bluuebunny/crossref_metadata_2025 huggingface dataset:
A possible mantle instability due to superplastic deformation associated with phase transitions
Authors: Parmentier E. M.
Published: February 2008

Laboratory deformation studies of metals and some oxides indicate that these solids are easily deformed while undergoing a phase transformation. This superplastic effect, if it occurs for mantle silicates, may result in an instability of mantle flow. The instability is illustrated by considering a sheared layer of viscous fluid containing a phase transition. With a simple idealization of the phase transition weakening effect, an oscillatory fluid motion which cycles material through the phase transition is shown to reduce the rate of viscous dissipation associated with shearing the fluid layer. Some possible consequences for mantle flow include the partial decoupling of mantle layers at phase transitions and short wavelength free air gravity anomalies due to induced normal stress variations at the base of the lithosphere.
Wave‐particle interactions at the magnetopause: Contributions to the dayside aurora
Authors: Tsurutani B. T. , Smith E. J. , Thorne R. M. , Anderson R. R. , Gurnett D. A. , Parks G. K. , Lin C. S. , Russell C. T.
Published: February 2008

A strong correlation between intense, broad‐band 10‐105 Hz plasma waves and 1‐6 keV electrons and protons are observed on ISEE 1 and 2 at the low latitude dayside magnetopause. Wave and particle features have been characterized by taking averages over ten events. The 10‐10³ Hz magnetic waves and the 10‐105 Hz electric emissions can be represented by the power‐law spectra, Im = 10 f−3.9 nT2/Hz and Ie = 3 × 10−5 f−2.8 V²/m² Hz, respectively. The electron and proton fluxes and spectral shapes are nearly constant from event‐to‐event, and are characterized by j− = 3 × 105 E−1.8 cm−2sec−1ster−1keV−1 and j+ = 107 E−2.5 cm−2sec−1ster−1keV−1. Using typical magnetopause plasma and field values of 20 cm−3 and 50 nT, it is shown that the 1‐10 keV electrons and protons are scattered near the limit of strong pitch angle diffusion by the observed waves. A precipitation flux of ∼0.15 ergs/cm² sec is calculated, indicating a significant contribution to the dayside aurora.
The Somalian earthquakes of May, 1980, East Africa
Authors: Ruegg J. C. , Lépine J. C. , Tarantola A. , Lévêque J. J.
Published: February 2008

A seismic crisis, with a mb = 5.3 main shock, occured in the Somali Republic, East Africa (10°N, 43°E) from April to November 1980. Up to 2000 earthquakes with ML > 2 have been recorded during this period. This earthquake sequence is of particular interest because it occured in a seismically inactive zone and include a rather long aftershock sequence. Two groups of epicenters were identified using a relative location procedure. Aftershocks observed during the first two weeks fall very close to the Borama city, while latter shocks are situated 10km west. This may suggest that the second group of earthquakes has been induced by the first one. These data show that the continental margin between the Somalian Plateau shield and the quasi‐oceanic crust of the Afar‐Gulf of Aden region, remains active to day and is relevant to intraplate seismicity.
A simulation study of east‐west IMF effects on the magnetosphere
Authors: Brecht S. H. , Lyon J. , Fedder J. A. , Hain K.
Published: February 2008

The effect of adding a By magnetic component to a solar wind already carrying a Bz magnetic component is studied using 3‐D MHD computer simulations. It is found that the tail structure and the Bx lobe fields are rotated and become asymmetric. In addition a By component is generated in the neutral sheet. These results are found to correlate with observational data.
Acceleration of energetic ions at the Earth's bow shock
Authors: Lee M. A. , Skadron G. , Fisk L. A.
Published: February 2008

A simple analytical solution is presented which incorporates many of the processes believed to be important in the acceleration of the ‘diffuse’ component of energetic ions at the Earth's bow shock, and which can account for many of the characteristics observed for these events. The solution can account for the observed spectral shape, the observed spatial dependence of the intensity, and the observed magnitude and spatial dependence of the anisotropy.
Anomalous chemical changes in well waters and possible relation to earthquakes
Authors: King Chi‐Yu , Evans William C. , Presser Theresa , Husk Robert H.
Published: February 2008

Water level, temperature, salinity, electric conductivity, and pH have been measured periodically for several years at three water wells located along a 17‐km segment of the San Andreas fault between San Juan Bautista and Cienega Winery in central California. Water samples were collected at the same time for subsequent chemical analyses in the laboratory. Some sudden large changes in salinity and conductivity were recorded in early March 1980 at the two wells near San Juan Bautista. These changes coincided approximately with the beginning of an episode of increased local seismicity, including a magnitude 4.8 earthquake on April 13. Analyses of water samples revealed corresponding changes in ion concentrations, especially of Na+, Ca++, Mg++, SO4−−, HCO3−, F−, and Cl−. The observed changes may be the result of mixing of waters from different aquifers through cracks developed in the water barriers by a possible crustal strain episode that may have occurred in the study area.
Variations in stable‐isotope ratios of ground waters in seismically active regions of California
Authors: O'Neil James R. , King Chi‐Yu
Published: February 2008

Measurements of D and 18O concentrations of ground waters in seismically active regions are potentially useful in earthquake prediction and in elucidating mechanisms operative during earthquakes. Principles of this method are discussed and some preliminary data regarding a magnitude 5.7 earthquake at the Oroville Dam in 1975 and a series of events near San Juan Bautista in 1980 are presented to support the utility of such measurements. After earthquakes, the D content of nearby ground waters increased by several permil while the 18O content remained constant. This increase implies that H2O may have either decomposed or reacted to form molecular H2 at depth. It is emphasized that many areas must be investigated for these effects in order to find a sufficient number of "sensitive" water wells and springs to permit a truly effective program of earthquake research.
Anomalous water‐level changes and possible relation with earthquakes
Authors: Merifield P. M. , Lamar D. L.
Published: February 2008

Since late 1976 abandoned water wells have been monitored along the San Andreas and San Jacinto faults to detect water‐level changes which may be premonitory to earthquakes. An M5.5 earthquake occurred 25 February 1980 within the San Jacinto fault zone near Anza. The water level in a continuously recorded well in Borrego Valley 35 km from the epicenter rose 0.5 m and returned to its prior level during a four‐hour period beginning 88 hours before the earthquake. The water level in this well had been remarkably steady compared to other wells being monitored. Another well in Borrego Valley showed a much smaller rise and fall in water level at the same time. Because these changes are unique for the long‐term records of these wells, they may represent precursors to the earthquake.

Several wells along the Palmdale‐Valyermo segment of the San Andreas fault showed possibly anomalous, long‐term water‐level changes which are not clearly related to rainfall. Between early 1979 and early 1980, water levels in six wells were .6 to 4.5 m higher and levels in two wells were about 3 m lower than would have been predicted based on the previous records. The water‐level increases could have been the result of delayed response to seasonal rainfall, following a long drought. However, it is interesting that the possibly anomalous water‐level changes first occurred at the same time as the reported changes in strain pattern from compression to expansion along the San Andreas fault in the same area.
Density of the mantle of Mars
Authors: Goettel Kenneth A.
Published: February 2008

The range of zero pressure densities of the Martian mantle which are compatible with the mean density and moment of inertia factor of Mars has been explored by: a) considering the full range of plausible core compositions and densities, and b) investigating the sensitivity of computed mantle densities to uncertainties in the input parameters. Ni, Fe, Fe3O4, and FeS cores were considered; corresponding zero pressure mantle densities range from 3.47 to 3.41 g/cm³. Uncertainty in the mantle density of about 0.04 g/cm³ for the Fe core model and about 0.05 g/cm³ for the FeS core model results from uncertainties in the input parameters. The zero pressure density of the Martian mantle is estimated to be 3.44 ± 0.06 g/cm³.
Jovian auroral secondary electrons and their influence on the Io plasma torus
Authors: Thorne R. M.
Published: February 2008

A direct coupling is proposed between Jovian auroral energy dissipation (estimated to be as much as 1014 W) and ultraviolet emissions (≈ 2.5 × 1012 W) from the heavy ion torus surrounding Io. This association was motivated by the realization that there are serious discrepancies in all previous theories for either the auroral input or the energy source required to maintain hot electrons (> 10 eV) in the emitting torus. It is demonstrated that both problems can be resolved by adopting the plausible assumption that the dominant auroral precipitation occurs in an energy range yet to be reported, in particular heavy ions below 500 KeV. As these enter the atmosphere a dominant fraction of their energy is dissipated in producing secondary electrons with mean energy in the range 20‐40 eV. Most of the secondary electrons subsequently yield their energy to further ionization or excitation. However, those produced above an altitude where the atmospheric density is ∼ 1010 cm−3 can escape into the magnetosphere. The electron heat flux to the magnetosphere can exceed 1% of the auroral dissipation if the dominant precipitation flux consists of heavy ions (O+ or S+) with an energy between 100 to 1000 KeV. This could provide the source of electron energy required to balance radiative loss from the Io torus and it would inject ionospheric H+ ions into the magnetosphere at a rate (≈ 2 × 1029 sec−1) comparable to the upper estimates of heavy ion injection near Io.
The altitude distribution of the Venus ultraviolet nightglow and implications on vertical transport
Authors: Gérard J. C. , Stewart A. I. F. , Bougher S. W.
Published: February 2008

The altitude distribution of the nitric oxide nightglow has been measured with the ultraviolet spectrometer on board Pioneer Venus. Limb profiles obtained near periapsis with a ∼ 5 km vertical resolution have been fitted using a method independent of the spacecraft attitude data. It is found that the altitude of the maximum of the layer is 115 ± 2 km and the topside scale height ≃ 3 km. It is shown that downward transport by diffusion alone is insufficient. If vertical motion is parametrized by eddi diffusion, an eddy diffusion coefficient K ≃ 8−4+8 × 1012 / {M}1/2 cm².s−1 is deduced from the altitude of the layer.
Size effect in rock testing
Authors: Baecher Gregory B. , Einstein Herbert H.
Published: February 2008

Empirical relations between size and strength have found ample treatment in the literature, not so the effect of size on the underlying mechanism. This paper examines size effect on fracture mechanism in unconfined and triaxial tests between intact specimens of various sizes and on jointed specimens with various spacings. Statistical size effect and volume dependent strain energy effect can be distinguished and are shown to differently affect crack propagation and failure mechanism.
Some aspects of size‐Effect in rock failure
Authors: Dey T. , Halleck P.
Published: February 2008

The Los Alamos National Laboratory is developing a program in large‐volume testing of rocks. One part of this program is the measurement of size effects on the constitutive properties of rock. The other part is the development of models to explain and predict these effects. We use a unique 44‐MN hydraulic press to load large specimens to failure, while measuring stress‐strain behavior, failure strength, and acoustic emission. In this paper, results of stress‐strain measurements taken on a single sample of "Texas Pink" granite are reported. We took two sets of data with gauge lengths of 0.3 and 10.0 cm. We also discuss existing models of size effect on strength and conclude that a stochastic model is needed to replace existing empirical deter ministic ones. Estimates of initial crack abundance together with our simple model of failure explain the variation of strength with size reported by some investigators.
High temperature creep of forsterite polycrystalline aggregates
Authors: Relandeau Christian
Published: February 2008

Sintered polycrystalline aggregates of forsterite have been deformed in compression. The densities of the samples were higher than 93% of the theoretical density. Creep tests have been performed for a range of grain size (60 to 132µm) at high temperatures (T ⩾ 1450°C) and low stresses (3<σ<20 MPa) in a dead weight creep apparatus at room pressure. The creep law determined is: . It compares very well to other aggregate or single crystal data.
Local Mars dust storm generation mechanism
Authors: Ryan J. A. , Sharman R. D. , Lucich R. D.
Published: February 2008

On Ls = 340°, first Mars year of Viking on the surface, a local dust storm was observed at the Viking Lander #1 site by Viking Orbiter A. The storm lasted less than one martian day (sol) with the dust raised affecting the site for about three sols. It is concluded that this storm was caused by baroclinic waves and that the threshold wind speed for saltation was 25‐30 m sec−1.
ISEE‐1, ‐2 and ‐3 observation of the interaction between an interplanetary shock and the Earth’s magnetosphere: A rapid traversal of the magnetopause
Authors: Winterhalter Daniel , Kivelson Margaret G. , Russell Christopher T. , Smith Edward J.
Published: February 2008

The interaction between an interplanetary shock and the earth’s magnetosphere was observed by ISEE‐1 and ‐2 on August 27, 1978. The two spacecraft were initially inside and near the nose of the magnetosphere, separated by about 1000 km. The shock, identified by ISEE‐3, reached the vicinity of the earth in approximately half an hour. As a result of the interaction the magnetospheric boundaries moved rapidly earthward, so that in less than three minutes both the magnetopause and the bowshock passed over the ISEE‐2 and ‐1 spacecraft. Time delays between the two spacecraft yielded a boundary speed of 195 km/sec for the magnetopause. This exceptionally large speed provided a rapid scan of the boundary at the time and place of observation, but important differences in boundary structure existed in data taken 5 seconds apart by the two spacecraft. A rotational MHD wave seemed present during the ISEE‐2 crossing and absent during the ISEE‐1 crossing. The magnetopause thickness was found to be 860 km at ISEE‐2, and 780 km at ISEE‐1. The data indicated boundary structure on a scale of 370 km or less, and/or high frequency (⩾ 0.21 Hz) large amplitude temporal variations. These results are inconsistent with steady state reconnection but are compatible with localized patchy reconnection.
Measurements of middle‐atmosphere electric fields and associated electrical conductivities
Authors: Hale L. C. , Croskey C. L. , Mitchell J. D.
Published: February 2008

A simple antenna for measuring the vertical electric field in the "middle atmosphere" has been flown on a number of rocket‐launched parachute‐borne payloads. We present here the data from the first nine such flights, launched under a variety of geophysical conditions, along with electrical conductivities measured simultaneously. The data include indications of layered peaks of several volts per meter in the mesospheric field at high and low latitudes in situations of relatively low conductivity. During an auroral "REP" event the electric field reversed direction in the lower stratosphere, accompanied by a substantial enhancement in conductivity. The data generally do not confirm speculations based only on the extension of the thunderstorm circuit from below or the mapping of ionospheric and magnetospheric fields from above, but seem to require, in addition, internal generation processes in the middle atmosphere.
Rate constant for the reaction C+ + CO2 at collision energies 0.04 to 2.5eV
Authors: Fahey D. W. , Fehsenfeld F. C. , Ferguson E. E.
Published: February 2008

The rate constant for the reaction C+ + CO2 has been measured over the energy range of thermal to 2.5eV. The present results yield (1.1 ± 0.2) (−9) cm³s−1 at thermal energy which agrees well with previous measurements. No energy dependence was found for the rate constant below 1eV. Above 1eV the rate constant was found to decrease with increasing energy. The present results indicate that energetic C+ ions produced from the photoionization of CO2 in the Venus ionosphere will not have loss rates greatly reduced from that of thermal C+ ions.
The excitation of long period seismic waves by a source spanning a structural discontinuity
Authors: Woodhouse J. H.
Published: February 2008

Simple theoretical results are obtained for the excitation of seismic waves by an indigenous seismic source in the case that the source volume is intersected by a structural discontinuity. In the long wavelength approximation the seismic radiation is identical to that of a point source placed on one side of the discontinuity or of a different point source placed on the other side. The moment tensors of these two equivalent sources are related by a specific linear transformation and may differ appreciably both in magnitude and geometry. Either of these sources could be obtained by linear inversion of seismic data but the physical interpretation is more complicated than in the usual case. A source which involved no volume change would, for example, yield an isotropic component if, during inversion, it were assumed to lie on the wrong side of the discontinuity. The problem of determining the true moment tensor of the source is indeterminate unless further assumptions are made about the stress glut distribution; one way to resolve this indeterminancy is to assume proportionality between the integrated stress glut on each side of the discontinuity.
Observational, reference and model data on solar EUV, from measurements on AE‐E
Authors: Hinteregger Hans E. , Fukui Katsura , Gilson Bruce R.
Published: February 2008

Information on solar irradiance at wavelengths below 185 nm, observed by the EUVS experiment on the AE‐E satellite over the entire development of the present sunspot cycle 21, is important to many investigations of planetary thermospheres and ionospheres. Strictly observational information is generally lacking in both the completeness and the spectral detail required by the more advanced study programs. Therefore, it has been necessary also to develop computer models in connection with fully detailed compilations of an appropriate reference spectrum. Our selection of appropriate forms of effective publication has been difficult for various reasons. Recognizing that full reproduction of our various lists of observational, reference, and model data in scientific journals would be impracticable, we started a more or less informal procedure of timely release of information to a limited number of particularly interested colleagues. With the present letter, we hope to mitigate at least some of the dissatisfactory aspects of this procedure.
The AKR emission cone at low frequencies
Authors: Calvert W.
Published: February 2008

Certain of the ISEE‐1 observations between the plasmasphere and the auroral zone have revealed the emission cone of auroral kilometric radiation (AKR) unaffected by plasmaspheric refraction. At some distance from the source, this cone produced a sharp low‐frequency boundary in the AKR signals, which was displaced above the cyclotron frequency. The variation of this boundary, plus other aspects of the AKR signals, indicated that the AKR emission cone closed toward a hollow, roughly forty‐five degree limit cone with decreasing frequency, duplicating the behavior previously found with ISIS‐1 at the opposite end of the AKR spectrum.
First ozone profiles measured with ECC sondes at Natal (5.9°S, 35.2°W)
Authors: Kirchhoff V. W. J. H. , Sahai Y. , Motta A. G.
Published: February 2008

The average ozone profile obtained from 43 balloon flights at Natal is compared to data obtained elsewhere, in particular to an average profile obtained between latitudes ± 30°. At pressures above 100 mbar and below about 15 mbar the ozone density at Natal is higher than predicted by the model.
Probing the melt zone of Kilauea Iki Lava Lake, Kilauea Volcano, Hawaii
Authors: Hardee H. C. , Dunn J. C. , Hills R. G. , Ward R. W.
Published: February 2008

New drilling techniques were recently used to drill and core the melt zone of Kilauea Iki lava lake to a depth of 93 m. A partial melt zone was found to exist at depths between 58 m and 89 m consisting of 40 volume percent melt. Downhole seismic shots detonated in and below the melt zone resulted in the first in situ measurements of seismic velocity directly through a well characterized partial melt zone. Periodic seismic sources were used to effectively penetrate the highly fractured hydrothermal zone of the lava lake crust. Low velocity P‐wave layers (≤ 2.0 km/s) were found at the surface, at 40 m depth, and at 90 m depth.

Thermal convective experiments in the melt zone resulted in the first controlled in situ measurements of the interaction of water with a basaltic melt zone. Transient energy rates of 900 kW (980 kW/m²) and steady rates of 85 kW (93 kW/m²) were observed. The full water recovery (100%), high downhole steam temperatures (670 C), and high energy transfer rates (93 to 980 kW/m²) observed in these thermal experiments are consistent with a closed cavity model where the injected water/steam directly contacted basaltic melt or near melt.

In addition to understanding lava lakes, these seismic and thermal experiments have applications for the location of magma bodies in the crust and for the efficient extraction of energy from these bodies.
Dynamical cooling induced by dissipating internal gravity waves
Authors: Walterscheid R. L.
Published: February 2008

In this analysis we show that vertically propagating internal gravity waves induce a downward transfer of sensible heat from regions of wave dissipation, and that this transfer of heat may result in a net cooling of regions of the upper atmosphere.
Energization of ionospheric ions by electrostatic hydrogen cyclotron waves
Authors: Singh Nagendra , Schunk R. W. , Sojka J. J.
Published: February 2008

Interactions between ionospheric ions and a monochromatic electrostatic hydrogen cyclotron wave were studied numerically for conditions corresponding to the auroral plasma. Strong heating of the minority ions He+, He++, and O+ were observed. The fraction of the initial ion population which underwent heating was found to strongly depend on the mass, charge, and initial temperature of the ion species.
Lava flow layer‐East Pacific Rise
Authors: Herron Thomas J.
Published: February 2008

A multichannel seismic reflection profile across the East Pacific Rise near 9°N reveals an approximately 400 m thick layer at the top of the oceanic crust with seismic velocity of about 2.8 km/s at the Rise crest. This velocity increases to about 3.8 km/s, 210 km east of the Rise crest. These low velocities suggest that this layer is probably a porous lava flow layer (layer 2A of seismic refraction studies) generated by volcanic activity at the spreading center. Reflections from the base of the layer imply a relatively sharp transition between the lava flows and the underlying layer (presumably a sheeted dike complex). The underlying layer is a zone about 1.4 km thick (with velocity about 5.7 km/s) whose base may coincide with the top of a low velocity magma chamber from which the crust develops.
The Geoid: effect of compensated topography and uncompensated oceanic trenches
Authors: Chase Clement G. , McNutt Marcia K.
Published: February 2008

The geoid is becoming increasingly important in interpretation of global tectonics. Most of the topography of the earth is isostatically compensated, so removal of its effect from the geoid is appropriate before tectonic modeling. The oceanic trenches, however, are dynamically depressed features and cannot be isostatically compensated in the classical way. Continental topography compensated at 35 km gives intracontinental geoidal undulations of up to 15 m over mountain ranges in a spherical harmonic expansion to order and degree 22. Oceanic topography compensated at 40 km, reasonable for the thermally supported long wavelengths, matches the +10 m difference between old continents and old oceans in a detailed NASA/GSFC geoid. Removing the assumed compensation for the oceanic trenches leaves negative anomalies of up to 9 m amplitude caused by their uncompensated mass deficit. This mass deficit acts as a partial "regional compensation" for the excess mass of the subducting slabs, and partly explains why geoidal (and gravity) anomalies over the cold slabs are less than thermal models predict.
Limits on the lunar temperature profile
Authors: Hood L. L. , Sonett C. P.
Published: February 2008

Limits on the selenotherm are estimated using (1) a preferred set of bounds on the lunar electrical conductivity profile; (2) published laboratory conductivity vs. temperature data for an olivine and several aluminous orthopyroxenes; and (3) estimates for the Al2O3 content of the deep interior suggested by bulk composition models. The inferred limits are narrowest in the depth range 450 to 1350 km and are in accord with independent geophysical constraints. Thermal history models which yield present‐day selenotherms that are in best agreement with these limits are those which permit subsolidus convection at depths greater than 800 km in the moon.
Investigations on biogenic ice nuclei in the Arctic atmosphere
Authors: Jayaweera Kolf , Flanagan Patrick
Published: February 2008

Air samples collected at several heights above the Arctic Ocean contained at least two types of bacteria and five different fungal spores which could elevate the freezing temperature of water droplets. It was observed that the freezing temperature increased logarithmically with the number of cells per drop up to a maximum temperature dependent upon species. Bacteria were more effective than fungal spores but, unlike the spores, they lost their activity under laboratory growth conditions.

Maximum concentration of nearly 10 microbial cells per liter occurs in clouds and 1 per liter in air outside clouds. However, numbers and varieties of microbial cells in excess of those found near sea ice surface level were observed up to 7 km.
Optical signature of an ionospheric hole
Authors: Mendillo Michael , Baumgardner Jeffrey
Published: February 2008

The recent launch of a NOAA weather satellite provided an “experiment of opportunity” for simultaneous radio and optical diagnostics of a large artificially‐induced ionospheric modification. The rocket plume caused disturbances that were monitored using intensified imaging and photometer observations at 6300 Å along the same raypath as VHF polarimeter measurements of the ionosphere’s total electron content (TEC). A rapid chemical depletion of TEC by −16.8 × 1012 el/cm² caused a burst of 6300 Å radiation that expanded to more than 60° of the sky, with peak intensities near 9 k R. The event was used as an active space plasma experiment to test theoretical estimates for atmospheric diffusion and O(¹D) quenching rates.
Correlated Birkeland current signatures from the Triad and MAGSAT magnetic field data
Authors: Zanetti L. J. , Potemra T. A.
Published: February 2008

On November 1, 1979, the MAGSAT satellite was successfully launched into a 400 km polar orbit from which it could measure the earth’s magnetic field. During the first part of MAGSAT’s eight‐month lifetime, the orbit was nearly coplanar with that of the TRIAD satellite at 800 km altitude. This study has concentrated on transverse magnetic disturbances, associated with Birkeland currents, measured by the two spacecraft. The satellites were nearly coplanar from November through the middle of December 1979. Data were compared when the satellites were over the TRIAD/Chatanika receiving station. Of the approximately 150 comparisons of magnetic disturbances, 75% are very similar in shape and magnitude. For these cases, the TRIAD peak disturbances were, on the average, larger than the peak MAGSAT disturbances by 7%, which is less than many uncertainties in these measurements (due to baselines, calibration). Better agreement in the large‐scale well‐defined field‐aligned currrent signatures occurs during periods of higher Kp even with time separations as large as 45 minutes. The discrepancies in the remaining cases may be due to temporal, longitudinal and height effects of the Birkeland current system.
Evidence of an effect of heat flux from the East Pacific Rise upon the characteristics of the mid‐depth waters
Authors: Reid Joseph L.
Published: February 2008

On an isopycnal surface that lies at mid‐depth in the South Pacific Ocean there is a zone of high temperature near 10°S ‐ 20°S. Heat flux into the water from the crest of the East Pacific Rise and westward flow of the heated water may account for this temperature pattern.
Shock‐loading experiments on eclogite
Authors: Jakubith Manuel , Seidel Peter
Published: February 2008

Samples of omphacitic eclogite from Fattigau / Germany were shock‐loaded to pressures of 18, 45 and 59 GPa. The recovered specimens were investigated by X‐ray diffraction experiments and showed all those reflections typical of the well known high‐pressure phases. The unusual appearence of the perovskite ‐ structured MgSiO3 at the shock‐loading pressure of 18 GPa is in contrast to results of Liu (1980) and could be attributed to strong nonequilibrium processes caused by shock‐waves.
Crystallization of a S‐saturated Fe,Ni‐melt, and the origin of iron meteorite groups IAB and IIICD
Authors: Kracher Alfred
Published: February 2008

New data on trace element partitioning in the Fe‐Ni‐S‐P system suggest that iron meteorites of groups IAB and IIICD come from one or more S‐rich parent bodies. Heating of the IAB parent body melted all troilite, but caused only very minor partial melting of silicates. Cocrystallization of metal and troilite produced the high‐Ni "tail" of group IAB. The trace element patterns are consistent with a parent body with CI sulfur and siderophile abundances. Compositionally the parent body was intermediate between ordinary and E4 chondrites, its thermal history was in between ordinary chondrite and fully differentiated (achondrite, group IIIAB iron) parent bodies.

IAB and IIICD may be complementary fractional crystallization/partial melting suites from the same parent body. Since the model also explains some unusual irons, it seems for the first time possible to understand the genesis of almost all irons, and link them to the major groups of primitive and differentiated meteorites.
Global increase in atmospheric methane concentrations between 1978 and 1980
Authors: Blake Donald R. , Mayer Edward W. , Tyler Stanley C. , Makide Yoshihiro , Montague Derek C. , Rowland F. S.
Published: February 2008

The concentration of methane has been measured in tropospheric air samples collected in remote locations between 55°N and 53°S during six collection periods between November 1977 and November 1980. The observed concentrations of CH4 have increased in each of six latitude locations by an average of 0.052±0.005 ppmv between January 1978 and January 1980.

This (1.4±0.2)×1014 gram increase in the total atmospheric burden of CH4 corresponds to 35±12% of the yearly flux of (4.0±1.3)×1014 grams needed to maintain the CH4 concentration in steady‐state at its recent level of about 1.6 ppmv. The 1978‐1980 excess of about 0.7×1014 grams per year of sources over sinks for CH4 could arise from either an increase in biogenic releases or from a decrease in the average OH radical concentration in the lower troposphere, or from both.
Large horizontal electric fields measured at balloon heights of the Brazilian magnetic anomaly and association to local energetic particle precipitation
Authors: Gonzalez W. D. , Pereira A. E. C. , Gonzalez A. L. C. , Martin I. M. , Dutra S. L. G. , Pinto O. , Wygant J. , Mozer F. S.
Published: February 2008

During a stratospheric balloon flight on April 9, 1980, large scale electric fields have been measured, for the first time, at the Brazilian Magnetic Anomaly with a double‐probe detector. We report here the results of this flight performed during a time interval with fair weather at the observing region and enhanced geomagnetic activity. These results suggest that a BAND of precipitating energetic particles, moving equatorwards with respect to the balloon, could have produced a conductivity enhancement down to the middle atmosphere, distorting the vertical atmospheric electric field and giving rise to the type of horizontal fields observed.
Observations of mass addition to the shocked solar wind of the Venusian ionosheath
Authors: Intriligator D. S.
Published: February 2008

Analyzed are the proton and heavy ion populations observed by the Pioneer Venus Orbiter plasma analyzer in the region downstream (11.5 Rv) of Venus. The ion energy per unit charge (E/Q) ratios for protons and heavy ions are consistent with the identification of oxygen (O+) as a prevalent constituent of the heavy ions. The speeds of the heavy ions and protons are often comparable with the number densities of the heavy ions being 1% of those of the protons. The azimuthal flow angles for the heavy ions and the protons are similar and the polar flow angles of both are usually within ±½° of the ecliptic plane. The apparent intermittent nature of the heavy ion fluxes may be an indication that erosion of the ionosphere is taking place over a limited spatial range and that the orbit of the Pioneer Venus spacecraft is such that it does not intercept the “layers” of heavy ions in a continuous manner. The efficiency of the erosion process may be time variable, e.g., dependent on external ionsheath flow conditions, the state of the ionosphere. Evidence is found of a shear layer, the presence of oxygen ions of varying speeds or of other ionospheric constituents. The heavy ion observations are consistent with a viscous interaction and several other processes that have been suggested as giving rise to the removal and acceleration of ionospheric ions. The analyses reported here may be relevant to an understanding of the plasma interactions associated with comets and Mars and perhaps even with the subsonic interaction at Io and at Titan.
Natural tritium deposition over Antarctica and estimation of the mean global production rate
Authors: Jouzel J. , Merlivat L. , Mazaudier D. , Pourchet M. , Lorius C.
Published: February 2008

Tritium content was measured in snow deposited in Antarctica before the first arrival of artificial tritium (1954), both at Dome C (74°39′S) and South Pole. The mean tritium values at the time of precipitation are equal to 32 ± 2 and 26 ± 3 TU at South Pole (1939‐1942) and Dome C (1951) respectively. A seasonal pattern of natural tritium fallout identical to the artificial pattern (with a winter maximum) is observed in the South Pole profile.

The deposition rate of natural tritium is 0.6 and 0.2 tritium atoms cm−2.sec−1 at South Pole and Dome C respectively. Its geographical variation over Antarctica appears quite similar to that existing for artificial tritium, clearly showing that the same mechanisms govern the deposition of natural and artificial tritium, in particular tritium injection over polar regions during Antarctic winter. A mean deposition rate of 0.37 tritium atoms cm−2.sec−1, over Antarctica is derived giving an estimated mean global production rate of 0.2 tritium atoms cm−2.sec−1.

This strongly suggests that natural tritium results only from cosmic ray production.
Mississippi River Seismic Survey
Authors: Shedlock Kaye M. , Harding Samuel T.
Published: February 2008

A small boat‐based seismic reflection survey was conducted on the Mississippi River across the New Madrid seismic zone. One second (1400‐2000 m depths) of 12 fold, high resolution data were recorded along approximately 240 km of the river. Because of differences in the quality of the data along some parts of the river and because of geologic complexities, a mixture of marine‐based and land‐based data‐processing methods were used to get the best profiles. The data suggest reflections from Paleozoic, Late Mesozoic and Cenozoic strata and some faults and slight local flexures. A probable extension of the Cottonwood Grove fault, a feature discovered with land‐based seismic reflection profiling, was identified about 5 km southeast of Caruthersville, Missouri. This fault is subparallel with the northeast trend of epicenters in the New Madrid seismic zone. In addition to providing subsurface data along the river where land‐based reflection surveying cannot be done, the river survey provided data on a wealth of shallow geologic features at minimal cost.
Evidence of coastal Seiche excitation by tide‐generated internal solitary waves
Authors: Giese G. S. , Hollander R. B. , Fancher J. E. , Giese B. S.
Published: February 2008

Coastal seiches at Magueyes Island, Puerto Rico, occur in distinct fortnightly groups with maximum seiche activity following new and full moon by 7 days. The size of the fortnightly groups depends upon the amplitude of the preceding spring tide and upon the Caribbean surface water temperature. Temperature records from the upper thermocline on the slope seaward of the shelf edge off Magueyes Island indicate the arrival of semidiurnal packets of negative internal solitary waves. We suggest that these internal waves are generated by tides in the southeastern Caribbean Sea and that they are responsible for exciting the coastal seiches. This hypothesis is supported by the characteristics of coastal seiching at Puerto Princesa on Palawan Island in the Philippines which indicate excitation by the Sulu Sea internal waves reported by Apel, Holbrook and Tsai (1980).
Evidence for specularly reflected ions upstream from the quasi‐parallel bow shock
Authors: Gosling J. T. , Thomsen M. F. , Bame S. J. , Feldman W. C. , Paschmann G. , Sckopke N.
Published: February 2008

Ion velocity distributions in the form of bunches of gyrating particles traveling along helical paths have been observed moving sunward immediately upstream from quasi‐parallel parts of the earth's bow shock using Los Alamos/Garching instruments on ISEE‐1 and ‐2. These distributions have characteristics which indicate that they are produced by the nearly specular reflection at the shock of a portion of the incident solar wind ions. In particular, the guiding center motion and the gyrospeeds of the gyrating ions are quantitatively consistent with simple geometrical considerations for specular reflection. These considerations reveal that specularly reflected ions can escape upstream for θBn < 45° but not for θBn > 45° (where θBn is the angle between the upstream magnetic field, B, and the local shock normal

). These upstream gyrating ions are an important signature of one of the processes by which solar wind streaming energy is dissipated into other forms of energy at the shock.
The possible role of ionospheric oxygen in the initiation and development of plasma sheet instabilities
Authors: Baker D. N. , Hones E. W. , Young D. T. , Birn J.
Published: February 2008

We relate measurements made during substorm growth and expansion to available plasma compositional observations and propose that asymmetries in the distribution of enhanced densities of O+ (of ionospheric origin) may define regions of the plasma sheet in which tearing mode growth rates are increased and the instability threshold is lowered. We make qualitative estimates of the growth rates of the linear ion tearing mode using statistical models of the dusk‐dawn and earthward‐tailward distributions of O+. The theoretical results predict maximum ion tearing growth rate in the range XGSM = −10 to −15 RE and YGSM ∼ 5 RE. These values are in reasonable accord with substorm observations since many asymmetries in particle and field phenomena associated with substorms favor the interpretation that substorm onset occurs in the dusk sector of the near‐earth plasma sheet. Present results therefore suggest that substorm initiation and development may be closely related to distribution patterns of ionospheric ions.
Vertical movements following a dip‐slip earthquake
Authors: Melosh H. J.
Published: February 2008

Fault motion during a dip‐slip earthquake induces elastic stresses in the earth which are well modeled by elastic dislocation theory. Shortly after the earthquake, flow in the asthenosphere begins to relax these stresses and leads to postseismic motions observable at the earth's surface. Recent work has led to apparently contradictory results on the sign of the vertical motion following a dip‐slip earthquake: some workers find downwarping in the region overlying a thrust fault; others find upwarping. This controversy is now resolved by a finite element study of postseismic rebound following a thrust earthquake on a 30° dip fault in an initially planar elastic lithosphere which overlies a Maxwell viscoelastic asthenosphere. If the fault penetrates less than 0.68 of the way through the lithosphere, downwarping follows the earthquake. If the fault penetrates more than 0.68 of the lithosphere, upwarping results. The magnitude as well as the sign of the postseismic rebound is a sensitive indicator of the ratio between the thickness of the elastic lithosphere and the fault depth. Observations of postseismic rebound may thus be used to measure lithosphere thicknesses at time scales on the order of years.
Path dependence of acoustic velocity and attenuation in experimentally deformed westerly granite
Authors: Granryd Lizbeth , Getting Ivan C. , Spetzler Hartmut
Published: February 2008

Brittle failure in rocks is generally preceded by a localization of deformation in the region of the final macrofracture. This process is associated with a non‐uniform distribution of subcritical microcracks which should be reflected in the distribution of acoustic velocities and surface deformation. The temporal and spatial development of such deformation zones has been studied by monitoring these quantities during the deformation of Westerly granite samples.

Holographic interferometry revealed localization of surface deformation above about 70% of the tangential strain at failure. As loading proceeded, acoustic velocities became highly anisotropic, finally varying by a factor of 2 in different directions. They were smoothly dependent on path orientation, but not on path position within the sample. Thus, surprisingly, they did not reflect the localized deformation observed with holography.
Surface deformation of westerly granite during creep
Authors: Kurita K. , Swanson P. L. , Getting I. C. , Spetzler H.
Published: February 2008

Holographic interferometry has been used to observe the surface deformation of Westerly granite during creep experiments at 50 MPa (500 bars) confining pressure. Interference fringes on the holograms produced by this technique constitute contour maps of the sample surface shape change between exposures. Several distinctive characteristics of the surface shape change have been observed. In general, surface deformation during primary and secondary creep, while highly inhomogeneous, is distributed fairly uniformly. No large scale pattern is seen in the surface shape changes. At approximately the onset of tertiary creep, surface displacements become more locallized. Eventually (∼85‐90% of time‐to‐failure) a distinct ridge is formed which exactly coincides with the location of the final fracture.
On the demagnetizing energy and demagnetizing factor of a multidomain ferromagnetic cube
Authors: Dunlop David J.
Published: February 2008

The equations Ed = ½NJ² + const for demagnetizing energy and Hd = −NJ for average internal demagnetizing field (J is magnetization; N is demagnetizing factor, assumed constant) are central to multidomain (MD) theories of thermoremanence (TRM) and hysteresis. Theoretical calculations reported here, based on Rhodes and Rowlands' (1954) equations for Ed of an MD cube, test the variation of N with the number n of domains and with domain wall displacement x. For n even, Ed(x) − Ed(0) is nearly proportional to x² or J², so that N is practically constant (to ≈ 20% if n = 2, ≈ 10% if n = 4 and ≈ 5% if n = 8) for 0 ≤ J ≤ Js. This result reaffirms the validity of traditional MD rock magnetic theories. However, if n is small, N is significantly less than 4 π/3 (the single‐domain or n → ∞ value); N ≈ 2 for n = 2 and (4π/3 − N) decreases as 1/n, so that N → 4π/3 when n = 8 or 10. Grains with n odd possess a spontaneous remanence even in the absence of wall pinning that is substantial (Jr ≈ 0.1 Js) for n = 3 but decreases rapidly for larger n. This spontaneous remanence is a possible source of so‐called pseudo‐single‐domain enhancement of TRM in small MD grains.
An explanation for contradictory geodetic strain and fault plane solution data in western North America
Authors: Sbar Marc L.
Published: February 2008

In a few areas of western North America the principal strain azimuths from geodetic strain measurements differ dramatically from the principal stress directions inferred from fault plane solutions of earthquakes. The reason for this difference may be related to the amount of strain measured by each technique. The strain relieved in an earthquake is about two orders of magnitude greater than that observed by geodetic measurements taken over approximately a seven year time span. Strain measurements may thus sense short‐term fluctuations in strain, while earthquakes may average these short‐term fluctuations responding to the total strain accumulated to produce a more reliable measure of the longer‐term tectonic strain.
Neutral sheet current interruption and field‐aligned current generation by three dimensional driven reconnection
Authors: Sato Tetsuya , Hayashi Takaya , Walker Raymond J. , Ashour‐Abdalla Maha
Published: February 2008

We have simulated externally drived reconnection by solving the magnetohydrodynamic equations in a three‐dimensional, tail‐like geometry. As reconnection proceeds, the tail current is interrupted locally and field aligned currents are generated. The field aligned current flows towards the ionosphere on the morning side and away from the ionosphere in the evening. The field aligned currents flow in a narrow band at the outer edge of the plasma sheet. Thus, the simulation demonstrates that the nightside substorm current system is a natural consequence of the driven reconnection model.
A model for repetitive cycles of large earthquakes
Authors: Newman William I. , Knopoff Leon
Published: February 2008

The theory of the fusion of small cracks into large ones reproduces certain features also observed in the clustering of earthquake sequences. By modifying our earlier model to take into account the stress release associated with the occurrence of large earthquakes, we obtain repetitive periodic cycles of large earthquakes. A preliminary conclusion is that a combination of the stress release or elastic rebound mechanism plus time delays in the fusion process are sufficient to destabilize the crack populations and, ultimately, give rise to repetitive episodes of seismicity.