bluuebunny/crossref_metadata_2025 huggingface dataset:
Source phase shift: A new phenomenon in wave propagation due to anelasticity
Authors: Buland Ray , Yuen David A. , Konstanty Kevin , Widmer Rudolf
Published: February 2008

By appealing to the correspondence principle, it is possible to compute free oscillations of an anelastic earth model directly. This formulation reveals a source phase due to anelasticity which is not predicted by first order perturbation theory. For toroidal modes, this source phase is found to be largest for source components which are proportional to the radial strain scalar rather than to the radial displacement scalar. The source phase is found to increase with overtone number. Also, large relative differences in both excitation modulus and phase with respect to an elastic model are found when the elastic excitation becomes small. This effect may be large enough to bias estimates of source properties and elastic structure.
Magnitude bias in the Great Basin and its implications for explosion magnitude versus yield estimates
Authors: Priestley Keith F. , Chávez David E.
Published: February 2008

Comparison of teleseismic P‐wave delays in the vicinity of the Central Nevada Test Site in Hot Creek Valley, Nevada, with P‐delay data over a wider region in the Great Basin, shows that upper mantle speeds under Hot Creek Valley stations are higher than the average for the Great Basin as a whole, but lower than those beneath Pahute Mesa. These observations indicate that the caldera complex in Hot Creek Valley may have a high speed root similar to that proposed to exist beneath the Silent Canyon caldera at Pahute Mesa, however the Hot Creek Valley anomaly is not as strong as the Pahute Mesa anomaly. These high‐speed upper mantle structures cause defocusing for outgoing rays resulting in a shadow zone at the distance range corresponding to many European stations. The shadow zone caused by the Pahute Mesa structure is much more pronounced and consequently magnitudes of Pahute Mesa explosions can be underestimated relative to the magnitude of Hot Creek Valley explosions of similar yield. When magnitude versus yield relationships developed using Pahute Mesa data are applied to other areas, such as Hot Creek Valley, they can result in a biased estimate of yield.
Periodic variations of grain size in Pleistocene sediments in Lake Biwa and Earth‐orbital cycles
Authors: Yamamoto Atsuyuki , Kashiwaya Kenji , Fukuyama Kaoru
Published: February 2008

A time sequence of grain size distributions from the Pleistocene sediments in Lake Biwa, located in the central part of Japan (35° N, 136° E), has dominant periodicities of 41,000, 23,000, and 19,000 years which are very close to those predicted from the astronomical theory of paleoclimate introduced by Milankovitch. The time variation of the grain size is very similar to that of insolation of caloric summer in the Northern Hemisphere.
Enhanced seasonal variations for chemical rates with inverse temperature dependencies: Application to seasonal abundance of mesospheric sodium
Authors: Swider William
Published: February 2008

For a fixed altitude, the known seasonal variations of pressure in the mesosphere are less than a factor of two. However, the components of the pressure, the total concentration and temperature, vary in opposition to each other. Thus, a rate for a process with an inverse temperature dependence can undergo a much larger seasonal variation than does the pressure. In particular, the loss rate associated with the three‐body process , which has a negative temperature dependence, annually varies by a factor of four at 80 and 85 km for 60°N and by less than a factor of two at 30°N. Using a recent sodium model, sodium concentrations for 60°N at 80 and 85 km are shown to change by factors of three and two, respectively. Other possible contributors to the seasonal variation of mesospheric sodium are argued as less important.
Analysis and prediction of sunspot numbers
Authors: Paul Adolf K.
Published: February 2008

An extension of anharmonic frequency analysis (AFA) is used to analyze and extrapolate the sunspot numbers. The higher resolution possible with this new approach in principle permits a better accuracy of the prediction for a given extrapolation range, provided the time series is stationary. The results indicate that the extremas of the sunspot numbers of the next three solar cycles will not exceed a magnitude of 100 significantly.
The effects of northward IMF on the structure of the magnetosphere
Authors: Wu C. C.
Published: February 2008

Effects of northward IMF on the structure of the magnetosphere were studied by using a global MHD model. The model suggests a mechanism for creating high latitude sunward convection. The mechanism is not due to magnetic merging over the cusp region. Instead, the model indicates that the northward IMF field lines, which move around the magnetosphere, tend to squeeze the magnetotail at the boundary. This leads to formation of vortex flows in the tail and the observed sunward convection in the polar cap.
Electric fields and convection velocities associated with flux transfer events
Authors: Dailey R. , Cattell C. A. , Mozer F. S. , Berchem J.
Published: February 2008

The electric field and E × B/B² velocities associated with 23 flux transfer events in the magnetosheath and magnetosphere have been examined using data from the University of California, Berkeley double probe experiment on ISEE 1. Twelve‐second averaged electric field data show perturbations in the component of the electric field perpendicular to the magnetopause with an average magnitude of 3.5 mV/m associated with the FTE's. Direct flux transfer events (those with an outward perturbation in B followed by an inward one) were found to have a northward component of the E × B velocity, while reverse flux transfer events were found to have a southward E × B velocity component, in agreement with the current FTE model. The flux tubes moved across the magnetopause plane at an average E × B speed of 125 km/s with respect to the ambient E × B flow, with events located on the dawn (dusk) side tending to move dawnward (duskward). Study of higher time resolution electric field data showed no large spiky electric fields of the type observed elsewhere in the magnetosphere (bow shock, plasmasheet boundary). Examination of the three electric field filters during FTE's showed average enhancements in the power at frequencies between 3 and 250 Hz by factors of 4–20, with maximum enhancements by two orders of magnitude.
Enhanced heat transfer in partially‐saturated hydrothermal systems
Authors: Bixler Nathan E. , Carrigan Charles R.
Published: February 2008

The role of capillarity is potentially important for determining heat transfer in hydrothermal regions. Capillarity allows mixing of phases in liquid/vapor systems and results in enhanced two‐phase convection. Comparisons involving a numerical model with capillarity and analytical models without indicate that heat transfer can be enhanced by about an order of magnitude. Whether capillarity can be important for a particular hydrothermal region will depend on the nature of mineral precipitation as well as pore and fracture size distributions.
DE‐2 mass spectrometer observations relevant to the shuttle glow
Authors: Engebretson Mark J. , Hedin Alan E.
Published: February 2008

A comparison of satellite mass spectrometer data from Dynamics Explorer‐2 and Atmosphere Explorer‐C and ‐D provides new evidence supporting the hypothesis that NO2 is the source of the observed continuum glow near ram‐facing surfaces of the space shuttle. Surface reactions of thermospheric N and O in mass spectrometer ion sources produce NO and NO2 in amounts highly dependent on surface temperature and composition, with direct exposure of ion source surfaces to rammed gas a necessary condition for the production of large amounts of NO2. Initial orbit data indicate that a period of surface conditioning is necessary before these odd nitrogen molecules can be produced efficiently.
Determination of natural and anthropogenic 129I in marine sediments
Authors: Fehn U. , Holdren G. R. , Elmore D. , Brunelle T. , Teng R. , Kubik P. W.
Published: February 2008

129I concentrations in two sediment cores from the continental slope near Cape Hatteras were determined with tandem accelerator mass spectrometry (TAMS). The natural 129I/127I ratios in these cores are approximately 10−12. The input of anthropogenic 129I has increased this ratio to values close to 10−10 at the surface of the sediments. The observed natural level of 129I is about two orders of magnitude above the current detection limit with TAMS, which opens up the possibility for applications of 129I in the marine system such as dating of sediments and crude oils and tracing of slow water movement in sediments.
Solubility of hydroxyl in natural quartz annealed in water at 900°C and 1.5 GPa
Authors: Rovetta Mark R. , Holloway John R. , Blacic James D.
Published: February 2008

We have measured the infrared spectra of a natural quartz after annealing it for up to 37 hours in water at 900°‐1000°C and 1.0‐1.5 GPa under chemical conditions buffered through a hydrogen membrane with an assemblage of water, nickel metal, and nickel oxide. From integral absorbances in the 3400 and 2500 cm−1 regions we calculated the concentration of hydrogen and deuterium present in the samples as hydroxyl. Concentrations reported in this work are calibrated to the deuterium content of a sample annealed 37 hours in D2O18 as determined by nuclear reaction analysis. Hydrothermal annealing increased the hydroxyl content of natural quartz (A‐1) from 26 to 75 ± 11 H/106Si. Absorption increased by growth of O‐H bands it 3318, 3483, and 3432 cm−1 associated with A13+. Samples annealed in D2O18 showed an increase in bands near 2500 cm−1 associated with O‐D and A13+. An O‐H band in the starting material at 3485 cm−1, associated with Li+, was absent from the spectra of annealed samples. Fractured samples were characterized by the appearance of a sharp band at 3580 cm−1 and absorption several times larger than unfractured samples. Microscopic examination of fractured samples showed that they contained water inclusions and healed fractures. Previous hydroxyl solubility measurements made on fractured samples may be too large due to hydroxyl contamination along fractures. At 900°C, experiments equilibrated in times consistent with a diffusivity for hydrogen impurity in quartz of 10−7 cm²/s.
Acceleration of charged particles in magnetic reconnection: Solar flares, the magnetosphere, and solar wind
Authors: Goldstein M. L. , Matthaeus W. H. , Ambrosiano J. J.
Published: February 2008

A possible source of free energy available for accelerating charged particles is conversion of magnetic energy to particle energy in reconnecting magnetic fields. Recent simulations using test particles suggests that reconnection may efficiently accelerate particles to the maximum energies that are observed in several astrophysical contexts. A simple analytic formula is used in conjunction with the simulation results to predict the maximum energy achievable in a particular plasma environment with the result that in solar flares reconnection is capable of accelerating particles to several GeV. In magnetospheric substorms the predicted maximum can reach several hundred keV, and near magnetic sector crossings in the solar wind the maximum energy can approach 100 keV.
Experimental determination of the dominant wave mode in the active near‐Earth magnetotail
Authors: Cattell C. A. , Mozer F. S.
Published: February 2008

Observations of the electric field at frequencies from 2‐128 Hz, using the burst mode of the spherical double probe on ISEE‐1, have been examined for a time period previously identified as containing the passage of a near‐earth neutral line past the satellite. Most of the power occurred at frequencies less than 20 to 50 Hz. Intense waves (3‐>30 mV/m) at approximately half the lower hybrid frequency, were observed throughout the plasma sheet from the neutral sheet to the high latitude boundary, but only during the period of the large dc electric field and E×B velocity associated with the substorm neutral line. The wavenumber obtained by including a Doppler shift term in linear fits of the frequency of the peaks of the power spectra was comparable to the inverse electron gyroradius (k ρe<1). These results are consistent with the lower hybrid drift instability and inconsistent with ion beam driven instabilities (which may explain the much weaker waves observed at higher frequencies). The largest amplitude waves occurred at the neutral sheet when the southward component of the magnetic field was 6 gammas, in contrast to theoretical work which has suggested that the instability would be suppressed there. The observed waves could provide an anomalous resistivity of ∼3×10−7 to 1×10−4 s (compared to the classical value of 1×10−18 s).
Reanalysis of Pioneer Orbiter ultraviolet spectrometer data: OI 1304 intensities and atomic oxygen densities
Authors: Paxton L. J. , Meier R. R.
Published: February 2008

The Pioneer Venus Orbiter Ultraviolet Spectrometer (PVOUVS) measured the OI 1304 Å intensity over a range of spacecraft altitudes (150 to 300 km at periapsis). The atomic oxygen density is determined from the dayglow by comparing the data to the intensities predicted in a Monte Carlo model which correctly simulates the partial frequency redistribution of photons in a non‐isothermal, absorbing atmosphere. The analysis yields atomic oxygen densities consistent with the in situ determinations of the PV Bus Neutral Mass Spectrometer and PVO Neutral Mass Spectrometer and supports recent laboratory measurements of the electron impact excitation cross section of atomic oxygen. Furthermore, the potential inherent in ultraviolet remote sensing for determining the global distribution of atomic oxygen is demonstrated.
Pioneer Venus lyman‐α observations of comet P/Giacobini‐Zinner and the life expectancy of cometary hydrogen
Authors: Combi M. R. , Stewart A. I. F. , Smyth W. H.
Published: February 2008

Pioneer Venus observed the hydrogen coma of Comet P/Giacobini‐Zinner on 11 September 1985 during the ICE fly‐by. Analysis of these data with a time‐dependent 3‐D particle‐trajectory model implies a water production rate of 2.2 × 1028 s−1 on that day. The model includes the irregular variations in the H lifetime and the H Lyman‐α fluorescence rate determined from simultaneous measurements of the solar wind by ICE and of the solar UV by SME, respectively. The H lifetime varied from 2 × 105 to 3 × 106 s during the 42 days preceding the observation.
Simulation of the solar wind interaction with the outer regions of the Coma
Authors: Omidi Nojan , Winske Dan
Published: February 2008

Interaction of the solar wind with newly born cometary ions (O+) is studied through hybrid simulations (particle ions, fluid electrons). The results show that depending on the orientation of the interplanetary magnetic field (IMF) with respect to the solar wind velocity, two kinds of interaction are possible. When IMF is exactly or nearly parallel to the solar wind velocity, momentum transfer between the protons and the O+ ions takes place solely through the excitation of large amplitude electromagnetic waves. On the other hand, as IMF becomes more oblique to the solar wind velocity, momentum transfer occurs on a faster time scale through the motional electric field in the solar wind. This more rapid deceleration can lead to the formation of a shock.
Electron‐impact of the OI λ1641.3 Å line emission
Authors: Erdman P. W. , Zipf E. C.
Published: February 2008

We have measured the cross section for the dissociative excitation of the forbidden OI(2p4 ¹D—3s³S, λ1641.3 Å) transition by electron impact on O2. At 100 eV, we find a cross section value of 1.22 × 10−23 cm² ±35%. This result is consistent with recent estimates of this branching ratio from theoretical calculations and aeronomical observations and supports the suggestion by Meier et al. [1985] that observation of the OI λ1641.3 Å line would be useful for remote monitoring of atomic oxygen in the upper atmosphere.
The interplanetary magnetic field during solar cycle 21: ISEE‐3/ICE observations
Authors: Slavin J. A. , Jungman G. , Smith E. J.
Published: February 2008

Magnetic field observations from the JPL vector helium magnetometer on the ISEE‐3/ICE spacecraft are used to investigate long term temporal variations in the interplanetary magnetic field during solar cycle 21. As reported by previous studies, IMF intensity exhibited a broad decrease during the last sunspot minimum with average values of only 4.7 nT being measured in mid‐1976. It is shown in this study that IMF magnitude peaked in late 1982 at 9.0 nT, or approximately twice its solar minimum intensity. The strength of the interplanetary field decreased rapidly during 1983 and 1984 to a value of 6.2 nT in early 1985. Comparison with the auroral AE index indicates that the post‐maximum peak in IMF strength in 1981‐83 was associated with a ∼50% increase in mean substorm activity levels. This is the first time that a long term variation in the IMF has been observed to produce an increase in geomagnetic activity comparable to, or greater than the enhancements accompanying the well known declining phase high speed streams. A marked decrease in Parker spiral angle, which indicated the presence of high speed streams in 1973‐75 during the declining phase of solar cycle 20, is also observed 11 years later in 1984‐85. The variations in the intensity of the interplanetary magnetic field, and its components, are shown to be only moderately correlated with the Mt. Wilson magnetograph measurements of full disk magnetic flux, i.e., linear correlation coefficients of 0.5 to 0.7. The implications of these results for the long term evolution of the interplanetary magnetic field and its effects on geomagnetic activity are discussed.
Comment on the Paper “On the influx of small comets into the Earth's upper atmosphere II. Interpretation” by L. A. Frank, J. B. Sigwarth and J. D. Graven
Authors: Donahue Thomas M.
Published: February 2008

The suggestion that the Earth is being bombarded by cometoids that subject it to an influx of 3×1011 water molecules/cm²‐sec encounters severe aeronomical problems. There is a serious disposal problem for water molecules deposited near 100 km. The implications for Venus and Mars also present serious problems. It is argued that the proposable is untenable.
Comment on “Increase of Ion kinetic temperature across a collisionless shock: I. A new concept by L. C. Lee et al.” and “Ion acceleration in quasiperpendicular magnetosonic shock waves with subcritical Mach number by Y. Ohsawa and J. Sakai”
Authors: Winske D. , Gosling J. T. , Thomsen M. F.
Published: February 2008

The question of ion heating at subcritical collisionless shocks is reviewed in light of newly proposed mechanisms.
Factors contributing to the catastrophe in Mexico City during the earthquake of September 19, 1985
Authors: Beck James L. , Hall John F.
Published: February 2008

The extensive damage to high‐rise buildings in Mexico City during the September 19, 1985 earthquake is primarily due to the intensity of the ground shaking exceeding what was previously considered credible for the city by Mexican engineers. There were two major factors contributing to the catastrophe, resonance in the sediments of an ancient lake that once existed in the Valley of Mexico, and the long duration of shaking compared with other coastal earthquakes in the last 50 years. Both of these factors would be operative again if the Guerrero seismic gap ruptured in a single earthquake.
Detection of a new “chemical” boundary at comet Halley
Authors: Gringauz K. I. , Gombosi T. I. , Tátrallyay M. , Verigin M. I. , Remizov A. P. , Richter A. K. , Apáthy I. , Szemerey I. , Dyachkov A. V. , Balakina O. V. , Nagy A. F.
Published: February 2008

Plasma observations near comet Halley indicate that around 1.6×105km from the nucleus a newly discovered sharp boundary (cometopause) separates the solar wind controlled external and the heavy cometary ion dominated internal regions. Such a discontinuity was previously not predicted by theoretical models. Inside the cometopause (in the cometary plasma region) the protons and heavy ions move with different speeds: the heavy ion velocity is less than a few km/s throughout this region, while the protons decelerate from several tens of km/s (observed near the cometopause) to a few km/s (near 1.5×104km).
Voyager 2 at Uranus: Grain impacts in the ring plane
Authors: Meyer‐Vernet N. , Aubier M. G. , Pedersen B. M.
Published: February 2008

During the Uranus ring plane crossing at 4.57 Uranus radii, the PRA instrument aboard Voyager 2 recorded a characteristic intense noise extending 104 km perpendicular to the ring plane. This is interpreted as due to impact ionization of dust grains striking the spacecraft. The noise level is smaller by a factor ∼ 170 than the same kind of event recorded during Voyager 2 Saturn encounter just outside the G‐ring. The results indicate a maximum concentration of about 10−9 cm−3 of grains larger than 1 µm with a scale height ∼ 150 km across the ring plane. The distribution is asymmetrical, extending farther on the sunlit side. The inferred geometric optical depth is of order 10−8.
The relationship between proton temperature and momentum flux density in the solar wind
Authors: Lopez R. E. , Freeman J. W. , Roelof E. C.
Published: February 2008

The relationship between proton temperature and momentum flux density per unit mass at 1 AU is examined using Helios 1 solar wind data from 1974 to 1980. In high‐speed plasma (V > 500 km s−1) Tp increases with increasing n0V², where n0 and Tp are the density and proton temperature at 1 AU and V is the flow speed. In low‐speed plasma (V < 500 km s−1), Tp does not increase with increasing n0V², and perhaps tends to decrease slightly. These basic relationships between Tp and n0V² are not significantly affected by stream interactions. A qualitative explanation of these results is offered in the context of a solar wind model that includes deposition of momentum and energy extending well outward into the interplanetary medium.
ISEE‐1 and 2 observations of magnetic flux ropes in the magnetotail: FTE's in the plasma sheet?
Authors: Elphic R. C. , Cattell C. A. , Takahashi K. , Bame S. J. , Russell C. T.
Published: February 2008

Magnetic field observations on ISEE‐1 and 2 in and near the neutral sheet about 20 Re down the near‐Earth magnetotail reveal the occurrence of structures resembling magnetic flux ropes. Both electric field and fast plasma data show that these structures convect across the spacecraft at speeds of 200 ‐ 600 km/s, and that they have scale sizes of roughly 3 ‐ 5 Re. The rope axis orientation is across the tail, approximately in the −Y GSM direction. Their magnetic structure is strikingly similar to magnetic flux ropes observed in the Venus ionosphere, and to flux transfer events observed at the dayside magnetopause. The total field‐aligned current within these ropes may approach a million amps. These structures may arise because of patchy reconnection within the plasma sheet, or may be tearing islands formed when the plasma sheet magnetic field has a cross‐tail component. Plasma sheet flux ropes are not a common feature at ISEE orbital altitudes; this suggests that near‐Earth neutral line formation within ISEE apogee (22 Re) may be equally rare.
Flexure and thickening of the lithosphere at the East Pacific Rise
Authors: Kuo Ban‐Yuan , Forsyth Donald F. , Parmentier E. Marc
Published: February 2008

We have formulated a new class of plate‐bending equations which simulates the flexure of the lithosphere at mid‐ocean ridges. The stress‐accumulation effect in a growing (moving and thickening) lithosphere significantly changes the flexural behavior. It is shown that the growing plate flexes more easily than the conventional static plate due to the fact that the bending stress vanishes on the base of the plate. We apply this new plate model to the East Pacific Rise. Compared with Madsen et al. (1984), the fits to the gravity and topography observations are improved. Assuming the thickness varies in proportion to the square‐root of distance from the ridge crest, the best fitting thickening rate for the growing plate model is 0.7 (km1/2), or 5.5 km/(m.y.)1/2, which further implies that the 600 or 700°C isotherm marks the bottom boundary of the effective elastic thickness of the lithosphere.
Rheology of Ice II and Ice III from High‐Pressure Extrusion
Authors: Echelmeyer Keith , Kamb Barclay
Published: February 2008

Rheological parameters for ice II and ice III, needed in tectonic models of the icy satellites of the major planets, are obtained from extrusion experiments and compared with the rheology of ice I at pressures ∼2 kbar and temperatures ∼240K. Ice II has a higher effective viscosity (by a factor ∼10) than ice I at similar stress levels, whereas ice III has a lower viscosity (by a factor ∼0.01). The Rheological contrasts among the ice phases are related to differences in the dielectric relaxation behavior and state of proton order/disorder in the structures in a way that sheds light on the nature of dislocation motion in ice. A striking transformation plasticity accompanies the ice I‐III transition and could have large tectonic effects.
Formation of field‐twisting flux tubes on the magnetopause and solar wind particle entry into the magnetosphere
Authors: Sato Tetsuya , Shimada Toshiaki , Tanaka Motohiko , Hayashi Takaya , Watanabe Kunihiko
Published: February 2008

A global interaction between the solar wind with a southward interplanetary magnetic field (IMF) and the magnetosphere is studied using a semi‐global simulation model. A magnetic flux tube in which field lines are twisted is created as a result of repeated reconnection between the IMF and the outermost earth‐rooted magnetic field near the equatorial plane and propagates to higher latitudes. When crossing the polar cusp, the flux tube penetrates into the magnetosphere reiterating reconnection with the earth‐rooted higher latitude magnetic field, whereby solar wind particles are freely brought inside the magnetosphere. The flux tube structure has similarities in many aspects to the flux transfer events (FTEs) observed near the dayside magnetopause.
Laboratory formation of a simulated comet
Authors: Minami S. , Baum P. J. , Kamin G. , White R. S.
Published: February 2008

A laboratory simulation experiment to study the interaction between a cometary plasma and the solar wind has been performed using the UCR‐Tl space simulation facility (dia. 1.3m, length llm). Intense plasma flow simulating the solar wind interacts with another light‐emitting plasma composed of Ba, Sr, and/or C by a plasma emitter which simulates a cometary coma. The purposes of this experiment are to investigate how the solar wind parameters contribute to the formation of the cometary ion tail and to determine the magnetic field structure of a comet. In order to estimate the solar wind parameters by ground‐based observations of actual comets, knowledges of such relationships are essential. Our experimental results show that the interplanetary magnetic field (IMF) of the solar wind is very important in forming the cometary tail. The origin of the so‐called "tail rays" and the magnetic field structure in a simulated cometary ion tail are introduced.
Bookshelf tectonics: Rotated crustal blocks within the Sovanco Fracture Zone
Authors: Cowan Darrel S. , Botros Mona , Johnson H. Paul
Published: February 2008

The 15 kilometer wide Sovanco Fracture Zone is a dextral‐slip transform fault linking the Juan de Fuca and Explorer Ridges in the N.E. Pacific. SEABEAM bathymetry shows that the Sovanco comprises several rhomb‐shaped elevated blocks of oceanic crust bounded by northeast‐ and northwest‐trending lineaments. We hypothesize that the northeast‐trending lineaments are sinistral strike‐slip faults that are reactivated ridge‐parallel normal faults. Both the sinistral block‐bounding faults and the blocks themselves have rotated clockwise about 30 degrees in response to dextral shear within the Sovanco zone.
Earthquakes related to active salt doming near Kulyab, Tadjikistan, USSR
Authors: Leith William , Simpson David W.
Published: February 2008

In the region near Kulyab, Tadjikistan, hundreds of shallow earthquakes with magnitudes greater than 2½ have been reported in Soviet yearly catalogs since 1964. This area appears as a well‐defined cluster of activity, distant from the line of epicenters that defines the Gissar‐Kokshal seismic zone, to the north of the Pamir ranges. The geology of this region is dominated by the presence of numerous salt domes, surrounded by Neogene and Quaternary continental deposits. The spatial relationship between these earthquakes and the salt domes suggests that the two phenomena may be related. Moderate earthquakes (M > 5) occurred in 1972 and 1973, and intensities of surface shaking greater than MM=6 were reported from earthquakes in 1937, 1952, 1969, 1972, 1973 and 1978. The earthquake on 2 April 1973 and its aftershocks were located in a region where no salt domes have been mapped at the surface. However, a buried salt diapir has been mapped at depth by geophysical means. These earthquakes may result from active salt diapirism at depth. The mechanism for producing this seismicity could be either the active fracturing of the cap rock by the rising diapir, or the concentration of tectonic stresses in the thinned section above and adjacent to the diapir. The salt‐related earthquakes may produce lower frequency radiation than other events of the same size.
The Venus ultraviolet aurora: Observations at 130.4 nm
Authors: Phillips J. L. , Stewart A. I. F. , Luhmann J. G.
Published: February 2008

Continuous and highly variable emissions at 130.4 nm are observed on the night‐side of Venus by the Pioneer Venus Orbiter ultraviolet spectrometer. The emissions have a typical intensity of 10‐20 R, occasionally exceed 100 R, and have a dawn‐dusk asymmetry in brightness during periods of unusual intensity. A possible energy source for this "aurora" is the precipitation of suprathermal electrons. Field and particle observations suggest an additional source for the brightest emissions which is associated with solar flares and/or interplanetary shocks.
Comment on the Paper “On the influx of small comets into the Earth's upper atmosphere I. Observations”
Authors: Chubb Talbot A.
Published: February 2008

Arguments are presented that the evidence for euv dayglow holes (Frank et al., 1986a) is best interpreted as an instrumentation artifact. The main arguments are that: (1) The holes are seen in several data streams derived from a single photomultiplier, a single "Signal Conditioner" circuit, and a single "PM Tube Protection Circuit". These common elements might be a source of cosmic ray‐induced transients which interfere with the two data accumulation registers which they feed. (2) Most holes are single data words differing from normal data words by a single bit. (3) Holes seen at apogee are not distinct in signature from lower altitude observations, despite a requirement for a longer duration data even if the same physical event were observed at lower altitude. (4) Most holes look the same in the scan direction as compared with a direction orthogonal to the scan, which is, on the average, impossible if the geophysical interpretation is valid.
The structure of a cometary Type I tail: Ground‐based and ice observations of P/Giacobini‐Zinner
Authors: Slavin J. A. , Goldberg B. A. , Smith E. J. , McComas D. J. , Bame S. J. , Strauss M. A. , Spinrad H.
Published: February 2008

The in situ magnetic field and plasma measurements from the International Cometary Explorer (ICE) Mission obtained on September 11, 1985 are compared with CCD images of P/Giacobini‐Zinner (G‐Z) acquired with the 3.6 m Canada‐France‐Hawaii Telescope (CFHT) on Mauna Kea, Hawaii and a slit spectrogram from Lick Observatory during the same period. The CFHT image at ∼3.5 hr after the ICE encounter showed a short central ion tail with a diameter of ∼3 × 10³ km and a length of ∼2 × 104 km as observed in the H2O+ bandpass centered at 7025 Å. There was no distinct evidence of fine structure or ray activity. The Lick spectrogram of the H2O+ emissions taken ∼0.5 hr post‐encounter with the slit perpendicular to the sun‐comet line showed an ion tail with a diameter of 1.2 × 104 km. The ICE observations revealed a well defined 9.6 × 10³ km diameter magnetotail composed of two magnetic lobes in pressure equilibrium with a high beta central plasma sheet. These differing measures of tail width are found to be mutually consistent if the ion emissions observed at Earth originate in a slab‐shaped plasma sheet whose orientation is controlled by the direction of the interplanetary magnetic field. The results of this study also suggest that some thinning and thickening of cometary type I tails, usually attributed to plasma instabilities, may be due to changes in the angle at which the plasma sheet is viewed as IMF direction varies.
Comparisons of horizontal and vertical velocity spectra in the mesosphere, stratosphere and troposphere: Observations and theory
Authors: Gage K. S. , Balsley B. B. , Garello R.
Published: February 2008

Simultaneous observations of oblique and vertical velocities using the Poker Flat MST Radar are analyzed to determine spectra of horizontal and vertical motions in the upper troposphere, lower stratosphere and mesopause region. These spectra are compared with predictions from an internal wave spectral model and significant discrepancies are found. These discrepancies raise important questions regarding the interpretation of the observed spectra solely in terms of internal waves.
On the existence of an extraterrestrial source of water vapor in the middle atmosphere
Authors: Reid George C. , Solomon Susan
Published: February 2008

Observations of the ultraviolet dayglow of atomic oxygen from the DE‐1 spacecraft (Frank et al., 1986a,b) have revealed the existence of frequent localized decreases ("holes") in the emitted intensity. These have been interpreted as evidence of a steady influx of small "comets" whose icy envelope would provide a source of H2O molecules in the upper thermosphere. Using a one‐dimensional model of middle‐atmosphere composition, we show that the mesospheric water‐vapor concentration implied by this influx is much larger than the range of observed values.

We suggest that the entry of such an icy object into the atmosphere at meteoric speeds is likely to lead to dissociation of H2O molecules, and to a primary downward flux of OH rather than H2O. This would reduce significantly the predicted increase in H2O concentrations in the mesosphere, and would introduce a different mechanism for the production of the airglow holes, i.e., chemical destruction of atomic oxygen by the fast reaction with OH.

The constraints imposed on this scenario by the mesospheric water‐vapor measurements are examined, and we conclude that the permissible flux is some 30 times smaller than that proposed by Frank et al. The individual airglow holes would then have diameters of order 10 km instead of 50 km, and would be much less intense as seen by the DE‐1 instrument than those reported. We conclude that the mechanism, though relaxing the constraints on extraterrestrial water fluxes considerably, falls well short of explaining the observations.
Electrostatic charging and dust transport at Mercury's surface
Authors: Ip W.‐H.
Published: February 2008

A consideration of the presence of energetic charged particles in the magnetosphere of Mercury and their direct interaction with the planetary surface leads to the tentative conclusion that the nightside hemisphere could be occasionally charged to a surface potential of a few kilo‐Volts. This electrostatic charging process, if feasible, would further imply that electrostatic transport of sub‐micron dust particles on the surface of Mercury could play a significant role in the evolution and modification of the surface dust layer. Electromagnetic perturbation on the motion of the charged sub‐micron ejecta from meteoroid impacts could also lead to the development of a tenuous dust coma or dust tail near Mercury.
Comment on the Letter “On the influx of small comets into the Earth's upper atmosphere, II. Interpretation”
Authors: Nakamura Yosio , Oberst Jürgen , Clifford Stephen M. , Bills Bruce G.
Published: February 2008

The interpretation of the ‘atmospheric holes’ in terms of an influx of comet‐like objects is difficult to reconcile with the fact that the lunar seismic network, set up during the Apollo project, did not detect the postulated influx of such objects.
The final warming and polar vortex disappearance during the Southern Hemisphere spring
Authors: Newman Paul A.
Published: February 2008

Seven years (1979‐1985) of NMC data are used to analyze Southern Hemisphere middle stratosphere winter‐to‐summer circulation transitions. These transitions are classified into two extreme categories: 1) a mid‐October final warming accompanied by a major mid‐October wave event (1979 and 1982), and 2) a mid‐November final warming with no strong October wave event (1980 and 1981). After the final warming a wave event in late November‐early December results in the disappearance of the polar vortex. All of these wave events in conjunction with zonal mean mass motions act to reduce zonal mean gradients of potential vorticity and ozone through horizontal mixing, and hence they act to destroy the vortex and fill the ozone hole. Additionally, it is noted that the final warming and the vortex breakdown are two distinct events separated by 15‐40 days. Finally, past studies show that the time of these events has not radically changed.
A GCM simulation of the ozone seasonal variations at high latitudes in the Southern Hemisphere
Authors: Cariolle D. , Déqué M. , Morcrette J.‐J.
Published: February 2008

A General Circulation Model is used to simulate the O3 seasonal variations in the Southern Hemisphere at high latitudes. The model reproduces many features of the stratospheric circulation and the ozone distribution.

In particular a very cold and intense polar vortex develops from mid‐winter through spring and lasts until early November. The ozone content is minimum in the polar vortex, below 300 Dobsons, in spring. This value is still significantly higher than the amounts near 200 Dobsons recently measured in several Dobson stations in Antarctica. The possible deficiencies of the model photochemistry responsible for this discrepancy are discussed.

The rapid polar ozone increase which follows the final warming is fairly well reproduced by the model. The warming starts in early November and is associated with an increase of the planetary wave 1 amplitude beyond 60° of latitude. The polar vortex follows a westward trajectory which starts from the pole and crosses over the Argentine Islands before vanishing at midlatitudes, in good agreement with observations.
Low‐latitude ionospheric disturbances: Results for March 22, 1979, and their general characteristics
Authors: Tanaka T.
Published: February 2008

Low‐latitude ionospheric disturbances, which were characterized by severe scintillations in the C‐band range accompanied by complex dynamical behavior of the low‐latitude ionosphere, were examined, taking into consideration previous results. From the analyses of foF2 and h′F data, these disturbance events are found to be characterized by a two‐stage process. During the first stage, which starts during the magnetospheric energy storage process before the onset of substorms, h′F begins to increase simultaneously at all observing stations due to eastward electric fields penetrating from the magnetosphere. At subequatorial stations, increases of foF2 follow as a signature of enhancements of the equatorial anomaly. During the second stage, values of h′F increase again, indicating a motion from north to south, with no increase of foF2. In this stage, dynamical effects including neutral winds become important, as well as electric fields. In addition, it is shown from the analysis of one year's data for 1978 that the occurrence of disturbance events as presented in this paper is a general feature in the evening section under the condition of ring current developments.
First paleomagnetic results from Neocene Formations in Evia, Skyros and the Volos Region and the deformation of Central Aegea
Authors: Kissel Catherine , Laj Carlo , Mazaud Alain
Published: February 2008

Paleomagnetic results from Neogene volcanic and sedimentary formations in central Aegea indicate that Evia and Skyros have undergone a 48° and 26° clockwise rotation respectively. The Volos region does not show any significant rotation in the last 3 Ma. The rotation of Evia is about twice as large as the one measured from coeval formations in the external Hellenic arc. The results are interpreted in terms of a published model of distributed deformation by faulting, which also provides an explanation for the significant differential rotation of Evia and Skyros.
Strong anisotropic flow in a finely layered asthenosphere
Authors: Honda Satoru
Published: February 2008

We derive the long wave length equivalents of the constitutive relations for finely stratified fluids as suggested by Saito and Abe [1984]. The results show the transversely isotropic relations characterized by two effective viscosities. One is associated with shear stress applied on the plane parallel to the layering and the other is with normal stress applied perpendicular to the layering. If thin soft layers exist in the low velocity zone, there may be a significant difference in these two viscosities. A simple calculation simulating mantle flow with large apparent anisotropy shows the possible existence of convection having large aspect ratio.
Interpretation of the D″ zone at the base of the mantle: Dependence on assumed values of thermal conductivity
Authors: Brown J. Michael
Published: February 2008

A common assumption in modeling dynamic processes in the earth's lower mantle is that thermal conductivity is sensibly constant throughout the lower mantle and equal to approximately 4 W m−1 K−1. This value is the result of extrapolation using a linearized theory with estimated parameters for lattice contributions to thermal conductivity. Furthermore, this value is highly dependent on the assumed geotherm. Excluding theoretical uncertainties in the extrapolation, recent experimental data for the pressure dependence of conductivity coupled with a revised geotherm lead to substantially higher estimated values for the lower mantle. The hypothesis that the seismically resolved anomalous zone at the base of the mantle (D″) is a thermal boundary layer can be questioned in this case of a higher estimation for thermal conductivity.
Steady surficial core motions: An alternate method
Authors: Voorhies Coerte V.
Published: February 2008

A new method for deriving steady surficial core motions from geomagnetic field models is presented and applied. The original method determines the steady velocity field at the top of a frozen‐flux core which best fits, in both the spatial and temporal linear least squares sense, a model of the large scale geomagnetic secular variation (SV) at the base of a source‐free mantle [Voorhies, 1986]. The new method is based upon the same physical assumptions, but fits SV at earth's surface instead of the core‐mantle boundary (CMB). The newly derived flow differs somewhat from prior solutions, and shows but slight westward drift; however, other key global properties are virtually unchanged. Over a 15 year interval the new method provides a better fit to the time‐varying geomagnetic field at earth's surface than does the old.
Geodetic measurements of plate motions across the central Gulf of California, 1982‐1986
Authors: Kasser M. , Ruegg J.‐C. , Lesage Ph. , Ortlieb L. , Pagarete J. , Duch N. , Guerrero J. , Roldan J.
Published: February 2008

A trilateration network was set up in early 1982 by a team of French and Mexican institutions across the central part of the Gulf of California in order to study the plate boundary related movements in this transition area between the San Andreas fault system and the East Pacific Rise. The reobservation of this network in March 1986 provides a first set of data on the present day deformations in this area. Both surveys used AGA8 Laser geodimeter measurements between 11 stations located on elevated points of Baja California and Sonora and on the islands between the peninsula and mainland coasts. Deformation patterns during the 1982‐1986 interval, obtained through three different methods indicate mainly a right lateral shear movement in the Gulf axis direction N46°W. Between Baja California Peninsula and Angel de la Guarda Island 17 ± 4 cm of dextral slip occurred. Between the coast of Sonora and the central islands of the Gulf the mean displacement amount to about 23 ± 12 cm. In the southwestern part of the network, weaker movements seem to have occurred, and are smaller than estimated errors. This may indicate either that the boundary is locked in this part or is deflected towards the ESE. These results, which give an estimation of the relative plate velocity of 8 ± 3 cm/a, are consistent with the generally accepted relative movement between North American and Pacific plates (about 6 cm/a).
Climatic warming and basal melting of large ice sheets: Possible implications for east Antarctica
Authors: Saari Marc R. , Yuen David A. , Schubert Gerald
Published: February 2008

Climatic warming is shown to be capable of inducing shear heating instability and basal melting in a model ice sheet that is creeping slowly downslope. Growth times of the instability are calculated from a nonlinear analysis of temperature and flow in the model ice sheet whose surface undergoes a prescribed increase of temperature. The source of instability lies in the decrease of maximum ice thickness for steady downslope creep with increasing surface temperature. A surface temperature increase of 5 to 10 K can cause instability on a 104 year time scale for realistic ice rheology. The instability occurs suddenly after a prolonged period of dormancy. The instability might be relevant to the East Antarctic ice sheet. Warming associated with the Holocene interglacial epoch that heralded the end of the last ice age may have set the East Antarctic ice sheet on a course toward widespread instability some 104 years later. The present CO2‐induced climate warming is also a potential trigger for instability and basal melting of the East Antarctic ice sheet.
Observations of HF‐enhanced ion waves in the ionosphere
Authors: Djuth F. T. , Jost R. J. , Ierkic H. M. , Sulzer M. P. , Noble S. T.
Published: February 2008

A 138.8 MHz backscatter radar has been deployed at Arecibo Observatory in Puerto Rico to monitor modifications to the ionospheric F region produced by a high‐power, HF (3‐5 MHz) radio wave. This radar provides a new diagnostic tool for examining wave production in the plasma at long (∼ 1 m) wavelengths. When high‐power radio waves are transmitted, strongly enhanced ion‐acoustic waves are detected. The temporal development of the HF‐enhanced ion waves at 138.8 MHz exhibits an "overshoot" behavior similar to that of HF‐induced Langmuir waves and ion waves monitored in the past with the Arecibo 430 MHz radar.
Heat flow, heat production and granite depth in western France
Authors: Vigneresse J. L. , Jolivet J. , Cuney M. , Bienfait G.
Published: February 2008

Newly measured heat flow and full heat production determinations over the Armorican Massif, Western France, are tested against a linear relationship as proposed through Birch's law. The data do not fit a strict linear relationship but are within an elongated cluster which can be approximated (in mW/m² and km) by: These parameters are compared with those of surrounding Hercynian regions. Data from the Central Massif and previously failed to fit any linear relationship. Data for Scotland and Southern England could not be fitted to a single line. However, the present data and those from Southern and Central England do fit a single line, suggesting that the three regions form a single geothermal province. The depth parameter is greater than the root depths of the granitic plutons, indicating that heat sources can exist at depths below the granitic intrusions. The deep crustal structure revealed from seismic studies agrees with the radiogenic elements distribution deduced from thermal data.