Showing papers in "Journal of Geophysical Research in 1985"
TL;DR: In this paper, a set of difference measures are used to evaluate the operational performance of a wide spectrum of geophysical models, regardless of whether the model predictions are manifested as scalars, directions, or vectors.
Abstract: Procedures that may be used to evaluate the operational performance of a wide spectrum of geophysical models are introduced. Primarily using a complementary set of difference measures, both model accuracy and precision can be meaningfully estimated, regardless of whether the model predictions are manifested as scalars, directions, or vectors. It is additionally suggested that the reliability of the accuracy and precision measures can be determined from bootstrap estimates of confidence and significance. Recommended procedures are illustrated with a comparative evaluation of two models that estimate wind velocity over the South Atlantic Bight.
1,832 citations
TL;DR: In this paper, two modes of seasonal behavior are noted for surface ozone at mid-latitudes: a broad summer maximum within a few hundred km of industrial/urban areas in Europe and the U.S., and a minimum in summer or autumn in sparcely populated regions that are remote from industrial activity.
Abstract: In the present analysis of tropospheric ozone data, attention is given to spatial and temporal variations. Two modes of seasonal behavior are noted for surface ozone at mid-latitudes: a broad summer maximum within a few hundred km of industrial/urban areas in Europe and the U.S., and a minimum in summer or autumn in sparcely populated regions that are remote from industrial activity. These and limited historical data indicate that summertime concentrations of ozone near the surface in the rural areas of Europe and the U.S. may have increased between 20 and 100 percent since the 1940s. It is suggested that the summer maximum in ozone and other observed trends are due to photochemical production associated with anthropogenic emissions of NO(x), hydrocarbons, and CO from fossil fuel combustion.
997 citations
TL;DR: In this paper, a brief outline of the basic concepts of cloud filtering and atmospheric attenuation corrections used in the Multi-Channel Sea Surface Temperature (MCSST) method is given, and the operational MCSST procedures and products are described in detail.
Abstract: A brief outline of the basic concepts of cloud filtering and atmospheric attenuation corrections used in the Multi-channel Sea Surface Temperature (MCSST) method is given The operational MCSST procedures and products are described in detail The comparative performance of AVHRR-based MCSST'S is discussed via the use of the results of the JPL Satellite-Derived Sea Surface Temperature workshops For the four data periods there is surprisingly good correspondence in the sign and location of the major monthly mean SST anomaly features derived from MCSST's and those from a screened set of ship-based SST's With the partial exception of the one data period severely affected in some areas by volcanic aerosol from El Chichon eruptions, global statistical measures of the MCSST anomalies relative to the the ship data are as follows: biases, 03–04°C (MCSST lower than ship); standard deviations, 05–06°C; and cross-correlations, +03 to +07 A refined technique in use with NOAA 9 data in 1985 has yielded consistent biases and rms differences near −01°C and 05°C, respectively
978 citations
TL;DR: In this paper, the second-order moment (cross-correlation function) of earthquakes in the U.S. Geological Survey central California catalog between 1969 and 1982 was calculated with respect to a magnitude threshold M ≥ 4.0 over interevent distances up to 80 km.
Abstract: The second-order moment (cross-correlation function) of earthquakes in the U.S. Geological Survey central California catalog between 1969 and 1982 was calculated with respect to a magnitude threshold M ≥ 4.0 over interevent distances up to 80 km and interevent times up to 320 days. The statistical procedure results in a representation of the spatial-temporal structure of the catalog associated with M ≥ 4.0 earthquakes and is capable of revealing patterns too weak to be detected in the space-time distribution of seismicity for individual earthquake sequences. A method is introduced for identifying aftershocks based on a physical two-parameter model of the earthquake interaction process. The results show that the aftershock process dominates the second-order moment and may even obscure the statistical expression of a precursory process. A concentration of foreshocks within 15 km and 3 days of M ≥ 4.0 main shocks exhibits an apparent migration toward the main shock loci with velocity 2.6–5.3 km/d. This concentration may be related to an observed tendency for M ≥ 4.0 events to cluster (auto-correlate) over this interevent range. With the identified aftershocks removed, the residual catalog is Poissonion in space and time. When two M ≥ 4.0 earthquakes occur within 80 km and 40 days of each other, aftershock productivity appears to be relatively enhanced in the earlier sequence. This suggests that aftershock populations are not solely dependent on their main shocks and that unusually productive aftershock sequences may be predictors of future moderate earthquakes.
977 citations
TL;DR: In this paper, the elasticity boundary value problem associated with cracks growing from the tips of a model flaw is solved, and the variations of the "ultimate strength" and the orientation of the overall fault plane with confining pressure are estimated.
Abstract: Micromechanisms of rock failure (axial splitting and shear failure) are examined in light of simple mathematical models motivated by microscopic observations. The elasticity boundary value problem associated with cracks growing from the tips of a model flaw is solved. It is shown that under axial compression, tension cracks nucleate at the tips of the preexisting model flaw, grow with increasing compression, and become parallel to the direction of the maximum far-field compression. When a lateral compression also exists, the crack growth is stable and stops at some finite crack length. With a small lateral tension, on the other hand, the crack growth becomes unstable after a certain crack length is attained. This is considered to be the fundamental mechanism of axial splitting observed in uniaxially compressed rock specimens. To model the mechanism of shear failure, a row of suitably oriented model flaws is considered and the elasticity boundary value problem associated with the out-of-plane crack growth from the tips of the flaws is solved. It is shown that for a certain overall orientation of the flaws the growth of the out-of-plane cracks may become unstable, leading to possible macroscopic faulting. On the basis of this model the variations of the “ultimate strength” and the orientation of the overall fault plane with confining pressure are estimated, and the results are compared with published experimental data. In addition, the results of a set of model experiments on plates of Columbia resin CR39 containing preexisting flaws are reported. These experiments are specifically designed in order to show the effect of confining pressure on the crack growth regime. The experiments seem to support qualitatively the analytical results.
821 citations
TL;DR: In this article, the authors studied the topography of various natural rock surfaces from wavelengths less than 20 microns to nearly 1 meter, including fresh natural joints (mode I cracks) in both crystalline and sedimentary rocks, a frictional wear surface formed by glaciation and a bedding plane surface.
Abstract: The mechanical and hydraulic behavior of discontinuities in rock, such as joints and faults, depends strongly on the topography of the contacting surfaces and the degree of correlation between them. Understanding this behavior over the scales of interest in the earth requires knowledge of how topography or roughness varies with surface size. Using two surface profilers, each sensitive to a particular scale of topographic features, we have studied the topography of various natural rock surfaces from wavelengths less than 20 microns to nearly 1 meter. The surfaces studied included fresh natural joints (mode I cracks) in both crystalline and sedimentary rocks, a frictional wear surface formed by glaciation, and a bedding plane surface. There is remarkable similarity among these surfaces. Each surface has a “red noise” power spectrum over the entire frequency band studied, with the power falling off on average between 2 and 3 orders of magnitude per decade increase in spatial frequency. This implies a strong increase in rms height with surface size, which has little tendency to level off for wavelengths up to 1 meter. These observations can be interpreted using a fractal model of topography. In this model the scaling of the surface roughness is described by the fractal dimension D. The topography of these natural rock surfaces cannot be described by a single fractal dimension, for this parameter was found to vary significantly with the frequency band considered. This observed inhomogeneity in the scaling parameter implies that extrapolation of roughness to other bands of interest should be done with care. Study of the increase in rms height with profile length for two extreme cases from our data provides an idea of the expected variation in mechanical and hydraulic properties for natural discontinuities in rock. This indicates that in addition to the scaling of topography, the degree of correlation between the contacting surfaces is important to quantify.
813 citations
TL;DR: In this paper, the influence of breaking gravity waves on the dynamics and chemical composition of the 60- to 110-km region has been investigated with a two-dimensional dynamical/chemical model that includes a parameterization of gravity wave drag and diffusion.
Abstract: The influence of breaking gravity waves on the dynamics and chemical composition of the 60- to 110-km region has been investigated with a two-dimensional dynamical/chemical model that includes a parameterization of gravity wave drag and diffusion. The momentum deposited by breaking waves at mesospheric altitudes reverses the zonal winds, drives a strong mean meridional circulation, and produces a very cold summer and warm winter mesopause, in general agreement with observations. The seasonal variations of the computed eddy diffusion coefficient are consistent with the behavior of mesospheric turbulence inferred from MST radar echoes. In particular, it is found that eddy diffusion is strong in summer and winter but much weaker at the equinoxes and that this seasonal behavior has important consequences for the distribution of chemical species. Comparison between computed atomic oxygen and ozone, and the abundances of these constituents inferred from the 557.7-nm and 1.27-μm airglow emissions, reveals excellent agreement. The consistency between model results and these diverse types of observations lends strong support to the hypothesis that gravity waves play a very important role in determining the zonally averaged structure of the mesosphere and lower thermosphere.
805 citations
TL;DR: In this paper, the authors present a characterization of the trace gases, taking into account the observed abundances, known sources, and sinks in the present-day atmosphere, and their potentials for climate changes.
Abstract: It is pointed out that the release of chemicals into the atmosphere has grown greatly over the last 50 years. Contributed to the observed perturbations of trace chemicals in the atmosphere have an increased reliance on synthetic chemicals, deforestation, biomass burning, and fossil fuel combustion. As trace chemicals modify the radiation energy of the earth-atmosphere system, the considered developments can produce an alteration of the earth's climate. One of the major objectives of the present study is related to the characterization of the trace gases, taking into account the observed abundances, known sources, and sinks in the present-day atmosphere. Other objectives include an estimate of the future concentration of trace gases, an inference of the preindustrial concentrations of trace gases, and an estimate of the radiative effects of the trace gases and their potentials for climate changes. 103 references.
747 citations
TL;DR: The renewal of the deep North Atlantic by the various overflows of the Greenland-Scotland ridges is only one manifestation of the convective and mixing processes which occur in the various basins and shelf areas to the north: the Arctic Ocean and the Greenland, Iceland, and Norwegian seas, collectively called the Arctic Mediterranean.
Abstract: The renewal of the deep North Atlantic by the various overflows of the Greenland-Scotland ridges is only one manifestation of the convective and mixing processes which occur in the various basins and shelf areas to the north: the Arctic Ocean and the Greenland, Iceland, and Norwegian seas, collectively called the Arctic Mediterranean The traditional site of deep ventilation for these basins is the Greenland Sea, but a growing body of evidence also points to the Arctic Ocean as a major source of deep water This deep water is relatively warm and saline, and it appears to be a mixture of dense, brine-enriched shelf water with intermediate strata in the Arctic Ocean The deep water exits the Arctic Ocean along the Greenland slope to mix with the Greenland Sea deep water Conversely, very cold low-salinity deep water from the Greenland Sea enters the Arctic Ocean west of Spitsbergen Within the Arctic Ocean, the Lomonosov Ridge excludes the Greenland Sea deep water from the Canadian Basin, leaving the latter warm, saline, and rich in silica In general, the entire deep-water sphere of the Arctic Mediterranean is constrained by the Greenland-Scotland ridges to circulate internally Therefore it is certain of the intermediate waters formed in the Greenland and Iceland seas which ventilate the North Atlantic These waters have a very short residence time in their formation areas and are therefore able to rapidly transmit surface-induced signals into the deep North Atlantic
734 citations
TL;DR: In this article, the composition of the organic matter oxidized within the thermocline of the Atlantic and Indian oceans has been estimated from the chemical data along the σθ 27.0 and 27.2 horizons.
Abstract: The composition of the organic matter oxidized within the thermocline of the Atlantic and Indian oceans has been estimated from the chemical data along the σθ 27.0 and 27.2 horizons. These estimates are based on the differences between the preformed and observed concentrations of PO4, NO3, total inorganic CO2, alkalinity, and O2. Since these isopycnal horizons are ventilated both from the north and the south, the preformed concentration estimates take into account the relative contributions of these two end-members. The proportions of these end-members are estimated on the basis of the potential temperature of the water, assuming that no cross-isopycnal mixing occurred. Except for the northern Indian Ocean, the composition of the waters entering the isopycnal horizons is established through linear extrapolation of the property-oxygen trends to oxygen saturation. The σθ 27.0 and 27.2 waters do not outcrop in the northern Indian Ocean, and these horizons receive waters spilling into the Indian Ocean from the Red Sea. Therefore the composition of the Red Sea overflow water with these densities is taken to be the northern Indian end-member. The results of this study indicate that the accepted Redfield P:N:C: −O2 ratio of 1:16:106:138 requires revision. Our analysis yields a ratio of 1:16:103:172 if the carbon value is represented by the observed increase in the total CO2 concentration. On the other hand, if the carbon value is assumed to be represented by the oxygen utilization minus the oxygen used for oxidation of NH3 with two moles of O2 per nitrogen atom, a ratio of 1:16:140:172 is obtained. Thus the P: −O2 ratio lies between 1:103 and 1:140. This discrepancy may be accounted for by the increased CO2 concentrations in the source waters as a result of the uptake of anthropogenic CO2 or by an excess demand of oxygen for oxidation of hydrogenated organic molecules. Therefore, without a firm knowledge of either the corrections for the anthropogenic CO2 effect or the hydrogen content of the biological residues, the true P:C ratio cannot be obtained. The ratio of P:CaCO3 dissolution has been estimated to be about 1:12. This indicates that the CO2 produced by the oxidation of organic carbon to that derived from the dissolution of CaCO3 is bout 10:1 at these density horizons.
690 citations
TL;DR: In this article, the cross-sectional shape of stress induced well bore breakouts has been studied using specially processed ultrasonic borehole televiewer data and a simple elastic failure model was introduced to explain many features of the observations.
Abstract: The detailed cross-sectional shape of stress induced well bore breakouts has been studied using specially processed ultrasonic borehole televiewer data. We show breakout shapes for a variety of rock types and introduce a simple elastic failure model which explains many features of the observations. Both the observations and calculations indicate that the breakouts define relatively broad and flat curvilinear surfaces which enlarge the borehole in the direction of minimum horizontal compression. This work supports the hypothesis that breakouts result from shear failure of the rock where the compressive stress concentration around the well bore is greatest and that breakouts can be used to determine the orientation of the horizontal principal stresses in situ.
TL;DR: In this paper, the authors performed two-dimensional numerical calculations of convection in a domain containing a divariant phase change and found that the critical value of the negative Clapeyron slope, which must be surpassed in order to induce layered convection, decreases in magnitude with increasing Rayleigh number Ra in the range 104 ≤ Ra ≤ 2×106.
Abstract: We report a systematic study on the conditions under which an endothermic phase transition can enforce layered convection. Two-dimensional numerical calculations of convection in a domain containing a divariant phase change were performed in the framework of the “extended Boussinesq approximation,” i.e., considering the effects of adiabatic gradient, latent heat, and frictional heating in the energy equation. We find that the critical value of the negative Clapeyron slope, which must be surpassed in order to induce layered convection, decreases in magnitude with increasing Rayleigh number Ra in the range 104 ≤ Ra ≤ 2×106. Near the critical Clapeyron slope, vacillations between double- and single-layer convection or strongly leaking double-layer convection are possible. The breakdown into layers is influenced very little by the latent heat release but depends solely on the phase boundary deflection caused by lateral temperature differences. The value of the critical Clapeyron slope also seems little affected by the width of the transition zone or by its depth. A possible superplastic rheology within the transition zone would tend to favor layered convection. Scaling the model results to the 670-km discontinuity in the earth's mantle as a possible endothermic phase boundary, we estimate the critical Clapeyron slope to be in the range of −4 to −8 MPa/K (−40 to −80 bar/K). The possibility that the spinel → perovskite + periclase transition is within this range appears to be remote but certainly cannot be neglected.
TL;DR: The qualitative convection pattern presented by Burch et al. as discussed by the authors was extended to all interplanetary magnetic field orientations and applied to newly observed phenomena, such as theta aurora.
Abstract: The qualitative convection pattern presented by Burch et al. (1984) is extended here to all interplanetary magnetic field orientations. The model of Burch et al. is based on the antiparallel merging hypothesis of Crooker (1979) with the addition of small but finite cells driven by quasi-viscous processes on the dawn and dusk edges of the polar cap. Although the treatment presented here is only qualitative, interesting predictions are made about newly observed phenomena, such as theta auroras.
TL;DR: In this article, the average characteristics of auroral electron precipitation as a function of magnetic local time, magnetic latitude, and geomagnetic activity as measured by Kp were determined for each whole number value of Kp from 0 to 5 and for Kp ≥ 6.
Abstract: A statistical study has been completed using data from the Defense Meteorological Satellite Program F2 and F4 and the Satellite Test Program P78-1 satellites to determine the average characteristics of auroral electron precipitation as a function of magnetic local time, magnetic latitude, and geomagnetic activity as measured by Kp. The characteristics were determined for each whole number value of Kp from 0 to 5 and for Kp ≥ 6-. At each level of Kp, the high-latitude region was gridded, and the average electron spectrum in the energy range from 50 eV to 20 keV was determined in each grid element. The results show that the high-latitude precipitation region separates into two parts based on the electron average energy. There is a region of relatively hot electrons (EAVE ≥ 600 eV). In this region, the electron average energies are highest on the morningside of the oval. There are two average energy maxima at each Kp level: one postmidnight and the other prenoon. The hot electron region is generally not continuous in MLT but shows a gap between 1200 and 1800 MLT. The hotter electrons carry most of the energy flux into the oval. The energy flux on the nightside increases with Kp, while the level at noon increases with Kp when Kp is small but decreases at higher Kp. The average energy of the hot electrons increases from Kp = 0 to Kp = 3 but is approximately constant for higher Kp. In the second region, average energies are low (EAVE < 600 eV). This region extends from the poleward edge of the hot electron region to the pole. The precipitating electrons in this region carry the majority of the number flux at high latitudes. The largest number fluxes are found on the dayside. The highest fluxes are confined to a crescent-shaped region centered slightly prenoon and extending in MLT over most of dayside and, in some cases, into the nightside. There is a prenoon maximum in the number flux that shows little variability in MLT or in intensity with Kp. The average energy shows a minimum typically between 1100 and 1200 MLT and located toward the poleward edge of the crescent-shaped region of highest integral number flux. We identify the cusp as the region near the average energy minimum and the cleft as the crescent-shaped region.
TL;DR: In this paper, the climate influence of the land ice that existed 18,000 years before present (18K B.P.) is investigated by use of a general circulation model of the atmosphere coupled with a static mixed layer ocean.
Abstract: The climate influence of the land ice that existed 18,000 years before present (18K B.P.) is investigated by use of a general circulation model of the atmosphere coupled with a static mixed layer ocean. Simulated climates are obtained from two versions of the model: one with the land ice distribution of the present and the other with that of 18K B.P. In the northern hemisphere the tropospheric flow field is strongly influenced by the Laurentide ice sheet and features a split flow straddling the ice sheet, with a strong jet stream forming the southern branch. The northern branch of the flow brings very cold air over the North Atlantic Ocean, where thick sea ice is maintained. The distribution of sea surface temperature (SST) difference between the two experiments in the northern hemisphere resembles the difference between the SST at 18K B.P. and at present, as estimated by the CLIMAP Project (1981). The 18K B.P. ice sheets have very little influence upon atmospheric temperature and SST in the southern hemisphere. This is because the interhemispheric heat transport hardly changes as the loss of heat energy due to the reflection of solar radiation by continental ice sheets in the northern hemisphere is almost completely counterbalanced by the in situ reduction of upward terrestrial radiation. Hydrologic changes in the model climate are also found, with statistically significant decreases in soil moisture occurring in a zone located to the south of the ice sheets in North America and Eurasia. These findings are consistent with some geological evidence of regionally drier climates from the last glacial maximum.
TL;DR: In this article, the authors reviewed basic synthetic aperture radar (SAR) theory of ocean wave imaging mechanisms, using both known work and recent experimental and theoretical results from the Marine Remote Sensing (MARSEN) Experiment.
Abstract: This paper reviews basic synthetic aperture radar (SAR) theory of ocean wave imaging mechanisms, using both known work and recent experimental and theoretical results from the Marine Remote Sensing (MARSEN) Experiment. Several viewpoints that have contributed to the field are drawn together in a general analysis of the backscatter statistics of a moving sea surface. A common focus for different scattering models is provided by the mean image impulse response function, which is shown to be identical to the (spatially varying) frequency variance spectrum of the local complex reflectivity coefficient. From the analysis has emerged a more complete view of the SAR imaging phenomenon than has been previously available. A new, generalized imaging model is proposed.
TL;DR: An overview of observations of coronal mass ejections (CMEs) during the interval March 28, 1979 through December 31, 1981 is presented in this paper, where an introduction is provided to the instrument used in the observations, the method of identifying CMEs, the concepts of CME structural classes, CME importance categories, and the distribution of mass ejection among these classes and categories.
Abstract: An overview of observations of coronal mass ejections (CMEs) during the interval March 28, 1979 through December 31, 1981 is presented. An introduction is first provided to the instrument used in the observations, the method of identifying CMEs, the concepts of CME structural classes, CME importance categories, and the distribution of mass ejections among these classes and categories. The properties of CMEs are given for all mass ejections regardless of their structural classes or importance categories, and then for each class and category. After a brief discussion of the instrument duty cycle, the occurrence rate is presented for all CMEs and for major CMEs, for fast CMEs only, and finally for equatorial CMEs only. The results are compared to those obtained previously.
TL;DR: In this article, the seasonal maxima in scintillation activity coincide with the times of year when the solar terminator is most nearly aligned with the geomagnetic flux tubes, and the occurrence of plasma density irregularities responsible for scintillations is most likely when the integrated E-region Pedersen conductivity is changing most rapidly.
Abstract: An enigma of equatorial research has been the observed seasonal and longitudinal occurrence patterns of equatorial scintillations (and range-type spread F). We resolve this problem by showing that the seasonal maxima in scintillation activity coincide with the times of year when the solar terminator is most nearly aligned with the geomagnetic flux tubes. That is, occurrence of plasma density irregularities responsible for scintillations is most likely when the integrated E-region Pedersen conductivity is changing most rapidly. Hence the hitherto puzzling seasonal pattern of scintillation activity, at a given longitude, becomes a simple deterministic function of the magnetic declination and geographic latitude of the magnetic dip equator. This demonstrated relationship is consistent with equatorial irregularity generation by the collisional Rayleigh-Taylor instability and irregularity growth enhancement by the current convective and (wind-driven) gradient drift instabilities. Some discrepancies in this relationship, however, have been found in scintillation data obtained at lower radio frequencies (below, say, 300 MHz) that suggest the presence of other irregularity-influencing processes. The role of field-aligned currents, associated with the longitudinal gradient in integrated E-region Pedersen conductivity produced at the solar terminator, in equatorial irregularity generation via the current convective instability has not been discussed previously.
TL;DR: In this paper, a series of spatial wave images recorded by a conventional marine radar is analyzed to determine the three-dimensional E(kx, ky, ω) spectrum.
Abstract: A series of spatial wave images recorded by a conventional marine radar is analyzed to determine the three-dimensional E(kx, ky, ω) spectrum. In the absence of a surface current the spectral energy in this three-dimensional wave number frequency space will lie on a shell defined by the dispersion relationship. Any deviation from the expected dispersion relationship can be interpreted as being due to a current induced Doppler shift of the wave frequency. A least squares curve fitting technique is used to determine the surface current required to account for the observed Doppler shift. A comparison of the radar determined spectra and surface currents with ground truth data indicates that the radar system and analysis technique produces results consistent with conventional instrumentation.
TL;DR: In this article, a self-similar spectral shape (the TMA spectrum) was proposed to describe wind waves in water of finite depth, where the parametric spectral form is depth dependent and an extension of the deep water JONSWAP spectrum.
Abstract: A self-similar spectral shape (the TMA spectrum) to describe wind waves in water of finite depth is presented. The parametric spectral form is depth dependent and an extension of the deep water JONSWAP spectrum. The behavior of the spectrum in frequency and wave number space is discussed. About 2800 spectra selected from three data sets (TEXEL storm, MARSEN, ARSLOE) are investigated to show the general validity of the proposal self-similar spectral shape.
TL;DR: In this paper, sea level observations are used to estimate the amounts of warm water exchanged during the 1982 to 1983 El Nino event, indicating an eastward flux of about 40 x 10/sup 6/ m/sup 3/ s/sup -1/.
Abstract: Sea level observations are used to estimate the amounts of warm water exchanged during the 1982 to 1983 El Nino event, indicating an eastward flux of about 40 x 10/sup 6/ m/sup 3/ s/sup -1/. At the end of El Nino the equatorial Pacific is depleted of warm water which is lost toward higher latitudes. The duration of a complete El Nino cycle is determined by the time required for the slow accumulation of warm water in the western Pacific. The cycle constitutes an energy relaxation of the ocean-atmosphere system.
TL;DR: In this paper, a new numerical method is proposed to calculate compaction-driven groundwater flow and associated heat transfer in evolving sedimentary basins, and the model is formulated in Lagrangian coordinates and considers two-dimensional flow in heterogeneous, anisotropic, and accreting domains.
Abstract: A new numerical method allows calculation of compaction-driven groundwater flow and associated heat transfer in evolving sedimentary basins. The model is formulated in Lagrangian coordinates and considers two-dimensional flow in heterogeneous, anisotropic, and accreting domains. Both the continuity of the deforming medium and aquathermal pressuring are explicitly taken into account. A calculation of compaction-driven flow during evolution of an idealized intracratonic sedimentary basin including a basal aquifer predicts slow groundwater movement over long time periods. Fluids in shallow sediments tend to move upward toward the sedimentation surface, and deeper fluids move laterally. The hydraulic potential gradient with depth reverses itself near the basal aquifer, and fluids in this area have a tendency to migrate obliquely into stratigraphically lower sediments. Only small excess pressures develop, suggesting that intracratonic basins are not subject to overpressuring during their evolutions. Owing to the small fluid velocities, heat transfer is conduction-dominated, and the geothermal gradient is not disturbed. Variational studies show that excess hydraulic potentials, but not fluid velocities, depend on assumptions of permeability and that both excess potentials and velocities scale with sedimentation rate. Aquathermal pressuring is found to account for <1% of the excess potentials developed during compaction. These results cast doubt on roles of compaction-driven flow within intracratonic basins in processes of secondary petroleum migration, osmotic concentration of sedimentary brines, and formation of Mississippi Valley-type ore deposits. Results might also be combined with chemical models to investigate the relationship of compaction flow to cementation in sediments.
TL;DR: In this article, the capacitance and charge of an individual grain in the presence of neighboring grains and the surrounding plasma is investigated. And the effect of neighbors on charging currents is explored.
Abstract: Voyager 1 and 2 observations of the Saturnian ring system have led to the discovery of several interesting phenomena associated with its fine dust component. The dust grains are immersed in a plasma. The present paper is concerned with the electrostatics of a dusty plasma, giving particular attention to the capacitance and charge of an individual grain in the presence of neighboring grains and the surrounding plasma. The Poisson equation and gauge considerations are discussed along with a solution of the Poisson equation for several models, taking into account impermeable grains, permeable grains, and a spherical capacitor model. A comparison of potential shapes for three models is conducted, and the effect of neighbors on charging currents is explored.
TL;DR: In this paper, the authors show that surface and subsurface loading are approximately equal in importance in the vicinity of the Kenya rift valley, and the flexural rigidity of the East African lithosphere is about 2×1023 N m.
Abstract: The flexural rigidity of the lithosphere is often estimated from the linear transfer function (admittance) between gravity anomalies and topography. Admittance estimates strongly weight provinces with large topographic relief, which will tend to be those provinces with low flexural rigidity if the cause of the topography is subsurface variations in density. If the observed admittance of continents is modeled in terms of surface loading of an elastic plate, there is a strong bias toward low flexural rigidities. Models incorporating both surface and subsurface loading yield much higher rigidities. Although the two models may match the observed admittance equally well, only those with both surface and subsurface loading are consistent with the observed pattern of coherence between gravity and topography as a function of wavelength. A new method of analysis shows that surface and subsurface loading are approximately equal in importance in the vicinity of the Kenya rift valley. The flexural rigidity of the East African lithosphere is about 2×1023 N m, or an effective elastic thickness of the plate of 25–30 km. Data from the conterminous United States are consistent with the presence of provinces with a wide range of flexural rigidities, averaging tens of kilometers in effective elastic thickness.
TL;DR: The 3He/4He and 4He/20Ne ratios of 115 natural gas samples, including various types of gases from volcanoes, hot springs, mineral springs, water wells, petroleum fields, and natural gas fields, were measured using a mass spectrometer as mentioned in this paper.
Abstract: The 3He/4He and 4He/20Ne ratios of 115 natural gas samples, including various types of gases from volcanoes, hot springs, mineral springs, water wells, petroleum fields, and natural gas fields, were measured using a mass spectrometer. The observed 3He/4He and 4He/20Ne ratios range from 7.47×10−8 to 9.65×10 −6 and from 0.26 to 1100, respectively. The 3He/4He ratios reflect well the geotectonic structure of the Japanese Islands. In northeastern (NE) Japan there is a clear geographical difference in the 3He/4He ratios between the frontal arc (forearc) and volcanic arc (back arc) regions. Lower ratios were found in the trench side region and higher ratios in the back arc side. This result suggests that the mantle-derived helium in the volcanic arc region is associated with the diapiric uprise of a magma. Lower 3He/4He ratios in the frontal arc region may be due to radiogenic He produced by radioactive decay of U and Th in the crustal and sedimentary rocks. In southwestern (SW) Japan there is no clear geographical contrast in the 3He/4He ratios. Some samples in the frontal arc region show quite high 3He/4He ratios. The tendency of the 3He/4He ratios agrees with the distribution of terrestrial heat flow data and reflects geotectonic structures different from NE Japan. The high 3He/4He ratios observed in the frontal arc region in SW Japan may be indicative of renewed or incipient magmatism due to a descending young and warm slab.
TL;DR: In this article, near-surface coastal currents were made off the Northern California coast during the Coastal Dynamics Experiment (CODE) by using 164 current-following drifters, and the results disclosed a number of energetic mesoscale features that dominate across-shelf transport.
Abstract: Observations of near-surface coastal currents were made off the Northern California coast during the Coastal Dynamics Experiment (CODE) by using 164 current-following drifters. Viewed as flow visualization descriptions, the results disclose a number of energetic mesoscale features that dominate across-shelf transport. Examples of eddies, jets, convergences and across-shelf “squirts” are shown and related to moored current observations, wind forcing, and mesoscale features observed in satellite surface temperature imagery. Convergences appear to be most common when currents reverse following relaxation of normally upwelling-favorable winds. Squirts are apparently the cause of cold water plumes extending away from the coast; they appear most frequently at coastal promontories.
TL;DR: In this article, the diffusion coefficients for the hydroxyl species giving rise to the sharp band and broadband features in the infrared spectrum of hydrothermally treated olivine have been determined to be greater than 10−10 m2 s−1 under all pressure and temperature conditions tested.
Abstract: Hydrothermal treatment experiments have been performed on single crystals of San Carlos olivine at 1100° to 1300°C and 300- and 1500-MPa confining pressure, with the oxygen fugacity around the specimen constrained near the Fe/FeO buffer. The diffusion coefficients for the hydroxyl species giving rise to the sharp band and broadband features in the infrared spectrum of hydrothermally treated olivine have been determined to be greater than 10−10 m2 s−1 under all pressure and temperature conditions tested; the solubility of the hydroxyl species seems to vary between crystals but to show little variability for specimens from the same crystal over the temperature range investigated at 300-MPa confining pressure. Crystals hydrothermally treated at 1300°C, 300-MPa confining pressure, and 10−5 s−1 strain rate are a factor of 1.5 to 2.5 weaker than those treated in an anhydrous environment. Microstructural investigations suggest that this reduction in strength is due to enhancement of the rate of climb of dislocations in the “wet” experiments. First-order calculations suggest a stress exponent of n ∼ 2.5 and a water fugacity exponent of m ∼ 1/5 for deformation under hydrous conditions, assuming that the deformation obeys a power law relation.
TL;DR: Water column inventories for bomb radiocarbon at all the stations occupied during the GEOSECS and NORPAX expeditions and for the available TTO stations were calculated in this article.
Abstract: Water column inventories are calculated for bomb radiocarbon at all the stations occupied during the GEOSECS and NORPAX expeditions and for the available TTO stations. The pattern of global inventories obtained in this way suggests that a sizable portion of the bomb radiocarbon that entered the Antarctic, the northern Pacific and the tropical ocean has been transported to the adjacent temperate zones. A strategy for utilizing these inventory anomalies as constraints on global ocean circulation models is presented. Essential to this strategy are the improvement of our knowledge of the pattern of wind speed over the ocean, the establishment of the wind speed dependence of the rate of gas exchange between the atmosphere and sea, and the continued mapping of the distribution of bomb-produced radiocarbon in the sea.
TL;DR: A comparison between Solwind observations of coronal mass ejections (CME's) and Helios 1 observations of interplanetary shocks during 1979-1982 indicates that 72 percent of the shocks were associated with large, low-latitude mass ejection on the nearby limb.
Abstract: A comparison between Solwind observations of coronal mass ejections (CME's) and Helios 1 observations of interplanetary shocks during 1979-1982 indicates that 72 percent of the shocks were associated with large, low-latitude mass ejections on the nearby limb. Most of the associated CME's had speeds in excess of 500 km/s, but some of them had speeds in the range 200-400 km/s. An additional 26 percent of the shocks may have been associated with CME's, but we were less confident of these associations because the sizes and locations of the CME's did not seem appreciably different from those of the numerous CME's without Helios shocks. Only 2 percent of the shocks clearly lacked CME's. As the average level of sunspot activity declined during 1982, the shock frequency also declined, but the observed shocks and some of their associated CME's had unusually high speeds well in excess of 1000 km/s.
TL;DR: In this paper, the authors present a theory of contact between two random flat elastic surfaces, which is a more general form of a theory presented previously by others for the elastic contact of a rough surface and a flat surface.
Abstract: The physical contact between two rough surfaces is referred to as a “joint,” and the deformation of such a joint under normal stress is called the “joint closure.” Toward better understanding of joint closure, we present a theory of contact between two random nominally flat elastic surfaces. This theory is a more general form of a theory presented previously by others for the elastic contact of a rough surface and a flat surface. In agreement with the previous theory we show that the joint closure property depends as much on the details of the surface topography as on the elastic properties of the material. To apply these results by using linear surface profiles requires mapping of profile information to three dimensions. The mapping techniques described here require the probability density function for the contacting surfaces to be approximated well by either a Gaussian distribution or an inverted chi-square distribution. Laboratory experiments on ground surfaces of glass samples were done to test the theory. Both joint closure and surface topography were measured. In most cases, experimental results agreed quantitatively with predictions of the theory. However, in experiments on the smoothest surfaces, sample preparation problems often resulted in surfaces with a domed shape. These surfaces did not fit the assumptions of the theory, but the observed deviations from the theory were consistent with this domed shape. Surface topography measurements suggest that many surfaces are statistically similar. This implies that the success of the theory in predicting joint closure does not depend on a particular sample preparation technique. Therefore the theory should be valid for all nominally flat elastic surfaces. The form of the power spectrum implies that the surface topography and thus the joint closure depend on sample size.