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81.
The planet Jupiter possesses a magnetic field and is surrounded by a magnetosphere. The occurrence of auroral and polar cap phenomena similar to those found on earth is very likely. In this work auroral and polar cap emissions in a model Jovian atmosphere are determined for proton precipitation. The incident protons, which are characterized by representative spectra, are degraded in energy by applying the continuous slowing down approximation. All secondary and higher generation electrons are assumed to be absorbed locally and their contributions to the total emissions are included. Volume emission rates are calculated from the total direct excitation rates with corrections for cascading applied. Results show that most molecular hydrogen and helium emissions for polar cap precipitation are below the ambient dayglow values. Charge capture by precipitating protons is an important source of Lyman α and Balmer α emissions and offers a key to the detection of large fluxes of low energy protons. 相似文献
82.
Edgar L. Andreas 《Boundary-Layer Meteorology》2011,141(3):333-347
A common parametrization over snow-covered surfaces that are undergoing saltation is that the aerodynamic roughness length
for wind speed (z
0) scales as au*2/g{\alpha u_\ast^2/g}, where u
* is the friction velocity, g is the acceleration of gravity, and α is an empirical constant. Data analyses seem to support this scaling: many published plots of z
0 measured over snow demonstrate proportionality to u*2{u_\ast^2 }. In fact, I show similar plots here that are based on two large eddy-covariance datasets: one collected over snow-covered
Arctic sea ice; another collected over snow-covered Antarctic sea ice. But in these and in most such plots from the literature,
the independent variable, u
*, was used to compute z
0 in the first place; the plots thus suffer from fictitious correlation that causes z
0 to unavoidably increase with u
* without any intervening physics. For these two datasets, when I plot z
0 against u
* derived from a bulk flux algorithm—and thus minimize the fictitious correlation—z
0 is independent of u
* in the drifting snow region, u
* ≥ 0.30 ms−1. I conclude that the relation z0 = au*2/g{z_0 = \alpha u_\ast^2/g} when snow is drifting is a fallacy fostered by analyses that suffer from fictitious correlation. 相似文献
83.
Gilbert Mille Jan Yu Chen Henri Dou Edgar Azoulay Maryse Colin Jean-Claude Bertrand 《Marine environmental research》1985,17(1):65-80
Coastal Mediterranean sediments highly polluted by refinery effluents have been studied for their hydrocarbon content and bacterial activity. The study has taken into account both the distance from the refinery and depth of sampling. Very high hydrocarbon concentrations have been found (1–250 g/kg dry sediment). Micro-organisms in the sediments have a high bacterial activity and a good correlation exists between hydrocarbon concentrations and bacteria able to use these substrates as a carbon and energy source. 相似文献
84.
D. H. Green A. D. Edgar P. Beasley E. Kiss N. G. Ware 《Contributions to Mineralogy and Petrology》1974,48(1):33-43
Chemical analyses of over seventy lavas or dykes containing spinel lherzolite inclusions of high pressure mineralogy, show that most host magmas are of alkali olivine basalt or basanite composition with relatively rare olivine nephelinites, and olivine melilitites. The 100 Mg/Mg+Fe++ ratios of host magmas display a strong maximum at about Mg70 consistent with partial melting of source peridotite with olivine of Fo88–90. In contrast to these primary magmas, there occur some host magmas with 100 Mg/Mg+Fe++<60 and with chemical compositions resembling those of classical hawaiite, mugearite, and nepheline benmoreite magmas. It is inferred that these magmas have been produced by crystal fractionation, within the upper mantle, of parental basanites or alkali olivine basalts. The presence of kaersutitic hornblende xenocrysts accompanying the lherzolite inclusions, and the nature of the chemical variation between associated basanites and nepheline benmoreites suggests that crystal fractionation has been dominated by kaersutitic hornblende, together with olivine and, in some cases, probably clinopyroxene. The mantle-derived nepheline benmoreite magmas also show similarities to some plutonic nepheline syenites. 相似文献
85.
Edgar L Andreas Rachel E. Jordan Aleksandar P. Makshtas 《Boundary-Layer Meteorology》2005,114(2):439-460
A 4-month deployment on Ice Station Weddell (ISW) in the western Weddell Sea yielded over 2000 h of nearly continuous surface-level meteorological data, including eddy-covariance measurements of the turbulent surface fluxes of momentum, and sensible and latent heat. Those data lead to a new parameterization for the roughness length for wind speed, z0, for snow-covered sea ice that combines three regimes: an aerodynamically smooth regime, a high-wind saltation regime, and an intermediate regime between these two extremes where the macroscale or `permanent' roughness of the snow and ice determines z0. Roughness lengths for temperature, zT, computed from this data set corroborate the theoretical model that Andreas published in 1987. Roughness lengths for humidity,zQ, do not support this model as conclusively but are all, on average, within an order of magnitude of its predictions. Only rarely arezTand zQ equal to z0. These parameterizations have implications for models that treat the atmosphere-ice-ocean system. 相似文献
86.
Kathryn M. Stack John P. Grotzinger Michael P. Lamb Sanjeev Gupta David M. Rubin Linda C. Kah Lauren A. Edgar Deirdra M. Fey Joel A. Hurowitz Marie McBride Frances Rivera‐Hernndez Dawn Y. Sumner Jason K. Van Beek Rebecca M. E. Williams Robin Aileen Yingst 《Sedimentology》2019,66(5):1768-1802
Recent robotic missions to Mars have offered new insights into the extent, diversity and habitability of the Martian sedimentary rock record. Since the Curiosity rover landed in Gale crater in August 2012, the Mars Science Laboratory Science Team has explored the origins and habitability of ancient fluvial, deltaic, lacustrine and aeolian deposits preserved within the crater. This study describes the sedimentology of a ca 13 m thick succession named the Pahrump Hills member of the Murray formation, the first thick fine‐grained deposit discovered in situ on Mars. This work evaluates the depositional processes responsible for its formation and reconstructs its palaeoenvironmental setting. The Pahrump Hills succession can be sub‐divided into four distinct sedimentary facies: (i) thinly laminated mudstone; (ii) low‐angle cross‐stratified mudstone; (iii) cross‐stratified sandstone; and (iv) thickly laminated mudstone–sandstone. The very fine grain size of the mudstone facies and abundant millimetre‐scale and sub‐millimetre‐scale laminations exhibiting quasi‐uniform thickness throughout the Pahrump Hills succession are most consistent with lacustrine deposition. Low‐angle geometric discordances in the mudstone facies are interpreted as ‘scour and drape’ structures and suggest the action of currents, such as those associated with hyperpycnal river‐generated plumes plunging into a lake. Observation of an overall upward coarsening in grain size and thickening of laminae throughout the Pahrump Hills succession is consistent with deposition from basinward progradation of a fluvial‐deltaic system derived from the northern crater rim into the Gale crater lake. Palaeohydraulic modelling constrains the salinity of the ancient lake in Gale crater: assuming river sediment concentrations typical of floods on Earth, plunging river plumes and sedimentary structures like those observed at Pahrump Hills would have required lake densities near freshwater to form. The depositional model for the Pahrump Hills member presented here implies the presence of an ancient sustained, habitable freshwater lake in Gale crater for at least ca 103 to 107 Earth years. 相似文献
87.
M. de Val-Borro R. G. Edgar P. Artymowicz P. Ciecielag P. Cresswell G. D'Angelo E. J. Delgado-Donate G. Dirksen S. Fromang A. Gawryszczak H. Klahr W. Kley W. Lyra F. Masset G. Mellema R. P. Nelson S.-J. Paardekooper A. Peplinski A. Pierens T. Plewa K. Rice C. Schäfer R. Speith 《Monthly notices of the Royal Astronomical Society》2006,370(2):529-558
88.
Experimental investigation of the formation of cordierite-orthopyroxene parageneses in pelitic rocks
Cordierite and orthopyroxene (or orthoamphibole) are widespread in migmatitic terranes, and partial melting of pelitic rocks may be important in their production. In particular, the reaction quartz +albite+biotite+garnet+water vapor = cordierite +orthopyroxene or orthoamphibole+melt was among reactions discussed by Grant (1973) but poorly constrained in pressure-temperature space.This reaction involves too many phases to be readily studied experimentally. Therefore simpler melting and dehydration reactions involving quartzalbite-biotite-cordierite-orthopyroxene were investigated.In conjunction with the work of Hoffer (1976, 1978) these experiments place useful constraints on the above reaction and on the reaction quartz+albite+aluminosilicate+biotite+vapor = cordierite+garnet+melt. In pelitic rocks near the second illimanite isograd, cordierite and garnet may coexist with melt as low as 660° C and cordierite and orthopyroxene may coexist with melt at temperatures less than 675° C. In the absence of significant Mn or Ca, in pelitic rocks within the realm of melting, biotite+garnet assemblages are probably limited to pressures greater than 2kb and aluminosilicate+biotite assemblages to pressures greater than 3kb. 相似文献
89.
90.
Summary Supra-solidus phase relations at temperatures and pressures ranging from 800 to 1700 °C and 2 to 6.4 GPa have been determined
experimentally for three silica-rich lamproites: hyalo-leucite phlogopite lamproite (Oscar, West Kimberley); sanidine richterite
lamproite (Cancarix, Murcia-Almeria); and phlogopite transitional madupitic lamproite (Middle Table Mountain, Wyoming). All
samples have extended melting intervals (500–600 °C). Bulk composition has a significant control on the nature of the initial
liquidus phases, with orthopyroxene occurring at low pressures (<4 GPa) in the relatively calcium-poor Oscar and Cancarix
lamproites. At higher pressure (>6 GPa) orthopyroxene is replaced by garnet plus clinopyroxene as near-liquidus phases in
the Oscar lamproite and by orthopyroxene plus clinopyroxene in the Cancarix sample. Clinopyroxene is a near-liquidus phase
at all pressures in the Middle Table Mountain lamproite. Near-solidus phase assemblages at high pressure (>5 GPa) are: clinopyroxene + phlogopite + coesite + rutile + garnet
(Oscar); clinopyroxene + garnet + coesite + K–Ti-silicate (Cancarix); clinopyroxene + phlogopite + apatite + K–Ti-silicate
(Middle Table Mountain). In all compositions olivine is never found as a liquidus phase at any of the temperatures or pressures
studied here. The phase relationships are interpreted to suggest that silica-rich lamproites cannot be derived by the partial
melting of lherzolitic sources. Their genesis is considered to involve high degrees of partial melting of ancient metasomatic
veins within a harzburgitic-lherzolitic lithospheric substrate mantle. The veins are considered in their mineralogy to be
similar to the experimentally-observed, high pressure, near-solidus phase assemblages. The composition of silica-rich primary
lamproite magmas differs between cratons as a consequence of differing mineralogical modes of the source veins and different
relative contributions from the veins and wall-rocks to the partial melts.
Received February 21, 2000; revised version accepted July 3, 2001 相似文献