Showing papers in "Geophysical Research Letters in 1974"
TL;DR: The first systematic data from Apollo photogrammetry provided a high standard of accuracy for the depth/diameter relation of fresh lunar craters as mentioned in this paper, which resembles results obtained by measuring shadows on Lunar Orbiter imagery.
Abstract: The first systematic data from Apollo photogrammetry provide a high standard of accuracy for the depth/diameter relation of fresh lunar craters. Apollo depth-diameter results resemble results obtained by measuring shadows on Lunar Orbiter imagery. The depth-diameter distribution inflects at a crater diameter of 10 to 15 km. Lunar craters less than 15 km across are at least 50% deeper than older, telescopic data indicated, but larger craters are not much deeper. There is no marked depth-diameter difference between fresh upland and postmare craters. The new depth-diameter relation for small lunar craters resembles those of experimental and impact craters on earth.
238 citations
TL;DR: In this paper, both natural and synthetic pyrope has been compressed to pressures above 300 kbar in a diamond-anvil press and heated to temperatures above 800°C by a continuous YAG laser.
Abstract: Both natural and synthetic pyrope have been compressed to pressures above 300 kbar in a diamond-anvil press and heated to temperatures above 800°C by a continuous YAG laser. After quenching and release of pressure, X-ray diffraction shows that the natural pyrope transforms to a single phase with perovskite-like structure whereas the synthetic pyrope disproportinates into a mixture of MgSiO3 (perovskite) plus Al2O3 (corundum). The orthorhombic perovskite lattice parameters for the natural pyrope are ao = 4.816 ± 0.004 A, bo = 4.973 ± 0.004 A, and co = 6.997 ± 0.006 A with Z = 4. The orthorhombic cell dimensions for MgSiO3 (perovskite) are ao = 4.818 ± 0.005 A, bo = 4.869 ± 0.005 A, and co = 6.906 ± 0.007 A with Z=4. The calculated density of MgSiO3 perovskite is thus 4.12 g/cm³, or 3.7% denser than the isochemical mixed oxides. These experiments are the first demonstration of static high pressure phase transformations in silicate garnets and the first examples of a pure silicate existing in the perovskite structure.
208 citations
TL;DR: In this paper, a model is presented in which the Jovian magnetosphere is severely inflated by the centrifugal stress of partially corotating plasma streaming out along field lines from the ionosphere.
Abstract: A model is presented in which the Jovian magnetosphere is severely inflated by the centrifugal stress of partially corotating plasma streaming out along field lines from the ionosphere. The model is consistent with observations reported from the Pioneer 10 encounter, including the disk-like field configuration, the diurnal modulation of trapped-particle fluxes, and the inferred departure from rigid corotation in the outer magnetosphere. The field configuration is closed on the dayside, but on the nightside the plasma can force the magnetic field open to form a planetary wind flowing in the antisolar direction.
188 citations
TL;DR: In this article, a manganese oxide crust from an extensive deposit in the median valley of the Mid-Atlantic Ridge was found to be unusually high in Manganese (up to 39.4% Mn), low in Fe (as low as.01% Fe), and deficient in Th230 and Pa231 with respect to the parent uranium isotopes in the sample.
Abstract: A manganese oxide crust from an extensive deposit in the median valley of the Mid-Atlantic Ridge was found to be unusually high in manganese (up to 39.4% Mn), low in Fe (as low as .01% Fe), low in trace metals and deficient in Th230 and Pa231 with respect to the parent uranium isotopes in the sample. The accumulation rate is 100 to 200 mm/106 y, or 2 orders of magnitude faster than the typical rate for deep-sea ferromanganese deposits. The rapid growth rate and unusual chemistry are consistent with a hydrothermal origin or with a diagenetic origin by manganese remobilized from reduced sediments. Because of the association with an active ridge, geophysical evidence indicative of hydrothermal activity, and a scarcity of sediment in the sampling area, we suggest that a submarine hot spring has created the deposit.
183 citations
TL;DR: In this article, the distribution coefficients of diopside liquid pairs for strontium and nine rare-earth elements in the system CaMgSi2O6-NaAlSi3O8-CaAl2Si2 O8.
Abstract: Experimental determination of the distribution coefficients in diopside-liquid pairs for strontium and nine rare-earth elements in the system CaMgSi2O6-NaAlSi3O8-CaAl2Si2O8. In experiments in air at 1265 C it is found that most of the Sr(2+), Eu(2+), and RE(3+) ions substitute for Ca(2+) and, in addition, a coupled substitution of Al(3+) for Si(4+) occurs. All of the trace ions considered are found to be excluded from the diopside lattice relative to the liquid. In the case of the trivalent ions the exclusion is much more pronounced for La and Ce, which have ionic radii larger than that of Ca(2+) in 8-fold oxygen coordination. Divalent Sr and Eu with even larger radii are also strongly excluded.
158 citations
TL;DR: In this paper, it was concluded that very large reductions in ozone concentrations above about 30 km may result from the continued use of fluoro-chloro-methanes (CF2Cl2 and CFCl3), which are dissociated by ultraviolet radiation in the stratosphere and mesosphere, thereby giving rise to ozone-attacking Cl and ClO.
Abstract: In agreement with arguments put forward by Molina and Rowland (1974) it is concluded that very large reductions in ozone concentrations above about 30 km may result from the continued use of fluoro-chloro-methanes (CF2Cl2 and CFCl3), which are dissociated by ultraviolet radiation in the stratosphere and mesosphere, thereby giving rise to ozone-attacking Cl and ClO. Below about 30 km the reductions in ozone are much smaller and even a slight increase in ozone concentrations may result. The total column abundance of ozone in the atmosphere is, however, reduced by about 10%, assuming that the present rate of production of CF2Cl2 and CFCl3 remains unaltered.
145 citations
TL;DR: In this article, Mg isotopic anomalies were determined on inclusions in the Allende meteorite, which correspond to enrichment of 24Mg or 26Mg of up to 3 per mil or depletion of 25Mg up to 1.5 per mil.
Abstract: Mg isotopic anomalies were determined on inclusions in the Allende meteorite. Measured Mg isotopic ratios were corrected for mass fractionation by normalizing to the terrestrial (normal) 25Mg/24Mg. Relative to normal Mg, Allende samples show distinct isotopic anomalies which correspond to enrichment of 24Mg or 26Mg of up to 3 per mil or depletion of 25Mg of up to 1.5 per mil. One sample shows a depletion of 24Mg or 26Mg by 1.7 per mil or an enrichment of 25Mg by 0.85 per mil. These anomalies are smaller by a factor of ten than found for the oxygen isotopes. Samples with large oxygen effects (up to 5%) yield normal Mg indicating a lack of correlation between the O and Mg effects. A Ca-Al rich chondrule with primitive 87Sr/86Sr and normal 84Sr/86Sr has a significant Mg anomaly. The Mg anomalies do not correlate with Al/Mg and do not appear to be due to 26Al decay. The anomaly in the only sample depleted in 26Mg cannot be due to 26Al decay. The isotopic composition of Mg in a sample of the total meteorite is normal. These results accentuate the important character of Allende inclusions but do not uniquely identify the nuclear processes responsible for the Mg and O effects.
144 citations
TL;DR: In this article, an analysis of recent data from lunar seismic events shows significant deviations of P- and S-wave travel times from those expected if the lunar interior were homogeneous below the crust.
Abstract: Analysis of recent data from lunar seismic events shows significant deviations of P- and S-wave travel times from those expected if the lunar interior were homogeneous below the crust. The interpretation of these data results in a lunar model consisting of at least four and possibly five distinguishable zones whose probable characteristics are discussed.
143 citations
TL;DR: In this article, a preliminary report discusses the detection of strong low-frequency electromagnetic signals and moderate electrostatic noise enhancements near local midnight during a substorm period on Oct. 28, 1972, when there were multiple crossings of the neutral sheet and boundary of the plasma sheet.
Abstract: The orbit of IMP 7 frequently takes the spacecraft across the neutral sheet in the geomagnetic tail at a downstream distance of about 35 earth radii. This preliminary report discusses the detection of strong low-frequency electromagnetic signals and moderate electrostatic noise enhancements near local midnight. Data used were obtained during a substorm period on Oct. 28, 1972, when there were multiple crossings of the neutral sheet and the boundary of the plasma sheet.
138 citations
TL;DR: In this article, the authors performed a model calculation of the ion heating rate due to electrostatic ion cyclotron turbulence in the topside ionosphere, with the assumption that the formation of a plateau on the electron velocity distribution is inhibited.
Abstract: We have performed a model calculation of the ion heating rate due to electrostatic ion cyclotron turbulence in the topside ionosphere, with the assumption that the formation of a plateau on the electron velocity distribution is inhibited. Ion temperature profiles are obtained and the implications of the heating effect on anomalous resistivity calculations are discussed.
114 citations
TL;DR: In this article, current and sea level observations made on the New England continental shelf during several winter storms show that these short intense wind events dominate the circulation over the shelf, and account for most of the observed net flow.
Abstract: Current and sea level observations made on the New England continental shelf during several winter storms show that these short intense wind events dominate the circulation over the shelf, and account for most of the observed net flow. The observations show that large westward mass transports along the shelf were produced by strong easterly winds, while westerly winds produced little along-shore flow. Significant cross-shelf and along-shelf surface pressure gradients occur during the storms. A simple conceptual model is proposed to explain the observations.
TL;DR: In this paper, the authors observed the magnetic ELF emissions (100-1000 Hz) observed on the polar-orbiting OGO-6 satellite within three hours of the dawn-dusk meridian consistently exhibit a predictable response to isolated substorm activity.
Abstract: Electromagnetic ELF emissions (100-1000 Hz) observed on the polar-orbiting OGO-6 satellite within three hours of the dawn-dusk meridian consistently exhibit a predictable response to isolated substorm activity. Near dawn, the emissions intensify during the substorm and then subside following the magnetic activity; the waves are most intense at L greater than 4, exhibit considerable structure and have been primarily identified as chorus. At dusk the response is entirely different; the wave intensity falls to background levels during substorm activity but subsequently intensifies, usually reaching levels well in excess of that before the disturbance. The emissions near dusk extend to low L, are relatively featureless, and have been identified as plasmaspheric hiss. These features are interpreted in terms of changes in the drift orbits of outer-zone electrons which cyclotron resonate with ELF waves.
TL;DR: In this article, the authors have determined an age T = 1.37 AE for Nakhla and an initial δ(87)Sr/δ(86)-Sr, I = 0.7023.
Abstract: We have determined an age T=1.37 AE for Nakhla and an initial ^(87)Sr/^(86)Sr, I = 0.7023. A rather thorough Sr equilibration took place at this time between all the phases of this meteorite, but there is clear evidence of somewhat incomplete isotopic equilibrium during the 1.37 AE event, which is not consistent with the derivation of Nakhla from a magma at this time. Nakhla has a young model age of 3.6-2.9 AE which requires that gross differentiation processes for its parent body occur between 3.6 and 1.37 AE, significantly later than 4.6 AE. The most reasonable model is that Nakhla formed as an igneous rock at ∼3 AE and was metamorphosed at 1.37 AE. Several similarities exist between the Nakhla parent planet and the Earth and indicate the existence of other objects with close terrestrial chemical affinities.
TL;DR: In this paper, it was deduced that NO(+) should be an important constituent of the high-latitude F-region ionic reactions, due to the rapid increase of the reaction O(+) + N2 yields NO(+, + N with ion velocity and temperature, high latitude electric fields and consequent E x B drifts act to deplete O(+ in favor of NO(+), as a consequence of this and the reduced rate of NO+ dissociative recombination arising from high electron temperatures.
Abstract: From an analysis of ionic reactions, it is deduced that NO(+) should be an important constituent of the high-latitude F-region. Owing to the rapid increase of the reaction O(+) + N2 yields NO(+) + N with ion velocity and temperature, high latitude electric fields and consequent E x B drifts act to deplete O(+) in favor of NO(+). As a consequence of this and the reduced rate of NO(+) dissociative recombination arising from high electron temperatures, it seems that NO(+) can, at times, replace O(+) as the major F2-region ion in the vicinity of the auroral ovals. The same processes should also be effective in creating nighttime electron density troughs composed primarily of NO(+) in regions equatorward of the auroral ovals where large electric fields are often present.
TL;DR: In this paper, it was found that the traditional first-order Compton-getting effect, which relates particle distributions as observed in two frames of reference moving with constant relative velocity, is inadequate for the description of low energy particles in the solar system.
Abstract: It was found that the traditional first-order Compton-Getting effect, which relates particle distributions as observed in two frames of reference moving with constant relative velocity, is inadequate for the description of low energy particles (less than a few hundred keV/nucleon) in the solar system. An exact procedure is given for recovering both isotropic and anisotropic distributions in the solar wind frame from observations made in a spacecraft frame. The method was illustrated by analyzing a particle event observed on IPM-7.
TL;DR: In this paper, a dilatancy model without extensive pore fluid diffusion is proposed as an explanation for time-dependent geophysical anomalies occurring prior to earthquakes, where the creation of thin dry or undersaturated cracks due to progressive distortion near the focal region is assumed.
Abstract: A dilatancy model without extensive pore fluid diffusion is proposed as an explanation for time-dependent geophysical anomalies occurring prior to earthquakes. As with the fluid flow models, the creation of thin dry or undersaturated cracks due to progressive distortion near the focal region is assumed. Rather than invoking fluid migration from the surrounding crust to fill cracks, the cracks are thought to close again before the earthquake because of decreasing stress levels imposed by strongly nonlinear constitutive properties of fault zone material. The proposed model and the fluid flow model predict qualitatively similar Vp/Vs, and resistivity histories. Whereas the fluid flow model predicts maximum epicentral uplift due to dilatancy at the time of the earthquake, the diffusionless model predicts uplift followed by subsidence prior to the earthquake, as well as premonitory creep in the focal region.
TL;DR: The dayside ionosphere of Venus observed by Mariner 10 may be understood in terms of a dynamic interaction with the solar wind which results in a compressed topside above an 'F2 ledge' consisting of O(+) and a dynamically unaffected F1 layer corresponding to a neutral temperature of about 380 K as discussed by the authors.
Abstract: The dayside ionosphere of Venus observed by Mariner 10 may be understood in terms of a dynamic interaction with the solar wind which results in a compressed topside above an 'F2 ledge' consisting of O(+) and a dynamically unaffected F1 layer corresponding to a neutral temperature of about 380 K and consisting of O2(+) and CO2(+). The top of the upper ledge appears to be an ionopause caused by solar wind scavenging of He(+), representing a solar-wind obstacle consistent with the bow shock observations.
TL;DR: In this article, a fluorocarbon, freon 11, has been used as an aerosol propellant during the past 15 years and its presence in ground water should indicate recent recharge of the water from atmospheric sources.
Abstract: Fluorocarbons are a stable, non-reactive, and generally non-toxic group of chemicals which can be detected in concentrations of 1 part per 1012 by electron capture gas chromatography. A fluorocarbon, freon 11, has been used widely as an aerosol propellant during the past 15 years. Its presence in ground water should indicate recent recharge of the water from atmospheric sources. Another fluorocarbon, which is not as yet detectable in the hydrosphere, has been tested for its suitability as a tracer in streams and ground water. This compound, perfluoro-1, 3-dimethyl-cyclohexane, appears useful for measuring stream discharge and detecting the direction of ground-water flow.
Abstract: We have calculated that stratospheric photodissociation in the 1950–2250 A range removes CCl4 at a rate corresponding to an atmospheric lifetime of 30-50 years. Whether CCl4 is of natural or anthropogenic (in use since early 1900's) origin, the ratios between it and its photodissociation products should be approximately those characteristic of a steady state. The present level of 7 × 10−11 v/v for CCl4 in tropospheric air can thus be used to estimate the present minimum levels of HCl, ClO, and Cl which should be present in the stratosphere from the photodissociation of CCl4. The current average HCl concentration is predicted to be about 10−10 v/v above 30 kms from this source, while ClO is predicted to approach 10−10 v/v near 35 kms.
TL;DR: In this article, a model in which magnetic merging near the nose of the magnetosphere results in energy transfer from the solar wind by means of a tangential force on the geomagnetic tail is developed, with a linear relation between the time rate of change of Dst, representing energy transfer to the magnetic field, and the merging electric field.
Abstract: Using a model in which magnetic merging near the nose of the magnetosphere results in energy transfer from the solar wind by means of a tangential force on the geomagnetic tail, a linear relation between the time rate of change of Dst, representing energy transfer to the magnetosphere, and the merging electric field is developed, with the proportionality factor an explicit function of magnetospheric parameters. The linear relation is in agreement with a recent empirical result; and, using the empirical numerical coefficient, it is found that the distance from the earth to the neutral line in the tail during substorms is in the range from 10 to 30 earth radii.
TL;DR: In this article, ultrasonic shear waves indicate splitting along the direction of minimum principal stress of ∼11% for confined (20 MPa) and ∼16% for unconfined specimens of Westerly granite loaded in uniaxial stress.
Abstract: Laboratory observations of ultrasonic shear waves indicate splitting along the direction of minimum principal stress of ∼11% for confined (20 MPa) and ∼16% for unconfined specimens of Westerly granite loaded in uniaxial stress. Dilatant strains increase birefringence except at > 80-90% of the ultimate strength, when processes related to shear failure apparently become important. If seismic birefringence observed in the field can be related to anisotropic dilatant strains, these laboratory measurements of precursory velocity changes should prove useful in predicting earthquakes.
TL;DR: In this article, a rocket-borne spectrophotometer was used to detect nitrogen oxide twilight emission above 140 km in the gamma-and delta-bands in the Gamma and Delta bands.
Abstract: Nitric oxide twilight emission above 140 km in the gamma- and delta-bands was observed with a rocket-borne spectrophotometer. The relative intensity of the two band systems indicates that the emission is produced predominantly by the chemiluminescent preassociation of oxygen and nitrogen atoms.
TL;DR: In this article, a theory of quasi-periodic VLF emissions associated with ULF geomagnetic pulsations is presented, which is based on an approach of treating as adiabatic the interactions between the emissions and the externally-excited ULF waves.
Abstract: A theory of quasi-periodic VLF emissions associated with ULF geomagnetic pulsations is presented. The theory is based on an approach of treating as adiabatic the interactions between the VLF emissions and the externally-excited ULF waves. The obtained theoretical results are consistent with available observations.
TL;DR: In this paper, a 1,262 m-deep bore hole in the area inferred to overlie the magma reservoir of Kilauea Volcano, Hawaii, support earlier interpretations based on surface geophysical surveys that brackish or saline water lies above the reservoir.
Abstract: Drilling and geophysical logging data for a 1,262 m-deep bore hole in the area inferred to overlie the magma reservoir of Kilauea Volcano, Hawaii, support earlier interpretations based on surface geophysical surveys that a zone of brackish or saline water lies above the reservoir. Temperatures encountered within the hole are not sufficiently high to warrant commercial interest; the maximum temperature, 137°C, is at the hole bottom. However, the temperature gradient toward the bottom of the hole (approximately 160 m below sea level) increases sharply to about 370°C/km, perhaps partly reflecting the effect of decreased water circulation as suggested by the geophysical logging data. If this gradient persists or increases with depth, magmatic temperatures would be attained within 3 km from the hole bottom (i.e., approximately 4 km from ground surface)—a depth in accord with data from ground-deformation and seismic studies.
TL;DR: In this article, an individual site approach to storm water detention may actually increase the potential for localized flooding, which may increase the risk of localized flooding due to increased storm water runoff due to urban development.
Abstract: To control the increase in storm water runoff due to urban development many states require some form of storm water detention. However, existing laws use an “individual-site” approach to storm water management rather than the more efficient regional approach. An individual site approach to storm water detention may actually increase the potential for localized flooding.
TL;DR: In this article, the reaction of OH radicals with CH4 has been investigated over the temperature range 290-440°K in a flow system with UV resonance fluorescence detection of OH, and its rate constant can be represented in Arrhenius form as k1 = 3.83 × 10−12 exp(−3660(cal/mole)/RT) cm³ sec−1.
Abstract: The reaction of OH radicals with CH4 has been investigated over the temperature range 290-440°K in a flow system with UV resonance fluorescence detection of OH. Its rate constant can be represented in Arrhenius form as k1 = 3.83 × 10−12 exp(−3660(cal/mole)/RT) cm³ sec−1. This result is compared with the results of other experimenters and is used to calculate stratospheric destruction rates of methane.
TL;DR: In this article, it was shown that between one and ten billion ice crystals per cubic meter of order 10 nanometers in diameter can dominate ionization loss processes in the mesosphere and can explain a variety of experimental observations, including observed solar angle dependence and seasonal variability of electron density.
Abstract: The observations of noctilucent clouds, the measurements of hydrated and of large immobile ions, and the light-scattering layer detected by the OGO-6 satellite suggest the presence of particulates, probably ice, in the mesosphere. The correlation between temperature and positive ion conductivity where the vapor pressure over ice becomes greater than atmospheric pressure in the stratopause region indicates the presence of ice crystals throughout the mesosphere over a wide range of latitudes during all seasons. Between one and ten billion ice crystals per cubic meter of order 10 nanometers in diameter can dominate ionization loss processes in the mesosphere, and can explain a variety of experimental observations, including observed solar angle dependence and seasonal variability of electron density.
TL;DR: In this paper, the motion of the Hawaiian hot spot with respect to the plate is calculated from seamount ages, and the absolute northward motion of plate is given by paleoequator positions.
Abstract: It now appears that hot spots do not provide a fixed reference frame for plate motions. However, if individual hot spots trace the motion of particular zones in the mantle, knowledge of their motions can give insight into the kinematics of the deeper flow. The motion of the Hawaiian hot spot with respect to the plate is calculated from seamount ages, and the absolute northward motion of the plate is given by paleoequator positions. In a fixed reference frame, the southward velocity of the hot spot is comparable to the northward motion of the plate. For a simple two-layer convention model, the zone of return flow (asthenosphere) must then be about twice as thick as the plate.
TL;DR: In this paper, the authors show that solid-state convection is the mechanism that prevents large scale melting of the Martian mantle, if the viscosity of mantle material is lower than 10 to 22nd to 10 to the 23rd sq cm/sec at temperatures in excess of about 1500 C.
Abstract: If internal heating in the mantle of Mars is similar to that in the earth, solid-state convection is the mechanism preventing large scale melting of the Martian mantle. Convection is efficient enough in transporting heat to preclude the existence of a liquid core and hence a dynamo-driven intrinsic magnetic field, if the viscosity of mantle material is lower than 10 to the 22nd to 10 to the 23rd sq cm/sec at temperatures in excess of about 1500 C. The Martian lithosphere is probably several hundred kilometers thick, intermediate in size between that of the earth and Moon.
TL;DR: The quasi-open-source mass spectrometer carried on the Atmospheric Explorer-C satellite has a mode of operation which utilizes the velocity of the vehicle to distinguish between incoming ambient particles and ambient particles which have struck instrument surfaces and become accommodated.
Abstract: The quasi-open-source mass spectrometer carried on the Atmospheric Explorer-C satellite has a mode of operation which utilizes the velocity of the vehicle to distinguish between incoming ambient particles and ambient particles which have struck instrument surfaces and become accommodated. Utilization of this mode has made possible the simultaneous measurement of atomic and molecular ambient oxygen without the ambiguity which usually arises due to surface reactions in the instrument. The method appears promising as a means for analyzing planetary atmospheres or the gas surrounding comets.