Showing papers in "Geophysical Research Letters in 1975"

The chemistry of atmospheric bromine

Abstract: Bromine may act as a catalyst for recombination of ozone and could be more efficient than either nitric oxide or chlorine. The lower atmosphere contains small concentrations of gaseous bromine produced in part by marine activity and volatilization of particulate material released during the combustion of leaded gasoline, with an additional contribution due to the use of methyl bromide as an agricultural fumigant. Observations by Lazrus et al., (1975) indicate small concentrations of bromine, about 10 to the -11th power (v/v), in the contemporary stratosphere and appear to imply a reduction of approximately 0.3% in the global budget of O3. Estimates are given for future reductions in O3 which might occur if the use of CH3Br as an agricultural fumigant were to continue to grow at present rates.

Mathematical representation of the auroral oval

Abstract: A curve fitting procedure for mathematically representing the auroral oval is described It is shown that the Feldstein ovals and quiet auroral ovals of the night side in DMSP photographs can be approximated by an offset circle, plus a small (≲ 1° magnitude) Fourier component in corrected geomagnetic coordinates Parameters are introduced, Θ and (θo, ϕo), that indicate the dynamic motion of the auroral oval size and center location, respectively Using the parameter Θ, an analysis of several DMSP photographs shows a strong correlation between the southward interplanetary magnetic field (−Bz) and the size of the auroral oval

On the stability of open hydraulic fractures in the Earth's crust

Abstract: It has been suggested that a substantial amount of heat energy could be extracted from dry hot rocks near the earth's surface by circulating a fluid through large hydraulic fractures. However a theoretical analysis of propagation and closure of hydraulic fractures subject to realistic stress gradients indicates an upper limit for the size of a stable fracture. For example, if the vertical gradient of the least principal stress exceeds the unit weight of the fluid by ∼100 dynes/cm³ a stable vertical fracture in granite held open by fluid pressure may not be more than ∼2 × 104 cm high. This limit should be taken into account in the design of dry hot rock heat recovery systems.

The partitioning of rare earth elements between garnet and liquid at high pressures: Preliminary experiments

Abstract: Preliminary experiments were made to determine the partition coefficients of rare earth elements between garnet and liquid at 30 kb and 1275°C in the system diopside(30 wt%)-pyrope(70%)-water. REE were added to the system by titration at concentration levels in the range of natural basalts. The phases were separated by differential dissolution technique(DDT) and analized for REE by isotope dilution. The partition coefficients(solid/liquid) are: 0.021 for Ce, 0.087 for Nd, 0.217 for Sm, 0.320 for Eu, 0.498 for Gd, 1.06 for Er and 4.03 for Yb. They are in excellent agreement with those estimated from cpx-liq and cpx-gar relationships currently used in the literature.

Pressure-induced coordination changes in magmatic liquids

Abstract: It is probable that many of the gross physical properties of melts and partial melts at depth within the earth are substantially modified by pressure-induced cationic coordination transformations. An isochemical extension of the Bottinga-Weill viscosity model is suggested to account for the effects of coordination changes on melt viscosities. Resulting predictions are that tholeiitic and andesitic melts will undergo, with increasing pressure, decreases in viscosity of factors of 14 and 47 respectively on transformation of aluminum from four- to six-fold oxygen coordination. Analogous transformations in solid phases suggest their occurrence in melts at pressures below 35 kilobars for temperatures not exceeding 1400C. Associated changes in liquid specific volume are estimated to be roughly three and four percent respectively for the aforementioned melt compositions. Transformation of aluminum from four- to six-coordination also greatly decreases shear wave attenuation in partial melts.

Post-oxide phases of forsterite and enstatite

Abstract: Both forsterite (Mg2SiO4) and enstatite (MgSiO3) enter a post-oxide phase characterized by the orthorhombic perovskite structure when subjected to high pressure and temperature in the diamond-anvil press coupled with laser heating. The lattice parameters for the perovskite phase of MgSiO3 are ao = 4.790 ± 0.002, bo = 4.943 ± 0.002, and co = 6.897 ± 0.003 A with Z = 4. The calculated density of MgSiO3 (perovskite) is thus 4.083 g/cm³, or 2.8% denser than its isochemical mixed oxides with rocksalt and rutile structures. The density of a mixture of MgSiO3 (perovskite) plus MgO (periclase) is 1.9% greater than that of the mixed oxides with the forsterite stoichiometry.

A new plasma regime in the distant geomagnetic tail

Abstract: Observations are reported of an extensive region of low-energy plasma particles (LEP) flowing antisunward along the ordered field lines in the lobes of the geomagnetic tail at lunar distances. The flow was detected by three suprathermal ion detectors deployed on the lunar surface during the Apollo 12, 14, and 15 missions. This particle regime is found to be similar to the 'boundary layer' and 'plasma mantle' observed at smaller geocentric distances and to an interior flow region parallel to the magnetopause in the dayside magnetosphere. It is located exterior to the plasma sheet across essentially the entire tail and adjacent to the magnetopause on both the dawn and dusk sides of the magnetosphere. Variations in the integral flux, temperature, and number density are described. It is suggested that this flow and the three similar regimes are simply connected along the inner surface of the magnetopause and are, in fact, the same phenomenon.

Elasticity of microcrystals

Abstract: Acoustic velocities for a very small crystal are presented. The longitudinal velocities in the .3 mm single crystal of quartz are accurate to about 1–2%. The technique involves only optical measurements and is based on analysis of Brillouin scattering. The minimal sample size for acoustic velocity measurements using this technique is estimated to be about 0.01–0.03 mm.

Evidence for local ion heating in solar wind high speed streams

Abstract: The thermal anisotropies near the peaks of proton distributions are observed to vary characteristically across two simple high speed streams. Before the time of maximum velocity gradient T∥ of the core distribution is greater than T⊥ but afterwards, and persisting throughout the remainder of the high speed region, T∥ < T⊥. This implies that it may not be necessary to invoke extended ion heating close to the sun to explain enhanced ion temperatures associated with high speed streams and that the T-V relation may be primarily the result of local heating near 1 AU.

Is there an electrostatic field tangential to the dayside magnetopause and neutral line

Abstract: Energy considerations are put forward which lead to the conclusion that the magnetopause current does not flow through the magnetospheric potential difference (of 60,000 V), and that the magnetopause is roughly an equipotential surface. Because of the necessary continuity of the tangential component of the electric field, this conclusion implies that no steady-state electric field exists along the neutral line located near the dayside magnetopause (in an open magnetospheric model). Since such an electric field is an essential part of the theory of merging of magnetic lines of force, it is concluded that the merging model does not hold for the electric field.

Variations in the solar wind stand-off distance at Mercury

Abstract: The intrinsic dipole model of the magnetosphere of Mercury is combined with statistics on the solar wind dynamic pressure from Explorers 33 and 35 to obtain histograms of the solar wind stand-off distance for aphelion, perihelion and median distance of Mercury from the sun. The results show that even at perihelion the stand-off distance lies above the surface the great majority of the time. On rare occasions, direct impact of the solar wind onto the surface will occur.

Lidar observations of a stratospheric dust cloud layer in the tropics

Abstract: A transparent whitish cloud veil was observed over Hawaii from early October throughout January 2, 1975, the date of submission of this paper. Lidar measurements made from the Mauna Loa Observatory during this period established the height of the layer at about 19.5 km MSL with a typical thickness at half maximum of 800 meters. The nearest Rawinsonde data clearly indicated this height to be above the tropopause. During the month of November, a stratospheric layer was observed by several other workers in the United States which has been attributed to the eruption of Fuego volcano in Guatemala during the month of October. However, the backscatter coefficient observed in the layer over Hawaii was occasionally 20 times greater than that observed at other locations. Although our data support the volcanic hypothesis, there are still some unanswered questions. For example, we observed the layer prior to the major eruption period and the time of appearance of the layer over other observatories in the United States. Furthermore, high altitude aircraft were operating in the stratosphere over Hawaii during the first two weeks of October which may have influenced the cloud formation.

A study of lateral inhomogeneities in the upper mantle by multiple Scs travel‐time residuals

Abstract: An analysis of records of multiply reflected ScS phases from ten deep-focus earthquakes yields near-vertical one-way travel-time residuals varying from +5.0 to −3.5 s. Continental and oceanic residuals overlap and both indicate large lateral variations. Similar values are found for the older oceanic basins and for continental shields. Most, if not all, of the variations can be attributed to differences in the lithosphere and asthenosphere. The mantle under Hawaii, Iceland and Trindade (South Atlantic) Islands is anomalously slow, all being postulated hotspots. In the case of Trindade, petrological data is consistent with a pronounced low-velocity zone and large S delays. Some recent studies assumed that stations on oceanic islands were representative of the ocean as a whole and it has been suggested that continent-ocean differences extend deeper than 400 km. The present results indicate that oceanic islands are anomalous, and that differences between oceans and continents need not extend below 200 km. This does not rule out the existence of deep lateral inhomogeneities, but only the proposal that continents, in general, are faster than oceans to depths greater than 400 km.

Higher Rayleigh modes in western Europe

Abstract: An array of standard long period stations is applied to measure phase velocities of seismic surface waves by way of frequency-wavenumber analysis. The number of interfering modes is reduced by windowing the signal for successive group velocity intervals. The method is powerful, even with relatively small arrays: up to 6 higher Rayleigh modes at periods between 20 and 100 sec. have been resolved.

Can the Earth's magnetic field be sustained by core oscillations?

Abstract: Some recent suggestions for generating the earth's magnetic field via short period oscillations of the liquid core are critically examined. Seismic energy seems inadequate for the purpose. Limits on the minimum amplitude of such oscillations are derived and these are shown to be so large that they would be accompanied by observable gravity anomalies. It is concluded that waves with periods much less than years are unimportant for the dynamo problem.

Electron heat flux instabilities in the solar wind

Abstract: There are at least three plasma instabilities associated with the electron heat flux in the solar wind. This letter reports the study of the unstable fast magnetosonic, Alfven and whistler modes via a computer code which solves the full electromagnetic, linear, Vlasov dispersion relation. Linear theory demonstrates that both the magnetosonic and Alfven instabilities are candidates for turbulent limitation of the heat flux in the solar wind at 1 A.U.

Source mechanism for terrestrial kilometric radiation

Abstract: The intense electromagnetic radiation of near earth origin, observed by the OGO, IMP, and Hawkeye satellites, can be explained in terms of plasma oscillations near the upper hybrid frequency which are stimulated in the high latitude regions at distances within 5 earth radii. The wave energy is converted from the longitudinal electrostatic mode to the transverse electromagnetic mode as it travels in the slightly inhomogeneous magnetosphere, and it is reflected at the point where the wave frequency equals the local electron plasma frequency. Peak emission region occurs near 2 earth radii. The original plasma oscillations are generated in the turbulent plasma produced by precipitating electrons associated with discrete auroral arcs. The mechanism has possible applications to studies of the irregular structure of the magnetospheric thermal plasma and to models for the decametric radiation from Jupiter.

Age of the apatite at Cerro de Mercado, Mexico: A problem for fission-track annealing corrections

Abstract: Fission-track dating and K-Ar dating indicate that the age of apatite from Cerro de Mercado, Mexico, is 30 m.y., in contradiction to previous corrected fission track ages of 40 and 57 m.y. by other works. Annealing data for the “plateau method” correction of fission-track ages for the Cerro de Mercado apatite lead to corrections by a factor of sixty or more, which give geologically unreasonable ages. In addition, published data concerning the length of fission tracks and the annealing of minerals imply that the basic assumptions used in an alternative procedure, the length-reduction-correction method, are also invalid for many crystal types and must be approached with caution unless individually justified for a particular mineral.

Seasonal and latitudinal variation of the stratospheric concentration of HNO3

Abstract: A sensitive spectral radiometer system capable of measuring the atmospheric emission in the 6.5µm to 13.0µm region has been constructed for use on the WB57F aircraft used on the Department of Transportation Climatic Impact Assessment Program. The data obtained with this instrument on a number of flights have been analyzed to determine the total HNO3 column density above the aircraft at various latitudes and seasons. Examination of these data indicate a definite variation of HNO3 column density with latitude and possible seasonal variations.

High‐order magnetic multipoles as a source of gross asymmetry in the distant Jovian magnetosphere

Abstract: The longitudinal asymmetry of the surface magnetic-field strength at Jupiter causes a longitudinal asymmetry in the equatorial plasma mass density within the Jovian magnetosphere. The rotation of these density variations with the planet causes a diurnal variation of the radial distance on the night side at which the centrifugal stress of the magnetospheric plasma exceeds the local magnetic-field tension. This is approximately the distance at which the magnetic field opens to interplanetary space; we estimate that the opening distance can vary by as much as 14% as a result of the observed surface field asymmetry. Such a diurnal variation of the boundary of the particle trapping region can account for the observed ten-hour modulation of relativistic electrons emitted from Jupiter into interplanetary space.

Measurements of stratospheric CFCl3, CF2Cl2, and N2O

Abstract: Stratospheric air samples have been obtained at 17.7, 22.3, and 26.2 km using balloon borne sampling spheres launched from Laramie, Wyo. These samples have been analyzed for CFCl3, CF2Cl2 and N2O, using electron capture detector gas chromatography. The concentrations of all three constituents are compared with theoretical models and found to be in excellent agreement. The dissociation products of N2O, CFCl3, and CF2Cl2 (NO and chlorine atoms) catalytically destroy ozone in the stratosphere. A knowledge of the concentrations of these species in the stratosphere is therefore essential to an understanding of the ozone balance.

Temperature profile in the molecular sublayer near the interface of a fluid in turbulent motion

Abstract: The molecular sublayers adjacent to the air-sea interface are assumed to undergo cyclic growth and destruction in order to explain the exponential temperature profiles measured by Khundzhua and Andreyev. The duration of such cycles is taken to be randomly distributed in forced convection and a constant period is used to determine the temperature profile in free convection.

The absolute concentration of O(³P) in the Earth's stratosphere

Abstract: Results are presented for an experimental application of the laminar flow-through/resonance technique, which allows direct observations of the absolute concentration of atoms and radicals in the earth's upper atmosphere. Atomic resonance fluorescence was used in conjunction with a parachute-borne flow-through module deployed from a balloon at a height of 40 km to determine the concentration of ground-state atomic oxygen at 40 to 25 km in the atmosphere. The equipment is described, and the measurements and experimental uncertainties are plotted. It is shown that the observed absolute concentration of ground-state atomic oxygen is similar to that predicted by model calculations, and it is concluded that this technique provides a simple and direct means of measuring atomic and radical concentrations in the part-per-trillion range in unperturbed stratospheric samples.

New cross sections for the absorption of near ultraviolet radiation by nitrous oxide (N2O)

Abstract: A re-investigation of the ultraviolet absorption spectrum of nitrous oxide (N2O) agrees with previous results in the range 210 to 235 nm, but contrary to previous results it indicates a vanishingly small cross section above 260 nm. The absence of the relatively long wave length absorption implies a negligible rate of photolysis of nitrous oxide in the troposphere. These results plus the previously estimated atmospheric mean residence times of N2O indicate that there is a large, unknown tropospheric sink for nitrous oxide.

The gravity field of Mars

Abstract: A complete sixth-degree spherical-harmonic model of the gravitational potential of Mars has been produced from an analysis of Doppler data obtained from the radio tracking of the Mariner-9 spacecraft for over 200 orbital revolutions. The equipotential surface defined by this model is estimated to be accurate to within 100 m below 60° North Latitude and to within 300 m above. The dominant feature of this surface is a Tharsis-related bulge which rises nearly two kilometers above the surrounding areas. Gravitational “lows” are found to correspond to the Hellas depression and the Valles Marineris.

Stratospheric profiles of CCl3F and CCl2F2

Abstract: This is a brief note intended to report recent measurements of CCl3F and CCl2F2 in stratospheric samples obtained in 1973 through 1975. The samples were collected by a balloon-cryogenic sampling system which has been described previously (Lueb, Ehhalt, and Heidt, 1975). The method allows us to collect large air samples (10 l STP) for the laboratory analysis of a number of trace gases. It has been used since September 1973. Aliquots of the samples had been stored and were analyzed this year for their halocarbon content by gas chromatography with an electron capture detector. Results of these measurements are compared to calculated predictions.

Application of synchronous meteorological satellite data to the study of time dependent sea surface temperature changes along the boundary of the Gulf Stream

Abstract: Thermal infrared imagery from the Synchronous Meteorological Satellite (SMS), located above the equator at 75°W, was used to produce a time-lapse film of the Gulf Stream off Florida Northward propagating cyclonic eddies with a speed of 39 cm/sec, spacial scale of 265 km, and low frequency (ω/f <015), where ω is a wave frequency and f is the Coriolis parameter, were detected at the inshore edge of the current's boundary These results demonstrate an application of the SMS to the study of time dependent sea surface thermal patterns

Estimate of late 1974 stratospheric concentration of gaseous chlorine compounds (ClX)

Abstract: The total concentration (ClX) versus altitude of Cl-containing molecules (principally HCl, Cl, ClO) is estimated. It is shown that the predicted present stratospheric concentrations are due to photolysis near 30 km of man-made CF2Cl2 and CFCl3, and CCl4 from a ground-level source, either man-made or natural. The contribution of CH3Cl to stratospheric ClX is evaluated from preliminary measurements of the compound at ground level. Although ground-level sources of HCl and Cl2 are large, tropospheric processes preclude significant impact on the stratosphere.

Fluorine photochemistry in the stratosphere

Abstract: The photochemistry of fluorine in the stratosphere is surveyed in order to estimate the effect on ozone of fluorine atoms released by the breakdown of chlorofluoromethanes. The catalytic efficiency for ozone destruction by fluorine is found to be less than .0001 that of chlorine in the altitude range from 25 to 50 km.

Rotational bursting of interplanetary dust particles

Abstract: Solar radiation pressure can cause rotational bursting and eventual elimination from the solar system of small asymmetric interplanetary particles by a windmill effect. The life span determined by this process for stony meteoritic material or tektite glass with radii of 1 cm is on the order of 105 years.Same size material which contains iron, nickel or aluminum, with properties. such that it is subject to 5 percent of the amount of spin damping as pure metals, can be removed from the solar system on the order of 106 years by this process. Ordinary chondritic material, despite its high resistivity, is subject to a type of magnetic spin damping, in addition to the normal spin damping, with the consequent result that this type material cannot be removed from the solar system by this process.This depletion mechanism appears to work faster than the traditional Poynting-Robertson effect by approximately two orders of magnitude for the nonmetallic particles and one order of magnitude for the metallic particles.