bluuebunny/crossref_metadata_2025 huggingface dataset:
Luni‐solar periodic components in precipitation data
Authors: Cevolani G. , Bonelli P. , Isnardi C.
Published: February 2008

Evidence of a tidal influence from luni‐solar gravitational fields has been high‐lighted by analysing daily precipitation data collected at many stations in the Alps and the Po Valley (Italy) over the 1970‐81 period. Tidal influence as the possible result of a modulation effect caused by luni‐solar cycles having similar lengths, does not appear to be strictly constant over time. Time variations in daily precipitation data as a function of some particular cycles show that gravitational tides affect heavy precipitation more than mean precipitation values. "Semi‐monthly" oscillations have been derived from trends in daily precipitation data grouped according to the age of distinct lunar months. The investigation of the combined effects of different luni‐solar components, relating to years of particular climatological interest, might assist in the prediction of extreme precipitation.
Observations of comet Halley at Hα and 6300 Å
Authors: Kerr R. B. , Tepley C. A. , Cageao R. P. , Atreya S. K. , Donahue T. M. , Cherchneff I. M.
Published: February 2008

A small aperture telescope has been used with the Fabry‐Perot interferometer at the Arecibo Observatory to make high spectral resolution measurements of Comet Halley emissions at 6562.72 Å (Hα) and 6300.30 Å (O¹D). Observations in March, 1986, are characterized by a highly structured spectral signature at Hα. The Hα spectra imply non‐isotropic outflow of hydrogen atoms following dissociation of the parent species. The Hα surface brightness for a 5′.9 field of view centered on the comet head was 59 ± 13 rayleighs(R) on March 12, 1986, decreasing to 25 ± 6R on March 23 (after correction for atmospheric extinction). Calculation of atomic hydrogen production rates and outflow velocities is not straightforward due to the non‐isotropic nature of the atomic hydrogen outflow. The O(¹D) emission at 6300.3 Å was accompanied by a feature at 6300.8 Å that we attribute to NH2. The brightness of the O(¹D) emission for a 6′ field of view was 260 ± 50 R on March 15 and 17. This brightness decreased by a factor of about 2 when the comet was viewed with a 5′.9 field of view centered 6′ off the comet nucleus (sunward or tailward). The width of the O(¹D) emission line was 3.9 ± 1.5 kms−1 on March 15, and 7.4 ± 2.2 km s−1 on March 17. The O(¹D) spectral line profiles on March 17 were skewed to the red side of line center.
On the heating of electrons in the tail of Giacobini‐Zinner
Authors: Marconi M. L.
Published: February 2008

The temperature and density of electrons are computed for Comet Giacobini‐Zinner, and are compared with ICE observations. The computations differ from the previous model of Marconi and Mendis [1986a] in that very recently calculated cooling rates are employed and the photo‐electron collisions with neutrals are treated separately from the thermalized electrons. While Marconi and Mendis [1986a] obtained electron temperatures and densities which were high relative to ICE observations, the present calculation yields temperatures which are low relative to the ICE observations, but densities which are consistent with the observations. Plasma dissipative processes in the tail are suggested as a significant additional heat source.
Observational constraints on interchange models at Jupiter
Authors: Richardson John D. , McNutt Ralph L.
Published: February 2008

Data from the Voyager plasma science instrument is used to set limits on transport models for the inner Jovian magnetosphere. The instrument has an effective time resolution for detecting changes in density of 0.24 s, which corresponds to a spatial resolution of about 20 km (equal to the gyroradius of an oxygen ion) in the region just outside of Io. This resolution enables us to put an upper limit of about 10% on changes in density between adjacent magnetic flux tubes, which rules out transport models which invoke inward motion of near empty flux tubes to replace outward‐moving flux tubes carrying Iogenic plasma.
Ozone isotope measurements in the stratosphere
Authors: Mauersberger K.
Published: February 2008

Mass spectrometer measurements of ozone made during two balloon flights included its heavy isotopes at mass 49 and 50. Both flights were flown during the day and during summer from Palestine, TX. At float altitudes above 42 km the enrichments in heavy ozone were 41% and 23%, respectively. The enrichment appears to be mass independent since, at high altitudes, both 49 and 50 show the same enhancement. During the descent the enrichment in heavy ozone decreased, faster during the first flight than during the second, reaching values between 15 and 20% above 30 km. Near and below this altitude another increase is observed. During a night flight, previously reported, an enhancement in heavy ozone of over 40% at 32 km was found, decreasing both toward higher and lower altitudes.
Strong loop heating by the fast reconnection in a closed system
Authors: Ugai M.
Published: February 2008

It is numerically shown that the fast reconnection in a closed system gives rise to strong heating of a magnetic loop. The supersonic plasma jet resulting downstream of the slow shocks collides with the loop and is effectively converted into plasma heating by the fast shock standing in front of the loop. The heated plasma (by a factor of more than 10) is accumulated in the loop head and is finally distributed along the loop boundary.
Stochastic acceleration of cometary ions by lower hybrid waves
Authors: Buti B. , Lakhina G. S.
Published: February 2008

The turbulence produced by lower hybrid waves, during interaction of solar wind with the cometary pick‐up ions, leads to stochastic acceleration of these ions. The resulting energies of the cometary ions, calculated on the assumption that the entire turbulent electric field is used up for accelerating particles, are much larger compared to the recently observed energies of water‐group ions in the vicinity of comets Halley as well as Giacobini‐Zinner. Accounting for the fact that only a fraction of the field would lead to acceleration and the rest to heating, lower hybrid waves seem to be a potential source for the observed energetic cometary ions.
The minimum bandwidths of auroral kilometric radiation
Authors: Baumback M. M. , Calvert W.
Published: February 2008

The bandwidths of the discrete spectral components of the auroral kilometric radiation can sometimes be as narrow as 5 Hz. Since this would imply an apparent source thickness of substantially less than the wavelength, it is inconsistent with the previous explanation for such discrete components based simply upon vertical localization of a cyclotron source. Instead, such narrow bandwidths can only be explained by radio lasing.
Heterogeneous chemical reaction of chlorine nitrate and water on sulfuric‐acid surfaces at room temperature
Authors: Rossi Michel J. , Malhotra Ripudaman , Golden David M.
Published: February 2008

It has been demonstrated that the reaction between gaseous chlorine nitrate and water on room temperature liquid sulfuric acid (95.6%) surfaces yields hypochlorous acid in the gas phase. First‐order loss rate constants for chlorine nitrate (equivalent to a value of the sticking coefficient γ = 3.2 × 10−4) have been determined. This value is five orders‐of‐magnitude greater than reported values on similar areas of more inert surfaces. Application of results of this type to stratospheric models must await ongoing studies at lower temperatures.
The 1942 Southwest Indian Ocean Ridge Earthquake: Largest ever recorded on an oceanic transform
Authors: Okal Emile A. , Stein Seth
Published: February 2008

The 1942 Southwest Indian Ocean earthquake is the largest ever recorded on an oceanic transform. Its mechanism has essentially the expected pure strike‐slip geometry. Using long‐period surface wave techniques, the seismic moment is found to be 1.3 × 1028 dyn‐cm; directivity suggests southwestward rupture propagation over approximately 130 km. This shock is then much smaller than previously reported on the basis of its high unified Richter magnitude (M = 8.3). It does not show the slow energy release occasionally found in large transform fault events. Scaling laws and thermal modeling suggest that seismic slip extended at least to the 600° C isotherm.
Reply to Kamide and Richmond
Authors: Foster J. C.
Published: February 2008

Detailed empirical models of the ionospheric convection electric field and auroral‐latitude conductance are used to show that at 04 magnetic local time (MLT) the electric field magnitude peaks at least 5° poleward of the Hall conductance and is the stronger contributor to the poleward half of the westward electrojet current in the morning sector. At 20 MLT the eastward electrojet current is centered on the electric field and conductance profiles, which have a similar peak latitude and extent.
Source‐surface model of the magnetosphere
Authors: Schulz Michael , McNab Michael C.
Published: February 2008

A new concept for modeling a planetary magnetosphere is implemented by juxtaposing the sunward portion of the magnetosphere (in which the magnetic field
is expressed formally as an analytical expansion) and the tail region (in which field lines are constructed geometrically). The expansion coefficients for the sunward region are determined by means of a variational principle, according to which a user‐specified linear combination of the mean‐square normal component of
on the prescribed magnetopause and the mean‐square tangential component of
on the innermost cross‐magnetospheric surface normal to the tail field lines must be minimized. The contour of vanishing normal component of
on this latter surface corresponds to the inner edge of the neutral sheet in the planetary magnetotail. In its present form the source‐surface model accommodates an arbitrary angle of incidence between the solar‐wind velocity and the planetary magnetic‐dipole moment.
Linear relationship between heat flow and heat production in Panxi Paleorift Zone, southwestern China
Authors: Wang Ji‐yang , Huang Shao‐peng
Published: February 2008

The Panzhihua‐Xichang (Panxi) area of southwestern China (approximately 26°00′N to 28°48′N and 101°00′E to 103°00′E) is a paleorift zone of Hercynian age. The last major tectono‐thermal event occurred 200 to 250 Ma ago with extensive basaltic eruptions. Regional surface heat flow values vary from 40 to 90 mW/m² with the average of 63±15 mW/m². The U, Th contents increase with the acidity of igneous rocks. The highest contents (U 9.57 ppm, Th 27.67 ppm) are observed in biotite granite. The U, Th contents are well correlated with each other and the correlation coefficient is 0.9646, indicating the poor migration of U in epimagmatic state. On the basis of heat flow and heat production data, a linear relationship was obtained for the region.
A heat production model of a shield area and its implications for the heat flow ‐ Heat production relationship
Authors: Fountain David M. , Furlong Kevin P. , Salisbury Matthew H.
Published: February 2008

The Pikwitonei and Sachigo subprovinces of central Manitoba provide a cross‐sectional view of the Superior Province Crust. To constrain thermal models of the crust, we measured heat production and thermal conductivity in rocks from this terrain using standard gamma‐ray spectrometry and divided bar techniques. These data, when used in a two‐dimensional model of shield crust, show that estimates of surface heat flow and surface heat production yield the well‐known linear relationship between surface heat production and surface heat flow observed for heat flow provinces. This demonstrates that determinations of heat production with depth based on inversion of the linear heat production‐heat flow relationship are non‐unique.
Auroral intensifications in the evening sector observed by the Viking ultra violet imager
Authors: Shepherd G. G. , Anger C. D. , Murphree J. S. , Jones A. Vallance
Published: February 2008

The Ultra Violet Imager on the Swedish Viking spacecraft frequently detects localized intensifications in the evening sector that expand poleward at about 0.4 km/s and eastward at up to 7.8 km/s, stopping abruptly at midnight. The events occur in a previously quiet auroral oval and seem to be associated with the formation of discrete aurora. If westward travelling surges are associated with these intensifications, they must be too small in size to be detected by the imager. The events are rather frequent in time, and comparatively small in extent and duration on a global scale; however they would appear as substantial breakups when viewed overhead at a ground‐based station. Further study is needed to determine just how these events fit into the framework of currently existing substorm knowledge, and how they differ from the larger scale events observed by the imager.
High latitude currents in the 0600 to 0900 MLT sector: Observations from Viking and DMSP‐F7
Authors: Bythrow P. F. , Potemra T. A. , Zanetti L. J. , Erlandson R. A. , Hardy D. A. , Rich F. J. , Acuna M. H.
Published: February 2008

Magnetic field and charged particle measurements were acquired by the Viking and DMSP‐F7 satellites on March 25, 1986, as they traversed the dawn sector auroral zone on nearly anti‐parallel trajectories within 40 minutes of each other. Viking was at a geocentric distance of 3.1 Re, and DMSP‐F7 was at a geocentric distance of about 1.1 Re. Magnetic field measurements made by Viking at 0850 MLT and by DMSP at 0630 MLT indicated the presence of a large‐scale earthward‐directed region 1 current and an upward‐flowing region 2 Birkeland current. Both satellites observed a third Birkeland current adjacent to and poleward of the region 1 system with opposite flow. This poleward Birkeland current system is about 0.5° invariant latitude wide and has a current density comparable to the region 1 and 2 system (∼2.5 µA/m² when projected to a 800 km altitude). The similarity of the magnetic perturbations observed by these widely separated satellites supports the view that the associated Birkeland currents flow in sheets that extend over several hours of local time and that they comprise a large‐scale and stable feature of the magnetosphere‐ionosphere coupling system. As suggested by previous studies, we identify the upward‐flowing poleward Birkeland current as the “region 0” system. Charged particle data from both spacecraft show a sharp increase in the flux of electrons with energy > 2 keV at the equator‐ward edge of the region 1 current system. Cooler ( < 1 keV) and more structured electrons were observed poleward of this boundary. We conclude that the transition between region 2 and region 1 currents in these observations maps to the interface between the plasma sheet and a region of low energy particles with the characteristics of the low latitude boundary layer and that the region 1 and region 0 currents at higher latitudes map to this region.
Impulsive electrostatic waves and field‐aligned currents observed in the entry layer
Authors: Erlandson R. E. , Pottelette R. , Potemra T. A. , Zanetti L. J. , Bahnsen A. , Lundin R. , Hamelin M.
Published: February 2008

Impulsive electrostatic waves have been observed in regions of downward‐flowing region 1 Birkeland currents in data acquired by the High Frequency Wave and Magnetic Field instruments on the Viking satellite. These data were obtained at approximately 11,000 km altitude and in the 1100 MLT and 76° invariant latitude sector near the equatorward boundary of the dayside polar cusp. Wave and magnetic field data are presented from Viking orbit 1219 on October 1, 1986, and wave, magnetic field, and particle data acquired with the Hot Plasma instrument from orbit 1197 on September 27, 1986. The high frequency waves are observed between the electron plasma and cyclotron frequencies. Since the broadband electrostatic waves extend in frequency above the cold plasma frequency, a nonlinear treatment must be made to explain the observation. We suggest that electron acoustic waves may couple with other electron plasma waves, resulting in the distribution of wave power over a wide range of frequencies. A strong correlation exists between large‐scale downward‐flowing Birkeland currents (region 1 system) and impulsive electrostatic waves. The Viking Magnetic Field experiment allows one to resolve, in high time‐resolution, electron beams that may be unstable to the impulsive electrostatic waves.
Ion waves and upgoing ion beams observed by the Viking satellite
Authors: André Mats , Koskinen Hannu , Gustafsson Georg , Lundin Rickard
Published: February 2008

Simultaneous observations of waves and ion beams by the Viking satellite can be used to study wave‐particle interaction on auroral field lines. The characteristics of the observed beams may be rather stable during long periods, at least up to 20 minutes. However, the wave charateristics during such events may vary within seconds. Sometimes the wave experiment detects narrowband EHC waves, sometimes broadband emissions up to several times the proton gyro frequency, and sometimes just an increased level of turbulence. The variations of the wave characteristics may at least partly be due to variations in a cool, low density electron population.
Detection of spatial density irregularities with the Viking plasma wave interferometer
Authors: Kintner P. M. , Kelley M. C. , Holmgren G. , Koskinen H. , Gustafsson G. , LaBelle J.
Published: February 2008

The Viking spacecraft carried a plasma wave interferometer consisting of two Langmuir probes separated by 80 m. The interferometer has measured density irregularities in the frequency range 1‐200 Hz which can be interpreted as field aligned structures with phase velocities transverse to the geomagnetic field which are small compared to the spacecraft velocity relative to the plasma. The spatial structures which have nearly zero frequency in the plasma frame are Doppler shifted up to frequencies as large as 200 Hz in the spacecraft frame. The broadband amplitude of the density irregularities is typically .1% to .5%. The density irregularities appear to be a common feature of the high latitude ionosphere probed by Viking.
Analysis of Raman scattered LY‐α emissions from the atmosphere of Uranus
Authors: Yelle R. V. , Doose L. R. , Tomasko M. G. , Strobel D. F.
Published: February 2008

A line at 1280 Å, due to Raman scattering of solar Lyman alpha (Ly‐α) in the atmosphere of Uranus, has been detected by the Voyager Ultraviolet Spectrometer. The measured intensity of 40 ± 20 R implies that 200 R to 500 R of the measured 1500 R Ly‐α intensity at the sub‐solar point is due to Rayleigh scattering of the solar line. The presence of Rayleigh and Raman scattering at 1216 Å suggests that the Uranian atmosphere is largely devoid of absorbing hydrocarbons above the 0.5 mbar level. The most natural explanation of this depletion is very weak vertical mixing equivalent to an eddy coefficient on the order of 200 cm² s−1 between 0.5 mbar and 100 mbar.
On the polarization, compression and nonoscillatory behavior of hydromagnetic waves associated with pickup ions
Authors: Brinca Armando L. , Tsurutani Bruce T.
Published: February 2008

Newborn ions acquire highly unstable velocity distributions that, in the solar wind frame, might range from beam‐ to ring‐like. Solution of the kinetic dispersion equation shows that heavy pickup ions with large perpendicular energies excite a new hydromagnetic wave mode with maximum growth, high (magnetic field and mass density) compression ratios, and almost linear polarization coexisting slightly away (6° ‐ 15°) from parallel propagation. The mode arises from the coupling of the heavy ion beam to the modified left‐hand wave dispersion caused by the multi‐ion nature of the medium. The ion beam can also bring about nonoscillatory, purely growing structures distinct from the mirror wave through the coupling of a counter‐streaming left‐hand mode to a co‐streaming right‐hand wave. The free energy source parameters are varied to determine their relative influence and define the domain of existence of the instability. Its characteristics may prove helpful in the interpretation of recent cometary (Halley and Giacobini‐Zinner) and artificial release (AMPTE) observations.
Viking observations of auroral kilometric radiation from the plasmasphere to night auroral oval source regions
Authors: de Feraudy H. , Pedersen B. M. , Bahnsen A. , Jespersen M.
Published: February 2008

For two VIKING orbits crossing the night oval source region of Auroral Kilometric Radiation (AKR), we derive the AKR polarization from the cutoff‐frequencies and from the spin modulated pattern of the emission. The R‐X mode is predominant, but can be accompanied by L‐O mode and Z mode band. The Z mode is observed continuously from inside the plasmasphere to the AKR source region. An offset in the spin modulation pattern near the AKR source region during one of the orbits shows that steep gradients of the plasma density at the edge of the source region can play an important role for the orientation of the wave polarization plane or for the mode conversion.
The distribution function of diffuse ions and the magnetic field power spectrum upstream of Earth's bow shock
Authors: Möbius E. , Scholer M. , Sckopke N. , Lühr H. , Paschmann G. , Hovestadt D.
Published: February 2008

During two diffuse energetic ion events upstream of the Earth's bow shock with radial interplanetary magnetic field conditions comprehensive energy spectra of the protons and power spectra of the magnetic field fluctuations were obtained with the instrumentation on AMPTE/IRM. For diffuse ions a continuous distribution from ≈ 5 keV (starting above the solar wind energy) to the instrumental limit (230 keV/e) is found upstream and downstream of the shock. This strongly indicates a single source for the upstream diffuse ion population over the total energy range. Assuming that the ions are shock accelerated, an efficiency for the production of upstream energetic ions of ≈ 4 to 11% is found by comparing the energy flux densities of the energetic ions and of the incoming solar wind. The lower value is observed during the period with a low interplanetary magnetic field strength. The measured energy densities of the particles and the waves are compared with the self‐consistent model of Fermi acceleration by Lee (1982) which includes the coupled wave and particle behaviour. The theoretically predicted wave energy density is in excellent agreement with the observed wave energy density.
Observations of the spatial distribution of energetic O3+, O4+, and O5+ ions in the magnetosphere
Authors: Kremser G. , Stüdemann W. , Wilken B. , Gloeckler G.
Published: February 2008

The Charge‐Energy‐Mass Spectrometer CHEM on the AMPTE/CCE spacecraft provides measurements of oxygen ions with charge states between 1 and 6 in the magnetosphere close to the equatorial plane. The first investigations of the spatial distribution of O3+, O4+, and O5+ ions revealed that these ions are continuously present in the magnetosphere. Their L profiles exhibit broad maxima that are located at 6 ⩽ L ⩽ 7 for O3+ and O4+ and at 7 ⩽ L ⩽ 8 for O5+ ions during periods of low to medium geomagnetic activity (Kp < 4). With increasing Kp the flux versus L distributions extend further earthward and the maxima move to slightly lower L values. While the flux decrease earthward of the maximum is very steep, the gradual decrease outward of the maximum becomes flatter with increasing charge state. Comparison of these profiles to those of O+, O2+, and O6+ ions suggests that O3+, O4+, and O5+ ions are produced predominantly by charge exchange processes, and that the O4+ and O5+ ions are produced from the solar wind origin O6+. Our measurements of O3+ indicate that both the solar wind O6+ and the terrestrial ions O+ and O2+ contribute to the production of this ion species.
Melting experiment on a model chondritic mantle composition at 25 GPa
Authors: Ohtani Eiji , Sawamoto Hiroshi
Published: February 2008

We have conducted melting experiments on a chondritic mantle composition in the five‐component system CaO‐FeO‐MgO‐Al2O3‐SiO2 at 25 GPa. The liquidus phase at this pressure is majorite garnet, and the second crystallizing phase is Mg‐silicate perovskite or magnesiowustite; these phases seem to be consumed into the melt at almost the same temperature. The present experiments indicate that majorite garnet fractionation might have occurred in the chondritic primitive mantle, if the partial molten zone extended to a depth equivalent to the upper part of the lower mantle in the early stages of terrestrial evolution.
Azimuthal dependence in the gravity field induced by recent and past cryospheric forcings
Authors: Yuen David A. , Gasperini Paolo , Sabadini Roberto , Boschi Enzo
Published: February 2008

Present‐day glacial activities and the current variability of the Antarctic ice volume can cause variations in the long‐wavelength gravity field as a consequence of transient viscoelastic responses in the mantle. We study the azimuthal dependence of the secular variations of the gravitational potential and find that the non‐axisymmetric contributions are more important for recent glacial retreats than for Pleistocene deglaciation. Changes in land‐based ice covering Antarctica can be detected by monitoring satellite orbits and their sensitivity to variations in gravitational harmonic for degree l greater than 3. Resonances in satellite orbits may be useful for detecting these azimuthally‐dependent gravity signals.
Mm: Theory of a variable‐period mantle magnitude
Authors: Okal Emile A. , Talandier Jacques
Published: February 2008

We use classic expressions of the excitation and propagation of Rayleigh waves to develop a mantle magnitude Mm, measured at variable period between 40 and 300 s. We justify theoretically the use of distance and source excitation corrections, and obtain simplified expressions for them. We also explore the possible influence of the presence of a corner frequency in the spectrum. Finally, we relate frequency‐domain measurements to the standard practice of measuring magnitudes in the time domain, and justify the latter for wavetrains with strong dispersion.
A revised estimate of Pacific‐North America motion and implications for Western North America Plate boundary zone tectonics
Authors: DeMets Charles , Gordon Richard G. , Stein Seth , Argus Donald F.
Published: February 2008

For the past 20 years, much effort has been directed to determining the present‐day relative motion of the Pacific and North American plates using two independent approaches. One uses geologic observations and geodetic measurements along the San Andreas Fault and other faults in the plate boundary zone. The other is based on plate motion models that incorporate spreading rates from marine magnetic anomalies, transform azimuths, and earthquake slip vectors. Geologic and geodetic studies find two principal elements of deformation: slip along the San Andreas of ∼34 mm/yr directed N41°W, and extension across the Basin and Range province of about 10 mm/yr directed N56°W. In contrast, plate motion studies find 56‐60 mm/yr directed N35°W. The discrepancy between these estimates, a vector of about 15 mm/yr oriented nearly due north, is often attributed to a combination of slip along faults parallel to the San Andreas and shortening normal to it. Here we revise the estimate of Pacific‐North America motion by analyzing marine magnetic profiles from the Gulf of California. Since 3 Ma, spreading has averaged 48 mm/yr, 10 mm/yr slower than estimated before, and consistent with the 49 mm/yr spreading predicted by a new global plate motion model derived without any data along the Pacific‐North America boundary. The discrepancy with geodetic and geologic estimates is thus reduced to only 5 mm/yr parallel to the San Andreas, 60% less than estimated before, and 7 mm/yr of shortening across the San Andreas, similar to prior estimates. These results suggest that strike‐slip motion on faults west of the San Andreas is less than thought before, a conclusion consistent with geodetic, seismological, and other geologic observations.
Large F‐region electron‐temperature enhancements generated by high‐power HF radio waves
Authors: Djuth F. T. , Thidé B. , Ierkic H. M. , Sulzer M. P.
Published: February 2008

During recent experiments at Arecibo, Puerto Rico, large (1000‐2000 K) enhancements in electron temperature have been observed when high‐power radio waves reflect near the nighttime F region peak. The electron temperature enhancements are accompanied by significant (50‐300 K) increases in ion temperature, large (10‐15%) reductions in electron density, and strong HF‐induced spread F. When large electron temperature enhancements develop, the ionosphere appears to become dynamically unstable resulting in the production of geomagnetic field‐aligned striations having elevated electron temperatures and depleted electron densities.
Acceleration of cometary plasma in the vicinity of comet Halley associated with an interplanetary magnetic field polarity change
Authors: Verigin M. I. , Axford W. I. , Gringauz K. I. , Richter A. K.
Published: February 2008

Based on the ion plasma and magnetic field observations of Vega−1 near its closest approach to comet Halley a self‐consistent scenario is developed according to which the observed magnetic field topology, the observed burst of ions at energies 200–600 eV, and the observed directional dependence of the flow of these ions leads to the conclusion that these burst‐particles are cometary ions which have been accelerated by the process of merging of magnetic field lines of opposite polarity.
The variation of protons, alpha particles, and the magnetic field across the bow shock of comet Halley
Authors: Neugebauer M. , Neubauer F. M. , Balsiger H. , Fuselier S. A. , Goldstein B. E. , Goldstein R. , Mariani F. , Rosenbauer H. , Schwenn R. , Shelley E. G.
Published: February 2008

Data from the Ion Mass Spectrometer and the magnetometer on the Giotto spacecraft are used to examine the structure of the inbound crossing of the comet Halley bow shock on March 13, 1986. It is found that the velocity decrease, the field strength increase, and the heating of picked up cometary protons occurred over a broad region corresponding to several heavy‐ion gyroradii. The solar‐wind protons and alphas, on the other hand, were compressed and heated at a narrow structure, which might be called a subshock, on the leading edge of the broad shock region. The electrostatic potential difference across the shock was less than 40 V.
The magnetosphere as a source of energetic magnetosheath ions
Authors: Sibeck D. G. , McEntire R. W. , Lui A. T. Y. , Krimigis S. M. , Zanetti L. J. , Potemra T. A.
Published: February 2008

The dominant source of energetic ions upstream of the earth's bow shock remains controversial. Charge Composition Explorer (CCE) energetic (E > 10–15 keV) ion and magnetic field measurements near the spacecraft's 8.8 RE apogee during a period of greatly increased solar wind dynamic pressure on November 1, 1984 determine the sense of energetic ion streaming in the dayside magnetosphere, the magnetosheath, and the solar wind. The ions stream away from an appropriately compressed model magnetopause at all times in the magnetosheath and solar wind. The flux of energetic ions in the magnetosheath and solar wind rises to, but never exceeds, that in the magnetosphere. The observations are consistent with a magnetospheric, rather than a bow shock (Fermi acceleration) source for the ions in the magnetosheath during this event.
Electromagnetic fields from pulsed electron beam experiments in space: Spacelab‐2 results
Authors: Bush R. I. , Reeves G. D. , Banks P. M. , Neubert T. , Williamson P. R. , Raitt W. J. , Gurnett D. A.
Published: February 2008

During the Spacelab‐2 mission a small satellite carrying various plasma diagnostic instruments was released from the shuttle to co‐orbit at distances up to 300 m. During a magnetic conjunction of the shuttle and the satellite an electron beam modulated at 1.22 kHz was emitted from the shuttle during a 7 min period. The spatial structure of the electromagnetic fields generated by the beam was observed from the satellite out to a distance of 153 m perpendicular to the beam. Electromagnetic radiation at the fundamental and the harmonics of the modulation frequency was observed as well as broad‐banded electrostatic noise. The magnetic field amplitude of the strongest harmonics were comparable to the amplitude of simultaneously observed whistlers, while the electric field amplitudes were estimated to 1–10 mV/m. The observations are related to theories for radiation from pulsed electron beams.
The effect of cluster ions on anomalous VHF backscatter from the summer polar mesosphere
Authors: Kelley Michael C. , Farley Donald T. , Röttger Jurgen
Published: February 2008

Radar backscatter at 50 MHz from the summer polar mesosphere is sometimes much stronger than the scatter from other latitudes at any time or from polar latitudes in other seasons. Kelley and Ulwick [1987] suggested that heavy water cluster ions in this uniquely cold region of the atmosphere could be responsible because, in the presence of these ions, the enhanced, turbulence‐driven spectrum of the ionization irregularities could extend to considerably shorter wavelengths than that of the neutral turbulence itself. Here we explore this idea further and relate it to past and planned incoherent scatter measurements at EISCAT. These observations should be able to establish whether or not water cluster ions have an anomalously low diffusion coefficient.
Helium‐3 emission from Nevado Del Ruiz Volcano, Colombia
Authors: Williams Stanley N. , Sano Yuji , Wakita Hiroshi
Published: February 2008

High helium‐3/helium‐4 ratios, up to 6.6Ratm (6.6 times the atmospheric ratio of 1.40 × 10−6) were observed in nine samples of gases and hot waters from seven sites located around the volcano Nevado del Ruiz, Colombia. The values of the ratio decrease with distance from the crater. Such a tendency coincides well with the pattern first reported from the volcano Ontake, central Japan, and suggests a general signature of helium isotope ratios around individual volcanoes. The corrected helium‐3/helium‐4 ratios at one gas vent sampled twice over six months increased. This is interpreted to mean that the mantle contribution of helium may have increased with time.
Helium isotope evidence for magmatic gases in Lake Nyos, Cameroon
Authors: Sano Yuji , Wakita Hiroshi , Ohsumi Takashi , Kusakabe Minoru
Published: February 2008

We have measured ³He/4He and 4He/20Ne ratios of gas samples collected at Lake Nyos where a toxic gas disaster occurred on August 21, 1986 and at Lake Monoun in Cameroon, West Africa. The ³He/4He ratios, corrected for air contamination, are 5.39–5.75 Ratm (where Ratm is the atmospheric ratio of 1.40 × 10−6) for Lake Nyos and 3.56 Ratm for Lake Monoun. The data suggest a significant contribution of mantle‐derived helium in these Cameroon volcanic crater lakes. The origin of CO2 gas “erupted” during Lake Nyos disaster is inferred to be of magmatic origin based on the high ³He/4He ratio.
A continuing intraplate earthquake sequence near João Câmara, northeastern Brazil‐Preliminary results
Authors: Ferreira Joaquim M. , Takeya Mário , Costa João M. , Moreira José A. , Assumpção Marcelo , Veloso José A. V. , Pearce Robert G.
Published: February 2008

Shallow seismicity along a well‐defined section of reactivated Precambrian basement near João Câmara, Brazil (5.5°S, 33.7°W) has continued since August 1986. A magnitude 4.3 event on 21st August with a decaying aftershock sequence and another main shock‐aftershock sequence which started in September were followed by a magnitude 5.1 event on 30th November and 11 events of magnitude 4 or above up to February 1987. A network of up to four vertical component short period seismometers with smoked paper recorders has been deployed since late August 1986. Several thousand events have been recorded above magnitude 0, and activity was still being recorded (about 10 events per day) in May 1987. Simple velocity structure, good transmission and impulsive S arrivals on almost all seismograms combine to facilitate reliable hypocentral locations even for this sparse network, and epicenters define a 25 km linear pattern of seismicity with northeasterly strike, approximately coincident with a Precambrian structural trend. A composite fault plane solution shows dextral shear along this strike with a small normal component. Fault plane solutions and epicenter distribution in Northeastern Brazil suggest an overall picture of E‐W regional compression.
Statistical methods for describing seafloor topography
Authors: Shaw Peter R. , Smith Deborah K.
Published: February 2008

We present a method for objectively characterizing a swath of digitally sampled seafloor topography. Our method analyzes the distribution of surface slopes by compiling surface‐normal vectors into a two‐dimensional histogram using an equal‐area projection. The direction of maximum variance (first principal axis) of the histogram is used to determine the azimuth of lineations in the topography, and the variance is used as a measure of seafloor roughness. We apply the method to short sections of Sea Beam swath data and find that the histogram parameters are effective in describing the behavior of the topography. In particular, similar patterns are observed for a sequence of histograms derived from data collected over the Mendocino and the Surveyor fracture zones in the northeast Pacific. Because the method does not require any data modification and is suitable for irregularly‐shaped sample regions, it lends itself to real‐time analysis.
Anisotropy of electron temperature in the ionosphere
Authors: Oyama Koh‐ichiro , Abe Takumi
Published: February 2008

Electron temperature was measured by means of planar probes on Japan's ninth scientific satellite OHZORA. The measurement, which was carried out simultaneously both along and vertical to the geomagnetic line of force, showed anisotropy of electron temperature. The temperature of the electrons along the geomagnetic field, T∥, is very often higher than the temperature of electrons collected by the electrode whose normal is perpendicular to the geomagnetic field, T⟂. Anisotropy increases as we move to higher geomagnetic latitudes. Anisotropy occurs more often in the early morning than at any other time of day. There is also a tendency for anisotropy to occur more often at lower altitudes.

It is suggested that the existence of anisotropy of electron temperature can explain some puzzling phenomena that have previously not been explained.
New types of spherules from Antarctica: Meteoritic impact origin?
Authors: Tazawa Yuji , Fujii Yoshiyuki
Published: February 2008

Spherules collected form Antarctic ice have been studied by using instrumental neutron activation analysis, energy dispersive X‐ray spectrometry and X‐ray diffration photography. Peculiar spherules, Ca‐Ti‐rich (perovskite) type (CTS) and Fe‐Cr‐Ni‐rich type (FCN), were found in the Mizuho ice core at depths of 32 to 33.5 m. Both types have rare earth element (REE) abundances; i.e., significant relative enrichment of light REE over heavy REE, which is commonly seen for terrestrial perovskite, however, with anomalous enrichment of Nd and Sm. In the Allan Hills bare ice, only a "chondritic" type without depletion of Au and S (CAS) was recognized. Size distributions and influx rates of spherules for these ices and the Mizuho surface snow indicate that Antarctic spherules are composed of steady‐falling and occasional populations. All the results combine to suggest that CTS and FCN may be droplets strewn by the impact of a huge meteorite, and CAS must be debris from one of the chondrites that fell on the source region of the Allan Hills bare ice and survive terrestrial alterations.
Antarctic ozone: Meteoric control of HNO3
Authors: Prather Michael J. , Rodriguez José M.
Published: February 2008

Atmospheric circulation leads to an accumulation of debris from meteors in the Antarctic stratosphere at the beginning of austral spring. The major component of meteoric material is alkaline, comprised predominantly of the oxides of magnesium and iron. These metals may neutralize the natural acidity of stratospheric aerosols, remove nitric acid from the gas phase, and bond it as metal nitrates in the aerosol phase. Removal of nitric acid vapor has been previously shown to be a critical link in the photochemical depletion of ozone in the Antarctic spring, by allowing for increased catalytic loss from chlorine and bromine.
Methane and carbon dioxide increases in the urban boundary layer: Inferences from whole‐column infrared absorbance measurements
Authors: Gurney K. R. , Hansen A. D. A. , Rosen H.
Published: February 2008

Using the sun as an infrared source, we determined the total atmospheric column absorbance of methane and carbon dioxide spectral lines in the 8‐ to 10‐µm infrared region. At our laboratory located in an urban region, these absorbances showed fluctuations larger than can be accounted for by known variabilities in the background atmosphere. We interpret these observations in terms of large changes in concentration of methane and carbon dioxide within the urban boundary layer. These increases could affect the radiative balance in urban locations and contribute to the urban heat island.
Anisotropy of the asthenosphere: The higher mode data of the Pacific revisited
Authors: Cara M. , Lévêque J. J.
Published: February 2008

Surface‐wave data previously used by the authors to constrain upper mantle anisotropy in the Pacific Ocean are re‐examined after an error was found in the calculations of the Love‐wave phase‐velocities. Sub‐lithospheric anisotropy is still required by the corrected data but it extends to shallower depth than we originally proposed. Using different parameterizations of the upper‐mantle, we present strong evidence that the bottom of the anisotropic layer has been reached around 250 km in the Pacific. Beneath North‐America, no revision of our data is required and anisotropy could extend to around 400 km‐depth. Our results are in agreement with an upper mantle anisotropy due to preferred orientation of olivine crystals in an overall horizontal shear strain parallel to the present‐day plate motion. We suggest that this preferred orientation of the crystals mainly occurs within the upper mantle low‐velocity layer.
Antarctic chlorine chemistry: Possible global implications
Authors: Rodriguez Jose M. , Ko Malcolm K. W. , Dak Sze Nien
Published: February 2008

Ocurrence of heterogeneous reactions on the surface of Polar Stratospheric Clouds (PSC) is a necessary component of the chlorine‐related chemical mechanisms proposed to explain the recently observed decrease of ozone during antarctic spring. A one‐dimensional model is used to assess the impact of these heterogeneous reactions on future global ozone trends if they were to occur on the global aerosol layer. The impact of these reactions on the concentration of chlorine species in the present‐day atmosphere is also calculated to determine if observations can place any constraints on the rates of these reactions in the global atmosphere. Of the two heterogeneous processes considered here, the reaction (CℓNO3 + HCℓ) could have a larger impact on stratospheric ozone. A fast rate for this reaction would greatly enhance the present concentration of CℓO and reduce the abundance of HCℓ in the lower stratosphere. Because of the large differences between the antarctic and global environments, the calculated global O3 trends are smaller than those calculated for Antarctica. In addition to determining kinetic rates in the laboratory, concurrent monitoring of stratospheric concentrations of CℓO, HCℓ, OCℓO and aerosols at selected locations around the globe during the next 10 to 20 years may provide early clues as to whether such reactions are actually occurring.
Dynamical effects on the core‐mantle boundary from depth‐dependent thermodynamical properties of the lower mantle
Authors: Zhang Shuxia , Yuen David A.
Published: February 2008

A common assumption in modelling dynamical processes in the lower mantle is that both the thermal expansivity and thermal conductivity are reasonably constant. Recent work from seismic equation of state leads to substantially higher values for the thermal conductivity and much lower thermal expansivity values in the deep mantle. The dynamical consequences of incorporating depth‐dependent thermodynamic properties on the thermal‐mechanical state of the lower mantle are examined with the spherical‐shell mean‐field equations. We find that the thermal structure of the seismically resolved anomalous zone at the base of the mantle (D”) is strongly influenced by these variable properties and, in particular, that the convective distortion of the core‐mantle boundary (CMB) is reduced with the decreasing thermal expansivity. Such a reduction of the dynamically induced topography from pure thermal convection would suggest that some other dynamical mechanism, must be operating at the CMB.
Metastability threshold sizes in single‐domain magnetite particles
Authors: Shcherbakov V. P. , Lamash B. E.
Published: February 2008

A micromagnetic model was developed to calculate the maximum grain size for which an ideal parallelepiped‐shaped particle can have a metastable single‐domain (SD) structure. For mathematical tractability, the micromagnetic equations were described only by one‐dimensional deviations from a uniform SD state. It was found that for cubic‐shaped magnetite particles, the metastability threshold, acr was approximately 0.14 micrometers, well above the equilibrium threshold size for the single‐domain to two‐domain transition. The metastability threshold size also increased rapidly with particle elongation and for a length:width ratio greater then 2.6, magnetite grains of all sizes could theoretically support a metastable single‐domain state.
Magnetic Behavior of Natural Goethite During Thermal Demagnetization
Authors: Dekkers M. J.
Published: February 2008

Goethite maximum blocking temperatures (60–105°C) are governed by the amount of isomorphous substitution in the goethite lattice. The goethite dehydration reaction (250–350°C) is attended with a concurrent remanence decrease in finely intergrown hematite due to a change of the original hematite structure promoted by the liberated water vapor. This remanence decrease leads to a bending point in the thermal decay curve, which could be easily mistaken for the presence of another magnetic constituent. The magnetic properties of the minerals formed through goethite dehydration (hematite and traces magnetite) strongly depend on their growth history.
Lower crustal reflectivity patterns in wide‐angle seismic recordings
Authors: Gibson Bruce S. , Levander Alan R.
Published: February 2008

Many features of wide‐angle reflection data have been attributed to finely‐layered structure in the lower crust. Reflections with similar character, however, can be produced by small‐amplitude 2‐D random velocity variations. Finite‐difference seismograms for a lower crustal model with isotropic random velocity variations match field data recorded at the Black Forest, Germany. At source‐receiver offsets beyond about twice the target depth, waves scattered from a random zone produce the appearance of horizontal layering in wide‐angle data. Lower crustal reflectivity patterns can thus be explained by models that have lateral and vertical random fluctutations rather than fine‐scale layering.