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351.
Harvey Karen L. Jones Harrison P. Schrijver Carolus J. Penn Matthew J. 《Solar physics》1999,190(1-2):35-44
Simultaneous measurements of the magnetic fields in the photosphere and chromosphere were used to investigate if magnetic
flux is submerging at sites between adjacent opposite polarity magnetic network elements in which the flux is observed to
decrease or `cancel'. These data were compared with chromospheric and coronal intensity images to establish the timing of
the emission structures associated with these magnetic structures as a function of height. We found that most of the cancelation
sites show either that the bipole is observed longer in the photosphere than in the chromosphere and corona (44%) or that
the timing difference of the disappearance of the bipole between these levels of the atmosphere is unresolved. The magnetic
axis lengths of the structures associated with the cancelation sites are on average slightly smaller in the chromosphere than
the photosphere. These observations suggest that magnetic flux is retracting below the surface for most, if not all, of the
cancelation sites studied. 相似文献
352.
N. T. Arndt N. A. Teixeira W. M. White 《Contributions to Mineralogy and Petrology》1989,101(2):187-197
Komatiite lava flows in the Crixás greenstone belt, Goiás, Brazil, have textures and volcanic structures typical of Archean
komatiites, but are geochemically most unusual. The flows are porphyritic and massive, or layered with spinifex upper parts
and olivine cumulate lower parts. MgO contents range from 18 to 40%. In such lavas, only olivine (and minor chromite) can
have crystallized, but neither major nor trace elements fall on olivine control lines. In MgO variation diagrams, CaO and
Sr fall on lines with slopes steeper than olivine control lines; SiO2, FeO, Na2O, K2O and Y show little systematic variation; Zr shows a large variation that does not correlate with MgO; and Al2O3 decreases markedly with decreasing MgO. The aberrant behaviour is highlighted by the REE (rare earth elements) in spinifex
and olivine cumulate layers from three flows: in the spinifex layers, chondrite-normalized REE patterns are hump-shaped with
maxima at Nd or Sm ((La/Sm)N=0.6, (Gd/Yb)N=1.6–2.3), whereas cumulate zones in the same flows have steadily sloping patterns, with LREE enriched relative to HREE ((La/Sm)N=1.3, (Gd/Yb)N=1.4). Neither normal magmatic processes acting during emplacement of the komatiites, nor thermal erosion and wall-rock assimilation
can explain these effects, and we speculate that elements commonly thought of as “immobile” (e.g. Al, Zr, REE) migrated during
hydrothermal alteration or metamorphism. A Pb-Pb whole rock isochron gave an age of 2,728±140 Ma and selected Sm-Nd analyses
an apparent isochron age of 2,825±98 Ma (ɛNd≈0). The Pb-Pb age is believed to be the approximate time of emplacement. Interpretation of the Sm-Nd data is complicated
by the evidence of mobility of REE. 相似文献
353.
Y. Ohashi T. Kawabe Y. Shigeta Y. Hirano H. Kusaka H. Fudeyasu K. Fukao 《Theoretical and Applied Climatology》2009,95(3-4):279-289
We estimated wet-bulb globe temperature (WBGT) using measured meteorological data to understand the bioclimates of human living spaces during the summer season. Our research focused on commercial and residential areas of Okayama City, Japan (population ~700,000). The commercial spaces (CO) mainly consisted of multi-story office buildings, whereas the residential spaces (RE) consisted of one- or two-story residential buildings. On a fine day with southeast winds, the spatially averaged WBGT measured in the CO was higher than that in the RE. The difference was statistically significant and would have caused noticeable discomfort and a high risk of heat disorder for occupants of the CO over the long term. For instance, at 1900 Japan Standard Time (JST), the maximum difference in the WBGT between the CO and RE sites was 2.0°C (23.5°C for the CO and 21.5°C for the RE). From 1800 to 1900 JST, the wet-bulb temperature in the CO was still 1.5–2.0°C higher than that in the RE, even though both areas had the same dry-bulb temperature. This indicates that the CO retained greater amounts of water vapor for longer periods compared to the RE. The wet-bulb temperature in the CO increased rapidly at most observation points when the southeast sea breeze arrived. In contrast, in the RE, the wet-bulb temperature decreased until evening. This difference was caused by moist air transported from a river about 1 km upwind from the CO. The moist air forced an increase in the WBGT and elevated the risk of heat disorder in the CO. The spatially averaged globe temperature of the CO at 1500 JST was 6.2°C lower than that at the RE, causing the WBGT of the CO to decrease. The results suggest that the higher WBGT in the CO was caused by higher wet-bulb temperatures. On a day with southwest winds, the CO and RE showed no difference in WBGT because the river was not included in the upwind source area. 相似文献
354.
Selection of regional historical rainfall time series as input to urban drainage simulations at ungauged locations 总被引:1,自引:0,他引:1
P.S. Mikkelsen H. Madsen K. Arnbjerg-Nielsen D. Rosbjerg P. Harremoës 《Atmospheric Research》2005,77(1-4):4
It has become established practice during the past 20 years to use high-resolution historical rainfall time series as input to hydrological model packages for detailed simulation of urban drainage systems. However, sufficiently long rain series are rarely available from the exact catchment in question and simulations are hence often based on available rain series from other locations. Extreme rainfall properties of importance to the performance of urban storm drainage systems vary significantly even in regions with only minor physiographic differences. Part of this variation can be explained by regional variations of the mean annual rainfall and the remaining statistical residue can be interpreted as statistical uncertainty.In Denmark, more than 75 high-resolution rain gauges are installed across a total area of 43,000 m. About 40 gauges had sufficiently long records to be included in a comprehensive national investigation where newly developed statistical regionalisation procedures were used to model the regional variation of extreme rainfalls. On this basis, a spreadsheet model was made available for estimation of extreme design rainfalls and the associated uncertainty at any location in the country. Statistics were furthermore computed to classify historical rainfall time series according to the developed regional model, and this makes it possible to assess the uncertainty related with using different historical rain series for simulations at ungauged locations.This research indicates that use of historical point rainfall data at ungauged locations introduces a significant uncertainty that is largely overlooked in today's practice. The engineering recommendation is to select historical rain series based on an evaluation of the local physiographic characteristics (e.g., the mean annual rainfall) and a (pre-defined) desired safety level of the simulations. 相似文献
355.
Concentrations of the members of the 238U decay chain and 232Th were determined in volcanic rocks from convergent plate margins, intraplate volcanoes and oceanic spreading centers. Contemporary and historical volcanic rocks from Mt. St. Helens, Arenal, El Chichon, Hawaii and Iceland and submarine basaltic glass from the Galapagos spreading center all show no fractionation of U and Th in the mantle source or during magma formation at least for the past 300,000 years. Mauna Kea (Hawaii) rocks of alkaline composition greater than 4000 years old and an old submarine basalt show disequilibrium for several of the nuclides in the 238U decay chain. We interpret these as resulting from post-emplacement processes. 相似文献
356.
Sid P. Halsor 《Bulletin of Volcanology》1989,51(4):271-280
Irregularly shaped, large and clear (LAC) glass inclusions are present in plagioclase phenocrysts in several andesitic lavas erupted from Tolimán volcano, Guatemala. Their morphology is different from densely spaced, fine-grained glass inclusions that form concentric zones in dusty or cellular textured plagioclase phenocrysts. The large size of LAC inclusions make them suitable for microprobe analysis and average bulk compositions are presented for glasses in 30 phenocrysts from eight lava samples. Their compositions are rhyolitic and in disequilibrium, or out-range (Anderson 1976) with respect to whole-rock and groundmass glass compositions. LAC inclusions typically occur in large, tabular plagioclase phenocrysts with relatively uniform, sodic compositions (An 40–54). Compositions of feldspar phenocrysts not containing LAC inclusions range from An 41 to An 81. Petrographic and chemical data support a primary origin for LAC glasses, suggest mixing of mafic and silicic magmas, and also constrain a mechanism for magma mixing. Rapid growth of plagioclase and entrapment of LAC glass occurs during mixing in a vapor-rich silicic liquid under low degrees of undercooling. These conditions are possibly produced in a high-level magma body such as that envisioned by Huppert et al. (1982), where replenishment and subsequent crystallization of a hydrous magma induces density instability and mixing with the resident magma. 相似文献
357.
H. F. Assunção J. F. Escobedo A. P. Oliveira 《Theoretical and Applied Climatology》2007,90(3-4):235-248
Summary This work describes a new algorithm to characterize sky condition in intervals of 5 min using four categories of sun exposition:
apparent sun with cloud reflection effects; apparent sun without cloud effects; sun partially concealed by clouds; and sun
totally concealed by clouds. The algorithm can also be applied to estimate hourly and daily sky condition in terms of the
traditional three categories: clear, partially cloudy and cloudy day. It identifies sky conditions within a confidence interval
of 95% by minimizing local climate and measurement effects. This is accomplished by using a logistic cumulative probability
function to characterize clear sky and Weibull cumulative probability function to represent cloudy sky. Both probability functions
are derived from frequency distributions of clearness index, based on 5 minutes-averaged values of global solar irradiance
observed at the surface during a period of 6 years in Botucatu, Southeastern of Brazil. The relative sunshine estimated from
the new algorithm is statistically comparable to the one derived from Campbell-Stocks sunshine recorder for both daily and
monthly values. The new method indicates that the highest frequency of clear sky days occurs in Botucatu during winter (66%)
and the lowest during the summer (38%). Partially cloudy condition is the dominant feature during all months of the year. 相似文献
358.
The biogeochemical sulfur cycle in the marine boundary layer over the Northeast Pacific Ocean 总被引:1,自引:0,他引:1
T. S. Bates J. E. Johnson P. K. Quinn P. D. Goldan W. C. Kuster D. C. Covert C. J. Hahn 《Journal of Atmospheric Chemistry》1990,10(1):59-81
The major components of the marine boundary layer biogeochemical sulfur cycle were measured simultaneously onshore and off the coast of Washington State, U.S.A. during May 1987. Seawater dimethylsulfide (DMS) concentrations on the continental shelf were strongly influenced by coastal upwelling. Concentration further offshore were typical of summer values (2.2 nmol/L) at this latitude. Although seawater DMS concentrations were high on the biologically productive continental shelf (2–12 nmol/L), this region had no measurable effect on atmospheric DMS concentrations. Atmospheric DMS concentrations (0.1–12 nmol/m3), however, were extremely dependent upon wind speed and boundary layer height. Although there appeared to be an appreciable input of non-sea-salt sulfate to the marine boundary layer from the free troposphere, the local flux of DMS from the ocean to the atmosphere was sufficient to balance the remainder of the sulfur budget. 相似文献
359.
Paul F. McMillan Brent T. Poe Thomas R. Stanton Richard L. Remmele 《Physics and Chemistry of Minerals》1993,19(7):454-459
We have obtained high quality Raman spectra for two H/D isotopically substituted hydrous aluminosilicate glasses with compositions along the NaAlSi3O8-SiO2 join. Consistent with the results of previous studies, the isotope shift for the band near 900 cm–1, whose intensity grows with increasing water content, is extremely small: v
h
/v
d
= 1.004 ± 0.004. The lack of a definite H/D isotope shift for this band does not, however, preclude its association with a vibration of a hydrous species in the glass, because of likely strong coupling between different vibrational modes of hydrated framework species. The 900 cm–1 band could well be due to a T — OH (T = Si, Al) stretching or bending vibration in the hydrous glass, as required by the presence of a combination band near 4500 cm–1 in near-infrared spectra. 相似文献
360.
A. A. Sorokin A. B. Kotov V. P. Kovach V. A. Ponomarchuk V. M. Savatenkov 《Petrology》2014,22(1):65-76
Based on generalization of available geochronological data, Late Mesozoic magmatic associations in the northeastern part of the Amurian microcontinent are divided into three groups: 142–125, 124–115, and <110 Ma. The age of these associations decreases with approaching the Pacific margin of Asia. In the same direction, they show a change in sources of their parental melts: continental crust (142–125 Ma) → continental crust + PREMA (DM) (124–115 Ma) → continental crust + PREMA (DM) + EMII (<110 Ma). Isotope-geochemical (Sr-Nd) study indicates that intrusive and volcanic rocks of the Late Mesozoic magmatic associations in the northeastern part of the Amurian microcontinent were originated in geodynamic settings that provided access of enriched mantle sources to magma formation. The most probable of these settings are as follows: (1) plate sliding accompanying by the formation of slab window beneath continental margin; (2) passage of the Asian margin over the East Asian mantle hot field in the Late Mesozoic; (3) asthenospheric upwelling due to delamination of the lower crust during closure of the Mongolian-Okhotsk ocean caused by collision between the Amurian microcontinent, Dzhugdzhur-Stanovoy, and Selenga-Stanovoy superterranes in the Central Asian fold belt. 相似文献