bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetospheric ions and electrons in the distant magnetosheath at ∼50 RE and ∼180 RE: ISEE‐3 observations
Authors: Scholer M. , Hovestadt D. , Gloeckler G. , Klecker B. , Ipavich F. M. , Zwickl R. D.
Published: February 2008

We have analyzed energetic electron (75 ‐ 115 keV) and proton ( ∼ 30 keV) measurements at the dawn side of the distant magnetosheath at ∼ 50 RE and ∼ 180 RE. The data have been obtained during the recent ISEE‐3 Geotail Mission. At ∼ 50 RE electrons and protons occur almost simultaneously in bursts of ∼ 2 min duration. The electrons stream intensely away from the general magnetopause position along the magnetic field line. The proton angular distributions exhibit a large parallel anisotropy that is symmetric with respect to the magnetic field in the plasma frame of reference. At ∼ 180 RE almost no electrons have been so far observed above the threshold of our detector. The protons are isotropic in the plasma frame. The observations are discussed in terms of a possible model where magnetosheath flux tubes are connected to the tail magnetic field so that the magnetospheric particles can leak out. At ∼ 50RE propagation to the spacecraft is believed to be scatter‐free; after reaching ˜ 200 RE the particles have resided long enough in the magnetosheath so that they are then coupled to the magnetosheath flow via pitch angle scattering.
Ignition of beam plasma discharge in the electron beam experiment in space
Authors: Sasaki S. , Kawashima N. , Kuriki K. , Yanagisawa M. , Obayashi T. , Roberts W. T. , Reasoner D. L. , Taylor W. W. L. , Williamson P. R. , Banks P. M. , Burch J. L.
Published: February 2008

An ignition of Beam Plasma Discharge (BPD) in space was observed in a neutral gas‐electron beam interaction experiment by Space Shuttle/Spacelab‐1 in 1983. An electron beam of 8 kV 100 mA was injected into a high dense nitrogen gas cloud of 1023 molecules which was released during 100 msec from the orbiter. The appearence of the beam and its surroundings observed by a low‐light‐level TV camera showed a local ignition of the beam plasma discharge in the gas cloud. The enhanced plasma production, generation of auroral emission and associated wave emission were also detected by onboard diagnostic instruments.
Absorption properties and graphitic carbon emission factors of forest fire aerosols
Authors: Patterson E. M. , McMahon C. K. , Ward D. E.
Published: February 2008

Data on the optical absorption properties (expressed as a specific absorption, Ba) of the smoke emissions from fires with forest fuels have been determined for a series of low‐intensity field fires and a series of laboratory scale fires. The Ba data have been used to estimate the emission factors for graphitic carbon [EF(Ce)] for these test fires to provide data needed for regional visibility studies, tropospheric air chemistry studies, and studies evaluating nuclear winter scenarios.
Whistler‐mode radiation from the Spacelab 2 electron beam
Authors: Gurnett D. A. , Kurth W. S. , Steinberg J. T. , Banks P. M. , Bush R. I. , Raitt W. J.
Published: February 2008

During the Spacelab 2 mission the Plasma Diagnostics Package (PDP) performed a fly‐around of the shuttle at distances of up to 300 meters while an electron beam was being ejected from the shuttle. We discuss a magnetic conjunction of the shuttle and the PDP while the electron gun was operating in a steady (DC) mode. During this conjunction, the PDP detected a clear funnel‐shaped emission that is believed to be caused by whistler‐mode emission from the beam. Ray‐path calculations show that the shape of the funnel can be accounted for by whistler‐mode waves propagating near the resonance cone. Because the beam and waves are propagating in the same direction, the radiation must be produced by a Landau, ω/k∥ = vb, interaction with the beam. Other types of waves generated by the beam are also described.
The bow wave of comet Giacobini‐Zinner: Ice magnetic field observations
Authors: Jones D. E. , Smith E. J. , Slavin J. A. , Tsurutani B. T. , Siscoe G. L. , Mendis D. A.
Published: February 2008

Fitting of a Mach 2 shock surface to the ICE magnetic field data obtained near comet Giacobini‐Zinner has provided subsolar bow wave distances that infer neutral gas outflow rates comparable to previous measurements, and orientations of the bow wave symmetry axis that are consistent with the plasma measurements and motion of the comet relative to the solar wind. Mach values of 1.5‐2 and transition thicknesses of the order of 104 km are inferred when the field magnitude and variance data are compared. Cross spectra of the transverse field components in and near the bow wave exhibit a peak near 10−2 Hz, or near the cyclotron frequency of ions from the water group. However, the level of turbulence is not consistent with that observed for similar configurations at planetary bow shocks.
Dust particles detected near Giacobini‐Zinner by the ICE Plasma Wave Instrument
Authors: Gurnett D. A. , Averkamp T. F. , Scarf F. L. , Grün E.
Published: February 2008

During the ICE flyby of Giacobini‐Zinner the plasma wave instrument detected numerous impulsive signals caused by dust impacts on the spacecraft. Most of the impacts occurred within 30,000 km of the comet. The impact rate averaged over the inbound and outbound legs varies approximately as 1/r², as would be expected for an isotropic constant velocity radial outflow. Small differences between the inbound and outbound legs exist which may be indicative of azimuthal variations in the dust production rate. A simple model of the impact ionization and charge collection by the antenna indicates that the particles have a mass on the order of 10−12 to 10−10 gm, corresponding to particles with radii of a few microns.
Variations of galactic cosmic rays with heliolatitude in the outer heliosphere
Authors: McDonald Frank B. , Lal Nand
Published: February 2008

On 1 January 1986, Voyager 1 was at a heliolatitude of 30° above the ecliptic plane at a radial distance of 25.4 AU. The galactic cosmic ray latitudinal gradients in the outer heliosphere measured at that time were found to be negative, ∼1‐2%/AU, show no strong energy dependence and are approximately half the radial gradient.
Position and structure of the comet Halley bow shock: Vega‐ 1 and Vega‐2 measurements
Authors: Galeev A. A. , Gribov B. E. , Gombosi T. , Gringauz K. I. , Klimov S. I. , Oberz P. , Remizov A. P. , Riedler W. , Sagdeev R. Z. , Savin S. P. , Sokolov A. Yu. , Shapiro V. D. , Shevchenko V. I. , Szego K. , Verigin M. I. , Yeroshenko Ye. G.
Published: February 2008

The effect of solar wind loading by cometary ions on the position and structure of the comet Halley bow shock is discussed on the basis of simultaneous measurements of plasma, magnetic field and plasma waves aboard the "Vega‐1" and "Vega‐2" spacecraft. Data from the inbound crossings of the bow shock show that both quasiperpendiuclar ("Vega‐1") and quasiparallel ("Vega‐2") shocks were observed. The thickness of these shocks is greater than that of the Earth's bow shock at least by the ratio of the masses of cometary ions and protons. The bow shock position is reasonably well described by the kinetic model of solar wind loading by cometary ions.
Observations of plasma waves within regions of perpendicular ion acceleration
Authors: Kintner P. M. , LaBelle J. , Scales W. , Yau A. W. , Whalen B. A.
Published: February 2008

The acceleration of ionospheric ions transverse to the geomagnetic field by factors of 10³ is believed to be caused by plasma waves. We have made simultaneous measurements of electric fields (0‐16kHz) and energetic ions (50eV to 20keV) within regions of perpendicular ion acceleration from the sounding rocket MARIE. Perpendicular ion acceleration was correlated with plasma waves near and above the lower hybrid frequency. Ions were detected up to energies of 300 eV and the broadband lower hybrid waves reached an amplitude of 10‐30 mV/m (RMS) over the frequency band 4‐16 kHz. Although electric field amplitudes near the O+ cyclotron frequency reached a maximum value of 10 mV/m (RMS), there was no spectral evidence of electrostatic ion cyclotron waves associated with ion acceleration. There was spectral evidence of H+ Bernstein modes near the lower hybrid frequency. If we assume that whistler mode waves near and above the lower hybrid frequency were responsible for the ion acceleration then the conversion efficiency of wave energy to ion energy was .01 to .1.
Thermal catastrophe in the plasma sheet boundary layer
Authors: Smith Robert A. , Goertz Christoph K. , Grossman William
Published: February 2008

This Letter presents a first step towards a substorm model including particle heating and transport in the plasma sheet boundary layer (PSBL). The heating mechanism discussed is resonant absorption of Alfven waves. For some assumed MHD perturbation incident from the tail lobes onto the plasma sheet, the local heating rate in the PSBL has the form of a resonance function of the one‐fluid plasma temperature. Balancing the local heating by convective transport of the heated plasma toward the central plasma sheet, an "equation of state" is found for the steady‐state PSBL whose solution has the form of a mathematical catastrophe: at a critical value of a parameter containing the incident power flux, the local density, and the convection velocity, the equilibrium temperature jumps discontinuously. Associating this temperature increase with the abrupt onset of the substorm expansion phase, the catastrophe model indicates at least three ways in which the onset may be triggered. Several other consequences related to substorm dynamics are suggested by the simple catastrophe model
Cleopatra Patera on Venus: Venera 15/16 evidence for a volcanic origin
Authors: Schaber Gerald G. , Kozak Richard C. , Masursky Harold
Published: February 2008

The non‐concentric nature, anomalous depth, and terraced morphology of the nested craters that compose Cleopatra Patera are more closely analogous to volcanic craters (calderas) than multi‐ring impact structures. Associated deposits northeast and downslope of the Patera first recognized on Venera 15/16 radar images are interpreted as volcanic plains related to, and perhaps cogenetic with, Cleopatra. The plains lavas probably originated as effusions from a radial rift zone or ring fissures. Rim deposits surrounding Cleopatra are asymmetric along the structural fabric of the region, also indicating fissure‐type eruptions. Finally, a volcanic origin not only is easily reconciled with the tectonic setting of the Patera, it is almost required by the correlation between the Patera and regional structural trend.
Carbonyl sulfide hydrolysis as a source of hydrogen sulfide in open ocean seawater
Authors: Elliott Scott , Lu Eric , Rowland F. Sherwood
Published: February 2008

Two independent lines of evidence suggest that the hydrogen sulfides (H2S, SH−, S2−) are present in open surface seawater at pico to nanomolar levels. 1) Such concentrations are calculated for a chemical steady state involving carbonyl sulfide hydrolysis as source, followed by oxidative removal. 2) Although it is not yet certain that measurements of gaseous H2S over the open ocean are reliable, they require aqueous sulfide concentrations in this range in order to support sea‐to‐air flux. If pico to nanomolar of the hydrogen sulfides are included in standard equilibrium models of seawater complexation chemistry, several trace metals speciate predominantly as sulfide complexes and are supersaturated with respect to their solid sulfides. This supersaturation argues for solubilization of the metals through other unexpected complexes, perhaps involving reduced sulfur ligands associated with dissolved organics, or even intermediates along the hydrogen sulfide oxidation chain.
Biharmonic spline interpolation of GEOS‐3 and SEASAT altimeter data
Authors: Sandwell David T.
Published: February 2008

Green functions of the biharmonic operator, in one and two dimensions, are used for minimum curvature interpolation of irregularly spaced data points. The interpolating curve (or surface) is a linear combination of Green functions centered at each data point. The amplitudes of the Green functions are found by solving a linear system of equations. In one (or two) dimensions this technique is equivalent to cubic spline (or bicubic spline) interpolation while in three dimension it corresponds to multiquadric interpolation. Although this new technique is relatively slow, it is more flexible than the spline method since both slopes and values can be used to find a surface. Moreover, noisy data can be fit in a least squares sense by reducing the number of model parameters. These properties are well suited for interpolating irregularly spaced satellite altimeter profiles. The long wavelength radial orbit error is suppressed by differentiating each profile. The shorter wavelength noise is reduced by the least squares fit to nearby profiles. Using this technique with 0.5 million GEOS‐3 and SEASAT data points, it was found that the marine geoid of the Caribbean area is highly correlated with the sea floor topography. This suggests that similar applications, in more remote, areas may reveal new features of the sea floor.
A study of a magnetospheric substorm recorded by the Viking auroral imager
Authors: Hones E. W. , Anger C. D. , Birn J. , Murphree J. S. , Cogger L. L.
Published: February 2008

A substorm, recorded at 80 second time resolution in images from the Viking auroral imager, has been studied using data from ground observations, from a geosynchronous satellite and from ISEE 1 in the magnetotail plasma sheet. Substorm onset, marked by negative bays at the ground, particle injection at synchronous orbit and plasma sheet dropout at ISEE 1, appeared to produce only local brightening of the night side oval. A rapid poleward expansion of the auroras twenty minutes later was accompanied by a major reduction of tail energy density and swelling of the inner plasma sheet. Recovery, 15 minutes later, of auroral zone bays and the plasma sheet was accompanied by fading of the equatorward auroras that left a bright poleward arc as the primary auroral emission.
Plasma energization on auroral field lines as observed by the Viking spacecraft
Authors: Lundin R. , Eliasson L. , Hultqvist B. , Stasiewicz K.
Published: February 2008

High‐resolution particle measurements obtained from the VIKING spacecraft have provided interesting new observations of accelerated and heated plasma on auroral field lines. We present observations of upward ion and electron beams and conies which indicate that the acceleration/heating process is so variable that many different physical processes have to be taken into account. As a consequence of this variability a new classification scheme will be adopted.
Partial derivatives of synthetic seismograms for a laterally heterogeneous Earth model
Authors: Tsuboi Seiji , Geller Robert J.
Published: February 2008

We present a scheme for calculating the partial derivatives with respect to elastic properties of the eigenfrequencies and eigenfunctions of a laterally heterogeneous, rotating, anelastic and elliptical earth model. We use these results to obtain a formula for the partial derivatives of synthetic seismograms (or spectra) with respect to the elastic properties. These partial derivatives, which are based on the variational solution of the forward problem, make it possible to perform iterative linearized waveform inversion for the earth's laterally heterogeneous structure.
Eigenmode analysis of compressional waves in the magnetosphere
Authors: Cheng C. Z. , Lin C. S.
Published: February 2008

Recent multiple satellite observations of compressional Pc 5 waves indicate for the first time that the field‐aligned mode structure of the compressional magnetic field was antisymmetric with respect to the earth's magnetic equator. To understand the mode structures of low frequency compressional waves, a comprehensive eigenmode analysis of compressional Alfven instabilities was performed for a two component anisotropic plasma in a dipole magnetic field. The eigenmode equations derived from the gyrokinetic equations are solved analytically and numerically for both the drift mirror and the drift compressional instabilities. The solutions indicate that the drift mirror mode has an antisymmetric compressional component with respect to the magnetic equator, whereas the drift compressional mode has a symmetric one. For typical storm time plasma parameters near geosynchronous orbit, it is suggested that the recently observed compressional Pc 5 wave was in a nonlinearly saturated state of the drift mirror instability.
Highly relativistic magnetospheric electrons: A role in coupling to the middle atmosphere?
Authors: Baker D. N. , Blake J. B. , Gorney D. J. , Higbie P. R. , Klebesadel R. W. , King J. H.
Published: February 2008

Long‐term (1979‐present) observations of relativistic electrons (2–15 MeV) at geostationary orbit show a strong solar cycle dependence. Such electrons were largely absent near the last solar maximum (1979–80), while they were prominent during the approach to solar minimum (1983–85). This population now is dwindling as solar minimum has been reached. The strong magnetospheric presence of this population closely parallels the presence of high‐speed solar wind streams which results from solar coronal hole structures during the approach to solar activity (sunspot) minimum. We clearly observe 27‐day periodic enhancements of the relativistic electrons in association with concurrently measured solar wind streams (VSW ≳ 600 km/s). We have used a numerical transport code to study the coupling of these high‐energy electrons to earth's upper and middle atmosphere. We calculate using the observed energy spectra of the electrons that, when precipitated, these electrons show a large (maximum of ∼100 keV/cm³‐s) energy deposition at 40–60 km altitude, which is 3–4 orders of magnitude greater than the galactic cosmic ray or solar EUV energy deposition at these altitudes. We also find that the global energy deposition in the mid‐latitudes totals nearly 1021 ergs for a typical 2–3 day event period. We conclude that this previously unrecognized electron population could play an important role in coupling solar wind and magnetospheric variability (on 27‐day and 11‐year cycles) to the middle atmosphere through a modulating effect on lower D‐region ionization and, possibly, on upper level ozone chemistry. These electrons also may contribute to the recent Antarctic polar ozone depletion phenomenon.
A note on the description of surface roughness using fractal dimension
Authors: Brown Stephen R.
Published: February 2008

Self‐affine fractals are useful models of the surfaces of rock fractures. The scaling properties of these surfaces are described by two parameters, the fractal dimension and the crossover length. Two methods for estimating the fractal dimension of a profile of a rough surface are compared, the divider method and the spectral method. It is shown that the two methods yield the same results, if the horizontal resolution at which the profile is measured is smaller than the crossover length. However, for resolutions greater than the crossover length, the divider method always gives a fractal dimension close to 1. To guide future work, the crossover length is estimated for typical joint surfaces and for the San Andreas fault. Additionally, a simple method is proposed to obtain the correct fractal dimension without prior knowledge of the crossover length.
Observation by the incoherent scatter technique of the hot spots in the auroral zone ionosphere
Authors: Kofman W. , Lathuillere C.
Published: February 2008

In this paper, we show a first set of incoherent‐scatter data measured at EISCAT, showing profiles of very high ion temperature (greater than 8000K), observed along geomagnetic field lines. We analyze the incoherent‐scatter spectra, their form and the influence of the ionospheric electric field. We estimate the Joule heating energy input by two methods: from the electric field and from direct measurements of ion temperature. These estimations show that our measurements can be explained by the frictional heating between fast moving species.
Electrostatic ion instabilities in the presence of parallel currents and transverse electric fields
Authors: Ganguli G. , Palmadesso P. J.
Published: February 2008

The electrostatic ion instabilities are studied for oblique propagation in the presence of magnetic field‐aligned currents and transverse localized electric fields in a weakly collisional plasma. The presence of transverse electric fields result in mode excitation for magnetic field aligned current values that are otherwise stable. The electron collisions enhance the growth while ion collisions have a damping effect. These results are discussed in the context of observations of low frequency ion modes in the auroral ionosphere by radar and rocket experiments.
Mesozoic paleomagnetic results of the Tarim Craton: Tertiary relative motion between China and Siberia?
Authors: Li Yianping , Zhang Zhengkun , McWilliams Michael , Sharps Robert , Zhai Yongjian , Li Yongan , Li Qiang , Cox Allan
Published: February 2008

Paleomagnetic poles from two Late Jurassic to Late Cretaceous stratigraphic sections on the northern boundary of the Tarim Craton in western China are concordant with poles of similar age from eastern China. When combined with previously published data, these new results suggest that the major tectonic blocks which comprise China (the Tarim, Yangtze and Sino‐Korean cratons) have been arranged in approximately their present relative configuration since Cretaceous times. The averaged Cretaceous paleomagnetic pole for China is significantly different from the averaged Cretaceous pole for Siberia. The difference may reflect significant relative post‐Cretaceous motion between the composite China terrane and the Siberian craton. Alternatively, the Cretaceous pole for Siberia may not be reliable.
Iue observations of Neptune for H Lyman‐α emission
Authors: Clarke John T.
Published: February 2008

Neptune has been observed on seven occasions with the International Ultraviolet Explorer Observatory (IUE, Boggess et al. 1978) in an attempt to detect planetary H Ly‐α line emission. The observing technique is the same as previously employed in IUE observations of Uranus, described in detail by Clarke et al. (1986), and consists of spatial separation of the planetary emission from background geo‐coronal and interplanetary H Ly‐α emissions within the spectrograph aperture. No emission has been detected from Neptune in any of the observations, with 1 σ upper limits to the planet‐averaged surface brightness as low as 180 Rayleighs. Despite poorer sensitivity in observing Neptune from Earth orbit compared to the other planets, the intrinsic brightness is significantly less than the 400‐1500 R that would be expected from scaling arguments. This upper limit does not rule out scattered solar H Ly‐α emission from a Jupiter‐like atmosphere, and it does not rule out auroral emission from an active magnetosphere. The main significance is for the efficiency of the electroglow process on Neptune, and Neptune is significantly less efficient at producing bright aurora and/or electroglow than Uranus. This may further indicate that Neptune has a lower upper atmospheric temperature than Uranus.
Plasma wave turbulence around the shuttle: Results from the Spacelab‐2 flight
Authors: Gurnett D. A. , Kurth W. S. , Steinberg J. T. , Shawhan S. D.
Published: February 2008

During the Spacelab‐2 flight, which occurred from July 29, to August 6, 1985, a spacecraft called the Plasma Diagnostics Package (PDP) was released from the shuttle to explore the plasma environment around the shuttle. The plasma wave instrument on the PDP detected a region of intense broadband turbulence around the shuttle at frequencies extending from a few Hz to about 10 kHz. The noise has broadband intensities ranging from 1 to 5 mV/m and was observed at distances of up to 400 m from the shuttle. The highest intensities occurred in the region downstream of the shuttle and along magnetic field lines passing near the shuttle. The intensities also tended to increase during periods of high thruster activity, which provides strong evidence that the noise is caused by an interaction of the ionosphere with gaseous emissions from the shuttle, similar in many respects to the interaction of a comet with the solar wind. Antenna interference patterns observed in the wideband data show that the wavelength of the turbulence is very short, a few meters or less.
Observation of rain at vertical incidence with a 94 GHz Doppler radar: An insight on Mie scattering
Authors: Lhermitte Roger M.
Published: February 2008

A new method aimed at differentiating air vertical motion and raindrop terminal velocity in a velocity spectrum observed at vertical incidence identification based on Mie backscattering oscillations occurring within the raindrop size range at the 3.2 mm wavelength. The method is applicable to measurement of downdraft or microburst in rainshafts and dropsize distribution in all types of rain.
An MHD simulation of plasma flow past Io: Alfvén and slow mode perturbations
Authors: Linker Jon A. , Kivelson Margaret G. , Walker Raymond J.
Published: February 2008

We have studied the flow of plasma past Io using a time dependent, three‐dimensional magnetohydrodynamic (MHD) simulation. In addition to observing the “Alfvén wing”, a standing Alfvén wave perturbation expected from analytic theory, we have found that the other MHD modes contribute important perturbations. In particular, standing slow mode perturbations also are present in the flow.
Cause of a monochromatic inertia‐gravity wave breaking observed by the MU radar
Authors: Muraoka Yoshikazu , Sugiyama Takuya , Kawahira Kohji , Sato Toru , Tsuda Toshitaka , Fukao Shoichiro , Kato Susumu
Published: February 2008

Mesospheric wind measurements made by the MU radar at Shigaraki (34.9°N, 136.1°E), Japan, on September 20, 1985, allow us to study gravity wave breaking. The wind data has shown that a monochromatic inertia‐gravity wave was propagating vertically, indicating an exponential growth up to a mesospheric level with height. Above that level, however, the amplitude rather decreased. Moreover, the wave‐form broke remarkably at a level. In this paper, we show that the breaking of the monochromatic wave can be connected with the convective instability in the wave field, estimating the local stability from the wind data.
A numerical model simulation of a summer reversal of the Beaufort Gyre
Authors: Preller Ruth H. , Posey Pamela G.
Published: February 2008

Ice drift derived from the Polar Ice Prediction System (PIPS) is used to study the sea ice circulation of the Beaufort and Chukchi seas in the late summer. Model simulations for the years 1983, 1986 and 1987 show that the anticyclonic Beaufort Gyre reverses to cyclonic circulation in the late summer. This result is due to a change in the mean atmospheric surface pressure. Drifting buoys from 1983 confirm this reversal of the Beaufort Gyre.
Alpha particles in field‐aligned beams upstream of the bow shock: Simulations
Authors: Burgess D.
Published: February 2008

The results of self‐consistent hybrid simulations of an oblique collisionless, supercritical shock are presented in order to study the possibility that field‐aligned ion beams (FABs) formed by direct reflection could contain alpha particles. Alpha particles are included in the simulations self‐consistently, with care taken to ensure that sufficient simulation particles are present to give reasonable statistics. It is found that alpha particles can backstream from a shock with θBn = 45°, but less readily than protons. The deficit of alpha particles in the FABs, expressed as a relative density ratio to H+ (normalized to the solar wind He++ to H+ density ratio), varies between about 0.1 and < 0.01, and depends strongly on the upstream H+ and He++ temperatures.
The density of Triton: A prediction
Authors: McKinnon William B. , Mueller Steve
Published: February 2008

We predict the density of Triton, as a function of radius, based on the assumptions that it was captured from solar orbit and thus has a rock/ice ratio similar to that of the Pluto‐Charon system. The best present estimates for Triton's radius are 1000–2000 km, and if our origin hypothesis is correct, its density should be greater than 2.0 g cm−3, increasing slowly with radius. On the other hand, if Triton is an original regular satellite whose orbit has been perturbed, its density will be lower and more consistent with the derived rock fractions of other icy satellites.
Paleomagnetic results from the Upper Cretaceous Maudlow and Livingston formations, southwest Montana
Authors: Swenson Paul , McWilliams Michael
Published: February 2008

A paleomagnetic investigation of welded tuff units from the Late Cretaceous Livingston and Maudlow Formations was undertaken to refine the Late Cretaceous to Paleocene APWP for cratonic North America. After progressive AF and thermal demagnetization, the Maudlow Formation (46.1°N, 248.9°E) yields a paleomagnetic pole at 70°N, 208°E (11 sites, A95 = 9°, K = 22). Tectonic correction improves the directional grouping, and the change is statistically significant. Two normal polarity intervals bounding a single reversed polarity interval are present. We interpret the reversed interval to be Chron 33r, on the basis of: [1] stratigraphic correlation of the Maudlow Formation with the Campanian Sedan Formation located 40 km to the east, and [2] K‐Ar dates of 83 ± 2 Ma at the middle of the sampled section and 74.9 ± 1 Ma near the top of the sampled section.

The Livingston Formation (45.5°N, 250.1°E) yields a high Hc magnetization with a negative fold test, suggesting a post‐folding secondary magnetization. The Livingston mean direction yields a paleomagnetic pole at 72°N, 218°E (10 sites, A95 = 4°, K = 107) and is clearly distinguishable from a co‐existing lower Hc component reflecting a recent viscous overprint. We interpret the high Hc magnetization as Late Cretaceous to Paleocene in age.

Neither the Maudlow Formation pole nor the pole derived from the high Hc overprint in the Livingston Formation agree with previously published poles for either the Late Cretaceous or Tertiary, but they do lie on a simple continuation of the APWP between Late Cretaceous and Paleocene mean poles. Secondary magnetizations found in the Franciscan Complex of California also yield poles which lie on a proposed extension of the APWP. If the Franciscan secondary poles represent an overprint event associated with early Tertiary accretion, and if the Livingston secondary pole represents a deformational event related to Laramide uplift of the nearby Beartooth Range, then together these three poles suggest that the North American APWP may continue farther to the east and south to define a Cretaceous‐Tertiary cusp.
The Chernobyl Reference Horizon (?) in the Greenland Ice Sheet
Authors: Dibb Jack
Published: February 2008

Published reports of the presence of radioactive debris from the Chernobyl reactor accident in snow on the Greenland ice sheet raised the strong prospect that such debris might constitute a valuable time stratigraphic marker all over the ice sheet. Large volume snow samples to test this possibility were collected from 7 snowpits as part of a wide ranging regional snow chemistry survey conducted during 1987 and 1988. Snow “labeled” with Chernobyl derived radioactivity was detected in all of the pits. However, the total amount of radioactive debris found at the different locations varied over a 20 fold range. The variability in total fallout showed no clear large scale spatial pattern that could be related to the presumed progress of the radioactive plume over Greenland, suggesting that small scale differences in precipitation pattern and reworking of the snow by wind were predominantly responsible for the patchy preservation of the Chernobyl “layer” on the Greenland ice sheet.
Electromagnetic expression of axial magma chambers
Authors: Everett M. E. , Edwards R. N.
Published: February 2008

The electrical conductivity of sea floor materials is a strong function of porosity, pore geometry, fluid content, temperature and percentage of partial melt. These material properties are particularly volatile near the midocean ridge. Tracking electromagnetic eddy currents generated on the sea floor as they diffuse across the ridge can provide images of the subaxial electrical and through interpretation the geological structure. We have computed numerically in 2D the response of a crustal magma chamber located beneath the East Pacific Rise to excitation in two fundamental orthogonal modes, rise‐normal (TE) and rise‐parallel (TM) electric field. A finite element representation of the electromagnetic (EM) diffusion equations is solved in the Laplace domain and the results inverted into the time domain via the Gaver‐Stehfest algorithm. A sequence of snapshots for each mode for the time range 0.1 to 15 s shows the complete progression of the eddy currents into, through and around the magma chamber. The TE and TM signals at a receiver site above the conductive magma chamber are delayed and attenuated in comparison with those expected for normal layered oceanic crust.
Test particle acceleration in a magnetotail reconnection configuration
Authors: Sachsenweger D. , Scholer M. , Möbius E.
Published: February 2008

AMPTE/IRM measurements during a period of strong magnetic activity on April 8, 1985 exhibit a significant hardening of the energy spectra of all detected ion species (H+, He2+, He+, O+) following substorm expansion. In order to explain these observations in the framework of the substorm neutral line model, single‐particle trajectories of various ions (H+, He2+, O+) are followed numerically in the time‐dependent electric and magnetic fields obtained from a two‐dimensional magnetohydrodynamic simulation of magnetotail reconnection. Current sheet acceleration of a suitable plasma sheet ion distribution can explain the observed ordering of the flux increase of the various species in energy per charge. Starting from a cold lobe population, however, current sheet acceleration cannot account for the differential ion intensities observed after substorm expansion.
Modeling the Solar Cycle Dependence of Quiet‐Time Ion Upwelling at High Geomagnetic Latitudes
Authors: Cannata R. W. , Gombosi T. I.
Published: February 2008

In this letter, we summarize initial results showing how solar cycle variations of the thermosphere modify the composition and intensity of ion upflows at high geomagnetic latitudes. Using an improved version of the one‐dimensional hydrodynamic polar wind model developed by Gombosi et al. (1985), we obtain H+ and O+ vertical flow profiles using different thermospheric states corresponding to solar cycle minimum and maximum. In comparing the quasi‐equilibrium flux profiles for both cases, we find that H+ upwelling shows almost no variations in intensity with solar cycle while O+ exhibits a 10‐fold increase from solar minimum to solar maximum. These changes result in an O+‐dominated upflow at solar maximum while H+ flows dominate at solar minimum. We relate these different behaviors to long‐term thermospheric changes resulting from solar cycle EUV/UV differences and compare our results with observations.
Iridium‐bearing sublimates at a hot‐spot volcano (Piton De La Fournaise, Indian Ocean)
Authors: Toutain Jean‐Paul , Meyer Georges
Published: February 2008

Sublimates and incrustations derived upon the cooling of volcanic gases have been collected on various sites (Piton de la Fournaise, Poas, Momotombo, Etna, Ardoukoba and Erta‐Ale). They have been analysed for Ir and other volatile elements (Se, As, Cu, Au, Ag, Pb, Tl) by means of instrumental neutron activation analysis (INAA) and proton induced X‐Ray emission (PIXE). Among the investigated volcanoes, only Piton de la Fournaise is found to release detectable amounts of iridium. Ir in Piton de la Fournaise sublimates is associated with F‐minerals. This confirms its gaseous transport as a volatile fluoride compound.

Iridium seems to be preferentialy released by hot‐spot type volcanoes, and its detection in Piton de la Fournaise sublimates provides a positive argument in favour of a volcanic hypothesis to explain the KTB events.
The separatrix tentacle effect of ion acceleration to the plasma sheet boundary
Authors: Büchner Jörg , Zelenyi Lev M.
Published: February 2008

We describe the effect of a continuous ion ‐ acceleration in the Earth's magnetotail due to chaotic particle scattering caused by separatrix traversals in the velocity space. This effect operates almost everywhere in the plasma sheet, but outside and independent of neutral lines. Ae a distributed inner source it supports fast ion streams at the boundary of the plasma sheet.
Enhanced Crustal Reflection Continuity by Estimation of Staitcs From Coherence Filtered Sections
Authors: Varsek John L. , Cook Frederick A. , Cheadle Scott P.
Published: February 2008

Coherency filtered seismic sections provide excellent models for estimating residual statics, especially for deep crustal data with low signal to noise. A second coherency filter pass following residual statics collections provides even better structural clarity than is seen on sections with only a single coherency filter pass. Benefits of the technique include: increased lateral extent of individual reflections resulting in fewer isolated events, uniform wavelet shape throughout the section, and an increase in the number of detected events over line drawings. This processing flow results in appealing visual displays and may provide new information on structural complexities not recognized in line drawings based on the input data alone.
A New Kinetic Model for Time‐Dependent Polar Plasma Outflow: Initial Results
Authors: Wilson G. R. , Ho C. W. , Horwitz J. L. , Singh N. , Moore T. E.
Published: February 2008

We have developed a new time‐dependent kinetic plasma outflow model which uses a kinetic description of the parallel motions of the ion guiding centers, while assuming the electrons are a massless neutralizing fluid (i.e., Boltzmann distributed). The ions, O+ and H+, are followed as individual particles which respond to the gravitational, magnetic mirror and ambipolar electric forces as they move in one dimension along a magnetic flux tube. We show results for a case where the electron temperature in the flux tube is raised from a value near the ion temperature (3000° K) to a value of 10,000° K. The outflowing hydrogen is little affected by the change, but the barrier to the outflow of oxygen ions is greatly reduced with the result that an enhanced outflow of O+ ions travels up the flux tube. As the oxygen ions adjust to the higher electron temperature the flux of oxygen ions at the lower end of the flux tube increases very rapidly compared to the more gradual increase at the upper end. Also, an enhanced oxygen parallel temperature peak travels up the flux tube, increasing in magnitude as it goes. It travels at a speed significantly higher than the oxygen ion acoustic speed (found with Te = 10,000° K).
SAGE II observations of polar stratospheric clouds near 50°N January 31–February 2, 1989
Authors: Pitts M. C. , Poole L. R. , McCormick M. P.
Published: February 2008

Polar stratospheric clouds (PSCs) form at very cold temperatures which typically occur only at high latitudes during local winter. However, meteorological circumstances in the Arctic during late January 1989 led to PSC formation unusually far to the south, at latitudes (near 50°N) being sampled during the period (January 31–February 2) by the orbiting SAGE II instrument. These unusual PSC sightings and the evolution of meteorological conditions which produced the episode are described. Profiles of SAGE II extinction measurements at 0.525 and 1.02 μm show clear signatures of PSCs and indicate that the cloud particles were considerably larger than the background aerosol. It is most important to note that the clouds were sighted at a latitude where there was extensive sunlight, thus increasing the likelihood of ozone loss both locally and downstream due to enhancements in reactive chlorine expected from heterogeneous chemical processing within the PSCs.
Does the ponderomotive force move mass in the magnetosphere?
Authors: Allan W. , Manuel J. R. , Poulter E. M.
Published: February 2008

We apply a two‐dimensional, nonlinear hydromagnetic computer code to the problem of pure fast mode cavity resonances in a box model of the magnetosphere. The cavity modes are excited by a magnetopause compression and relaxation with maximum boundary velocity v0. The results show that significant mass transport of relatively low energy plasma by the wave fields may be possible for v0/A0 ∼ 0.2, where A0 is the Alfvén speed at the boundary. For a likely field‐aligned perturbatiou structure, the mass tends to accumulate at and near the equatorial plane. We interpret this mass transport as being driven by the ponderomotive force, which is finally limited by opposing pressure gradients in a finite β plasma. Heating by adiabatic compression of the plasma is also seen.
Balloon observations of nitric acid aerosol formation in the Arctic stratosphere: I. Gaseous nitric acid
Authors: Schlager H. , Arnold F. , Hofmann D. , Deshler T.
Published: February 2008

Measurements of the altitude distributions of gaseous nitric acid and aerosols were made in the winter arctic stratosphere using balloon‐borne mass spectrometer‐ and aerosol counter techniques. The measurements took place under conditions of very low stratospheric temperatures, with minimum values of 186 K around 24 km altitude being about 6 degrees below the existence temperature (T(NAT)) for NAT (Nitric Acid Trihydrate) aerosols. At these heights, a local depletion of gaseous nitric acid by up to about 60% was observed suggesting the occurrence of nitric acid incorporation into aerosols, which were in fact observed and whose inferred nitric acid content is roughly consistent with the missing gaseous nitric acid. Our data suggest that rapid formation of NAT‐aerosols associated with substantial condensational depletion of gaseous nitric acid occurred only at temperatures of about 3 to 4 degrees below T(NAT) corresponding to large HNO3‐supersaturations, which are probably required for activation of a major fraction of preexisting condensation nuclei.
Kinetic measurements of the ClO + O3 → ClOO + O2 reaction
Authors: Stevens Philip S. , Anderson James G.
Published: February 2008

Upper limits for the bimolecular rate constant for the reaction ClO + O3 → ClOO + O2 have been measured directly between 233 and 413 K using a discharge‐flow system at 1–2 torr total pressure. Production of ClO (which occurs quickly after thermal decomposition of ClOO in the presence of O3) was detected using Laser Magnetic Resonance spectroscopy, and distinguished from the reactant ClO through isotopic oxygen labelling. At 298 and 233 K, k1 was found to be less than 1.4 × 10−17 cm3 molecule−1 s−1. At 413 K1 k1 = (4.0 ±2.0) × 10−16 cm3 molecule−1 s−1. The experimental conditions were modelled using a kinetic simulation program to show that chemical and isotopic scrambling interferences were negligible. From these results, it is concluded that this bimolecular reaction does not contribute significantly to the observed ozone depletion within the antarctic vortex.
Seismicity in the twenty years preceding the Loma Prieta California Earthquake
Authors: Olson Jean A.
Published: February 2008

Persistent seismicity occurred at a low rate during at least the twenty years before the Loma Prieta earthquake along the 60 km‐long rupture zone. The depth distribution of this seismicity forms a broad “U”‐shape that delineates the previously locked rupture zone. Relocations of seismicity during the ten years before the earthquake relative to the Loma Prieta aftershocks show that this “U”‐shaped distribution can be partitioned lengthwise into activity on two adjacent subparallel structures: a vertical fault beneath the San Andreas fault trace and an eastward‐dipping blind fault beneath the Sargent fault trace. The 11–18 km deep, southwest‐dipping part of the Loma Prieta rupture was not active during at least the preceding ten years. The slip geometry of intersecting fault structures in this zone could contribute to both the preparation process and the complexity of the rupture.
On the ionosphere of Triton: An evaluation of the magnetospheric electron precipitation and photoionization effects
Authors: Ip W.‐H.
Published: February 2008

In order to explore the origin and physical nature of the ionosphere of Triton, a simple, 2‐dimensional electron drift model is developed to approximate the ionization effect of magnetospheric electrons. The derived profile of ion production rate is then applied to a steady‐state photochemical model calculation. It is shown that, as a result of the very low CH4 mixing ratio in Triton's atmosphere, the most dominant ion in the upper ionosphere could be N+. There are, however, difficulties in explaining the electron number density profile below 500 km as inferred from the radio science experiment on Voyager 2. One major factor is the increasing importance of the ion chemistry involving N+ and H2 from CH4 photolysis in this region. This problem may be partially resolved if we invoke a more efficient electron transport in the atmosphere or the possible presence of metallic ions like Si+, Ne+ and Na+ which do not react with N2 and H2 in the lower ionosphere.
Ionospheric outflow of plasma and compression relationship in the plasma sheet
Authors: Liu W. W. , Rostoker G.
Published: February 2008

We are concerned in this article with the curious finding of Huang et al. [1989] which suggests a polytropic index of plasma compression of about 0.7 in the quiet time central plasma sheet. We show that the reduction of this index from its adiabatic value (=5/3) can be achieved through an ionospheric outflow of plasma which lowers the plasma temperature by virtue of energy partition. The observed correlation between the plasma temperature and density is best reproduced by an ionospheric source of ∼5×1025 ions/s, consistent with independent experinental estimates and smaller than the average solar wind source by a factor of two or more. Despite the change in the polytropic relationship, we find that the global energy equation PV5/3=constant (V=volume of a unit flux tube) still holds approximately (in the absence of other energy‐loss mechanisms).
Method of variable bias and its application to estimating subsurface temperature
Authors: Deming David , Hanor Jeffrey S. , Nunn Jeffrey A.
Published: February 2008

A method of obtaining variable‐bias estimates of physical quantities from noisy and incomplete data is introduced, and its application to estimating subsurface temperature is illustrated by application to temperature data from the Iberia salt dome in south Louisiana.
The geoid roughness: A scanner for isostatic processes in oceanic areas
Authors: Goslin Jean , Gibert Dominique
Published: February 2008

Maps of bandpass‐filtered geoid height anomalies deduced from Seasat altimetry data – which are referred to as “geoid roughness maps”– are contoured over the Indian Ocean both in the short (30–90 km) bandwith and in an intermediate one (90–230 km). Interpretation of these maps essentially provides a guide as to where further detailed studies should be conducted. The roughness maps can thus be used as a fast and efficient “scanner” for isostatic processes at the scale of an entire ocean. Additionally, roughness maps provide a qualitative appraisal of the emplacement mechanisms of intraplate features: this can for example be appreciated by comparing the interpretations of the maps with the results of admittance studies over such features.