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991.
William G. Mankin M. T. Coffey K. V. Chance W. A. Traub B. Carli F. Mencaraglia S. Piccioli I. G. Nolt J. V. Radostitz R. Zander G. Roland Douglas W. Johnson Gerald M. Stokes C. B. Farmer R. K. Seals 《Journal of Atmospheric Chemistry》1990,10(2):219-236
Observations of the vertical profile of hydrogen fluoride (HF) vapor in the stratosphere and of the vertical column amounts of HF above certain altitudes were made using a variety of spectroscopic instruments in the 1982 and 1983 Balloon Intercomparison Campaigns. Both emission instruments working in the far infrared spectral region and absorption instruments using solar occultation in the 2.5m region were employed. No systematic differences were seen in results from the two spectral regions. A mean profile from 20–45 km is presented, with uncertainties ranging from 20% to 50%. Total columns measured from ground and from 12 km are consistent with the profile if the mixing ratio for HF is small in the tropophere and low stratosphere. 相似文献
992.
Cloud droplet chemistry is modelled for the first 150 m of rise in a wintertime, mid-latitude, marine stratus cloud using observations made at and near the Cape Grim Baseline Station as a source of input parameters. The emphasis in this work was to study the variation in droplet chemistry as a function of both droplet size and nucleus composition, with a particular focus on the way in which oxidation of dissolved sulfur dioxide varied.At 150 m above the condensation level, solute concentration as a function of droplet size was found to increase by as much as 2 to 3 orders of magnitude for only a factor of 2 increase in droplet radius, primarily as a consequence of the 1/r dependence in the droplet growth equation. This type of size dependence exists at all levels in the model cloud, and has a significant influence on oxidation rate of sulfur dioxide in droplets growing on sulfate nuclei, oxidation by ozone being favoured in the smallest droplets, but oxidation by hydrogen peroxide being favoured in the larger droplets. Oxidation by ozone is favoured at all sizes in droplets formed on sea-salt nuclei as a result of the initially high alkalinity of these droplets, and in the cloud overall is calculated to be the more important oxidation pathway. Although based on a simplified chemical scheme, these results suggest that both size-dependent and nucleus-dependent chemistry of cloud droplets may need to be considered explicitly in cloud modelling work.Volume-weighted mean pH values in the range 5 to 6 were predicted from sensitivity studies in which input variables were varied over reasonable ranges, in agreement with two sets of bulk cloud-water pH data obtained by aircraft near Cape Grim. 相似文献
993.
M. R. Ramesh Kumar Y. Sadhuram G. S. Michael L. V. Gangadhara Rao 《Boundary-Layer Meteorology》1990,52(1-2):177-191
The spatial variability of the structure of the lower troposphere over the northwestern Indian Ocean for the period 12th July to 2nd September, 1983 has been studied using upper air data collected during the first scientific cruise of ORV Sagar Kanya.An analysis of thermodynamic structure and kinematics of the marine boundary layer for different zonal and meridional sections revealed the following features: (a) Temperature and humidity inversions were generally absent over the study area except over a few locations in the western region; (b) Large-scale subsidence was found over the central equatorial Indian Ocean; (c) The convective activity over the western Indian Ocean was found to be moderately suppressed as compared to the eastern region; (d) The zonal and meridional components of winds along the equator and 10° N zonal section exhibited a mirror-image-like distribution. 相似文献
994.
Petrogenesis and paleotectonic history of the Wild Bight Group,an Ordovician rifted island arc in central Newfoundland 总被引:1,自引:0,他引:1
H. Scott Swinden G. A. Jenner B. J. Fryer J. Hertogen J. C. Roddick 《Contributions to Mineralogy and Petrology》1990,105(2):219-241
The Wild Bight Group (WBG) is a sequence of early and middle Ordovician volcanic, subvolcanic and epiclastic rocks, part of the Dunnage Tectonostratigraphic Zone of the Newfoundland Appalachians. A detailed geochemical and Nd-isotopic study of the volcanic and subvolcanic rocks has been carried out to determine the geochemical characteristics of the rocks, interpret their palcotectonic environments and constrain their petrogenetic history. The lower and central stratigraphic levels of the WBG contain mafic volcanic rocks with island-arc geochemical signatures, including LREE-enriched are tholeiites with
Nd(t)
=-0.1 to +2.2 (type A-I), LREE-depleted arc tholeiites with
Nd(t)
=+5.6 to +7.1 (type A-II) and an unusual suite of strongly incompatible-element depleted tholeiites in which
Nd(t)
ranges from-0.9 to +4.6 and is negatively correlated with147Sm/144Nd (type A-III). High-silica, low-K rhyolites occur locally in the central part of the stratigraphy, associated with mafic rocks of arc affinity, and have
Nd(t)
=+4.7 to +5.4. The upper stratigraphic levels of the WBG dominantly contain rocks with non-arc geochemical signatures, including alkalic basalts with
Nd(t)
=+4.6 to +5.5 (type N-I), strongly LREE- and incompatible element-enriched tholeiites that are transitional between alkalic and non-alkalic rocks with
Nd(t)
=+4.4 to +7.0 (type N-II) and rocks with flat to slightly LREE-enriched patterns and
Nd(t)
=+5.1 to +7.4 (type N-III). Rocks with non-arc and arc signatures are locally interbedded near the stratigraphic type of the WBG. Nd-isotopic data in the type A-I and A-II rocks are generally compatible with mixing/partial melting models involving depleted mantle, variably contaminated by a subducted crustally-derived sediment. The petrogenesis of type A-III rocks must involve source mixing and multi-stage partial melting, but the details are not clear. The geochemistry and Nd isotope data for types N-I, N-II and N-III rocks are compatible with petrogenetic models involving variable partial melting of a source similar to that postulated for modern oceanic island basalts. Comparison of the WBG with modern analogues suggests a 3-stage developmental model: stage 1) island-arc volcanism (eruption of type mafic volcancs); stage 2) arc-rifting (continued eruption of type A-I, A-I, eruption of types A-II and A-III mafic volcanics and high-silica, low-K rhyolites); and stage 3) back-arc basin volcanism (continued minor eruption of type A-I basalts, eruption of types N-I, N-II, N-III basalts). Stages 1 and 2 volcanism involved partial melting of subduction contaminated mantle, while stage 3 volcanism utilized depleted-mantle sources not affected by the subducting slab. This model provides a basis for interpreting coeval sequences in central Newfoundland and a comparative framework for some early Paleozoic oceanic volcanic sequences elsewhere in the Appalachian orogen. 相似文献
995.
Geochemistry and Intrusive History of the Ashland Pluton, Klamath Mountains, California and Oregon 总被引:3,自引:1,他引:2
GRIBBLE ROBERT F.; BARNES CALVIN G.; DONATO MARY M.; HOOVER JAMES D.; KISTLER RONALD W. 《Journal of Petrology》1990,31(4):883-923
The Ashland pluton is a calc-alkaline plutonic complex thatintruded the western Paleozoic and Triassic belt of the KlamathMountains in late Middle Jurassic time. The pluton comprisesa series of compositionally distinct magma pulses. The oldestrocks are hornblende gabbro and two-pyroxene quartz gabbro withinitial 87Sr/86Sr = 0{dot}7044, 18O = 8{dot}7%, and REE patternswith chondrite normalized La/Lu = 7. These units were followedby a suite of tonalitic rocks (LaN/LuN = 7) and then by a suiteof K2O- and P2O5 rocks of quartz monzodioritic affinity (LaN/LuN= 1321; LaN/SmN = 2{dot}43{dot}) The quartz monzodioriticrocks were then intruded by biotite granodiorite and granitewith lower REE abundances but more fractionated LREE(LaN/LuN= 1319; LaN/SmN = 4{dot}36 and they, in turn,were host to dikes and bosses of hornblende diorite. The latestintrusive activity consisted of aplitic and granitic dikes.Combined phase equilibria and mineral composition data, indicateemplacement conditions of approximately Ptotal = 2{dot}3kb,PH2O between 1{dot}5 and 2{dot}2 kb, and fO2 between the nickel-nickeloxide and hematite-magnetite buffers. Successive pulses of magma display increasing SiO2 togetherwith increasing 18O and decreasing initial 87Sr/86Sr. The isotopicdata are consistent with either (1) combined fractional crystallizationof andesitic magma and concurrent assimilation of crustal materialcharacterized by low Sr1 and high (18O or, more probably, (2)a series of partial melting events in which sources were successivelyless radiogenic but richer in 18O Each intrusive stage displaysevidence for some degree of crystal accumulation and/or fractionalcrystallization but neither process adequately accounts fortheir compositional differences. Consequently, each stage appearsto represent a distinct partial melting or assimilation event. The P2O5-rich nature of the quartz monzodiorite suite suggestsaccumulation of apatite. However, the suite contains abundantmafic microgranitoid enclaves and most apatite in the suiteis acicular. These observations suggest that magma mixing affectedthe compositional variation of the quartz monzodiorite suite.Mass balance calculations are consistent with a simple mixingprocess in which P2O5-rich alkalic basalt magma (representedby the mafic microgranitoid enclaves) was combined with a crystal-poorfelsic magma (represented by the tonalite suite), yielding aquartz monzodioritic magma that then underwent differentiationby crystal fractionation and accumulation. 相似文献
996.
The British Tertiary Volcanic Province (BTVP) comprises within-platecentral igneous complexes associated with plateau lavas andregional dyke swarms. Lundy is the southernmost complex of theBTVP and comprises granite ({small tilde}90%) emplaced intodeformed Devonian sedimentary rocks within the Hercynian Cornubiangranite province of southwest England. The complex is intrudedby a northwest-southeast trending dyke swarm. In common withother BTVP igneous complexes, Lundy is associated with positivegravity and magnetic anomalies which are interpreted in termsof the presena of an underlying basic intrusion at shallow depth,with a volume exceeding that of the overlying granite. The Lundy intrusion is a coarse-grained megacrystic granitecontaining up to 20% alkali feldspar megacrysts in a coarse-grainedgroundmass composed of alkali feldspar, quartz, lithium-bearingmuscovite, and biotite (lithian siderophyllite),with a range of aaxssory minerals. The main granite has a coarse-grained(locally miarolitic) pegmatitic facies and is intruded by thinsheets and veins of fine-grained aplite and microgranite. Themineralogy indicates crystallization of the Lundy granite froma highly fractionated H2O- and halogen-rich magma at a relativelyshallow crustal level. The main Lundy granite is a peraluminous leucogranite with Na2O=34%,K2O{small tilde}5%, low TiO2, MeO, CaO, Zr, and Sr, and highRb and Rb/Sr in comparison with many other peralurninous granites,including those from the Cornubian batholith and the BTVP. Anew Rb-Sr whole-rock isochron for the granite yields an ageof 58?7?1?6 Ma with an initial 87Sr/86Sr of 0?715?0?006. Ndvalues for the granite (0?9 to 1?9) plot betweencontemporaneous mantle (positive Nd and Cornubian granites (Nd=ca.11). The trace element data (Rb, Y, Nb) show affinities with syn-collisionand within-plate granites. As the Sr isotope data indicate amajor crustal component, and the Nd isotope data suggest bothmantle and crustal components, we propose that the Lundy graniteis derived from a parental magma comprising crustal components(derived from a similar source to that of the Cornubian granitebatholith) and a mantle-derived component (derived from a differentiateof contemporaneous basaltic magma This magma experienced fractionalcrystallization of plagioclase, alkai feldspar, Fe-Mg minerals,and REE-bearing accessory minerals before emplacement, and theLundy granite experienced further in situ fractional crystallization,associateded with crustal contamination by the Devonian shaleafter emplacement. 相似文献
997.
A progress report on cosmic fireballs is presented. The main new results are: (a) the phenomenon should be almost universal, and most explosive -ray sources should show the characteristic fireball spectrum; (b) even if the radiation density is insufficient, pair production in electron-proton or electron-electron scattering might start the fireball; (c) some computed fireball spectra are shown. They all have in common a 1/E low-energy behaviour, a 100 keV flattening, and a 0.5 MeV cut-off.Paper presented at the Symposium on Cosmic Gamma-Ray Bursts, held at Toulouse, France, 26–29 November, 1979. 相似文献
998.
Accurate numerical continuation of families of plane symmetric direct periodic orbits around the large primary in the Sun-Jupiter case of the restricted problem of three bodies allows the determination of the vertical branching points where families of three-dimensional symmetric periodic orbits bifurcate from the planar ones. Three families of plane periodic orbits, and the initial segments of ten bifurcating families of three-dimensional ones are determined. The stability of these families is examined and examples of their orbits are illustrated. 相似文献
999.
New spectrophotometry from 1.5 to 2.5 μm is reported for the Uranian satellites Titania, Oberon, and Umbriel. A spectrum of the rings of Uranus from 2.0 to 2.4 μm is also reported. No evidence is found for frost covering the surface of the ring material, consistent with the low albedo of the rings (PK = 0.03) previously reported by Nicholson and Jones (1980). The surfaces of the satellites are found to be covered by dirty water frost. Assuming albedos of the frost and gray components covering the Uranian satellites to be the same as the light and dark faces of Iapetus, radii are derived that are roughly twice those inferred from the assumption of a visual albedo of 0.5. 相似文献
1000.
A further development of the Kostyuk-Pikelner's model is presented. The response of the chromosphere heated by non-thermal electrons of the power-law energy spectrum has been studied on the basis of the numerical solution of the one-dimensional time-dependent equations of gravitational gas dynamics. The ionization and energy loss for the emissions in the Lyman and Balmer lines have been determined separately for the optically thin and thick L-line layers. Due to the initial heating, a higher-pressure region is formed. From this region, disturbances propagate upwards (a shock wave with a velocity of more than 1000 km s-1) and downwards. A temperature jump propagates downwards, and a shock is formed in front of the thermal wave. During a period of several seconds after the beginning of this process, the temperature jump intensifies the downward shock wave and the large radiative loss gives rise to the high density jump (
2/
1 100). The numerical solution has been analyzed in detail for the case heating of the ionized and neutral plasma, and a value of this heating is close to the upper limit of the admissible values. In this case, the condensation located between the temperature jump and the shock wave front, may emit in the observed optical continuum.In their essential features, the gas dynamic processes during the flares in red dwarf atmospheres are the same as those in the solar atmosphere. However, the high atmospheric densities, smaller height scale in red dwarf atmospheres, and greater energy of this processes in stellar flares, give rise, in practice, to the regular generation of optical continuum. The photometric parameters of a source with n 015 cm-3, T 9000 K, and
z 10 km are in a good agreement with observations. 相似文献