ephemeral regions appears to be much wider than that of sunspots and major active centers. Their frequency of occurrence does not appear to follow the sunspot cycle. 相似文献
534.
Rainer?ThomasEmail author Hans-Jürgen?F?rster Karen?Rickers James?D.?Webster 《Contributions to Mineralogy and Petrology》2005,148(5):582-601
Quartz crystals from topaz–zinnwaldite–albite granites from Zinnwald (Erzgebirge, Germany) contain, in addition to primary and secondary fluid inclusions (FIs), abundant crystalline silicate-melt inclusions (MIs) with diameters up to 200 m. These MIs represent various stages of evolution of a highly evolved melt system that finally gave rise to granite-related Sn–W mineralization. The combination of special experimental techniques with confocal laser Raman-microprobe spectroscopy and EMPA permits precise measurement of elevated contents of H2O, F, and B in re-homogenized MIs. The contents of H2O and F were observed to increase from 3 to 30 and 1.9 to 6.4 wt%, respectively, during magma differentiation. However, there is a second MI group, very rich in H2O, with values up to 55 wt% H2O and an F concentration of approximately 3 wt%. Ongoing enrichment of volatiles H2O, F, B, and Cl and of Cs and Rb can be explained in terms of magma differentiation triggered by fractional crystallization and thus, is suggested to reflect elemental abundances in natural magmas, and not boundary-layer melts. Partitioning between melt and cogenetic fluids has further modified the magmatic concentrations of some elements, particularly Sn. The coexistence of two types of MIs with primary FIs indicates fluid saturation early in the history of magma crystallization, connected with a continuous sequestration of Sn, F, and B. The results of this study provide additional evidence for the extraordinary importance of the interplay of H2O, F, and B in the enrichment of Sn during magma differentiation by decreasing the viscosity of and increasing the diffusivity in the melts as well as by the formation of various stable fluoride complexes in the melt and coexisting fluid.
相似文献
Rainer ThomasEmail: Phone: +49-331-2881474 |
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537.
Variability of dense water formation in the Ross Sea 总被引:1,自引:0,他引:1
This paper presents results from a model study of the interannual variability of high salinity shelf water (HSSW) properties
in the Ross Sea. Salinity and potential temperature of HSSW formed in the western Ross Sea show oscillatory behaviour at periods
of 5–6 and 9 years superimposed on long-term fluctuations. While the shorter oscillations are induced by wind variability,
variability on the scale of decades appears to be related to air temperature fluctuations. At least part of the strong decrease
of HSSW salinities deduced from observations for the period 1963–2000 is shown to be an aliasing artefact due to an undersampling
of the periodic signal. While sea ice formation is responsible for the yearly salinity increase that triggers the formation
of HSSW, interannual variability of net freezing rates hardly affects changes in the properties of the resulting water mass.
Instead, results from model experiments indicate that the interannual variability of dense water characteristics is predominantly
controlled by variations in the shelf inflow through a sub-surface salinity and a deep temperature signal. The origin of the
variability of inflow characteristics to the Ross Sea continental shelf can be traced into the Amundsen and Bellingshausen
Seas. The temperature anomalies are induced at the continental shelf break in the western Bellingshausen Sea by fluctuations
of the meridional transport of circumpolar deep water with the eastern cell of the Ross Gyre. In the Amundsen Sea, upwelling
due to a persistently cyclonic wind field carries the signal into the surface mixed layer, leading to fluctuations of the
vertical heat flux, anomalies of brine release near the sea ice edge, and consequently to a sub-surface salinity anomaly.
With the westward flowing coastal current, both the sub-surface salinity and deep temperature signals are advected onto the
Ross Sea continental shelf. Convection carries the signal of salinity variability into the deep ocean, where it interacts
with modified circumpolar deep water upwelled onto the continental shelf as the second source water mass of HSSW. Sea ice
formation on the Ross Sea continental shelf thus drives the vertical propagation of the signal rather than determining the
signal itself. 相似文献
538.
William C. Johnson Karen L. Willey Joseph A. Mason David W. May 《Quaternary Research》2007,67(3):474-486
The middle Wisconsinan Gilman Canyon Formation at the Buzzard's Roost type locality in southwestern Nebraska was investigated to document the stratigraphy and to reconstruct the environmental and climate record. The Gilman Canyon Formation was subdivided into three loess units and three soils, with radiocarbon ages constraining it between about 40 ka and 25 ka. Stable carbon isotope ratios, magnetic susceptibility, and carbon content were used to define and characterize soils within both the Gilman Canyon Formation and underlying Illinoian Loveland Loess. At the height of soil development within the Gilman Canyon Formation, climate was supporting C4-dominated grassland, with July temperatures equal to or exceeding those of today. Soil-forming intervals within the Loveland Loess, including the Sangamon Soil, also exhibited relative increases in C4 biomass. Climate, as recorded in the Gilman Canyon Formation, is corroborated by regional proxy data. The formation accumulated during MIS 3, and concurrent soil formation coincided with a summer insolation maximum. 相似文献
539.
User Assessment as Input for Useful Geospatial Representations within Mobile Location-Based Services
Karen Wealands Peter Benda Suzette Miller William E Cartwright 《Transactions in GIS》2007,11(2):283-309
Mobile Location‐Based Services (mLBS) are an increasingly consumer‐based concept borne from, and continually driven by, technology‐centred development; as opposed to the needs of end users. Where users have been made a focus, the research generally concerns issues of overall system appearance, functionality, information content and interaction methods, with little emphasis on the component geospatial representations. This paper describes the initial stages of a research project aimed at filling this void through the application of a qualitative User‐Centred Design (UCD) methodology for optimising geospatial representations within mLBS applications, in order to support a selected user group: Australian ‘leisure‐based travellers’. Presented in this paper is an account of two UCD activities adopted for the research. The first, user profiling, served to define the target user population in terms of their technological, geospatial and travel experiences, using an online questionnaire. The second, user task analysis, involved in‐depth interviews with a subset of users in order to obtain a deeper understanding of the geospatial goals, tasks, needs and preferences within the population, as well as the range of user differences and variability in tasks present. An overall user assessment, through combined analysis of the two result sets, highlighted considerations for the ongoing research, including a set of specific implications for the design of alternative models for geospatial services, representations and interactions. The themes described in this paper represent an initial and necessary component of UCD, which has been largely overlooked in research relating to mLBS. Whilst the focus here is on a specific user group and context of use, it is envisaged that many of the concepts tested and ratified by the resulting models will be relevant to mLBS applications in general. 相似文献
540.
Variability of dissolved Fe2+ and ∑H2S concentrations in porewaters were studied, using cathodic stripping voltammetry (CSV) microelectrodes, in sediments overlain
by hypoxic waters in the summer from the southeastern region of Corpus Christi Bay, Texas (CCB) and the Mississippi River
Bight (MRB), Louisiana. These measurements were complimented by sediment microcosm studies where oxygen concentrations in
the overlying water were manipulated. Sulfate reduction rates, benthic oxygen demand, total reduced sulfide, porewater sulfate,
and total organic carbon were also determined. Fe2+ and ∑H2S were the major dissolved redox-reactive dissolved species in these sediments. During hypoxic conditions, an upward migration
of porewater Fe2+ and ∑H2S occurred, with Fe2+ reaching much higher maximum concentrations than ∑H2S. Statistically significant (p < 0.05) differences in both Fe2+ and ∑H2S occurred between sediments at the CCB and MRB study sites. Although both sites were Fe-dominated, reactive and dissolved
iron were higher while ∑H2S was lower at the MRB site. However, there were no statistically significant (p > 0.05) difference in regard to ∑H2S between microcosm and field monitoring studies. Results indicated that, for Fe2+ and ∑H2S, relatively large and rapid changes occurred in both the concentrations and distributions of these important porewater constituents
in response to relatively short-term changes in overlying water oxygen content. Model calculations indicated that conditions
in the sediments can be responsible for the induction of hypoxic conditions in the formation of hypoxic overlying waters in
<6 days at CCB and ~20 days at MRB. 相似文献