bluuebunny/crossref_metadata_2025 huggingface dataset:
Dayside and nightside auroral arc systems
Authors: Akasofu S.‐I. , Kan J. R.
Published: February 2008

It is shown that the dayside and the nightside arc systems of the auroral oval are topologically distinct, although they constitute an annular belt of auroras, the auroral oval. It is suggested that the dayside arc system is associated with field‐aligned currents fed by the low‐latitude boundary layer dynamo, while the nightside arc system is associated with field‐aligned currents fed by the magnetotail dynamo.
Implications of stratospheric aerosol measurements for models of aerosol formation and evolution
Authors: Toon Owen B. , Turco R. P. , Whitten R. , Hamill P.
Published: February 2008

Calculations of the distribution of stratospheric sulfur gases and of stratospheric aerosols are compared with measurements obtained in Alaska during July 1979. Generally, the measurements are reasonably consistent with the model results. COS is the major sulfur‐bearing gas in the stratosphere while CS2 plays a lesser role in the formation of sulfate aerosols. Ammonia, which earlier measurements suggested was a major aerosol constituent, is found to be a contaminant, so models without ammonia chemistry may be justified. The model and the measurements suggest that stratospheric sulfuric acid aerosols nucleate just above the tropopause, but they are older and have grown to larger sizes at higher altitudes.
Model exospheres of the ringed planets
Authors: Luhmann J. G. , Walker R. J.
Published: February 2008

The theory of rotating ion exospheres in dipolar magnetic field geometries is used to predict some effects of the rings on the inner plasmaspheres of the ringed planets Jupiter, Saturn, and Uranus. Plasma exospheres consist of four types of particles: 1) ballistic particles with trajectories that intersect the exobase in the same hemisphere twice, 2) trapped particles with trajectories that do not intersect the exobase in either hemisphere, 3) escaping particles which travel from the exobase to the conjugate exobase and 4) incoming particles which similarly arrive at the exobase from the conjugate exobase. The analysis carried out herein assumes a purely ionospheric source. It is found that if rings affect the trapped plasma only, the cold plasma density at Saturn will be either reduced or increased by a factor of ∼2 at L = 1.65, depending on whether the ring populates or empties the trapped trajectories. The ionospheric plasma density at Uranus similarly depends on the properties of Uranus’ rings. At Jupiter, however, ionospheric particles in the inner plasmasphere are primarily on ballistic trajectories which do not intersect the rings except possibly at longitudes where the rings are far from the magnetic equator (due to the non‐dipolar magnetic components of Jupiter’s field). When the properties of the rings as sources and sinks of ions are more accurately determined, these conclusions may have to be altered. However, it is found that if all cold plasma particles on trapped orbits are absorbed and the rings are not a source of plasma, this simple exospheric theory can explain the ionospheric density profile inferred from the Pioneer 11 Saturn radio occultation experiment, in which a localized peak in the profile was observed on field lines threading the Guerin division between the C and D rings. The results of the imminent Voyager radio occultation observations will provide more data for quantitative analyses with the exospheric model.
Discrimination of a chestnut‐oak forest unit for geologic mapping by means of a principal component enhancement of Landsat multispectral scanner data
Authors: Krohn M. Dennis , Milton N. M. , Segal Donald , England Anthony
Published: February 2008

A principal component image enhancement has been effective in applying Landsat data to geologic mapping in a heavily forested area of eastern Virginia. A chestnut‐oak forest unit, which occurs on metavolcanic rocks and some metaclastic rocks in the western Piedmont and on highly weathered upland gravel deposits in the eastern Piedmont, can be discerned on a digitally enhanced Landsat winter image. The image enhancement procedure consists of a principal component transformation, a histogram normalization, and the inverse principal component transformation. The enhancement preserves the independence of the principal components, yet produces a more readily interpretable image than does a single principal component transformation.

To determine how the chestnut‐oak forest unit was being enhanced, average Landsat multispectral scanner (MSS) values were extracted for four sample forest types and were calculated through the inverted principal component transformation. Slope and intercept values for the linear histogram normalization were chosen to keep the scale between the raw MSS bands and the inverted principal component (PC) bands constant. Plots of the inverted principal component data show that the most separation between forest types is in inverted PC band 5. The chestnut‐oak forest unit is characterized by a high value for inverted PC band 5 as opposed to a low value for inverted PC band 4. In contrast, raw MSS band 4 is greater than MSS band 5 for the four forest types sampled in the winter image. Such observations cannot be readily deduced from analysis of only the principal component rotation matrix. They may ultimately provide a means to map the distribution of chestnut‐oak forest from Landsat.
Prediction of vertical displacements in a subsiding elastic layer
Authors: Savage William Z.
Published: February 2008

Subsidence over an underground cavity is modeled by assuming the subsiding region to be an infinitely long elastic layer that rests on a rigid base and deforms under its own weight into an opening under its lower surface. An approximate analytic solution based on Fourier transform methods is found for vertical displacements of the ground surface and the roof of the opening when the layer thickness is much greater than the width of the opening. This model differs from previous analytic models in allowing both the ground surface and cavity roof to be traction‐free. The shape of the surface subsidence trough is found to be controlled by the ratio of the layer thickness to the width of the opening; as the value of this ratio decreases the subsidence trough narrows and a peripheral ridge forms.
Tangential electric fields in a drifting auroral arc
Authors: Yau A. W. , Whalen B. A. , Creutzberg F.
Published: February 2008

We report rocket‐borne ion convection velocity and ground‐based optical measurements in an early evening, equatorward drifting, NW‐SE oriented auroral arc. Our measurements indicate a detailed correspondence between the normal component of the ion convection velocity (the component normal to the auroral arc) and the drift motion of the auroral arc. The two velocities were identical on a time scale of minutes, and correlated strongly with each other in smaller‐scale temporal variations. The correspondence implies a near‐zero tangential electric field in an auroral arc, in the frame of reference of the arc. Our observations have serious consequences on several auroral theories.
Natural annealing of Pleochroic haloes in biotite samples from deep drill holes, Fenton Hill, New Mexico
Authors: Laney Randy , Laughlin A. William
Published: February 2008

Examination of 46 thin‐sections of Precambrian metamorphic and igneous rocks from three deep drill holes in northern New Mexico reveals a narrow depth‐temperature range for annealing of pleochroic haloes in biotite. Annealing of the haloes is first observed in samples from a depth of 1850 m (134°C present temperature) and is complete in samples from a depth of 2120 m (151°C). The observed temperature of annealing of the haloes is in good agreement with earlier observations of fission track annealing in apatite from the same core samples.
Magmatic volatiles in explosive rhyolitic eruptions
Authors: Eichelberger J. C. , Westrich H. R.
Published: February 2008

Obsidian clasts in rhyolitic tephra deposits preserve preemption magmatic volatile contents, providing a direct means for determining the volatile content of explosively erupted magmas. Small to moderate volume Plinian eruptions (10−3 to 10−1 km³) appear to be driven by 0.5‐1.0 wt.% volatiles, consisting dominantly of H2O with minor CO2. Analysis of obsidian from eruptive sequences consisting of tephra and flows indicates that this hydrous magma abruptly overlies magma with only 0.1‐0.2 wt.% H2O.
Static electrical conductivity as an indicator of the sulfate content of polar ice cores
Authors: Maccagnan M. , Barnola J. M. , Delmas R. , Duval P.
Published: February 2008

Past atmospheric sulfate content is probably recorded in polar snow and ice. A simple method based on electrical conductivity measurements on ice cores has been proposed recently to easily detect atmospheric sulfate changes caused by violent volcanic eruptions in the past. We show that this method is particularly useful when used in central polar areas but that its application must be done carefully when analyzing coastal or bedrock ices for which aging effects are able to seriously disturb their electrical properties.
Influence of velocity shear on the Rayleigh‐Taylor instability
Authors: Guzdar P. N. , Satyanarayana P. , Huba J. D. , Ossakow S. L.
Published: February 2008

The influence of a transverse velocity shear on the Rayleigh‐Taylor instability is investigated. It is found that a sheared velocity flow can substantially reduce the growth rate of the Rayleigh‐Taylor instability in the short wavelength regime (i.e., kL > 1 where L is the scale length of the density inhomogeneity), and causes the growth rate to maximize at kL < 1.0. Applications of this result to ionospheric phenomena [equatorial spread F (ESF) and ionospheric plasma clouds] are discussed. In particular, the effect of shear could account for, at times, the 100’s of km modulation observed on the bottomside of the ESF ionosphere and the km scale size wavelengths observed in barium cloud prompt striation phenomena.
Space shuttle glow observations
Authors: Banks P. M. , Williamson P. R. , Raitt W. J.
Published: February 2008

Photographic and television observations made during the third flight of the Space Shuttle in March 1982 reveal the presence of a diffuse optical emission surrounding surfaces of the vehicle exposed to the atmosphere in the ram direction. The line of sight intensity of this emission is comparable to that of airglow emissions seen at the limb of the earth and competes with the brightness of stars seen within the field of view of the photographic and TV cameras. The glow emission appears to be a manifestation of an atmosphere‐vehicle interaction. Light from vehicle thruster operations was also seen, as well as the optical emissions resulting from the operation of a 100 mA electron beam.
Dawn‐dusk electric field asymmetry of the Io plasma torus
Authors: Barbosa D. D. , Kivelson M. G.
Published: February 2008

We consider the effects of a combined convection and corotation electric field across the Io plasma torus. A dawn‐to‐dusk electric field Ec will modify the orbits of charged particles shifting them toward dawn. The radial drift imposed by the perturbed orbits implies a local time‐dependent modulation of low‐energy ion and electron temperatures with particles hotter at dusk than at dawn. With Ec ≃ 4 mV/m, the orbits near 6 RJ would be shifted by approximately 0.2 RJ. Then the electron temperature would be 20% higher at dusk than at dawn, an effect which could explain the local time asymmetry of EUV intensity found by the Voyager ultraviolet spectrometer. The source of the convection electric field is internal to the magnetosphere and is attributed to the tailward escape of Iogenic and Jovian plasma beyond the Alfven surface.
Measurements of NO2 in the Earth's stratosphere using a limb scanning visible light spectrometer
Authors: Mount G. H. , Rusch D. W. , Zawodny J. M. , Noxon J. F. , Barth C. A. , Rottman G. J. , Thomas R. J. , Thomas G. E. , Sanders R. W. , Lawrence G. M.
Published: February 2008

NO2 densities determined from the limb scanning visible light spectrometer on board the Solar Mesosphere Explorer spacecraft are reported for winter 1981/82 in the altitude region 28‐40 km. The observational technique utilizes the photoabsorption by NO2 of Rayleigh scattered sunlight in the 440nm spectral region. The NO2 density varies from pole to pole and shows large variations at high northern latitudes during the winter months which are related to both the temperature and flow of air near 30 km.
Dispersion in tracer flow in fractured geothermal systems
Authors: Horne Roland N. , Rodriguez Fernando
Published: February 2008

Interpretation of tracer tests is commonly based on the analysis of flow through a porous medium. In geothermal reservoirs however the principal permeability arises from fractures, and a porous medium approach is not applicable. The dispersion of tracer material flowing in a fracture is shown to be dominated by molecular diffusion across the fracture ‐ a mechanism known as Taylor dispersion. For typical values of reservoir parameters, this transverse diffusion will obliterate any transverse tracer concentration gradients caused by the velocity profile across the fracture. The effective dispersivity is found to be a function of fracture aperture, mean flow velocity and molecular diffusivity, and is orders of magnitude greater than for porous medium flow. Typically Peclet numbers are anticipated to lie between orders 1 and 100, and field results confirm this range.
Simultaneous detection of FC‐11, FC‐12 and FC‐22, through 8 to 13 Micrometers IR solar observations from the ground
Authors: Zander Rodolphe , Stokes Gerald M. , Brault James W.
Published: February 2008

High‐resolution solar observations covering the 8 to 13 µm atmospheric window are now being carried out routinely at the Kitt Peak National Observatory (KPNO), Tucson, Arizona, using a 1 meter‐path difference Fourier transform spectrometer. Such observations allow the simultaneous measurement of a large number of trace gases. Preliminary results for the three most important fluorocarbons, FC‐11, FC‐12 and FC‐22 are reported here. These results, in the form of average mixing ratios, show the potential and illustrate the performance of the Kitt Peak interferometer for this application.
Ionospheric characteristics of a detached arc in the evening‐sector trough
Authors: Vondrak R. R. , Murphree J. S. , Anger C. D. , Wallis D. D.
Published: February 2008

Simultaneous measurements by the ISIS‐2 satellite and the Chatanika incoherent‐scatter radar have been used to identify the ionospheric characteristics of a detached arc in the evening‐sector trough region. On 26 February 1977 at 0737 UT, the ISIS‐2 Auroral Scanning Photometer detected a detached arc at 65° north geomagnetic latitude that extended from approximately 1900 MLT to 2100 MLT. The arc was about 2° wide in latitude and was separated by about 3° from the equatorward edge of the diffuse aurora. The ratio of observed emission intensity at 557.7 nm to that at 391.4 nm was low, indicating a fairly hard electron distribution. The ISIS‐2 Energetic Particle Detector observed energetic electron precipitation (E>40 keV) in the detached arc. The Chatanika radar found that the detached arc consisted of several narrow ionization enhancements, with peak E‐region electron densities of about 1 × 105 cm−3 at 95 km altitude. The major enhancements were about 20 km (0.2°) wide in latitude and were spaced about 50 km (0.5°) apart. Their widths and spacings were steady for about 40 minutes. This persistent spatial pattern suggests the presence of an energetic electron precipitation mechanism that is periodic in latitude and extended in longitude.
Outer‐rise earthquakes and seismic coupling
Authors: Christensen Douglas H. , Ruff Larry J.
Published: February 2008

Outer‐rise earthquakes can be separated into two basic categories based on focal mechanism: compressional and tensional events reflecting compressional and tensional outer‐rise stress regimes. We propose a model that connects the stress regime in the outer‐rise to the behavior of large subduction earthquakes and explains the focal mechanisms and both the temporal and spatial occurrence of outer‐rise earthquakes.

We find that compressional outer‐rise events tend to occur oceanward of seismic gaps in seismically coupled subduction zones, or equivalently just prior to large subduction zone earthquakes. The compressional stress regime is probably caused by slip in adjacent subduction zone segments. There are two modes of occurrence for tensional outer‐rise earthquakes depending on whether they occur in coupled or uncoupled subduction zones. In coupled subduction zones, tensional events tend to occur after large subduction events as tensional stress from slab pull is temporarily transmitted to the outer‐rise. In subduction zones that are inherently uncoupled, tensional events can occur at any time. Therefore, in uncoupled subduction zones the outer‐rise is always in tension, and only tensional outer‐rise events occur there; while in coupled subduction zones, the outer‐rise is in a compressional state prior to large subduction earthquakes and a tensional state afterwards due to the large displacements.
A re‐evaluation of laser heterodyne radiometer cℓo measurements
Authors: Menzies Robert T.
Published: February 2008

Previously reported measurements of stratospheric CℓO using a balloon‐borne laser heterodyne radiometer, launched from Palestine, Texas, are re‐evaluated as a result of recent spectroscopic data. A spectral feature which was observed during September, 1978 and November, 1979 flights was incorrectly identified as a CℓO absorption line, while a second feature observed during the latter flight with somewhat limited sensitivity is now believed to be due to CℓO. This new interpretation results in a measured CℓO profile which falls off more rapidly with decreasing altitude than the previous results indicated.
Antarctic Meteorite ALHA81005 – Not just another lunar anorthositic norite
Authors: Korotev Randy L. , Lindstrom Marilyn M. , Lindstrom David J. , Haskin Larry A.
Published: February 2008

Seven subsamples of meteorite ALHA81005, a regolith breccia from the lunar highlands, were analyzed by INAA for 32 elements. Four of them were also studied petrographically. In bulk composition the rock corresponds to anorthositic norite with a very small component of KREEP and is very similar to estimates of average lunar highlands surface. Compositions of the white clasts and the dark matrix are similar, but the clasts are more magnesian and 30‐50% as rich in KREEP‐related elements. The white clasts have fine‐grained granulitic textures and are generally similar to Apollo 16 and 17 granulitic anorthositic norites, but are more magnesian and only 20% as rich in KREEP‐related elements. Some granulitic clasts are dominated by a magnesian anorthositic norite component not represented among the "pristine" Apollo samples.
Formation of the El Chichon aerosol cloud
Authors: Barth C. A. , Sanders R. W. , Thomas R. J. , Thomas G. E. , Jakosky B. M. , West R. A.
Published: February 2008

Thermal emission at 6.8 µm and particle‐scattered radiation at 1.9 µm from the El Chichon aerosol cloud were measured by instruments on board the Solar Mesosphere Explorer satellite. The cloud moved westward circling the globe in twenty‐one days. During its initial formation the cloud was centered at an altitude of 27 km and was confined to the latitude band between the equator and 30°N. At the 27 km level, the maximum density was reached eight to nine weeks after the eruption. Following that time, the maximum in the density gradually moved lower in altitude.
Estimates of the amount of sulphur dioxide injected into the stratosphere by the explosive volcanic eruptions: El Chichon, Mystery Volcano, Mt. St. Helens
Authors: Evans W. F. J. , Kerr J. B.
Published: February 2008

Ground based remote sensing measurements of sulphur dioxide column amounts made with the Brewer spectrophotometer have been used to estimate the total amount of sulphur dioxide injected into the stratosphere by the El Chichon eruptions which occurred between March 28 and April 4, 1982. Measurements were made at the Mauna Loa Observatory in Hawaii, at Toronto and on NASA Convair 990 flights between 20°N and 50°N. The average amount of sulphur dioxide measured at Mauna Loa was about 4.7 matmcm during late April and early May, 1982. The aircraft remote sensing measurements suggest that the cloud was distributed up to 35°N in early May. Assuming that it was dispersed in a uniform belt around the globe between the equator and 35°N, we estimate that 13.4 megatons of sulphur dioxide were injected into the stratosphere by the El Chichon eruptions. The amount of sulphur dioxide from the January "mystery volcano" was estimated to be 5.6 megatons. Previously, in 1980, an estimate of 0.6 megatons was made for the Mt. St. Helens eruption.
Decay of electrostatic ion cyclotron waves
Authors: Yu M. Y. , Das A. C. , Shukla P. K.
Published: February 2008

It is shown that finite amplitude electrostatic ion cyclotron (EIC) waves can parametrically decay into daughter EIC waves and kinetic Alfvén waves. Since the current associated with the latter is d.c. in the EIC time scale, it can linearly excite EIC waves when the amplitude of the Alfvén waves is sufficiently high. This provides a mechanism for the simultaneous existence of EIC and Alfvén fluctuations. Application of the theory in the auroral zone of the ionosphere is discussed.
ISEE‐3 wave measurements in the distant geomagnetic tail and boundary layer
Authors: Scarf F. L. , Coroniti F. V. , Kennel C. F. , Fredricks R. W. , Gurnett D. A. , Smith E. J.
Published: February 2008

The ISEE‐3 excursion into the distant tail region reveals a complex structure with several wave, particle and field characteristics that differ significantly from those measured closer to earth. The most striking results are found within the distant boundary layer where intense electrostatic turbulence levels are detected in association with bi‐directional electron distributions. The wave amplitudes appear to increase with increasing downstream distance and the polarizations are those expected for ion acoustic oscillations. Near the boundary of the distant plasmas sheet the turbulence spectra are essentially identical to those measured much closer to earth on IMP‐8. We also find that in the distant tail the continuum radiation spectrum has a low frequency cutoff that is much higher than the minimum value for the local plasma frequency.
Evidence against the stability of orthoenstatite above ∼1005°C at atmospheric pressure in CaO‐MgO‐SiO2
Authors: Carlson William D.
Published: February 2008

Reversals locating the equilibrium orthoenstatite = protoenstatite + diopside in CaO‐MgO‐SiO2 demonstrate that orthoenstatite cannot exist stably above 1005±10°C at one atmosphere pressure. This in turn suggests that the orthorhombic low‐Ca phase found near 1400°C at atmospheric pressure in this system (formerly identified as orthoenstatite) is in fact a previously unrecognized pyroxene polymorph.
Planetary waves near the mesospheric easterly jet
Authors: Burks Douglas , Leovy Conway
Published: February 2008

Analysis of temperatures retrieved from satellite limb radiance measurements of the stratosphere and mesosphere during January‐February 1979 reveals 3 prominent waves: wave number 3 with period 2.1 days, wave number 4 with period 1.8 days, and wave number 1 with period approximately 9 days. Each of these has maximum amplitude in the equatorward shear zone of the summer mesospheric easterly jet and propagates westward. Characteristics of the 1.8 day wave number 4 mode indicate that it arises from instability of the jet. The set of three waves may comprise an interacting triad.
Hydromagnetic waves and instabilities associated with cometary ion pickup: ICE observations
Authors: Tsurutani Bruce T. , Smith Edward J.
Published: February 2008

The hydromagnetic turbulence surrounding comet Giacobini‐Zinner is characterized by two dominent components: large amplitude, linearly polarized waves with periods near 10² s and circularly polarized wave packets with periods near 3 s. The latter appear in association with variations in field magnitude produced by the long period waves. A third, commonly observed feature is identified, consisting of a partial rotation of the magnetic field (a hook‐like structure) which also appears to be triggered by the long period waves. The possibility that the long period waves are generated by the pickup of freshly ionized cometary neutrals has been investigated. A resonant instability identified by Wu and Davidson (1972) appears able to account for the long period waves in terms of the pickup of cometary ions of the water group. Application of the theory also indicates that the growth rate of proton cyclotron waves, as a consequence of hydrogen ion pickup, is somewhat lower, due to both higher neutral velocities and longer ionization times. Several significant features of the wave packets and hooks are presently unexplained and will require further study.
Sound velocity of a sandstone saturated with oil and brine at different concentrations
Authors: Bacri Jean‐Claude , Salin Dominique
Published: February 2008

We have measured the velocity of sound in a sandstone saturated with oil and brine at different concentrations. The velocity variations with the concentration depend drastically on the way of entering the fluids in the sample : injection of non‐wetting fluid in a sandstone fully saturated with a totally wetting fluid (drainage) or vice versa (imbibition). We interpret our measurements with an extension of the Biot‐Gassmann theory to a wetted frame of the sandstone saturated with an effective oil‐brine fluid.
Ion dynamics and distribution around comet Halley: Suisei observation
Authors: Mukai T. , Miyake W. , Terasawa T. , Kitayama M. , Hirao K.
Published: February 2008

Ion dynamics inside the cometosheath of Halley is described based on the plasma observation by Suisei. The pickup shells of water‐group ions and protons of cometary origin are clearly identified. Field line draping around the comet is observed within 2 × 105 km of the Halley's nucleus, where magnetic field directions are derived from the symmetry axes of the ion‐pickup shells. Flow turbulence is observed as short‐term (period of ≲ 2min) fluctuations of the anisotropy direction in the outer cometosheath (2‐4.5 × 105 km from the nucleus), while the flow is found to be laminar near the closest approach (1.5‐2 × 105 km from the nucleus). Spatial distribution of density of water‐group ions (identified up to 4 × 106 km from the nucleus) is also presented.
Parallel acceleration and transport of ions from polar ionosphere to plasma sheet
Authors: Cladis J. B.
Published: February 2008

The effect of the convection electric field in accelerating ions that escape from the polar ionosphere is investigated. It is shown that at high altitudes the velocity component of the ions along the magnetic field may be increased by more than an order of magnitude. The highest velocities are acquired by ions that escape from the region of the ionosphere that is connected along magnetic field lines to the dayside cusps. During disturbed times, ions from that region intercept the center plane of the magnetotail in one to two hours at radial distances exceeding about 6 RE. Investigation of the resulting O+ properties in the center plane, viz., their locations, number densities, and energies, indicates that the polar ionosphere near the cusps is the principal source of the O+ observed in the plasma sheet. Moreover, a study of the ion motion at quiet and disturbed times indicates that the increase of O+ in the plasma sheet with increasing AE values [Lennartsson and Shelley, 1986] is due mainly to an increase in the source of O+ rather than alteration of its transport path.
Long‐period dynamic spectrograms of low‐frequency interplanetary radio emissions
Authors: Kurth W. S. , Gurnett D. A. , Scarf F. L. , Poynter R. L.
Published: February 2008

In this report we present dynamic spectrograms of the low‐frequency interplanetary radio emissions as observed by Voyagers 1 and 2 from 1983 through mid‐1986. The radio emissions were observed to be most intense in the latter portion of 1983 at 3 kHz but have also been detected at 2 kHz. The emission has been present almost continuously at either 2 or 3 kHz since late 1983. The spectrograms presented herein show that the phenomenon appears almost identically as observed by the two spacecraft separated by more that 10 AU, at least at the higher frequency. One feature revealed by the dynamic spectrograms which had not been noticed previously is a gradual rise in frequency of the 3‐kHz component following the onset of the late 1983 event. These new observations reinforce the conclusion that the low‐frequency emissions are freely propagating radio waves, but the two‐component spectral structure implies that the previous model of emission at twice the plasma frequency at the inner heliosphere shock is inadequate to fully account for the observations. Either an additional source region or source mechanism is suggested.
Frequency domain interferometry: A high resolution radar technique for studies of atmospheric turbulence
Authors: Kudeki Erhan , Stitt Gary R.
Published: February 2008

A new radar technique suitable for high resolution studies of narrow scattering layers in the atmosphere is introduced. The positions of the layers within the radar scattering volume are deduced from the phase differences between radar returns at two distinct transmitter frequencies. Initial mesospheric observations demonstrate the applicability of the technique, and show that the scattering layers are often a few hundred meters thick and widely separated in the mesosphere. Their vertical motions are generally consistent with vertical Doppler velocity estimates.
Production of isotopically heavy ozone by ultraviolet light photolysis of O2
Authors: Thiemens Mark H. , Jackson Teresa
Published: February 2008

Ozone was produced by UV photolysis (157‐200nm) of molecular oxygen. The product ozone is enriched in 17O, 18O on a mass‐independent basis, similar to the fractionations observed in an electrical discharge. The magnitude of 18O, 17O enrichment decreases with decreasing pressure, suggesting the presence of two fractionation mechanisms with differing δ17O/δ18O ratios. One of the end members would be mass‐independent with δ18O ≅ δ17O ≅ 90‰, which is dominant above ∼ 20 torr. The second process which is significant below ∼ 6 torr produces O3 with δ18O ≅ − 55‰, δ17O ≅ − 27.5, possibly due to isotopic selectivity in diffusion to the reaction systems wall. The δ17O = δ18O isotopic fractionation resembles that observed in stratospheric ozone, though the magnitude of fractionation is a factor of four less.
Convection and anisotropy of the inner core
Authors: Jeanloz Raymond , Wenk Hans‐Rudolf
Published: February 2008

Estimation of the Rayleigh number of the inner core suggests that this region is convecting. The flow pattern is likely to produce crystallographic preferred orientation of the elastically anisotropic hexagonal closest packed (ϵ) phase of iron, such that compressional‐wave velocities would be greater in the axial relative to the equatorial direction by roughly 1 percent. This result is in agreement with seismological evidence that the inner core is elastically anisotropic.
Development of texture and elastic anisotropy during deformation of hcp metals
Authors: Wenk H. R. , Takeshita T. , Jeanloz R. , Johnson G. C.
Published: February 2008

The inner core of the earth most likely consists of ϵ (hcp) iron and shows anisotropy of seismic velocities which could be explained by crystallographic preferred orientation developing during convective flow. This paper summarizes deformation mechanisms in hcp metals and applies the Taylor theory of polycrystal deformation to analogs of ϵ‐iron for different strain histories. The pattern of preferred orientation is then used to calculate elastic properties of deformed polycrystals with special emphasis on anisotropy.
Computer experiments on whistler and plasma wave emissions for Spacelab‐2 electron beam
Authors: Omura Yoshiharu , Matsumoto Hiroshi
Published: February 2008

A funnel‐shaped VLF emission observed in the Spacelab‐2 electron beam experiment is studied by computer experiments using an electromagnetic particle code. The computer experiments demonstrated that broad‐band plasma wave emissions extending from a low frequency to the local plasma frequency are excited by a spatially confined thin electron beam. The emissions have parallel phase velocities satisfying the Landau resonance condition with the electron beam. Parts of the emissions below the electron cyclotron frequency can propagate away from the beam as oblique whistler mode waves. The computer experiments show a very clear funnel‐shaped emission, and show a remarkable similarity with that in the Spacelab‐2 electron beam experiment. The funnel‐shape of the whistler emissions is interpreted in terms of the perpendicular group velocity and, as a possible additional mechanism, the wave damping in the background plasma.
New experimental evidence for the mechanism for production of isotopically heavy O3
Authors: Thiemens Mark H. , Jackson Teresa
Published: February 2008

The mass independent isotopic fractionation in O3 formation from O2 photolysis has been investigated as a function of pressure (2.1‐760 Torr), UV wavelength and differing third body. In the low pressure regime (⪝ 200 Torr room temp., ⪝ 10 Torr liquid nitrogen), O3 decomposition occurs, resulting in a secondary, mass‐dependent isotopic fractionation. It is demonstrated that wall effects produce O3 in a mass‐dependent fashion, thus indicating the involvement of rotational states in the mass independent fractionation process. For pressures in the intermediate range, to ∼600 Torr, a single‐stage fractionation is observed, presumably with δ17O≅δ18O≅85‐100‰, though secondary effects may be operative also. At pressures above 450 Torr, the δ18O of O3 decreases to 87‰ at 760 Torr. The fractionation process appears to be independent of UV wavelength and third body composition; photolysis of air produces O3 isotopically similar to pure O2 photolysis at comparable pressures.
A case study of magnetotail current sheet disruption and diversion
Authors: Lui A. T. Y. , Lopez R. E. , Krimigis S. M. , McEntire R. W. , Zanetti L. J. , Potemra T. A.
Published: February 2008

On 1 Jun 1985 the AMPTE/CCE spacecraft (at a geocentric distance of ∼8.8 RE at the midnight neutral sheet region) observed a dispersionless energetic particle injection and an increase in magnetic field magnitude, which are features commonly attributed to disruption of the near‐earth cross‐tail current sheet during substorm expansion onsets. An analysis based on high time‐resolution measurements from the magnetometer and the energetic particle detector indicates that the current sheet disruption region exhibited localized (< 1 RE) and transient (< 1 min) particle intensity enhancements, accompanied by complex magnetic field changes with occasional development of a southward magnetic field component. Similar features are seen in other current disruption/diversion events observed by the CCE. Our analysis suggests that the current disruption region is quite turbulent, similar to laboratory experiments on current sheet disruption, with signatures unlike those expected from an X‐type neutral line configuration. No clear indication of periodicity in any magnetic field parameter is discernible for this current disruption event.
A model for the spatial and energy distributions of energetic neutral atoms produced within the Saturn/Titan plasma system
Authors: Hsieh K. C. , Curtis C. C.
Published: February 2008

A model for the production of energetic neutral atoms (ENAs) in the Saturn/Titan system that takes into account existing data on the spatial distribution of the background neutral density, the energy and spatial distributions of the energetic ions, and the energy dependence of the charge‐exchange cross sections is presented. Hydrogen production via (H+, H) is presented in detail. The extended Saturn/Titan system is "imaged" in energetic neutral H at 66 Rs and 25° latitude. From this vantage point the energetic H flux is 6 ± 1 H cm−2 s−1 between 10 and 100 keV. Comparing our predicted H spectrum with that observed by Kirsch et al. (1981b), we estimate the production of neutral O, and conclude that (O+, H) charge exchange in the inner magnetosphere is sufficient to account for all the ENA O production.
A laboratory study of dissolved noble gas anomaly due to ice formation
Authors: Top Zafer , Martin Seelye , Becker Paul
Published: February 2008

In controlled laboratory experiments on the growth of frazil and columnar ice from sea water, we found that with the exception of helium, the dissolved noble gases were enriched in the water. Approximately 10% of neon, 45% of argon, 60% of krypton, and 50% of xenon were excluded from the ice while helium was enriched by 26% in the ice.
Permeability of rock samples from Cajon Pass, California
Authors: Morrow C. , Byerlee J.
Published: February 2008

Room temperature, steady‐state flow measurements of permeability were conducted on 15 unfractured core samples collected at depths between 270 and 2100 m in the Cajon Pass drillhole. Confining and pore pressures were set to the lithostat and hydrostat for each depth. The first 500 m encountered in the drill hole is composed of sandstones with typically high permeabilities of around 10−17m². The crystalline rocks between 500 and 2100 m show a systematic decrease in permeability with depth from 10−19 to less than 10−21m². These values are particularly low relative to the applied effective stresses of only 10‐30 MPa, and may be a result of the extensive crack healing that was observed in most samples.
Why the oxygen isotopic composition of sea water changes with time
Authors: Walker James C. G. , Lohmann K. C.
Published: February 2008

The oxygen isotopic composition of sea water is determined by interactions with fresh, silicate rocks. Interactions at high temperature, principally hydrothermal interactions on the sea floor, make sea water isotopically heavier. Interactions at low temperature, including sea floor weathering but principally weathering of fresh, crystalline rocks on the continents, make sea water isotopically lighter. Any change in the relative rates of these high and low temperature interactions will cause a change in the composition of sea water. Extreme limits might be −15 per mil relative to SMOW to +4 per mil. Possible rates of change appear to be quite slow, perhaps 1 per mil in 108 years, because of the large size of the oceanic reservoir. Evolution in tectonic style over the course of earth history may have caused a change in the oxygen isotopic composition of sea water as fresh crystalline rocks have been increasingly blanketed by weathered sediments and as deepening oceans have increasingly flooded the places where earth's internal heat is released at the surface.
First observations of stimulated electromagnetic emission at Arecibo
Authors: Thidé Bo , Hedberg Åke , Fejer Jules A. , Sulzer Michael P.
Published: February 2008

The first observations of HF heater stimulated electromagnetic emissions induced in the low‐latitude ionospheric plasma above Arecibo, Puerto Rico, are reported. Many systematic spectral features of the emissions bear a close resemblance to those observed in ionospheric modification experiments in the auroral zone and scale in accordance with detailed theory. This proves that these sideband emissions are not dependent on specific geophysical conditions but are due to fundamental interaction processes in the ionospheric plasma. We also report the discovery of unique, short‐lived HF sideband emissions that are less systematic than those observed previously and accompanied by a quenching of the HF enhanced plasma and ion lines in the Arecibo 430 MHz incoherent scatter radar spectra.
Melting curve of (Mg,Fe)SiO3 perovskite to 96 GPa: Evidence for a structural transition in lower mantle melts
Authors: Knittle Elise , Jeanloz Raymond
Published: February 2008

The melting temperature of (Mg,Fe)SiO3 perovskite, the dominant mineral phase of the Earth's lower mantle, has been measured to a pressure of 96 (±10) GPa. Below 60 GPa we find good agreement with the previous measurement of Heinz and Jeanloz [1987a], and above 60 GPa the melting curve of silicate perovskite has a small positive slope of 19.5 (±5.5) K/GPa. The melting point of (Mg0.9Fe0.1)SiO3 perovskite is 3800 (±300) K at 96 GPa; by extrapolation to 136 GPa, it is 4500 (±500) K at the core‐mantle boundary. These values provide an upper limit to the geotherm through the solid mantle, and they are compatible with recent estimates of the temperature in the core being high (∼4500 K at the core‐mantle boundary). Our melting curve implies that the volume change on melting increases at 60 GPa from ΔVm = 0.0 (±0.2) cm³/mole to ΔVm ≅ 0.16 (±0.03) cm³/mole. We derive an equation of state for the melt from our data, and find that a highly coordinated structure is required to explain the molar volume of liquid (Mg,Fe)SiO3 at pressures above ∼ 20 GPa.
Ice saturation at the tropopause observed from the ER‐2 aircraft
Authors: Murphy D. M. , Kelly K. K. , Tuck A. F. , Proffitt M. H. , Kinne S.
Published: February 2008

Ice saturation at or just above the tropopause was frequently observed during the ER‐2 vertical profiles over Stavanger (59°N) during the Airborne Arctic Stratospheric Expedition (AASE). On occasion, ice saturation extended as much as 500 m above the tropopause. Saturation was not observed over Punta Arenas (53°S) during the Airborne Antarctic Ozone Experiment (AAOE). Saturation extending just above the tropopause was observed at Moffett Field (38°N) in winter but not in summer. The top of a thick cirrus layer at the tropopause will be very strongly cooled, and a thin cloud layer at the tropopause will either be strongly heated or cooled depending on the presence of lower level clouds. Some ER‐2 data suggest removal of water and nitrogen species from the tropopause.
N2O as a dynamical tracer in the Arctic vortex
Authors: Loewenstein M. , Podolske J. R. , Chan K. R. , Strahan S. E.
Published: February 2008

We report N2O measurements obtained by the ATLAS instrument from 14 flights of the NASA ER‐2 aircraft during the 1989 Airborne Arctic Stratospheric Expedition (AASE) field campaign. In the altitude range expected for ozone loss N2O has a long photochemical lifetime, making it an excellent tracer of lower stratospheric air motions. As in the southern hemisphere, the zonal wind speed maximum and large gradients of potential vorticity and N2O identify the vortex edge. N2O profiles inside the vortex indicate net descent relative to outside the vortex and to the summer polar lower stratosphere. Descent of the N2O profile daring the Arctic night relative to the summer profile is comparable to the downward shift in the vertical profile observed in the 1987 Antarctic winter vortex. Winter profiles at the poles are very similar above the 435 K potential temperature surface, but divergent below.
Pressure dependency for heavy isotope enhancement in ozone formation
Authors: Thiemens Mark H. , Jackson Teresa
Published: February 2008

It has previously been shown that a 18O, 17O mass independent isotopic enrichment accompanies O3 formation. Precise definition of the mechanism has proven difficult and further experimental characterization of the mediating parameters is needed. The potential role of activated complex lifetime is determined by measuring the effect of pressure in the region where third body kinetic fall‐off is known to occur (∼ 4 atmospheres). In the pressure region ∼ 8 to 45 atmospheres, the 18O, 17O enrichment decreases by nearly 84‰. For pressures between 45 to 66 atmospheres (1.6 × 1021 molecules cm−3), the enhancement decreases by only 6‰ and is absent (δ18O = O) at 56 atmospheres. For pressures 56 to 87 atm, the product ozone is depleted in 18O in a nearly mass dependent fashion. The decrease in O3‐18O enrichment with pressure initiates at a significantly lower pressure than expected, based upon the known reaction order pressure dependency. At present, no theoretical model quantitatively accounts for the observations.
Observations of the flank of Earth's bow shock to −110 RE by ISEE 3/ICE
Authors: Greenstadt E. W. , Traver D. P. , Coroniti F. V. , Smith E. J. , Slavin J. A.
Published: February 2008

The ISEE 3/ICE spacecraft made well over 100 crossings of Earth's bow shock between x(SEC)=−20 and −110 RE, most of them further away than −60 RE, while resetting its course for comet Giacobini‐Zinner. Magnetosonic Mach numbers MMS normal to the shock in this extreme downwind flank of the bow shock were generally no more than about 60%, often less than 35%, of their values at the subsolar point, so that this set of crossings consists of many examples of low MMS (MMS<3) crossings, including rare quasi‐parallel, as well as quasi‐perpendicular, cases. We tabulate the parameters of the crossings, display some of their magnetic, plasma wave, and spectral profiles at low MMS, and compare loci of crossings with the extrapolation of a model of earlier statistical success, showing that the model remains useful in the far flank.
Kinetic instability associated with spherical shell distribution of cometary pickup ions
Authors: Yoon Peter H.
Published: February 2008

The stability of ion shell distribution is an interesting and important issue in view of the fact that it is stable under perturbations propagating parallel to the ambient magnetic field, despite large amount of free energy it contains [Freund and Wu, 1988; Brinca, 1990]. It was found, however, that if the shell distribution of ions has a sufficient amount of drift speed with respect to the solar wind hydromagnetic waves, it can become unstable [Gary and Sinha, 1989; Yoon et al., 1989]. In addition, recently Wu and Yoon [1990] have found the obliquely propagating hydromagnetic instability associated with the ion shell distribution. This letter presents the unified stability analysis of the ion shell distribution, and show under what condition the drift‐induced instability of the type first discussed by Gary and Sinha [1989], and the oblique hydromagnetic instability discussed by Wu and Yoon [1990] are excited and how the two types of instabilities are related.
Thermal energization of ions during impulsive field events
Authors: Newman Alice L.
Published: February 2008

In plasmas rapid thermal energization can result when sharp impulses occur within ambient fields. A familiar example of impulsive fields occurs in the ion pick‐up mechanism when newly‐ionized particles in the presence of ambient electric and magnetic fields suddenly gain substantial gyrational energy. Motions of ions in the presence of a magnetic field can similarly be disrupted by sudden impulsive changes in local electric fields over timescales shorter than the local ion cyclotron period. Impulsive external forces violate adiabatic invariants of motion, abruptly altering the distribution of kinetic energy and providing a mechanism for the transfer of energy from E × B drift into ion gyrational motion. Orbit integration shows order of magnitude increases in the particle thermal energy when the initial gyration speed is small compared to impulsive changes in the drift speed. On average, small random impulses increase the gyration speed, energizing and broadening ion velocity‐space distributions. This process will be shown to have an important influence on the outflux of warm ions from the magnetosphere.