bluuebunny/crossref_metadata_2025 huggingface dataset:
Velocity dependent friction of granite over a wide range of conditions
Authors: Kilgore Brian D. , Blanpied Michael L. , Dieterich James H.
Published: February 2008

Direct shear sliding experiments on bare ground surfaces of Westerly granite have been conducted over an exceptionally wide range of sliding rates (10−4 µm/s to 10³ µm/s) at unconfined normal stresses (σn) of 5, 15, 30, 70, and 150 MPa. A new sample configuration was developed that permitted measurements at normal stresses of 70 and 150 MPa without immediate sample failure. Measurements of steady‐state velocity dependence of friction at velocities between 10−4 and 1 µm/s show similar velocity weakening behavior at all normal stresses, with more negative dependence at lower slip rates. However, at rates above 10 µm/s, velocity weakening is observed only at σn=30, 70 and 150 MPa, while velocity neutral behavior is observed at σn=15 MPa and velocity strengthening is observed at σn=5 MPa. The greater velocity weakening observed at velocities below 10−2 µm/s may suggest a transition in competing deformation mechanisms, or the influence of additional mechanisms. The transition to velocity strengthening at high velocity and low normal stress implies that rapid slip on shallow faults could be arrested before resulting in true stick‐slip behavior. Stable fault creep and creep events observed at shallow levels on some natural faults may result from this transition in velocity dependence.
The Kephalonia Transform Fault and the rotation of the Apulian Platform: Evidence from satellite geodesy
Authors: Kahle Hans‐Gert , Müller Max V. , Mueller Stephan , Veis George
Published: February 2008

This paper describes a collaborative GPS‐Project to determine recent crustal movements and deformations across the NE Ionian Sea. This region is characterized by rifting in the African Foreland (Pelagian Sea), subduction along the Calabrian and West Hellenic Arcs, rotation of the Italian peninsula and distributed normal faulting in Central Greece. From GPS‐campaigns on the Ionian Islands and in NW Greece performed in 1989 and 1991 a kinematic field is deduced which is controlled by the deep trough following the NW coast of Kephalonia island. It is concluded that this prominent bathymetric feature resembles an active fault system (Kephalonia fault) which has the signature of a right‐lateral transform fault.
CIV Experiments on ATLAS‐1
Authors: Marshall J. A. , Burch J. L. , Choueiri E. Y. , Kawashima N.
Published: February 2008

A test of the Critical Ionization Velocity (CIV) theory was made with neutral xenon releases from the Space Experiments with Particle Accelerators (SEPAC) hollow cathode plasma contactor onboard the Shuttle Orbiter Atlantis during the ATLAS‐1 mission. The gas velocity perpendicular to the Earth's magnetic field was essentially the orbital velocity (7.5 km/s), and thus it exceeded the CIV for xenon. The releases were observed with onboard instrumentation. A factor of 60 enhancement was seen in the Langmuir probe current. Calculations confirmed that release conditions generally satisfied criteria for CIV and predicted a maximum factor of 20 increase in plasma density. Thus, CIV effects were likely to have occurred during the ATLAS‐1 experiments.
Rock magnetism of Lower/Middle Pleistocene marine sediments, Wanganui Basin, New Zealand
Authors: Roberts Andrew P. , Phillans Brad J.
Published: February 2008

Rock magnetic studies were carried out in order to identify the remanence carrying minerals and the domain state of magnetic grains in Lower/Middle Pleistocene marine sediments from the Wanganui Basin, southwestern North Island, New Zealand. Isothermal remanent magnetization (IRM) acquisition and stepwise thermal demagnetization of a three‐axis composite IRM suggest that titanomagnetite (or titanomaghaemite) is the dominant remanence carrier in these sediments. Other rock magnetic data suggest that these grains occur in a range of sizes in the superparamagnetic to pseudo‐single domain range, which helps account for the wide range of observed palaeomagnetic behaviour. Isolated occurrences of ferrimagnetic iron sulphides cannot be ruled out.
Long‐term expansion characteristics of CRRES barium release clouds
Authors: Hunton D. E.
Published: February 2008

A straightforward approach to calculating number densities of barium ions at the satellite position following CRRES low altitude chemical releases is described. The calculation is based on a phenomenological model of the neutral barium cloud which is taken to expand collisionlessly as a gaussian shell. Ion densities are derived by integrating the photoionization rate along a line extending from the spacecraft position forward into the velocity vector and going through the neutral cloud. Model predictions are compared with in‐situ mass spectrometer data, and shown to be in reasonable agreement.
Infrared absorption by volcanic stratospheric aerosols observed by ISAMS
Authors: Grainger R. G. , Lambert A. , Taylor F. W. , Remedios J. J. , Rodgers C. D. , Corney M. , Kerridge B. J.
Published: February 2008

The Improved Stratospheric and Mesospheric Sounder (ISAMS) aboard the Upper Atmosphere Research Satellite (UARS) senses in 14 wideband channels in the infrared. The absorption by the Mt. Pinatubo aerosol cloud for nine of the channels was averaged over heights from 20 km to 30 km for a 60° latitude band centred on the Equator. The absorption spectrum for sulphuric acid‐water aerosols was calculated for wavelengths from 4 μm to 17 μm and investigated as a function of the particle size distribution and the particle composition. The infrared spectrum is shown to be more sensitive to changes in particle composition than to drop size; the ISAMS results are consistent with drops composed of a 59% to 77% solution of sulphuric acid in water.
Observations of aerosol by the HALOE Experiment onboard UARS: A preliminary validation
Authors: Hervig Mark E. , Russell James M. , Gordley Larry L. , Park Jae H. , Drayson S. Roland
Published: February 2008

The HALOE experiment measures vertical profiles of aerosol extinction at five infrared wavelengths. Four of these observations are obtained using a combination of gas filter and broadband radiometer measurements in bands of HF, HCl, CH4, and NO centered at wavelengths of 2.45, 3.40, 3.45, and 5.26 μm, respectively. The fifth is obtained using broadband radiometer measurements of CO2 transmission at 2.79 μm. Error analysis shows that the random extinction uncertainties are generally less than 10% in the aerosol layer, increasing to over 20% at the profile tops. HALOE spectral extinction measurements are shown to be consistent with predicted spectral extinction for stratospheric sulfate aerosol. Profile comparisons between HALOE and independent sources result in generally good agreement in the shape and magnitude of peak extinction and the altitude where the peak extinction occurs. In addition, global aerosol distributions obtained from the data are consistent with expected aerosol morphology. Although the validation is preliminary, the HALOE aerosol data appear to be of excellent quality and to accurately represent optical characteristics and distribution of the aerosols.
The quasiperpendicular environment of large magnetic pulses in Earth's quasiparallel foreshock: ISEE 1&2 observations
Authors: Greenstadt E. W. , Moses S. L. , Coroniti F. V. , Farris M. H. , Russell C. T.
Published: February 2008

ULF waves in Earth;aposs foreshock cause the instantaneous angle ϑBn between the upstream magnetic field and the shock normal to deviate from its average value. Close to the quasiparallel (Q∥) shock the transverse components of the waves become so large that the orientation of the field to the normal becomes quasiperpendicular (Q⟂) during applicable phases of each wave cycle. Large upstream pulses of B were observed completely enclosed in excursions of ϑBn into the Q⟂ range. A recent numerical simulation included ϑBn among the parameters examined in Q∥ runs, and described a similar coincidence as intrinsic to a stage in development of the reformation process of such shocks. Thus, the natural environment of the Q∥ section of Earth's bow shock seems to include an identifiable class of enlarged magnetic pulses for which local Q⟂ geometry is a necessary association.
Variability of dayside convection and motions of the cusp/cleft aurora
Authors: Lockwood M. , Moen J. , Cowley S. W. H. , Farmer A. D. , Løvhaug U. P. , Lühr H. , Davda V. N.
Published: February 2008

We present measurements of the ionospheric plasma flow over the range of invariant latitudes 71–76°, observed at 10‐second resolution using both the EISCAT radars, with simultaneous observations of the 630 nm cusp/cleft aurora made by a meridian‐scanning photometer at Ny Ålesund, Svalbard. A major increase in the trans‐auroral voltage from 5 to 40 kV (associated with sunward convection in the early afternoon sector) is found to follow a southward motion of the aurora and coincide with the onset of regular transient auroral breakup events. It is shown that these observations are consistent with recent theoretical work on how ionospheric flows are excited by time‐dependent reconnection at the dayside magnetopause.
First in‐situ observations of neutral and plasma density fluctuations within a PMSE layer
Authors: Lübken Franz‐Josef , Lehmacher Gerald , Blix Tom , Hoppe Ulf‐Peter , Thrane Eivind , Cho John , Swartz Wesley
Published: February 2008

The NLC‐91 rocket and radar campaign provided the first opportunity for high resolution neutral and plasma turbulence measurements with simultaneous observations of PMSE (Polar Mesospheric Summer Echoes). During the flight of the TURBO payload on August 1, 1991, CUPRI and EISCAT observed double PMSE layers located at 86 and 88 km altitude, respectively. Strong neutral density fluctuations were observed in the upper layer but not in the lower layer. The fluctuation spectra of the ions and neutrals within the upper layer are consistent with standard turbulence theories. However, we show that there is no neutral turbulence present in the lower layer and that something else must have been operating here to create the plasma fluctuations and hence the radar echoes. Although the in situ measurements of the electron density fluctuations are much stronger in the lower layer, the higher absolute electron density of the upper layer more than compensated for the weaker fluctuations yielding comparable radar echo powers.
Upper crustal densities derived from sea floor gravity measurements: Northern Juan De Fuca Ridge
Authors: Holmes Mark L. , Johnson H. Paul
Published: February 2008

A transect of sea floor gravity stations has been analyzed to determine upper crustal densities on the Endeavour segment of the northern Juan de Fuca Ridge. Data were obtained using ALVIN along a corridor perpendicular to the axis of spreading, over crustal ages from 0 to 800,000 years. Calculated elevation factors from the gravity data show an abrupt increase in density with age (distance) for the upper 200 m of crust. This density change is interpreted as a systematic reduction in bulk porosity of the upper crustal section, from 23% for the axial ridge to 10% for the off‐axis flanking ridges. The porosity decrease is attributed to the collapse and filling of large‐scale voids as the abyssal hills move out of the crustal formation zone. Forward modeling of a plausible density structure for the near‐axis region agrees with the observed anomaly data only if the model includes narrow, along‐strike, low‐density regions adjacent to both inner and outer flanks of the abyssal hills. The required low density zones could be regions of systematic upper crustal fracturing and faulting that were mapped by submersible observers and side‐scan sonar images, and whose presence was suggested by the distribution of heat flow data in the same area.
Long‐term monitoring of hydrothermal heat flux using moored temperature sensors, cleft segment, Juan De Fuca Ridge
Authors: Baker Edward T. , Cannon Glenn A.
Published: February 2008

Heat flux from submarine vent fields can vary gradually on interannual scales, or nearly instantaneously in response to volcano‐tectonic events in the underlying crust. Neither case is well documented because measurements of vent‐field scale heat flux are scarce. We report here a new approach to hydrothermal plume monitoring sensitive to both progressive changes and hydrothermal events. From June 1991 to May 1992 we moored 35 self‐contained temperature sensors and six current meters on seven moorings located in and around the plume from a vent field on the Cleft segment, Juan de Fuca Ridge. The hydrothermal plume was identified by a local temperature anomaly of 0.01° to 0.03°C in the lowermost 200 m of the water column. Plume heat flux, defined as the net advection of this temperature anomaly, averaged about 250 MW during the deployment. This flux is less than previous estimates and thus supports speculation that the heat flux is declining after a sudden reinvigoration triggered by a seafloor rifting event in 1986.
Propagation characteristics of waves upstream and downstream of quasi‐parallel shocks
Authors: Krauss‐Varban D. , Omidi N.
Published: February 2008

The propagation characteristics of waves upstream and downstream of quasi‐parallel shocks are investigated by using two‐dimensional hybrid simulations. At low Alfvén Mach numbers MA ≲ 2, the shock is initially associated with upstream phase‐standing whistlers. At later times, backstreaming ions excite longer‐wavelength whistlers via the right‐hand resonant ion/ion instability. As anticipated from linear theory, these waves are found to propagate along the magnetic field. Their group velocity is larger than or comparable to the upstream flow speed, and as a result, the waves remain in the upstream region. At higher MA ≳3 these waves are convected back into the shock, causing its re‐formation and downstream perturbations. Shock transmitted waves mode‐convert into Alfvén / ion‐cyclotron waves which have a wavevector along the shock normal (pointing upstream) and convect downstream. The two‐dimensional simulation results confirm our earlier suggestion that the upstream waves should be field aligned, and that their convection into the downstream is associated with linear mode conversion into the Alfvén / ion‐cyclotron branch.
A model of the plumes above basaltic fissure eruptions
Authors: Woods Andrew W.
Published: February 2008

A simple model of the ascent of the volatiles above basaltic fissure eruptions shows that atmospheric moisture may play an important role in injecting volatiles high into the atmosphere. As ambient water vapour is entrained and carried upwards by the plume, it decompresses and some condensation may occur. This causes the release of latent heat which heats up the air and thereby increases the buoyancy of the plume enabling it to ascend several kilometres higher than in a dry atmosphere. The height of such plumes also increases with the mass fraction of fine ash in the fountain. Although very simple, the model predictions are in accord with observations of plume heights during historical eruptions including the 1984 eruption of Mauna Loa.
Hellas Planitia, Mars: Site of net dust erosion and implications for the nature of basin floor deposits
Authors: Moore Jeffrey M. , Edgett Kenneth S.
Published: February 2008

Hellas Planitia, located within an enclosed basin which includes the lowest topography on Mars, appears to be undergoing net erosion. Dust is removed from the basin. It probably contributes to global dust storms and should leave behind a coarse lag. The particle size distributions and particularly the rock or boulder populations in this lag might be useful for distinguishing between processes which formed the lithologic units that comprise Hellas Planitia. This report concludes that the abundance of rock particles larger than coarse sand is very low. Although this hypothesis awaits confirmation from forthcoming spacecraft data, the origins for Hellas floor deposits favored by this study are indurated volcanic airfall or ancient loess, lacustrine deposits, and some types of volcanic mud flows. The conclusions of this study tend to disfavor such geologic processes as blocky lava flows, glacial deposits (e.g., moraines), or boulder‐laden catastrophic flood outwash.
A model study of atmospheric temperatures and the concentrations of ozone, hydroxyl, and some other photochemically active gases during the glacial, the pre‐industrial Holocene and the present
Authors: Crutzen Paul J. , Brühl Christoph
Published: February 2008

Analysis of air trapped in ice cores shows that the atmospheric contents of the greenhouse gases CO2, CH4 and N2O have increased from the glacial to the pre‐industrial holocene. Further increases have been occurring during the industrial era. This may well have contributed to the observed global warming. In addition, CH4 and N2O play large roles in ozone and hydroxyl chemistry. Here we present a model analysis of the changes in atmospheric temperatures and the concentration of O3, OH and related gases between the three epochs. Surprisingly, despite large changes in the atmospheric contents of CO2, CH4 and N2O, total ozone and tropospheric OH hardly changed between the glacial and pre‐industrial holocene. The global annual atmospheric CH4 sink increased from 90 to 210 Tg (1012 g) between the glacial and pre‐industrial and since then to 510 Tg, largely following the changes in atmospheric concentrations. The corresponding figures for N2O are 7.8, 11.6 and 13.3 Tg. Our results indicate less than half as much CH4 production from tropical wetlands during the ice age than during the holocene.
Galileo observations of the motions of ion and electron plasmas in the magnetotail
Authors: Frank L. A. , Paterson W. R. , Kivelson M. G.
Published: February 2008

We report the first fully three‐dimensional determinations of the bulk motions of ion and electron plasmas in Earth's magnetotail at geocentric radial distances near the lunar orbit. The two regions that are examined are the plasma sheet and the plasma mantle. The magnitudes and directions of the bulk velocities are the same for the ion and electron plasmas in the plasma mantle. However, in the plasma sheet the electron bulk speeds are often substantially greater than the ion bulk speeds. This situation arises because the component of electron flow along the magnetic field is greater than the ion parallel flow. Most of the bulk flow of the electrons is often attributable to the presence of field‐aligned currents, not E × B convection of plasmas. Hence previously reported two‐dimensional electron velocity distributions do not give a reliable determination of mass transport and convection in the plasma sheet at these distances in the magnetotail.
The Yamal Peninsula‐Lake Baikal deep seismic sounding profile
Authors: Cipar John J. , Priestley Keith , Egorkin Anatoly V. , Pavlenkova Nina I.
Published: February 2008

Seismograms from three nuclear explosions recorded along a 2400‐km long deep seismic sounding profile extending from the Yamal Peninsula to Lake Baikal are presented. We have constructed a preliminary 1‐D compressional velocity model to fit the major travel time features of the data. Clear differences between the seismograms from each shot imply that the velocity structure of the crust and upper mantle is variable along the profile. Estimated crustal thicknesses range from 47 km beneath the west Siberian rift to 42 km beneath the Siberian craton. The structure of the upper mantle above the transition zone consists of material with P‐wave velocities ranging from 8.25 km/s at the Moho to 8.53 km/s at 225 km. Velocities increase abruptly at 225‐km depth to 8.63 km/s. There is little evidence for a pronounced low‐velocity zone, although small velocity reversals are required to terminate several branches of the travel time curve. The uppermantle transition zone discontinuity at 425‐km depth consists of a 5.6% first‐order velocity increase. The lower discontinuity has a 4.9% velocity increase over the depth range 656.5 to 659 km.
Momentum transfer collision frequency of O+‐O
Authors: Pesnell W. Dean , Omidvar Kazem , Hoegy Walter R.
Published: February 2008

The interaction of the thermosphere and ionosphere is largely governed by collisions between ions and neutral particles. On Venus and the Earth, O+ is a dominant ion, and atomic O dominates throughout much of the thermosphere; therefore an accurate O+‐O cross section is an important prerequisite for understanding the dynamics of planetary upper atmospheres. The cross section and momentum, transfer collision frequency are calculated with a quantum mechanical code which includes resonance charge exchange, polarization, and charge‐quadrupole effects. Our results agree well with earlier calculations of Stubbe [1968] and Stallcop et al [1991].
CUPRI system configuration for NLC‐91 and observations of PMSE during Salvo A
Authors: Swartz Wesley E. , Cho John Y. N. , Miller Clark A.
Published: February 2008

The Cornell University Portable Radar Interferometer (CUPRI) provided nearly continuous monitoring of the mesosphere above Esrange, Sweden during the noctilucent cloud rocket and radar campaign of the summer of 1991 (NLC‐91). CUPRI probed the mesosphere above Esrange from 78 to 91 km altitude with 300‐meter resolution and was sensitive to the enhanced Polar Mesospheric Summer Echoes (PMSE) that occur in the same altitude range as NLC formations. Out of the total of 264 hours of CUPRI observation time, PMSE were present for 140 hours. Rocket Salvo A was flown on the night of August 9–10 into an NLC event that occurred simultaneously with a thin and weakening PMSE layer. High‐resolution Doppler spectrograms of this PMSE event revealed sawtooth‐like discontinuities at ∼ 83 km altitude, which we interpret to be a distorted partial reflection layer which was advected across the radar beam.
Venus gravity and topography: 60th degree and order model
Authors: Konopliv A. S. , Borderies N. J. , Chodas P. W. , Christensen E. J. , Sjogren W. L. , Williams B. G. , Balmino G. , Barriot J. P.
Published: February 2008

We have combined the most recent Pioneer Venus Orbiter (PVO) and Magellan (MGN) data with the earlier 1978–1982 PVO data set to obtain a new 60th degree and order spherical harmonic gravity model and a 120th degree and order spherical harmonic topography model. Free‐air gravity maps are shown over regions where the most marked improvement has been obtained (Ishtar‐Terra, Alpha, Bell and Artemis). Gravity versus topography relationships are presented as correlations per degree and axes orientation.
Identification of modeled ocean plumes in Greenland Gyre ERS‐1 SAR data
Authors: Carsey Frank D. , Garwood Roland W.
Published: February 2008

Oceanic convective plumes modeled with a thermobaric large‐eddy simulation and driven by conditions similar to those of the Greenland Sea are compared to observations from ERS‐1 Synthetic Aperture Radar (SAR) data from the Greenland Sea for the winter of 1992. In both form and size the two representations are seen to compare favorably. The plume‐filled area of the SAR image occupies a region about 20 km by 90 km at the ice edge of the open water in “Nordbukta”, the large seasonal ice retreat, in the “Odden” ice protuberance in the southern Greenland gyre. In the SAR data the plumes appear to be ice covered while the convective‐return areas are open.
Time‐variable response characteristics of groundwater radon to earthquakes
Authors: Igarashi George , Tohjima Yasunori , Wakita Hiroshi
Published: February 2008

A clear coseismic anomaly of groundwater radon was observed for a magnitude 5.6 earthquake that occurred on May 11, 1992. The coseismic radon anomaly was observed at a station which is located right on a major active fault in northeast Japan, and about 140 km away from the hypocenter. This was the first time that an earthquake with M<6 had ever been accompanied by a clear radon anomaly at the station; although we had observed 12 similar coseismic radon anomalies at the station during the observation period from 1984 to 1987, all of the earthquakes that were accompanied by radon anomalies in that period had been with magnitude 6.0 and over. Surprisingly, the radon concentration has become more sensitive to show coseismic anomalies even for M<5 earthquakes since October 1992. This enhancement of sensitivity of the coseismic radon response may be attributed to the progress of micro‐crack formation in the fracture zone of the active fault, which could be related to unusual stress accumulation in the region.
stratospheric trace gas concentrations in the Arctic polar night derived by FTIR‐spectroscopy with the Moon as IR light source
Authors: Notholt J. , Neuber R. , Schrems O. , Clarmann T. V.
Published: February 2008

In winter 1992/93 we have performed ground‐based FTIR measurements in the Arctic (79°N, 12°E) to derive column densities of stratospheric trace gases within the polar vortex. Due to the polar night the moon had to serve as infrared light source instead of the sun. It was possible to perform FTIR‐measurements for about a week around full moon. Column densities of N2O, CH4, HF, HCl, O3, NO2, HNO3 and ClONO2 have been obtained.

The spectra were recorded at 0.01 cm−1 or 0.02 cm−1 resolution using MCT or InSb detectors.

Measurements with an aerosol lidar performed at the same site show that polar stratospheric clouds (PSCs) appeared several times during the polar night. It seems that the concentrations of the stratospheric trace gases are strongly influenced by the occurrence of PSCs.
Perpendicular transport in 1‐ and 2‐dimensional shock simulations
Authors: Jokipii J. R. , Kóta J. , Giacalone J.
Published: February 2008

We consider the foundations of 1‐ and 2‐dimensional shock simulations in which the physical quantities are independent of a coordinate which is not parallel to the magnetic field. We show analytically that in such simulations the ions are effectively tied to the convected magnetic lines of force because of the presence of an ignorable spatial coordinate. This conclusion has important consequences. In particular we conclude that the acceleration of energetic charged particles at quasi‐perpendicular shocks cannot be properly studied in such simulations because the role of perpendicular diffusion cannot be properly evaluated.
The melting relation of the system, iron and carbon at high pressure and its bearing on the early stage of the Earth
Authors: Hirayama Yoshiharu , Fujii Toshitsugu , Kurita Kei
Published: February 2008

The melting relation of iron‐carbon system is studied to see how iron takes in or disgorges carbon at high pressure (up to 12GPa). The understanding on these points is closely related to the problem of the reservoir of carbon in the earth's interior. The results are: (1) Iron‐carbon system shows eutectic melting till at least 12GPa. (2) The eutectic composition is about 3 or 4 wt% of carbon, which does not vary very much with pressure. (3) The eutectic temperature slightly goes up as pressure increases at a rate of 7°C/GPa. This gradient is fairly lower than that of the melting temperature of silicates.

Based on these results and other facts, the following scenario is inferred on the core formation during the early stage of the earth. Because carbon melts into iron forming eutectic system at low temperature, carbon within the accreted chondritic materials might be absorbed into iron melt near the surface of the magma ocean. The observation that the melting temperature of silicate goes up more rapidly as pressure increases than the eutectic temperature of iron‐carbon system, indicates that the temperature within the magma ocean is maintained higher than the melting temperature of iron‐carbon system. Therefore, the carbon‐bearing iron melt may sink into the deep interior of the earth without solidifying and disgorging carbon. After all, it is strongly suggested that carbon may settle with liquid iron forming core.
Estimation of thermal conductivity from the mineral composition: Influence of fabric and anisotropy
Authors: Pribnow Daniel , Umsonst Thorsten
Published: February 2008

Measured values of thermal conductivity from crystalline rocks are compared with values calculated from the mineral content using the layered model. First, thermal conductivity is estimated using data based on quasi‐isotropic mixtures of fragments or powder. Second, the approach is applied on core data considering the anisotropy of some rock forming minerals. The numerical value of estimated thermal conductivity is controlled by the quartz content. Sheet‐silicates control anisotropy and fabric in gneisses and their thermal consequences. If information about the fabric of the rock is available, the anisotropy of minerals can be considered in a layered model and this improves the estimation of thermal conductivity from mineral contents.
Spatiotemporal dynamics in oscillatory zoned magmatic plagioclase
Authors: Higman S. L. , Pearce T. H.
Published: February 2008

This work presents a quantitative analysis of spatiotemporal patterns that form during the growth of oscillatory zoned plagioclase. These patterns were imaged using Nomarski interference contrast imaging of etched polished surfaces. Analysis of these imaged patterns yields new information and constraints on how patterns form, and consequently on how oscillatory zoned crystals may develop in magmatic systems.

Utilizing mathematical techniques recently developed for the analysis of dynamical systems, we show that the irregular nature of oscillatory zoning is not compatible with random or stochastic processes. The analysis of our observations suggests that the plagioclase‐liquid system is a deterministic nonlinear system whose attractor has a relatively low dimension. Finally, comparison of our empirical results with computer models of other dynamical systems implies that as few as two variables may be sufficient to describe the dynamics of the plagioclase‐liquid system.
Neutral composition measurements by the Pioneer Venus Neutral Mass Spectrometer during Orbiter re‐entry
Authors: Kasprzak W. T. , Niemann H. B. , Hedin A. E. , Bougher S. W. , Hunten D. M.
Published: February 2008

Measurements by the Pioneer Venus Orbiter Neutral Mass Spectrometer (ONMS) instrument during Orbiter re‐entry have been made from 18–24 hours local solar time, above 170 km, of He, and from midnight to 4.5 hours below 200 km of He, N, O, CO, N2, and CO2. Preliminary results indicate that in the post‐midnight sector He is the dominant species above 170 km, O the dominant species from 140–170 km and CO2 the dominant species below 140 km. Estimated scale height temperatures for He, O and CO2 of about 105–120 K are similar to those observed in 1978–80 at higher solar activity. The densities at 1 am local solar time and at 150 km are within 35% of those measured earlier. The He bulge is also similar to that observed in 1978–80 confirming that thermosphere superrotation is still present. Comparison with the results of a Venus Thermosphere General Circulation Model suggests the nightside is not sensitive to changes in solar activity due to the isolation of the day and night thermospheres. Apparently, the relatively small changes in the dayside thermosphere with solar activity have little impact on the nightside thermosphere.
Electron kinetic effects in switch‐off slow shocks
Authors: Brackbill J. U. , Vu H. X.
Published: February 2008

Numerical simulations of the slow‐mode switch‐off shock with kinetic electrons give significantly different results from hybrid simulations with fluid electrons. With appropriate downstream boundary conditions there results a more coherent and more strongly damped trailing magnetic wave with fewer back‐streaming ions than with the hybrid model under the same conditions. Evidently, kinetic effects cause a more equal sharing of shock‐induced entropy increases between ions and electrons, which results in lower ion temperatures downstream and greater electron energy transport from downstream to upstream.
Distinctive field behavior following geomagnetic reversals
Authors: Bogue Scott W. , Paul Hilary A.
Published: February 2008

The paleomagnetism of lava flows from Kauai (Hawaii), erupted about 4 my ago immediately following a geomagnetic reversal, reveals that the post‐transitional field had several distinctive characteristics. While the directional dispersion was identical to that displayed by stable field over the past 5 my, the post‐transitional field intensity was unusually high. In both these respects, the field at Kauai resembles the one recorded at 15 Ma by lava flows at Steens Mountain in SE Oregon. The two records also differ in an important way: the large intensity oscillations that immediately followed the Steens Mountain reversal are not apparent in the data from Kauai. These results suggest that while the stability of the newly established dipole may vary significantly from one reversal to the next, strong dipolar field and normal directional dispersion may be systematic features of the post‐transitional geodynamo. Furthermore, the results lend support to the recent suggestion that the core remains in an unusual state for many tens of kyr following a reversal.
Highly rotationally excited nitric oxide in the terrestrial thermosphere
Authors: Sharma R. D. , Sun Y. , Dalgarno A.
Published: February 2008

Reaction of fast non‐thermal N(4S) atoms with O2 molecules is shown to produce NO with large rotational and vibrational excitation. It is suggested that the process is responsible for the highly rotationally excited nitric oxide detected by the space shuttle experiment CIRRIS IA.
Hydrologic drought in the contiguous United States, 1900–1989: Spatial patterns and multiple comparison of means
Authors: Soulé Peter T.
Published: February 2008

A basic question in drought climatology is whether there has been a shift toward drier or wetter conditions within the period of operational climatic records. This question is examined for the contiguous United States by analyzing mean values of the Palmer Hydrologic Drought index over the 90‐year period 1900–1989. Using isoline maps and difference of means tests, moisture conditions in the 1900–44 period are compared to conditions in the 1945–89 period, and multiple comparisons are made among the three discrete climatologically standard 30‐year periods (1900–29; 1930–59; 1960–1989). For each mapped time series there are distinct core regions with above‐ and below‐normal moisture conditions. Comparisons of the 45‐year means reveal significant differences at 39% of the nations' climatic divisions, with clear inverse relationships in the most abnormally wet or dry regions. Comparisons among the 30‐year mean periods show that the largest changes are in the interior, stretching from the northcentral Rocky Mountains into the northern Great Plains. A transition from a wetter to a drier moisture regime occurs between the early and middle 30‐year periods in this region, with drier conditions persisting through the last 30‐year period. The degree of regional heterogeneity in mean moisture conditions, coupled with the changing moisture status among the discrete time periods, suggests that the perception of trends in hydrologic drought conditions is subject to both spatial and temporal scaling.
On nonsinusoidal waves at the Earth‧s magnetopause
Authors: Chen S. ‐H. , Kivelson M. G.
Published: February 2008

We have examined ISEE 1 and 2 data during an interval of multiple magnetopause crossings along the flanks of the tail on January 22, 1978. During the event the interplanetary magnetic field was mainly northward. We found that the surface waves on the magnetopause were nonsinusoidal with steepened sunward facing surfaces. This result is consistent with observations reported for an analogous event by Chen et al. [1993]. The dawn‐dusk electric field E in the low‐latitude boundary layer was ∼10 kV/RE which is much greater than the ∼1 kV/RE dawn‐dusk E field typical of the sunward convecting plasma sheet plasma. The ratio of the dawn‐dusk E field in the LLBL to the dusk‐dawn E in the magnetosheath was ∼1/3. We propose that the magnetic field in the magnetosheath modulates the wave form in a way that may result in an anomalous transport of momentum across the magnetopause.
Wave‐like perturbations observed at low altitudes by the Pioneer Venus Orbiter Neutral Mass Spectrometer during orbiter entry
Authors: Kasprzak W. T. , Niemann H. B. , Hedin A. E. , Bougher S. W.
Published: February 2008

Wave‐like perturbations have been observed in the nightside neutral density data acquired for He, N, O, N2 and CO2 by the Pioneer Venus Orbiter Neutral Mass Spectrometer (ONMS) during entry in late 1992. The data cover an altitude range of 133–200 km from 0.5–4.5 hours local solar time and occur at medium solar activity (F10.7=120). The perturbations, with an effective wavelength along the orbit of about 100 to 600 km, have similar amplitudes for the various species and helium is out of phase with respect to the heavier mass species. The measurements are comparable to those observed in 1978–80 at solar maximum activity (F10.7=200) above 145 km. Between 133 and 160 km the rms amplitudes grow with altitude at a rate of about (1.6, 2.1, 2.7, 4.4) × 10−3 km−1 for N, O, N2, and CO2, respectively. The average rms amplitudes above 145 km of 0.08 for N and O and 0.1 for N2 are comparable in magnitude to those observed in the earlier 1978–80 data of 0.06, 0.08 and 0.095 respectively. CO2 is an exception for which the entry value is 0.17 compared to 0.09 earlier. By combining the two overlapping data sets there is a suggestion that the CO2 amplitudes grow in value with altitude up to about 140–170 km and then decrease in amplitude. Like the earlier data, the entry data are consistent with the interpretation that the neutral density perturbations are due to gravity waves propagating upward from the lower thermosphere. Earlier data sampled a higher altitude region where dissipation is important in limiting and ultimately reversing the growth of gravity waves while the lower altitude entry data probed the region where growth of these waves can be observed.
Thirty year variations in the Earth rotation and the geomagnetic Gauss coefficients
Authors: Yokoyama Yukiko
Published: February 2008

Decade variations in the three components of the Earth rotation and low‐degree geomagnetic Gauss coefficients are examined. Variations with a time scale of 20–30 years are confirmed in both the Earth rotation and the magnetic axial dipole moment. The second degree tesseral Gauss coefficients also appear to have a variation with the same time scale. The components are characterized by high ellipticity of the g‐h path in the direction of 34°W. They appear to have phase change at around 1940. Considering the phase change, paths of the components and the mean pole have great similarity.
Seasonal, latitudinal, and secular variations in temperature trend: Evidence for influence of anthropogenic sulfate
Authors: Hunter David E. , Schwartz Stephen E. , Wagener Richard , Benkovitz Carmen M.
Published: February 2008

Tropospheric aerosols increase the shortwave reflectivity of the Earth‐atmosphere system both by scattering light directly, in the absence of clouds, and by enhancing cloud reflectivity. The radiative forcing of climate exerted by anthropogenic sulfate aerosols, derived mainly from SO2 emitted from fossil fuel combustion, is opposite that due to anthropogenic greenhouse gases and is estimated to be of comparable average magnitude in Northern Hemisphere midlatitudes. However, persuasive evidence of climate response to this forcing has thus far been lacking. Here we examine patterns of seasonal and latitudinal variations in temperature anomaly trend for evidence of such a response. Pronounced minima in the rate of temperature increase in summer months in Northern Hemisphere midlatitudes are consistent with the latitudinal distribution of anthropogenic sulfate and changes in the rate of SO2 emissions over the industrial era.
Conductivity discontinuities in the upper mantle beneath a stable craton
Authors: Schultz A. , Kurtz R. D. , Chave A. D. , Jones A. G.
Published: February 2008

We present evidence for approximate collocation of seismic and electrical transitions in the upper mantle. More than two years of very long period magnetotelluric (MT) data were recorded at a lakebottom observatory in the central Canadian Shield. After processing to contend with non‐stationary source effects, and removal of galvanic distortion, the underlying structure is 1D for periods of one hour to four days. The response was extended to periods of 100 days by appending Geomagnetic Depth Sounding data to the MT curves. Minimum structure linearised inversion, nonlinear extremal inversion, and a new genetic algorithm for nonlinear hypothesis testing, reveal discrete jumps in conductivity at depths near the major upper mantle seismic discontinuities. The jumps occur over limited depth ranges.
Altitude profile of the polar wind velocity and its relationship to ionospheric conditions
Authors: Abe T. , Whalen B. A. , Yau A. W. , Watanabe S. , Sagawa E. , Oyama K. I.
Published: February 2008

We present Akebono observations of the polar wind velocity and the ambient electron temperature in the polar ionosphere. The velocity of the H+ polar wind increases from about 1 km/s at 2000 km altitude to about 6 km/s at 4000 km altitude, and correlates with the local electron temperature at a given altitude. It is only weakly dependent on magnetic activity, but is generally more variable at active times. Our observation demonstrates the direct relationship between the local magnitude of ion acceleration and that of the ambipolar electric field responsible for the acceleration.
A modelling investigation of sudden sodium layers
Authors: Cox R. M. , Plane J. M. C. , Green J. S. A.
Published: February 2008

A time‐resolved model, incorporating both vertical diffusion and chemistry, indicates that the minimum source strength required to produce a typical sudden sodium layer (SSL) is about 3 Na atoms cm−3s−1. However, many of the mechanisms proposed to explain the formation of SSLs are not able realistically to provide this source strength, or the source strength of about 1 Na atom cm−3s−1 that is required to maintain an SSL over several hours. Furthermore, the sodium reservoirs do not appear to contain sufficient sodium to produce an SSL, although sodium ions (Na+), and meteoric dust coated with sodium compounds, cannot be ruled out. An additional mechanism is proposed, namely, the release of atomic Na by dissociative electron attachment to sodium‐containing silicate molecules (e.g. Na2SiO3 or NaAlSiO4) that are produced by meteoric ablation.
NEw observations of the NOy/N2O correlation in the lower stratosphere
Authors: Loewenstein M. , Podolske J. R. , Fahey D. W. , Woodbridge E. L. , Tin P. , Weaver A. , Newman P. A. , Strahan S. E. , Kawa S. R. , Schoeberl M. R. , Lait L. R.
Published: February 2008

During the Airborne Arctic Stratospheric Expedition II (AASE II), September 1991 through March 1992, in situ measurements of reactive nitrogen (NOy) and N2O were made in the Northern Hemisphere lower stratosphere. We present an analysis of this new data and compare it with results from similar data taken during AASE in the winter of 1989. In the Northern Hemisphere there is a consistent linear correlation of N2O and NOy which shows no interannual variation. Cases of departure from a linear correlation are examined and classified as being due to denitrification (NOy loss) or sampling air from a region where the photochemical lifetime of NOy is decreased. The latter case was observed for the first time in the winter of 1992.
Multiple spacecraft survey of the north‐south asymmetry of the interplanetary magnetic field
Authors: Smith Charles W. , Bieber John W.
Published: February 2008

Twenty‐three years of spacecraft observations spanning 22 AU of heliocentric distance have been used in an examination of the north‐south asymmetry of the interplanetary magnetic field. Using the observed sector structure of the solar wind, we have examined the winding of the Parker spiral both north and south of the heliospheric current sheet as observed by the Pioneer‐Venus Orbiter and numerous near‐Earth spacecraft and conclude that a significant and persistent asymmetry exists between the two hemispheres at 0.7 and 1 AU. In keeping with previous analyses, we find that the Parker spiral north of the current sheet is more tightly wound than the Parker spiral south of the current sheet. Several definitions of the average winding angle are all consistent with an asymmetry of 2.4° ± 0.9° at 1 AU using 193 solar rotations. The asymmetry at 0.7 AU for the period 1979‐1987 is somewhat smaller, 2.1° ± 1.0°, but is consistent with 1 AU values during this time period. We conclude that neither the observed asymmetry of the solar rotation nor the observed asymmetry of the solar wind speed can account for the observed winding angle asymmetry. We evaluate the north‐south asymmetry of the large‐scale field beyond 1 AU as measured by Voyager 1 and 2 and Pioneer 10 and 11. The computed asymmetry in the winding angle of the field reaches very large values of the order of 30°, but the quantitative agreement among the four data sets is poor. This and other characteristics of the data suggest that residual zero level errors (at the ∼0.05 nT level) in the radial component of the field may be producing spuriously large asymmetries in the winding angle. In contrast, we find strong indications for a genuine asymmetry in the azimuthal component of the field, with all data sets examined in good agreement. The observations are consistent with a stronger azimuthal component in the northern hemisphere than in the southern hemisphere for the range in heliocentric distance from 0.7 to 10 AU.
Nonlinear evolution of magnetic flux ropes: 1. Low‐beta limit
Authors: Osherovich V. A. , Farrugia C. J. , Burlaga L. F.
Published: February 2008

An understanding of fully developed nonlinear MHD phenomena becomes increasingly essential for the interpretation of magnetospheric and interplanetary observations. In a series of four papers we shall study the nonlinear, self‐similar evolution of a cylindrical magnetic flux tube with two components of the magnetic field, axial (Bz) and azimuthal (Bϕ). In this first paper we restrict ourselves to the case of a plasma of low beta. (Subsequent papers deal with finite beta effects, with dissipation, and with a data example.) Introducing a special class of configurations we call “separable fields,” we reduce the problem to an ordinary differential equation. Two cases are to be distinguished: (1) when the total field minimizes on the symmetry axis, the magnetic configuration inexorably collapses, and (2) when, on the other hand, the total field maximizes on the symmetry axis, the magnetic configuration behaves analogously to a nonlinear oscillator. Here we focus on the latter case. The effective potential of the motion contains two terms: a strong, repulsive term associated with the gradient of Bz²/8π and a weak, restoring term associated with the pinch. We solve the nonlinear differential equation of motion numerically and find that the period of oscillations grows exponentially with the energy of the oscillator. Our treatment emphasizes the role of the force‐free configuration as the lowest potential energy state about which the system oscillates.