bluuebunny/crossref_metadata_2025 huggingface dataset:
High‐pressure metallization of FeO and implications for the Earth's core
Authors: Knittle Elise , Jeanloz Raymond
Published: February 2008

The phase diagram of FeO has been experimentally determined to pressures of 155 GPa and temperatures of 4000 K using shock‐wave and diamond‐cell techniques. We have discovered a metallic phase of FeO at pressures greater than 70 GPa and temperatures exceeding 1000 K. The metallization of FeO at high pressures implies that oxygen can be present as the light alloying element of the Earth's outer core, in accord with the geochemical predictions of Ringwood. The high pressures necessary for this metallization suggest that the core has acquired its composition well after the initial stages of the Earth's accretion. Direct experimental observations at elevated pressures and temperatures indicate that core‐forming alloy can react chemically with oxides such as those forming the mantle. The core and mantle may never have reached complete chemical equilibrium, however. If this is the case, the core‐mantle boundary is likely to be a zone of active chemical reactions.
Structuring of the Ampte magnetotail barium releases
Authors: Hassam A. B. , Huba J. D.
Published: February 2008

A new instability is proposed to explain the observed large‐scale structuring of the magnetotail AMPTE barium releases. The stability theory is based on a modified set of MHD equations which allows for large Larmor radius effects, i.e., ρi ∼ Rc which is typical of the AMPTE releases (here ρi is the ion Larmor radius and Rc is the transverse radius of the cloud). The mode is driven by the deceleration of the cloud and the density gradient at the edge of the cloud. The predicted linear growth rate and eigenmode structure are consistent with AMPTE observations.
Forced release of sodium from upper atmospheric dust particles
Authors: von Zahn U. , von der Gathen P. , Hansen G.
Published: February 2008

The almost explosive growth of narrow sodium layers at altitudes near 95 km was observed by ground‐based LIDAR located at 69°N, 16°E. Starting from typical conditions at these altitudes (sodium density approximately 1 to 2× 10³ cm−3) the density is observed to increase by large factors within a few minutes in a narrow layer, the half height of which is typically 1 km only. One of the more spectacular cases involved an increase by a factor 25 within 5 min and a layer width of 0.8 km (full width at half maximum). We propose that the sodium forming these sudden layers is released from upper atmospheric dust by energetic auroral particles. Prior to the auroral bombardment the dust particles were concentrated into a narrow layer by appropriate meteorological processes. Our observations thus imply that considerable amounts of sodium are stored on the surface of upper atmospheric dust.
Comment on the Paper “On the influx of small comets into the Earth's upper atmosphere”
Authors: Soter Steven
Published: February 2008

Frank et al. attribute the occurrence of transient dark spots in the terrestrial uv dayglow emission to absorption by water vapor from the tidal breakup and evaporation of small comets at high altitude. Such comets would be sufficiently large and numerous that they should already have been detected optically as faint slow‐moving objects. However, they have not been observed.
Partitioning of Fe within high‐pressure silicate perovskite: Evidence for unusual geochemistry in the lower mantle
Authors: Jackson W. E. , Knittle E. , Brown G. E. , Jeanloz R.
Published: February 2008

Using synchrotron radiation, Fe x‐ray absorption spectra have been collected from a Mg0.88Fe0.12SiO3 perovskite quenched from 50 GPa and ∼ 2000 K. Least‐squares fits of the Extended X‐ray Absorption Fine Structure (EXAFS) data yield an Fe coordination number of 5.5 (±0.8) oxygens, an Fe‐O distance of 214 (± 4) pm, and a static and thermal disorder parameter of 147 pm². The absorption edge spectrum shows a weak pre‐edge feature suggesting little deviation from centrosymmetry for the Fe site. These results indicate that Fe in this silicate perovskite partitions predominantly into the six‐coordinated site and may provide the first evidence for Si occupying an 8‐12 coordinated site.
Heat flow at the proposed Appalachian Ultradeep Core Hole (ADCOH) Site: Tectonic implications
Authors: Costain John K. , Decker Edward R.
Published: February 2008

The heat flow in northwestern South Carolina at the Appalachian Ultradeep Core Hole (ADCOH) site area is approximately 55 mW/m². This data supplements other data to the east in the Piedmont and Atlantic Coastal Plain provinces where heat flows > 55 mW/m² are characteristic of post‐ and late‐synmetamorphic granitoids. Piedmont heat flow and heat generation data for granites, metagranites, and one Slate Belt site, in a zone approximately parallel to major structural Appalachian trends, define a linear relation. Tectonic truncation of heat‐producing crust at a depth of about 8 km (a depth equal to the slope of the heat flow‐heat production line) is proposed to explain the linear relation. Using the value of reduced heat flow estimated from this empirical relation, and assuming thicknesses of heat‐producing crust defined by new ADCOH seismic data, the heat flow and heat production at the ADCOH site are consistent with a depth to the base of the Inner Piedmont crystalline allochthon of about 5.5 km. Seismic data at the ADCOH site confirm that the Inner Piedmont is tectonically truncated at about 5.5 km by the Blue Ridge master decollement. Temperatures at 10 km at the ADCOH site are predicted to be less than 200 °C.
Experimental evidence bearing on the stability of monazite during crustal anaatexis
Authors: Rapp Robert P. , Ryerson F. J. , Miller Calvin F.
Published: February 2008

A major host for LREE and the heat producing elements Th and U in peraluminous granites is monazite, and the stability of monazite will affect the redistribution of these elements within the crust during anatexis. The compositional stability of monazite in "granitic" melts ranging from peraluminous to metaluminous compostions has been investigated under water‐saturated conditions between 850‐1000°C, at 8 Kb. Monazite solubility (concentration of LREE's in saturated melts) increases with the values of M > 1.3 [=(2Ca+Na+K)/(AlXSi) in the melt], and is constant for M < 1.3. The temperature dependence of monazite saturation has been determined by Rapp and Watson [1986] for a melt of M = 1.3 and model should be applicable to all peraluminous magmas. Application of the monazite solubility model to crustal anatexis indicates that for fusion temperatures at or below 800°C, anatexis producing peraluminous magmas may lead to an enrichment of monazite in the restitic lower crust depending upon the initial LREE concentration in the source. At temperatures approaching 850°C, enrichment of monazite in the lower crust by anatexis is unlikely due to the high monazite‐saturation concentrations.
Viking in the plasma universe
Authors: Alfvén H.
Published: February 2008

Realizing that the magnetosphere cannot be understood until the electric field is mapped, Viking has placed emphasis on electric field measurements. Because energy is transferred from the solar wind mainly through electric currents in the active plasma regions, Viking's orbit is selected so as to include as much of the active regions as possible. The real‐time presentation of the results makes it possible to modify the observations as soon as interesting events are seen. As several of the project leaders have experience in plasma laboratory experiments, Viking can be characterized as a new type of space plasma experiment.

Some of the results of the Viking mission are important as a basis for drawing the circuit of energy transfer from the solar wind to the magnetosphere and ionosphere (Figure 1) and for understanding the general properties of collisionless plasmas in space (Table 1). They will constitute a platform for a systematic exploration of the plasma universe (Figure 2), which will have an impact on our views on cosmogony and cosmology.
Sunspots, the QBO, and the stratospheric temperature in the north polar region
Authors: Labitzke Karin
Published: February 2008

There is an association between the polar stratospheric temperature in the northern winter and the solar cycle in the winters when the 50‐mb equatorial winds are westerly: The lower the sunspot number in such winters, the lower is the temperature. No major mid‐winter warmings occurred in these winters when the sunspot number was below about 100. There is no such relationship in the easterly phase of the QBO. In that phase the temperatures are generally higher than in the westerly phase, and major mid‐winter warmings occur regardless of the state of the solar cycle.
Aftershocks monitored by a joint array of land stations and ocean bottom seismometers east of Taiwan
Authors: Hsu Vindell , Wang Chengsung , Liaw Zen‐Sen , Ten Shyu Chun , Duennebier Frederick K.
Published: February 2008

The aftershocks that followed three moderate size earthquakes occurring on June 12, 1985, off the east coast of Taiwan were monitored by land and ocean bottom seismographs. Hypocenters of aftershocks located by this sea‐land joint array outline a rupture plane striking northeast and dipping steeply to the southeast. The result agrees well with fault plane solutions of the three main shocks. These results combine to indicate a right‐lateral strike‐slip mechanism for the rupture. The earthquake sequence studied occurred behind an active subduction zone and is explained in terms of a forearc "sliver plate" movement resulting from the strong oblique convergence between the Phillipine Sea plate and the Eurasian plate along the trench just east of Taiwan.
Late Tertiary history of hydrothermal deposition at the East Pacific Rise, 19°S: Correlation to volcano‐tectonic events
Authors: Lyle Mitchell , Leinen Margaret , Owen Robert M. , Rea David K.
Published: February 2008

Commonly it is assumed that the intensity of mid‐ocean ridge hydrothermal activity should correlate with spreading rate, since high spreading rates are an indication of large subcrustal heat sources needed for intense hydrothermal activity. We have tested this hypothesis by modeling the deposition of hydrothermal precipitates from cores from Deep Sea Drilling Project Leg 92, taken on the west flank of the East Pacific Rise at 19°S. Although spreading rates at the East Pacific Rise and its predecessor, the Mendoza Rise, have varied by only 50% in the last 30 million years, we found certain episodes, at about 25, 18, 14, and 9 million years ago, of hydrothermal manganese deposition as much as a factor of 20 higher than equivalent Holocene accumulation. These eposides do not correlate with spreading rate changes and instead seem to occur at times of major tectonic reorganizations. We propose that ridge jumps and changes of ridge orientation may substantially increase hydrothermal activity by fracturing the ocean crust and providing seawater access to deep‐seated heat sources.
The decay of the El Chichon stratospheric perturbation, observed by lidar at northern midlatitudes
Authors: Jäger H. , Carnuth W.
Published: February 2008

The stratospheric perturbation caused by the April 1982 eruption of the Mexican volcano El Chichón (17.3°N) passed through a maximum at northern midlatitudes ten months after the event. The following decay of the aerosol layer could be investigated until the end of 1985 when this period was terminated by renewed volcanism. Lidar backscatter measurements exhibit seasonal decay variations which can primarily be attributed to stratospheric column height variations. In addition, advection of particle loaded air masses contribute to this effect. With respect to the 1977/79 background situation the stratospheric aerosol layer decayed with an e‐folding lifetime of about 1 year, when only summer observations were considered.
NO2/NO partitioning as a test of stratospheric ClO concentrations over Antarctica
Authors: Webster Christopher R.
Published: February 2008

Physical conditions in the 10–20 km region of the Antarctic stratosphere make the [NO2]/[NO] ratio particularly sensitive to high chlorine levels in the form of ClO. According to simple known photochemical relationships between NO2, NO, ClO, and O3, high ClO levels of 1 ppbv over Antarctica must be accompanied by large values of the [NO2]/[NO] ratio. At high ClO abundances, the [NO2]/[NO] ratio is approximately proportional to the ClO concentration. It is proposed that in‐situ measurements of the [NO2]/[NO] ratio could be used to test the high chlorine hypothesis.
Unusually deep earthquakes in East Africa: Constraints on the thermo‐mechanical structure of a continental rift system
Authors: Shudofsky Gordon N. , Cloetingh Sierd , Stein Seth , Wortel Rinus
Published: February 2008

Shudofsky [1985] has established that earthquakes associated with the East African rift system have well‐constrained focal depths as great as 25–30 km. Using published heat flow measurements as a guide to the local geotherm, we find through simple stress envelope calculations that the deepest earthquakes probably occur in the lower crust in a region where the lithosphere is strong. These results are at odds with the commonly held idea that seismicity in zones of continental extension is limited to the shallow upper crust because of elevated temperatures accompanying lithospheric thinning. Any model of the rifting process in East Africa must account for the fact that these regions exhibit considerable strength down to lower crustal levels.
Slab geometry of the Cascadia Subduction Zone beneath Washington from earthquake hypocenters and teleseismic converted waves
Authors: Crosson R. S. , Owens T. J.
Published: February 2008

Using earthquake hypocenters obtained from the Washington regional seismograph network and analysis of Ps converted phases from teleseisms at special temporary stations located south of the Olympic Peninsula, we have developed a preliminary model of the structure of the subducted slab beneath western Washington and southern British Columbia. The slab is smoothly arched beneath Puget Sound, subducting at a dip of about 10‐12° at the top of the arch. North and south of the arch crest the slab dips 15‐20°. Subcrustal earthquakes are localized near the top of the arch. This deformation, from planar slab geometry, is caused by the change in azimuth of the “trench” (or hinge line of the slab) from almost NS south of 47° north latitude, to approximately N30°W north of 48° north. The slab appears to be easily flexed, probably due to small elastic thickness, but its geometry reflects conservation of surface area and minimization of in‐plane strain. Crustal seismicity in the Puget Sound basin may result indirectly from the presence of the arch in the underlying Juan de Fuca plate.
Measurements of wind friction speeds over lava surfaces and assessment of sediment transport
Authors: Greeley Ronald , Iversen James D.
Published: February 2008

Wind velocity profiles were obtained over alluvial plains, lava flows, and a cinder cone in the Mojave Desert to determine the wind shear and the potential for particle transport. It was found that aerodynamic roughness, zo, for winds increases nearly a factor of 5 as flow crosses from the alluvium to the lava surface, resulting in wind shear that is 21% greater. Thus, wind erosion and sand flux may be substantially enhanced over the lava field. Moreover, wind flow turbulence is enhanced in the wake of the cinder cone, which also increases erosion and sediment transportation by the wind.
Ion energetics in the inner coma of comet Halley
Authors: Cravens T. E.
Published: February 2008

The cometary plasma in the magnetic barrier just outside the diamagnetic cavity which surrounds the nucleus of comet Halley is virtually stagnant. The outflowing neutral gas exerts an outward ion‐neutral drag force on this plasma, which balances the inward magnetic pressure gradient force in the vicinity of the contact surface. The cometary ions are frictionally heated due to the relative motion of the ion and neutral gases. The ion flow velocity must have a few km/s non‐radial component in order to explain the ion temperatures measured by the ion mass spectrometer on Giotto.
MHD wave breaking in the outer plasmasphere
Authors: Moore T. E. , Gallagher D. L. , Horwitz J. L. , Comfort R. H.
Published: February 2008

Empirical models of the average magnetospheric magnetic field, plasma density, and temperature distributions are used to construct a model of the distribution of MHD wave mode speeds within the magnetosphere. Although the MHD wave speeds in general have a smaller dynamic range than the magnetic field intensity or the plasma properties, considerable structure and variability is found which will lead to interesting “optical” effects on the propagation of low frequency waves. A persistent feature of the derived optical structure, which is qualitatively insensitive to known variability of the field or plasma, is a pronounced minimum of the wave speeds in the outer plasmasphere, i.e., a magnetospheric “shoal.” This feature does not map along magnetic field lines, but is confined to the equatorial region, leading to a positive radial gradient of wave speeds near synchronous orbit. The breaking of earthward propagating disturbances in this region may play an essential role in the formation of the substorm injection boundary and in the creation of equatorially trapped warm ion distributions.
Inclination shallowing in deep sea sediments from the North Atlantic
Authors: Celaya Michael A. , Clement Bradford M.
Published: February 2008

Paleomagnetic data from Miocene to Recent deep sea sediments recovered during Leg 94 of the Deep Sea Drilling Project (DSDP) in the North Atlantic exhibit a systematic shallowing of inclinations with depth at some sites. This shallowing is coincident with a downhole decrease in water content, and is observed only in sediments with a carbonate content consistently greater than 80%. Compaction due to overburden pressure is believed to be responsible for the shallow inclinations observed in these unconsolidated sediments. At sites where the carbonate content of the sediments is consistently below about 80% no significant downcore decreasing trends in the water content or inclination record are observed.
The Hellenic Subduction Zone: A tomographic image and its geodynamic implications
Authors: Spakman W. , Wortel M. J. R. , Vlaar N. J.
Published: February 2008

New tomographic images of the Hellenic subduction zone demonstrate slab penetration in the Aegean Upper Mantle to depths of at least 600 km. Beneath Greece the lower part of the slab appears to be detached at a depth of about 200 km whereas it still seems to be unruptured beneath the southern Aegean. Schematically we derive minimum time estimates for the duration of the Hellenic subduction zone that range from 26 to 40 Ma. This is considerably longer than earlier estimates which vary between 5 and about 13 Ma.
Ionospheric traveling convection vortices observed near the polar cleft: A triggered response to sudden changes in the solar wind
Authors: Friis‐Christensen E. , McHenry M. A. , Clauer C. R. , Vennerstrøm S.
Published: February 2008

Analysis of 20‐second resolution magnetometer data from an array of temporary stations operated around Søndre Strømfjord, Greenland during the summer of 1986 shows the signatures of localized ionospheric traveling convection vortices. An example of an isolated event of this kind observed near 08 local time is presented in detail. This event consists of a twin vortex pattern of convection consistent with the presence of two field‐aligned current filaments separated by about 600 km in the east‐west direction. This system of currents is observed to move westward (tailward) past the array of stations at about 4 km/sec. The event is associated with relative quiet time ionospheric convection and occurs during an interval of northward IMF. It is, however, associated with a large fluctuation in both the Z and Y components of the IMF and with a large sudden decrease in the solar wind number density. The propagation of the system is inconsistent with existing models of FTE current systems, but nevertheless appears to be related to a readjustment of the magnetopause boundary to a sudden change in the solar wind dynamic pressure and/or to a change in reconnection brought about by a sudden reorientation of the IMF.
The Nd and Sr isotopic evolution of Proterozoic seawater
Authors: Derry Louis A. , Jacobsen Stein B.
Published: February 2008

Nd and Sr isotopic measurements from a variety of marine chemical precipitates provide insight into processes controlling the chemistry of seawater during the Proterozoic. Nd isotope measurements on banded iron formations and phosphorites, and Sr isotope measurements on carbonates indicate that during both the Early and Late Proterozoic, hydrothermal input to the oceans was a significant fraction of the total input to ocean chemistry. Isotopic data from Early Proterozoic clastic sediments show systematic differences from coeval chemical sediments. These differences become less marked toward the end of the Proterozoic. This implies a higher hydrothermal water to river water flux ratio during the Early Proterozoic. The significant changes in seawater isotopic composition during the Proterozoic reflect the transition from mantle dominated Archean oceans to a typically modern system. Isotopic and mass balance constraints from banded iron formations indicate that oxidation of hydrothermal Fe2+ in seawater could have been an important control on the redox state of Proterozoic ocean‐atmosphere system. The present isotopic balances of carbon and sulfur could have been decoupled as a result.
Expectations for the microphysics of the Mars‐solar wind interaction
Authors: Moses S. L. , Coroniti F. V. , Scarf F. L.
Published: February 2008

The two Phobos spacecraft, which will start to orbit Mars early in 1989, will be capable of investigating in detail the microphysics of the Mars‐solar wind interaction. Simple scaling arguments and analogies with other planetary bow shocks indicate that the sub‐solar shock standoff distance should be small compared with plasma scalelengths, giving the shocked solar wind insufficient space in which to thermalize downstream before encountering the magnetospheric obstacle. Both the magnetosphere and ionosphere can be affected by particles and waves from the solar wind interaction.
In‐situ stress orientation and magnitude at the Fenton Geothermal Site, New Mexico, determined from wellbore breakouts
Authors: Barton Colleen A. , Zoback Mark D. , Burns Kerry L.
Published: February 2008

The acoustic borehole televiewer provides excellent data for the detection and measurement of stress‐induced wellbore breakouts. Analog televiewer data from the Fenton Geothermal well EE‐3 in New Mexico were digitized and interactively processed for detection and analysis of azimuth and shape of stress‐induced breakouts occurring in the well at depths of about 2.9–3.5 km. A statistical analysis of the measured breakout azimuths yields a well resolved orientation of least horizontal principal stress of 119°, consistent with least principal stress data from the Rio Grande Rift. As the magnitude of the least horizontal compressive stress, Shmin, in EE‐3 is known from hydraulic fracturing, we present a new method in which Shmin and data on breakout width are used to estimate the magnitude of the maximum horizontal principal stress.
Comment on: ‘Are fast atmospheric pulsations optical signatures of lightning‐induced electron precipitation?’ by J. LaBelle
Authors: Vampola A. L.
Published: February 2008

LaBelle [1987] proposed that Fast Atmospheric Light Pulsations (FAPs), which have been observed at L=1.5‐2.2 in the northern hemisphere, are optical signatures of ≥2 MeV electrons associated with Lightning‐induced Electron Precipitation events produced by strokes in the southern hemisphere. FAPs cannot be produced by ≥2 MeV electrons in the inner radiation belt because the upper limit for fluxes of such particles is only about 0.2% of the value that was used in the analysis and the correct value results in an unrealistically short electron lifetime prediction. The discrepancy comes from using an electron model, AE‐2, which included the Starfish fission electrons. Additionally, the use of a model in which southern hemisphere lightning strokes result in northern hemisphere FAPs via a cyclotron mode interaction between magnetospheric electrons and lightning‐generated waves is also untenable because it would result in FAP intensities two orders of magnitude greater in the southern hemisphere than in the northern hemisphere, leading to a further two orders of magnitude reduction in estimated inner zone electron lifetimes.
Lower bound for the electrical conductivity of the Earth's outer core
Authors: Honkura Yoshimori , Matsushima Masaki
Published: February 2008

The electrical conductivity of the Earth's outer core is an important physical quantity controlling the hydromagnetic process within the liquid outer core which is responsible for the creation and maintenance of the Earth's magnetic field. The conventional method, based on electromagnetic induction by external magnetic field variations, is not applicable to the core because of their insufficient penetration depth. Here we propose an alternative method based on non‐dipole magnetic field data, from which fluid velocity fields in the outer core are estimated, and show that a lower bound can be imposed on the electrical conductivity of the outer core from the consideration of the possibility of dynamo action sufficient to maintain the Earth's magnetic field. The conclusion is that the electrical conductivity is larger than about 1×105 S/m. This conclusion is consistent with the results of recent experiments made for possible core material.
Constraints on Titan's ionosphere
Authors: McNutt Ralph L. , Richardson John D.
Published: February 2008

The near flyby of Saturn's moon Titan by Voyager 1 revealed a Venus‐like interaction between the moon and Saturn's magnetospheric plasma. Although neither the radio science experiment occultation observation nor the in situ measurements directly detected the ionosphere, plasma of ionospheric origin was observed as Voyager 1 passed through Titan's wake. Balancing the magnetic pressure in this low‐β region of Saturn's magnetosphere with ionospheric particle pressure yields an upper limit on the ionospheric density. Using an ionospheric temperature equal to the exospheric temperature of 200°K yields a charge density of about 3000 cm−3, which is consistent with the peak ionospheric electron density inferred from a balance of electron impact ionization of molecular nitrogen and recombination loss. Both of these quantities are consistent with limits derived from Voyager 1 observations. Good constraints on these quantities are important in planning the Cassini mission to orbit Saturn and probe Titan's ionosphere and atmosphere at the beginning of the next century.
Resonance absorption of Alfvén waves at comet‐solar wind interaction regions
Authors: Sharma A. S. , Cargill P. J. , Papadopoulos K.
Published: February 2008

The interaction of the low frequency (10−2 Hz) MHD waves, observed upstream of comets, with the structured plasma near the cometary bow wave is examined. It is suggested that the waves undergo resonant absorption due to either ambient density gradients or localized shear in the background magnetic field. The absorption process can give rise to rapid heating of the solar wind protons, in agreement with observations from comet Halley. Since the free energy for the generation of MHD waves came from deceleration (without accompanying heating) of the solar wind protons during the pick up of cometary ions, the subsequent reabsorption of the energy is equivalent to a nonlocal transformation of ordered to random energy and can be described as nonlocal viscosity.
How deep can we see the high velocity anomalies beneath the Japan Islands?
Authors: Kamiya Shin'ichiro , Miyatake Takashi , Hirahara Kazuro
Published: February 2008

High velocity anomalies are found in the lower mantle beneath the Japan Islands and their vicinity through an analysis of detailed three‐dimensional P‐wave velocity structure based on a tomographic inversion of ISC data. Beneath the Sea of Japan, the high velocity anomalies in the lower mantle are slab‐like and appear to extend below the deep focus earthquakes of the high velocity Pacific slab descending from the Japan trench. This slab‐like high velocity body extending into the lower mantle steepens below a depth of 500‐600 km. Resolution analyses confirms the existence of a slab‐like high velocity region in the lower mantle, though the depth extent is not well resolved. On the other hand, the Pacific slab descending from the Izu‐Bonin trench seems to be fingering, that is, high velocity anomalies are penetrating into the lower mantle beneath latitude 26°N, and not penetrating but horizontally bending in the deeper portion of the upper mantle around 29°N.
Stratospheric O3 and NO2 observations at the southern polar circle in summer and fall 1988
Authors: Pommereau Jean Pierre , Goutail Florence
Published: February 2008

A visible spectrometer dedicated to ozone and NO2 monitoring for the next few years has been installed at the French Antarctica base of Dumont d'Urville at 66°S, 140°E. The first three months of data in Austral summer and fall allow the observation of the NO2 seasonal decay together with its diurnal variation. The data are found incompatible with the currently accepted NOX photochemistry. A conversion of nitrogen compounds into another storage species is required. The reaction which probably involves N2O5 should be active at temperature as high as ‐ 45°C.
Laumontite mineralization in rocks exposed north of San Andreas Fault at Cajon Pass, southern California
Authors: Vincent Mark W. , Ehlig Perry L.
Published: February 2008

Laumontite of hydrothermal origin occurs in veins and as a replacement of the anorthite component of plagioclase in granitic and gneissic basement and overlying arkosic sandstone and conglomerate of the San Francisquito(?), Vaqueros and Cajon formations exposed in Cajon Pass north of the San Andreas fault. Accompanying alteration includes exsolution of albite from plagioclase, conversion of orthoclase to microcline and perthite, and oxidation of iron in biotite and magnetite to form a disseminated hematite stain. These changes are pervasive within 1 km of the fault but diminish to no alteration at 4 km. Granitic rocks close to the fault are crushed to highly fractured and contain a mosaic of laumontite veins. Veins occur along joints and minor faults in sedimentary rocks. Most veins are nearly vertical and trend northwest at a more northerly angle than the San Andreas. This mineralization is attributed to deep circulation of ground water in fractured and frictionally heated rocks along the San Andreas fault.
Single‐domain particles in rocks and magnetic fabric analysis
Authors: Potter David K. , Stephenson Alan
Published: February 2008

Magnetic susceptibility anisotropy is commonly used as a guide for determining stress and flow axes in rocks, and for assessing the suitability of anisotropic rocks for palaeomagnetic purposes. We have recently demonstrated however in laboratory produced samples that, as theoretically expected, susceptibility anisotropy is dependent on particle size. Multidomain particles of magnetite, or similar strongly magnetic particles with shape anisotropy, exhibit a maximum susceptibility parallel to their easy (remanent) magnetization axes whereas uniaxial single‐domain particles exhibit a maximum susceptibility perpendicular to their easy magnetization axes. Hence susceptibility anisotropy does not yield an unambiguous determination of particle alignment in rocks independent of domain state. By demonstrating uniaxial single‐domain anisotropy characteristics for the first time in a rock specimen, we show here that susceptibility measurements by themselves may not correctly identify the degree or type of alignment of ferro‐ or ferrimagnetic particles in rocks. In particular, apparently foliated rocks can actually be lineated (and vice‐versa). Moreover rocks with low anisotropy of susceptibility can have a much higher anisotropy of remanence. Remanence anisotropy methods are shown to give unambiguous determinations of the degree and type of alignment.
On the expansion of ionospheric plasma into the near‐wake of the space shuttle orbiter
Authors: Stone N. H. , Wright K. H. , Samir U. , Hwang K. S.
Published: February 2008

During the Spacelab 2 mission, while the Plasma Diagnostics Package was attached to the Remote Manipulator System, differential ion vector measurements were obtained in the near wake at a distance of 4‐5 Shuttle radii. The Orbiter's wake was found to fill in at a much faster rate than can be explained by simple thermal motion. The measurements strongly suggest that filling of the Orbiter's wake is produced by the process of "collisionless plasma expansion into a vacuum" and that, for oblique angles of the magnetic field and velocity vectors, the near wake plasma depletion a few radii downstream is not sensitive to the body scale size.
Some constraints on a greenhouse atmosphere for Triton
Authors: Nolan Michael C. , Lunine Jonathan I.
Published: February 2008

We explore the likelihood of a thick atmosphere around Neptune's satellite Triton. The infrared optical depth in the grey atmosphere approximation is computed for a range of possible surface compositions, albedos, and gravities. If molecular nitrogen and/or hydrogen are present, a self‐sustaining optically‐thick atmosphere is possible. As such an atmosphere develops, the reradiation of insolation tends toward a uniform global distribution, which provides a strong negative feedback. Bimodal behavior of Triton's atmosphere is therefore possible as seasonal effects and volatile distribution alter the distribution of thermal emission.
Solar wind dynamic pressure variations and transient magnetospheric signatures
Authors: Sibeck D. G. , Baumjohann W. , Lopez R. E.
Published: February 2008

Contrary to the prevailing popular view, we find that some transient ground events with bipolar north‐south signatures are related to variations in solar wind dynamic pressure and not necessarily to magnetic merging. We present simultaneous solar wind plasma observations for two previously reported transient ground events observed at dayside auroral latitudes. During the first event, originally reported by Lanzerotti et al. [1987], conjugate ground magnetometers recorded north‐south magnetic field deflections accompanied by strong deflections in the east‐west and vertical directions. The second event was reported by Todd et al. [1986], who noted ground radar observations indicating strong northward then southward ionospheric flows. The events were associated with the postulated signatures of patchy, sporadic, merging of magnetosheath and magnetospheric magnetic field lines at the dayside magnetopause, known as flux transfer events. Conversely, we demonstrate that the event reported by Lanzerotti et al. was accompanied by a sharp increase in solar wind dynamic pressure, a magnetospheric compression, and a consequent ringing of the magnetospheric magnetic field. The event reported by Todd et al. was associated with a brief but sharp increase in the solar wind dynamic pressure.
Origin of the cusp Birkeland currents
Authors: Saunders M. A.
Published: February 2008

We argue that the cusp‐region field‐aligned (Birkeland) currents, first reported by Iijima and Potemra [1976b], arise from the motion of reconnected open field lines shortening over the dayside magnetopause. Initially, field tension is dominant so the open field lines have a significant east/west component to their motion. Later, as the field lines shorten, the magnetosheath flow becomes increasingly important, and the field lines are pulled antisunward into the polar cap. Where the field lines change their direction of movement from east/west to antisunward, the magnetic field must tilt and this is the site of the cusp Birkeland current. All the major observational features of the cusp Birkeland currents fit qualitatively well with our model.
rift propagation
Authors: Parmentier E. M. , Schubert G.
Published: February 2008

We formulate a model for rift propagation which treats the rift as a crack in an elastic plate which is filled from beneath by upwelling viscous asthenosphere as it lengthens and opens. Growth of the crack is driven by either remotely applied forces or the pressure of buoyant asthenosphere in the crack and is resisted by viscous stresses associated with filling the crack. The model predicts a time for a rift to form which depends primarily on the driving stress and asthenosphere viscosity. For a driving stress on the order of 10 MPa, as expected from the topography of rifted swells, the development of rifts over times of a few Myr requires an asthenosphere viscosity of 1016 Pa s (1017 poise). This viscosity, which is several orders of magnitude less than values determined by postglacial rebound and at least one order of magnitude less than that inferred for spreading center propagation, may reflect a high temperature or large amount of partial melting in the mantle beneath a rifted swell.
Determination of the polytropic index in the plasma sheet
Authors: Baumjohann Wolfgang , Paschmann Götz
Published: February 2008

Using eight months of magnetotail plasma data, we have done a statistical survey on the relation between ion density and pressure in the Earth's plasmasheet. More than 270,000 spin averaged (4.5s) samples of ion density and thermal pressure obtained in the central plasma sheet and the plasma sheet boundary layer were cross‐correlated in order to obtain typical values of the polytropic index γ for different tail regions and disturbance conditions. The plasma sheet ion population behaves, on average, adiabaticly both in the central plasma sheet and the plasma sheet boundary layer. However, a polytropic index of about 1.4 for the quiet plasma sheet indicates that the latter behaves like a poorly insulated vessel. Hence, there seems to be no quiet time magneto‐tail equilibrium (“ground state”), but rather continuous cooling until new energy is entering from the outside.
The δ18O record of phanerozoic abiotic marine calcite cements
Authors: Lohmann Kyger C. , Walker James C. G.
Published: February 2008

Monomineralic, abiotic marine cements formed in low‐latitude Phanerozoic reefs provide the direction and amplitude of secular variation of δ13C and δ18O in marine calcite and defines two end member compositions — 580 to 360 my (−7 to −5‰ δ18OPDB) and 360 to present (−3 to 0‰ δ18OPDB). Sampling of the Devono‐Carboniferous transition (375‐320 my) at several global sites reveals a rapid change in carbonate isotopic compositions. Bracketed within Fammenian to Early Visean‐aged strata, a 7 to 15 my time interval, this shift corresponds to a 2‰ offset in mean δ13C and 3‐4‰ offset in δ18O. The abruptness of such change, and its overall correlation with variations in 87Sr/86Sr, δ34S, δ13C, and Li/Al ratios in marine sediments suggests a primary offset in marine water composition.
Rate of change of the Quincy‐Monument Peak baseline from a translocation analysis of LAGEOS Laser Range Data
Authors: Stolz A. , Vincent M. A. , Bender P. L. , Eanes R. J. , Watkins M. M. , Tapley B. D.
Published: February 2008

Translocation studies of LAGEOS laser range data from Quincy and Monument Peak in California observed during 1984–1987 suggest that plate tectonic motion across the San Andreas fault system in the direction of the baseline between the two stations is uniform at a rate of −30(±3) mm/a. Changes in the components of the baseline vector were inferred from repeat determinations using the solutions from successive 0.5‐year intervals. The changes in the vertical and transverse components of the Quincy‐Monument Peak baseline are −0.4(±5) mm/a and +14(±5) mm/a respectively. The vertical component determinations attest to the height stability of the laser ranging method. LAGEOS measurements made from Quincy and Monument Peak before 1984 are inaccurate enough to limit their usefulness for plate tectonic studies.
Multispacecraft observations of energetic ions upstream and downstream of the bow shock
Authors: Scholer M. , Möbius E. , Kistler L. M. , Klecker B. , Ipavich F. M.
Published: February 2008

We present simultaneous measurements of energetic protons and alpha particles inside and outside of the magnetopause, immediately upstream, and downstream as well as further upstream of the bow shock. A comparison between the intensity at the bow shock and further upstream results in an e‐folding distance at 30 keV of ∼ 6.2 RE. After transformation of the angular distribution into the solar wind frame a diffusion coefficient of κ∥ ∼ 3 RE is obtained from the anisotropy and the intensity gradient. Immediately downstream of the bow shock the anisotropy in the shock frame is directed toward the magnetopause. After transformation into the plasma rest frame the distribution is isotropic. The intensity in the magnetosheath just outside the magnetopause is smaller than the intensity behind the bow shock. Thus, in the magnetosheath there is no gradient or streaming in the upstream direction. The spectra, intensities, and relative abundances in the magnetosheath and inside the magnetosphere are totally different. These observations are consistent with first order Fermi acceleration at the bow shock and subsequent downstream convection, and exclude a magnetospheric source for these particles.
VLF bursts in the night ionosphere of Venus: Estimates of the Poynting flux
Authors: Russell C. T. , von Dornum M. , Strangeway R. J.
Published: February 2008

Even though the Pioneer Venus plasma wave instrument returns a measure of only one component of the electric field due to waves, for the 100 Hz channel it is possible to calculate an approximate Poynting flux of the waves by making several assumptions. When this is done the Poynting flux at lowest altitudes in a 30 Hz band centered on 100 Hz is found to be about 10−7 W m−2 independent of ionospheric conditions as indicated by the strength of the magnetic field. The local time variation of the approximate Poynting flux shows a maximum from about 2000 to 2200 LT in accord with inferences from the higher frequency channels. The observed wave energy flux is consistent with that expected from lightning given rates and flash strengths on Venus that are similar to or greater than that of the Earth.
Evidence for a P‐wave velocity anomaly in D″
Authors: Baumgardt Douglas R.
Published: February 2008

A number of strong P‐coda phases have been observed on European WWSSN‐station short‐period recordings of intermediate‐magnitude, Kurile arc earthquakes which occurred at several different depths of focus. These phases have been observed for several different events and cannot be explained by known phases, such as PcP or source multiplicity. A lower‐mantle model, containing a first‐order discontinuity with a 2.75% P‐wave velocity contrast and located about 344 km above the core‐mantle boundary, produces synthetic seismograms which approximately reproduce the observed amplitudes and arrival times of the coda phases. However, the fact that these phases are not always observed and that their amplitudes vary significantly for different events and stations suggests that the discontinuity at the top of D″ may be a transition zone and may be laterally variable in thickness and contrast.
On the lower altitude limit of the Venusian ionopause
Authors: Mahajan K. K. , Mayr H. G. , Brace L. H. , Cloutier P. A.
Published: February 2008

It has been observed from the plasma experiments on the Pioneer Venus Orbiter that the altitude of the upper boundary of the ionosphere (viz ionopause) decreases in response to increasing solar wind dynamic pressure. However, at pressures above about 2.5 × 10−8 dynes cm−2, the further decrease in the ionopause height is rather small. Following the model of Cloutier et al., [1969] we suggest that during high solar wind conditions, when the ionopause is formed at lower altitudes, the solar wind induces vertical and horizontal flows which sweep away the ionospheric plasma that is produced locally by photoionization. As a result a disturbed photo‐dynamical ionosphere is formed which has the scale height of the ionizable neutral constituent. We show that such a photo‐dynamical ionosphere is observed at the subsolar ionopause under these conditions. As a consequence of this interaction, the ionopause altitude is observed to follow the small scale height of the ionizable species, atomic oxygen, showing only small changes with solar wind pressure.
High‐frequency radar observations of atmospheric gravity waves in the high‐latitude ionosphere
Authors: Samson J. C. , Greenwald R. A. , Ruohoniemi J. M. , Baker K. B.
Published: February 2008

The Johns Hopkins University high‐frequency coherent scatter radar at Goose Bay, Labrador, often observes the effects of propagating atmospheric gravity waves, particularly in ground backscatter returns. To date, these waves have been identified in late fall and early winter on propagation paths directed over the Davis Strait, between northeastern Canada and Greenland. The waves appear as spatially localized enhancements in the backscattered power and as quasiperiodic fluctuations in the backscattered powers, Doppler velocities, and reflection heights. They are generally observed during daylight hours and are usually accompanied by backscatter from higher‐latitude ionospheric irregularities that appear to be located near the ionospheric convection reversal boundary. The lowest frequencies associated with the gravity waves lie in the range 0.4 to 0.6 mHz, and the wavelengths lie in the range 300 to 600 km. The waves generally propagate equatorward at an angle of 150° to 180° east of geographic north. During intervals with an expanded polar cap, northward propagating gravity waves are sometimes observed. Measurements of the parameters of the waves and the ranges to the sources suggest that the waves are excited at a height of 100 to 150 km near the convection reversal boundary and the polar cusp, and that the bulk of the observed perturbations are due to Earth‐reflected waves.
Low‐altitude signatures of the cusp and flux transfer events
Authors: Lockwood Mike , Smith Mark F.
Published: February 2008

The usual interpretation of a flux transfer event (FTE) at the magnetopause, in terms of time‐dependent and possibly patchy reconnection, demands that it generate an ionospheric signature. Recent ground‐based observations have revealed that auroral transients in the cusp/cleft region have all the characteristics required of FTE effects. However, signatures in the major available dataset, namely that from low‐altitude polar‐orbiting satellites, have not yet been identified. In this paper, we consider a cusp pass of the DE‐2 spacecraft during strongly southward IMF. The particle detectors show magnetosheath ion injection signatures. However, the satellite motion and convection are opposed, and we discuss how the observed falling energy dispersion of the precipitating ions can have arisen from a static, moving or growing source. The spatial scale of the source is typical of an FTE. A simple model of the ionospheric signature of an FTE reproduces the observed electric and magnetic field perturbations. Precipitating electrons of peak energy ∼100eV are found to lie on the predicted boundary of the newly‐opened tube, very similar to those found on the edges of FTEs at the magnetopause. The injected ions are within this boundary and their dispersion is consistent with its growth as reconnection proceeds. The reconnection potential and the potential of the induced ionospheric motion are found to be the same (≃25kV). The scanning imager on DE‐1 shows a localised transient auroral feature around DE‐2 at this time, similar to the recent optical/radar observations of FTEs.