bluuebunny/crossref_metadata_2025 huggingface dataset:
Sondrestrom overview
Authors: Wickwar V. B. , Kelly J. D. , de la Beaujardière O. , Leger C. A. , Steenstrup F. , Dawson C. H.
Published: February 2008

This overview of the Sondrestrom radar provides background material to help understand the early scientific results discussed in the following series of papers. It describes the geophysical region probed by the radar, the data acquisition procedure, and the extensive set of physical parameters derived.
Dayside red auroras at very high latitudes: The importance of thermal excitation
Authors: Wickwar Vincent B. , Kofman Wlodek
Published: February 2008

Extensive radar observations have been made from Sondrestrom of the F region in the daytime sector between 70 and 79° Λ. Regions of enhanced electron temperature and electron density are found in close association with the velocity reversal in the morning and afternoon convection cells. From the radar measurements, calculations are made of the contributions to the atomic oxygen emission at 6300A from dissociative recombination and thermal excitation. The latter mechanism, in particular, in the enhancement regions gives rise to intensities that are comparable to those observed at very high latitudes during the past decade.
Pressure and electric fluctuations on the deep seafloor: Background noise for seismic detection
Authors: Webb Spahr , Cox Charles S.
Published: February 2008

Pressure and electric field fluctuations are suitable for detecting seismic disturbances on the seafloor in the frequency range of .02 to 2 Hz. The background noise has two maxima in this range. From .01 to .03 Hz the pressure spectrum decreases because hydrodynamic filtering increasingly removes the direct influence of long surface gravity waves. The electric spectrum decreases because of increasing absorption of ionospheric disturbances. From 0.09 to 0.11 Hz both spectra increase sharply to a series of peaks where the non‐linear interference of opposed surface wave trains generates microseisms. At 0.09 Hz the inferred vertical ground motion on the seafloor approaches that of quiet continental sites.
A possible observation of a cometary bow shock
Authors: Russell C. T. , Phillips J. L. , Arghavani M. R. , Mihalov J. D. , Knudsen W. C. , Miller K.
Published: February 2008

Three discontinuities within a large disturbance of the interplanetary field, observed at Venus and previously suggested to be due to the possible passage of a comet, are examined to see if they could possibly represent the first observation of a cometary shock. The changes in number density, temperature and velocity as well as the magnetic structure of the discontinuities are consistent with this hypothesis.
Baltic shield seismicity, The results of a regional network
Authors: Slunga Ragnar , Norrman Peter , Glans Anne‐Christine
Published: February 2008

The seismicity of the southern part of the Baltic shield has been studied for four years by a digital regional seismic network with a station spacing of 100km. Some 160 earthquakes have been analysed for location, focal depth, seismic moment, fault plane solution and static stress drop. More than 90% of the earthquakes occur at depths less than 19km. Orientation of the horizontal stresses relaxed by the events is very consistent, the principal compression is oriented in a NW‐SE direction. The geographical distributions of the events show relations to the regional geology. The consistency of the stress pattern means that the type of faulting is mainly determined by the strikes of the available faults.
Influence of the electron source distribution on field‐aligned currents
Authors: Brüning Kornelia , Goertz Christoph K.
Published: February 2008

The field‐aligned current density above a discrete auroral arc has been deduced from the downward electron flux and magnetic field measurements onboard the rocket Porcupine flight 4. Both measurements show that the field‐aligned current density is, in spite of decreasing peak energies towards the edge of the arc, about 4 times higher there than in the center of the arc. This can be explained by using the single particle description for an anisotropic electron source distribution.
On the origin of polar ion streams
Authors: Green James Lauer , Waite J. Hunter
Published: February 2008

It is reaffirmed in this reply that the "classical" polar wind is based on the thermal escape of the light ions H+ and He+. It is asserted that the polar ion flow observations presented in the Gurgiolo and Burch [1985] comment paper, made by the High Altitude Plasma Instrument (HAPI) instrument on Dynamics Explorer‐1 (DE), are O+ and that the probable origin of these ions, which is consistent with the observations, is a highly localized region in the dayside polar cleft ‐ a distinctly different source region than that of the polar wind. Velocity and mass selection, as a result of E × B convection acting on ions from a localized source region in the polar cusp or the dayside polar cap boundary, determines the measured HAPI ion distribution. The Retarding Ion Mass Spectrometer (RIMS) instrument on DE, during the same time period, was measuring the light ion polar wind with flow energies of less than 2.5 eV which originated in the polar cap ionosphere very near the north magnetic pole.
Triggered Jovian radio emissions
Authors: Calvert W.
Published: February 2008

Certain jovian radio emissions seem to be triggered from outside, by much weaker radio waves from the sun. Recently found in the Voyager observations near Jupiter, such triggering occurs at hectometric wavelengths during the arrival of solar radio bursts, with the triggered emissions lasting sometimes more than an hour as they slowly drifted toward higher frequencies. Like the previous discovery of similar triggered emissions at the earth, this suggests that Jupiter's emissions might also originate from natural radio lasers.
Ray tracing of Z‐mode emissions from source regions in the high‐altitude auroral zone
Authors: Menietti J. D. , Lin C. S.
Published: February 2008

Two‐dimensional ray tracing of Z‐mode radiation from sources in the auroral zone has been performed. The Z‐mode waves are assumed to be excited by the cyclotron maser mechanism at frequencies near the electron gyrofrequency and at wave normal angles near 90°. The emission is found to propagate primarily perpendicular to the magnetic field line (horizontal propagation) for all sources considered, and thus not to substantially lower altitudes. The frequency bandwidth estimated from the ray paths is much less than that observed by DE‐1. It is suggested that the wave source needs to be in the region of field‐aligned current in order for the cyclotron maser mechanism to explain the broad frequency bandwidth of Z‐mode emissions.
The temporal evolution of a small auroral substorm as viewed from high altitudes with Dynamics Explorer 1
Authors: Craven J. D. , Frank L. A.
Published: February 2008

A small auroral substorm is investigated with auroral imaging photometers carried on the spacecraft Dynamics Explorer 1. Initial brightening along the auroral oval and the subsequent westward and poleward motions of intense, localized emission regions are associated with auroral surges. Following substorm onset, another region of less intense emissions is observed to develop at lower latitudes and adjacent to the bright region near local midnight. This second region expands towards the east. The bright zone of auroral emissions associated with the surges is interpreted as the signature of electron acceleration along magnetic field lines threading the boundary layer of the plasma sheet in the magneto‐tail. The more diffuse, less intense region is identified with eastward‐drifting electrons injected into the plasma sheet and ring current following substorm onset. No rapid poleward motion of the discrete aurora is detected during substorm recovery.
Equatorial airglow depletions induced by thermospheric winds
Authors: Meriwether John W. , Biondi Manfred A. , Anderson David N.
Published: February 2008

Interferometric observations of the 630.0 nm nightglow brightness at the equatorial station of Arequipa, Peru [16.2°S, 71.4°W geographic, 3.2°S dip latitude] have revealed widespread areas of airglow depletion, with reductions in intensity as large as factors of 3 or 4. These depletions correlated closely with large increases of the equatorward (northward) wind and the 630.0 nm kinetic temperature. On occasion, the usually small meridional wind reached a velocity of 100 m/s near 22h LT lasting for 1 to 2 hours. The temperature increases of 100 K or more existed only in the poleward (southward) direction. Comparisons with modelling calculations suggest that this effect results from an upward movement of the ionosphere along the inclined magnetic field lines, driven by the equatorward neutral wind. The airglow column integrated emission rate is consequently decreased by the slower rate of formation and subsequent dissociative recombination of molecular oxygen ions within the higher F‐layer. We conclude that the transient period of equatorward wind is a result of the passage of the midnight pressure bulge.
Interaction of zonal winds with the equatorial midnight pressure bulge in the Earth's thermosphere: Empirical check of momentum balance
Authors: Herrero F. A. , Mayr H. G. , Spencer N. W. , Hedin A. E. , Fejer B. G.
Published: February 2008

A minimum is observed at midnight in the time variation of averaged zonal winds measured in‐situ near the equator at an average altitude of about 350 km, and we inquire whether observations of the equatorial midnight pressure bulge are consistent with this feature. The observed zonal wind maintains an eastward direction all night. It increases steadily in the early evening reaching a maximum of about 160 m/s at 2100 hrs local time (LT), dropping to a minimum of about 70 m/s around 2400 LT, then up to about 120 m/s around 0300 LT, decreasing thereafter and turning westward in the morning around 0500 LT. The nighttime eastward ion drift at Jicamarca, averaged over periods of similar solar activity (1970‐71), shows the same signature, but generally with amplitude between 70 and 90% of the zonal wind amplitude. The 1978‐81 Jicamarca ion drifts are similar except from 2400 to 0300 LT when they are about 30% larger than the in‐situ zonal wind averages. The ion‐drift is used together with the measured zonal winds to estimate the ion‐drag effect in the momentum equation. The pressure term of this equation is estimated using in‐situ measurements of the neutral temperature and density. The pressure term is found to be large before 2100 LT (∼0.05 m/s²), consistent with the steady increase in zonal wind before 2100LT, drops rapidly to near zero (roughly 0.005 m/s) before 2200 LT, and then increases slowly beginning at 2300 to about 0.015 m/s² just before 0300 LT when it is observed to reverse. The small pressure term observed from 2100 to 2400 LT is associated with the midnight pressure bulge and accounts for the decay of the wind from 160 m/s at 2100LT to 70 m/s at midnight. The larger value at 0300LT is consistent with the second maximum in the wind. It is found that the existing data sets are consistent in terms of zonal momentum balance. The striking similarity between the zonal wind and the eastward ion‐drift is responsible for the small ion‐drag term before midnight which is required to maintain the large zonal winds observed.
A seafloor magnetotelluric sounding in the Tasman Sea
Authors: Ferguson I. J. , Filloux J. H. , Lilley F. E. M. , Bindoff N. L. , Mulhearn P. J.
Published: February 2008

This paper reports an analysis of electromagnetic data from a site occupied on the floor of the Tasman Sea during an Australia‐U.S. research program, the Tasman Project of Seafloor Magnetotelluric Exploration. This site (37°33′S, 155°58′E, depth 4450 m) is in the central portion of the Tasman Sea, and near both a fossil spreading ridge and the Tasmantid Seamount Chain. The extensive electric and magnetic data sets, covering 60 days, exhibit the signals of a most energetic oceanic environment. Conspicuous features of the electric field include an unusually large component induced by mesoscale fluid motions, as well as sporadically occurring high‐frequency signal probably induced by ocean turbulence.

These motional fields contribute a significant background noise to the ionospheric storm and substorm magnetic activity from which the seafloor magnetotelluric impedance tensor is estimated, but permit a usable frequency band of 0.06 to 5.5 cph. Over this band the seafloor impedance is found to exhibit frequency‐independent skew and anisotropy. The skew suggests the presence of some nearby lateral conductivity heterogeneity. The anisotropy is characterised by a principal axes ratio of 3.5, the major axis being oriented 24° clockwise from true north.

Tentative inversion of the data implies the presence of an unusually high conductance in the uppermost seafloor. Altogether, information on upper mantle conductivity may reach a 500 km depth. The principal magnetotelluric axes are approximately aligned with both the trend of the seamount chain and with the Australian coastline. The ensemble of data from eight other sites occupied in the project should permit an assessment of the relative contribution of these two features.
Resonant lidar detection of Ca and Ca+ in the upper atmosphere
Authors: Granier G. , Jégou J. P. , Mégie G.
Published: February 2008

Resonant lidar detection of neutral (Ca‐423 nm) and ionized ( Ca+ ‐ 393 nm) calcium altitude distributions has been performed during nighttime at the Observatoire de Haute‐Provence. The emitter is composed of two Nd‐Yag pumped dye lasers, the 393 nm emission being obtained by three waves mixing in a non‐linear crystal. The first detection of Ca has been carried out in December, 1982 and has shown that the integrated abundance of the atomic form is low, with a value of about 1.5 × 107 cm−2, further confirmed by measurement performed in July, 1983. During this same month, the detection of Ca+ has been achieved, proving the lidar ability to follow rapid evolutions of Ca+ layers, which appear between 85 and 115 km altitudes.
Measurements in the marine boundary layer near a coastal front
Authors: Riordan A. J. , SethuRaman S. , Davis J. M. , Viessman S.
Published: February 2008

Measurements taken from aboard ship and from nearby fixed sites during a March 1985 research cruise near Cape Hatteras document some interesting boundary layer features of the coastal front which have been largely unexplored. The front, although commonly associated with the development of coastal cyclones is nevertheless shallow and often difficult to detect due to the scarcity of routinely available observations offshore.

During the particular case described, the coastal front, undetected by routine analyses, divides air masses of quite different character. To the east of the surface wind shift line a warm, statically unstable boundary layer is associated with strong fluxes of latent heat from the sea surface. To the west, however, the boundary layer is cold and stable with negligible air‐sea heat exchange. A low‐level jet in the frontal zone carries the warm moist air westward toward eastern North Carolina. Subsequent moderate precipitation and cyclone passage may be associated with the frontal boundary.
The satellite magnetic anomaly of Ahaggar: Evidence for African plate motion
Authors: Phillips R. J. , Brown C. R.
Published: February 2008

The Ahaggar volcanic province of North Central Africa is considered a region of excess heat flow (hot spot) and hence elevated Curie isotherm. Using a modified version of the Parker FFT potential field representation, magnetic signals were calculated at Magsat altitudes for models in which the African Plate is both fixed and moving. The moving‐plate model extends the Curie isotherm anomaly in the direction of plate motion and provides a satisfactory match to vertical component (ΔZ) anomaly data when the magnitude of plate velocity is 0.75 cm/yr. Although the signal levels are marginal for the scalar component anomalies of this region, the same model provides an adequate match to this data set and is clearly preferable to a fixed‐plate model.
Upper mantle converted waves beneath the Nars array
Authors: Paulssen Hanneke
Published: February 2008

Several registrations of teleseismic events on the NARS array show a phase which can be identified as a P to S conversion at the 670‐km discontinuity beneath western Europe. Variations in the amplitude and arrival time of the so‐called Ps phase are observed for different azimuths. A single station/multiple event stacking technique was applied to the data to determine the consistency of the phase. The results are indicative of amplitude, arrival time, and slowness variations of the converted phase on a local scale. These observations are most logically explained by a model with depth variations of the 670‐km discontinuity of the order of 20 km over a distance of 200 km.
Pb isotope evolution in the Earth: A proposal
Authors: Meijer Arend
Published: February 2008

A model is proposed in which Pb is preferentially partitioned into the melt during partial melting of the mantle resulting in a higher U/Pb ratio in the residual mantle. The degree of increase is suggested to be inversely correlated with the degree of melting. By combining subduction of oceanic crust (µcrust < µsource) into the lower mantle with intra‐crustal fractionation of U/Pb through magmatic and metamorphic differentiation, this model can explain the J‐type Pb in both the upper mantle (i.e., young oceanic volcanics) and the upper continental crust. It obviates the need for an extended period of core formation or recycling of continental materials into the mantle to explain the J‐type leads although it does not preclude the occurrence of either of these mechanisms.
Ionospheric heating with obliquely incident waves
Authors: Field E. C. , Warber C. R.
Published: February 2008

Nearly all ionospheric heaters operate at vertical incidence. Oblique waves cannot satisfy frequency‐matching conditions necessary to excite the parametric decay instability, and they are weakened by geometric spreading below the ionosphere. Those spreading losses are mitigated, however, by focussing near caustics. This paper calculates fields near the caustics of oblique waves and estimates the corresponding increases in electron temperature. It finds that a transmitter having a power‐gain product of 5 MW can raise the temperature of F‐layer electrons by a hundred degrees or more. Those temperature increases are initially concentrated in narrow regions near caustics, but spread by heat conduction over tens of kilometers.
The ionosphere of Uranus: A myriad of possibilities
Authors: Chandler M. O. , Waite J. H.
Published: February 2008

A one‐dimensional model has been used to study the effects of exospheric temperature, methane and water influx, ionospheric outflow, and electron precipitation on the composition and structure of the ionosphere of Uranus. Peak ion concentrations range from 10³ to 106 cm−3 with a wide variation in peak altitude, which depends strongly on the exospheric temperature. In all the cases we considered, H+ is the major ion in the topside ionosphere. At altitudes near or below the peak, H3+ and CH5+ can dominate, depending on the magnitude of CH4 and H2O influx. Atomic hydrogen column depths above the methane absorbing layer exceed 1017 cm−2 and can produce large (400 R) emissions of resonantly scattered Lyman‐alpha. In the sunlit polar cap, electron precipitation with energy fluxes of 0.6 to 1.0 erg cm−2 s−1 results in direct production of Lyman‐alpha emissions that exceed 1 kR.
A formalism for nonlinear inversion of seismic surface waves
Authors: Nolet Guust , van Trier Jos , Huisman Reina
Published: February 2008

We describe a formalism for waveform fitting using the conjugate gradient method for nonlinear optimization. The method is tested on synthetic Love waves, and on Rayleigh wave observations from the portable, broad‐band NARS array.
Melting experiment on natural lherzolite at 20 GPa: Formation of phase B coexisting with garnet
Authors: Kato Takumi , Kumazawa Mineo
Published: February 2008

A melting experiment has been made on a natural lherzolite (spinel lherzolite, KLB‐1) at 20 GPa and 2160°C under hydrous conditions. The stable phase assemblage is liquid, garnet, and modified spinel, which is replaced by phase B above the melting temperature of modified spinel, and garnet is the liquidus phase at this pressure.
Paleomagnetism of Early Jurassic rocks, Watchung Mountains, Newark Basin: Evidence for complex rotations along the border fault
Authors: Van Fossen Mickey C. , Flynn John J. , Forsythe Randall D.
Published: February 2008

A paleomagnetic study of late Triassic to early Jurassic rocks from the Watchung Syncline provides useful new constraints on the complex development of the Newark Basin independent of existing structural data. A baked contact test indicates stable remanent magnetizations are primary. Results from the eastern limb of the fold are used to calculate an early Jurassic pole at Long. 115.1°E, Lat. 62.2°N (alpha 95 = 10.5°, K = 41.4) which is similar to previous Newark Basin results. After results from the western limb were corrected for folding, 32° of clockwise discordance remained between data from the western and eastern limbs. This cryptic rotation of Newark Basin strata appears to be localized to the border fault zone and may be due to the presence of left lateral secondary brittle shear zones running parallel to strata of the western limb of the Watchung Syncline.
Solar absorption microwave measurement of upper atmospheric water vapor
Authors: Olivero J. J. , Tsou J. J. , Croskey C. L. , Hale L. C. , Joiner R. G.
Published: February 2008

Ground‐based microwave measurements of upper atmospheric water vapor were made during late 1981 at Penn State University using the spectral line decomposition of solar microwave (22.235 GHz) radiation transmitted through the atmosphere. One measurement per day was accomplished by integrating the signal over the daylight hours from sunrise to sunset while accurately tracking the sun with a 2.4 m cassegrain parabola antenna. Preliminary retrievals for the period 13‐21 December 1983 are presented, which show reasonable agreement with recent emission microwave measurements.
Physical parameters for hot and cold electron populations in comet Giacobini‐Zinner with the ICE Radio Experiment
Authors: Meyer‐Vernet N. , Couturier P. , Hoang S. , Perche C. , Steinberg J. L.
Published: February 2008

Thermal plasma noise spectroscopy using the ICE radio receiver yielded the parameters of the two maxwellian populations approximating the comet plasma electron distribution. Within 150,000 km around closest approach, we observe three regions : 1) the inner one coincides with the low magnetic field region or plasma sheet ; over 1200 km the density is nearly constant at 650 cm−3; the overall profile, 5000 km wide, is assymetrical and shows a narrow spike on each side of the maximum ; the temperature is 16,000 K; 2) from 9000 to 20,000 km from the nucleus, the density decreases as R−2. The distribution is slightly assymetrical, the density higher on the south side. 3) Further away, the density and temperature fluctuate widely around about solar wind values. The hot electron pressure is much smaller than that of the cold electrons except near the edges of the plasma sheet where heating processes probably occur.
Modeling of dust halo formation following comet outbursts: Preliminary results
Authors: Gombosi T. I. , Horányi M.
Published: February 2008

Evolution of gas and dust distributions following a spatially and temporally localized comet outburst was calculated using a hybrid kinetic ‐ hydrodynamic method. It was found that a comet outburst resulted in significantly increased dust terminal velocities. As these higher terminal velocity values result in larger apex distances, therefore the outburst generates distinct dust envelopes in front of the regular dust coma. Such envelopes were observed at several comets (cf. comet Donati).
Broadening and occultation of radio sources by comet Giacobini‐Zinner as observed from ICE
Authors: Steinberg J. L. , Fainberg J. , Meyer‐Vernet N. , Hoang S.
Published: February 2008

During the encounter of the International Cometary Explorer (ICE) with comet P/Giacobini‐Zinner, the radio astronomy experiment observed occultation and propagation effects on several distant radio sources. The observations of the partial occultation of the galactic radio source between 360 and 1000 kHz show that the 3‐dimensional large scale structure of the coma is consistent with the structure determined from in‐situ measurements made along the encounter trajectory. In addition, these observations remove a previously existing ambiguity in the position of the galactic source. Between 110 and 360 kHz the Earth source is broadened by scattering by the comet random density inhomogeneities. The amount of broadening indicates that the electron density fluctuations measured in situ by ICE along its trajectory (100% fluctuations with a scale length of 1 to 2 10³ km over a path length of 105 km) exist with the same properties in the perpendicular direction.
Deductions from space shuttle glow photographs
Authors: Slanger T. G.
Published: February 2008

It is shown that from the appearance of certain photographs taken from STS‐5, it is possible to make several useful statements about the production mechanism of the visible glow around the shuttle, and presumably other space vehicles. These are: 1) the electronic excitation of particles in the gas phase by either electrons or fast neutrals is probably not important, 2) the interaction of thermal atoms and molecules with the surfaces does not generate the glow, and 3) translational energy accommodation of fast particles is efficient enough that a single surface collision reduces the kinetic energy below the threshold for glow production. There is no glow without the direct interaction of fast particles with the surfaces, and the sum of the contributions of the three above processes does not exceed 14% of the observed surface intensity.
Phase transitions and convection in Icy satellites
Authors: Bercovici D. , Schubert G. , Reynolds R. T.
Published: February 2008

The effects of solid‐solid phase changes on subsolidus convection in the large icy moons of the outer solar system are considered. Phase transitions affect convection via processes that distort the phase change boundary and/or influence buoyancy through thermal expansion. Linear stability analyses are carried out for ice layers with a phase change at the midplane. Two exothermic phase transitions (ice I ‐ ice II, ice VI ‐ ice VIII) and two endothermic transitions (ice I ‐ ice III, ice II ‐ ice V) are considered. For the exothermic cases, the phase change can either impede or enhance whole‐layer convection. For the endothermic cases, the phase change always inhibits whole‐layer convective overturn and tends to enforce two‐layer convection. These results place some constraints on possible models of icy satellite evolution and structure.
A Bouguer anomaly gradient belt on the Pacific side of central Honshu, Japan
Authors: Yamamoto Akihiko , Fukao Yoshio , Furumoto Muneyoshi , Shichi Ryuichi , Shiraki Hideaki
Published: February 2008

Since 1978 we have conducted extensive gravity surveys in Central Honshu, Japan, to establish 5,345 new gravity stations. The results are synthesized into a Bouguer anomaly map with the data from other sources. The map shows a distinctive belt of gravity gradient on the Pacific side of Central Honshu. This belt is about 300 km long and 30‐50 km wide, across which Bouguer anomaly changes by about 30‐50 mGals. Broad Bouguer high prevailing further oceanward of Central Honshu is sharply bounded by this anomaly belt. There seems to be no apparent correlation between this anomaly belt and the surface geology.
A nitric oxide increase observed following the July 1982 solar proton event
Authors: McPeters R. D.
Published: February 2008

Following the solar proton event (SPE) of July 13, 1982, an increase in the strength of nitric oxide T bands was observed in spectral scans of the atmospheric albedo made by the solar backscattered ultraviolet instrument on Nimbus 7. Analysis of the (10), (01), and (02) T band strengths allows us to estimate the cumulative amount of nitric oxide above an altitude of 50 km. We observe an increase in nitric oxide in southern hemisphere high latitudes following the SPE amounting to about 5×1014 molecules per cm² above an altitude of approximately 50 km. The observed increase persists until the middle of September. A similar increase is not observed in the northern hemisphere, indicating that under summer conditions the mesospheric/thermospheric NO distribution returns to normal within a few days after the end of an SPE.
North American Central Plains conductivity anomaly goes east
Authors: Jones Alan G. , Savage Peter J.
Published: February 2008

The North American Central Plains electrical conductivity (NACP) anomaly has been known for almost two decades, and its influence on palaeotectonic models of the North American continent has been significant. Magnetometer array studies have located the structure in a gross sense, but there has not been, until now, a comprehensive magnetotelluric (MT) survey of it. In this letter we report on the preliminary interpretation of data from thirty‐five MT sites recorded along a 400 km East‐West profile just north of the US‐Canadian border. We show that the anomaly at this latitude is 75 km farther east of the location previously mapped by the array studies. Modelling indicates that the conductive body has its top surface at about 10 km depth and appears to be anticlinal in shape. The profile also extends sufficiently east that it traverses another previously known electrical structure, referred to herein as the TOBE anomaly. We consider briefly other geophysical and geological data for the region, and tentatively infer that the NACP structure is terminated to the east by the interpreted southern extension of the Tabbernor fault/fold system, and that the TOBE anomaly is an expression of the known southern extension of the Thompson nickel belt, both beneath Phanerozoic sediments of the Williston Basin.
The giant polygons of Utopia, northern Martian Plains
Authors: McGill George E.
Published: February 2008

Much of Utopia Planitia is underlain by polygonal terrane. Most of the troughs defining the polygons are 250 m to 1 km wide; typical diameters of polygons are 4‐5 km. These dimensions are orders of magnitude greater than the corresponding dimensions for familiar polygonal structures on Earth; consequently, the Earth structures are not valid mechanical analogues. Crater and superposition relationships indicate that trough formation was coeval with deposition of the polygonal terrane material. Based on crater age correlations with Elysium volcanism and outflow‐channel activity, either a volcanic or a sedimentary source for this material is possible. Tensile stresses responsible for the troughs were produced by cooling or dessication shrinkage plus differential compaction over a rough buried surface that is the structurally disrupted remnant of the cratered highlands. Shrinkage alone will produce polygons orders‐of‐magnitude smaller than those present, but differential compaction will reflect the scale and pattern of the buried topography, and thus control the scale and pattern of the giant polygons of Utopia.
The recovery phase of galactic cosmic ray modulation in the outer heliosphere
Authors: McDonald F. B. , von Rosenvinge T. T. , Lal N. , Trainor J. H. , Schuster P.
Published: February 2008

Energetic hydrogen and helium nuclei from the galaxy (cosmic rays) enter the solar system with varying degrees of difficulty during the 11‐year solar magnetic cycle, resulting in spatial and temporal variations of particle intensities in the heliosphere. We report observations of these variations from the ISEE‐3, Voyager 1 and 2, and Pioneer 10 spacecraft during the period from early 1981 to early 1986 and for heliocentric distances ranging from 1 to 37 AU. During this time the high energy intensities in the outer heliosphere have been increasing exponentially at a rate of approximately 20%/year with occasional interruptions due to enhanced solar activity. There are long delays (∼3 years) in the recovery of the intensity of low energy particles relative to high energy particles that significantly alter the energy spectra. The radial intensity gradients measured in the ecliptic plane are observed to remain constant or to decrease at the time of the reversal of the solar magnetic poles in 1980.
Jovian electron populations in the magnetosphere of Mercury
Authors: Baker D. N.
Published: February 2008

A mechanism to explain the existence of two distinctly different kinds of energetic electron bursts within the Hermean magnetosphere is presented. The spectrally‐soft, very intense increases of energetic electrons observed in situ by Mariner 10 are ascribed to "substorm‐like" dissipation events due to magnetic reconnection in Mercury's magneto tail. The other type of electron bursts observed in Mercury's magnetosphere, characterized by lower peak intensities and much harder energy spectra, are attributed to Jovian electrons which first enter and are subsequently confined in the Hermean system. This Jovian electron model at Mercury is closely analogous to a similar model of such Jovian electron effects within the terrestrial magnetosphere. Such a model eliminates the need for the Hermean magnetosphere to produce highly relativistic electron bursts by internal generation mechanisms.
Laboratory model of a tethered balloon – electron beam current system
Authors: Stenzel R. L. , Urrutia J. M.
Published: February 2008

In a large laboratory magneto‐plasma, the current flow is investigated between a field‐aligned electron beam and an electrode collecting return current on a separate flux tube. The space‐time evolution of the current system shows spiraling currents penetrating along
near electron thermal speeds (v ≲ vthe » vAlfvén). The electron beam propagates faster than the current, hence its front is current neutralized. Anomalous cross‐field currents shunt the field‐aligned currents, preventing the formation of a long current loop. Plasma expulsion by the return‐current collecting electrode disrupts the large initial currents which are one order of magnitude above the electron saturation current. The plasma dynamics causes repeated current bursts and periodic charging of the beam/electrode with respect to the plasma potential.
Simulation of double layers in a model auroral circuit with nonlinear impedance
Authors: Smith Robert A.
Published: February 2008

A reduced circuit description of the U‐shaped potential structure of a discrete auroral arc, consisting of the flank transmission line plus parallel‐electric‐field region, is used to provide the boundary condition for 1‐d simulations of the double‐layer evolution. The model yields asymptotic scalings of the double‐layer potential, as a function of an anomalous transport coefficient α and of the perpendicular length scale la of the arc. The arc potential ϕDL scales approximately linearly with α, and for α fixed ϕDL ∼ laz. Using parameters appropriate to the auroral‐ zone acceleration region, potentials of ϕDL ∼ 10 kV scale to projected ionospheric dimensions ∼ 1 km, with power flows of the order of magnitude of substorm dissipation rates.
An acceleration mechanism for cometary plasma tails
Authors: Minami Shigeyuki , White R. Stephen
Published: February 2008

Cometary plasma tail formation by the interaction between the solar wind plasma flow and the plasma at the head of the coma is discussed using unipolar electric generation theory. The cometary "plasma tail" here is defined as the part of the traditional type 1 ion tail. The plasma in the "plasma tail" is almost directly accelerated from the cometary ionopause along the sun‐nucleus line where the tail current flows. For steady state solar wind conditions, the cometary "plasma tail" velocity distribution is obtained self‐consistently. The solution of a kinetic equation gives the velocity of the cometary plasma as a function of the cometary tail position, x, as v=vo [1‐ exp(‐x/xo)], where xo, and vo are the characteristic length for the interaction and the solar wind velocity, respectively. The characteristic length, xo is 3×106 km when the plasma density near the nucleus of the comet, Nc, is 106 cm−3 and the component of the interplanetary magnetic field, IMF, perpendicular to the solar wind flow is 3 nT. The tailward cometary plasma is finally accelerated to the speed of the solar wind. The effect of a nonuniformly distributed magnetic field on the cometary tail is also treated. The theory is compared with the observational plasma velocities in the tails of comet Bennett (1970II) and comet Halley (1985)
Plasma wave turbulence in the strong coupling region at comet Giacobini‐Zinner
Authors: Coroniti F. V. , Kennel C. F. , Scarf F. L. , Smith E. J. , Tsurutani B. T. , Bame S. J. , Thomsen M. F. , Hynds R. , Wenzel K. P.
Published: February 2008

Within 105 km of comet Giacobini‐Zinner's nucleus, strong plasma wave turbulence was detected by the ICE electric and magnetic field wave instruments. The spatial profiles of the wave amplitudes are compared with measurements of the heavy ion fluxes of cometary origin, the plasma electron density, and the magnetic field strength. The general similarity of the wave and heavy ion profiles suggest that the waves might be generated by free energy in the pick‐up ion distribution function. However, the expected parallel streaming instability of electrostatic modes generates waves with frequencies that are too low to explain the observations. The observed low frequency magnetic turbulence is plausibly explained by the lower hybrid loss‐cone instability of heavy ions.
The hydrogen coma of comet Halley before perihelion: Preliminary observations with Dynamics Explorer 1
Authors: Craven J. D. , Frank L. A. , Rairden R. L. , Dvorsky M. R.
Published: February 2008

The hydrogen coma of Comet Halley has been observed in resonantly scattered solar Lyman‐α radiation during the period 1‐29 January 1986 as the comet approached perihelion. These observations were obtained with the imaging photometer for vacuum‐ultraviolet wavelengths on the spacecraft Dynamics Explorer 1. For the initial analysis of observations available in 17 orbits distributed throughout the period, least‐squares fits are computed for the observed exponential decrease in brightness with radial distance from the nucleus. Brightness at the nucleus increased from ∼ 3 to 17 kR during the observing period. Preliminary analysis yields water production rates of ∼ 3.6 × 1029 and 1.9 × 1030 molecules/sec on 1 and 29 January, respectively.
Preferential O+ heating in the topside ionosphere
Authors: Moore T. E. , Pollock C. J. , Arnoldy R. L. , Kintner P. M.
Published: February 2008

We report observations of preferential heating of the ionospheric majority ion species O+. The heating took the form of a hot (few electron volts) tail in the upgoing thermal O+. No such hot tail was observed in the light ion distributions. An event observed at 700‐800 km altitude was highly anisotropic with a much hotter tail transverse to the local magnetic field. A series of events observed at 250‐375 km were more nearly isotropic with respect to the local magnetic field. Broadband plasma wave emission near the lower hybrid resonance was observed in conjunction with the high altitude event. The low altitude events were tightly correlated with auroral electron precipitation, but broadband lower hybrid emission was much reduced. The observed hot tail formation is sufficient to produce significant O+ ion transport to higher altitude auroral acceleration regions.
The rate of formation of halomethyl peroxy nitrates in the stratosphere and their possible role as temporary reservoirs for ClOx and NOx species
Authors: Lesclaux R. , Caralp F. , Dognon A. M. , Cariolle D.
Published: February 2008

The rate constant for the combination reaction of CFCl2O2 and NO2 was measured as a function of pressure and temperature under stratospheric conditions. The results show that the reaction is fast and that significant amounts of the peroxynitrate CFCl2O2NO2 can be formed. The data were introduced into a 2D photochemical model in order to evaluate an upper limit for the amount of chlorine stored in the form of the peroxynitrate. The calculation shows that this reservoir effect cannot exceed a few percent of the total chlorine contained in the stratosphere.
Shallow structure from a seismic‐reflection profile across the Borah Peak, Idaho, Fault Scarp
Authors: Miller Richard D. , Steeples Don W.
Published: February 2008

A short 12‐fold CDP seismic‐reflection survey was performed along the road to Doublespring Pass across the fault scarp formed by the October 28, 1983, magnitude‐7.3, Idaho earthquake. This high‐resolution reflection survey was conducted to determine the feasibility of using reflection seismology to delineate shallow structures in a fault zone. Field‐recording parameters were designed to optimize seismic reflections in the 30‐150 msec range corresponding to 10‐100 m in depth. A modified 30‐06 hunting rifle was used as the energy source. Single 100‐Hz geophones at 1.5‐m group intervals in conjunction with 220‐Hz low‐cut recording filters (24 dB/octave) provided dominant frequencies above 150 Hz on field records. As would be expected from geologic considerations, the processed data suggest the existence of faulting in the subsurface. Strong events between 30 and 80 msec on the upthrown side of the scarp are of distinctly different character and frequency than those on the downdropped side at similar times. This indicates different geologic units are present at approximately the same reflection time on opposite sides of the fault zone. The northeastern edge of the scarp may not represent the true subsurface boundary of the upthrown block. Projection to the surface of the northeasternmost edge of the seismically determined subsurface graben is 10‐15 m farther northeast than expected from surface faulting. High‐frequency energy present within the subsurface expression of the graben is primarily noise and is related to the deformed and incoherent nature of materials within the graben.
Solar cycle variations of anomalous 4He as deduced by studies of cosmic ray ³He
Authors: Cummings A. C. , Mewaldt R. A. , Stone E. C.
Published: February 2008

Voyager 1 and 2 observations have been used to derive the energy spectrum of ‘anomalous’ cosmic ray (ACR) helium using a technique based on the separation of the isotopes of He. Previously reported observations show that the ACR oxygen spectrum underwent a change in shape following the solar magnetic field reversal in 1980; in this paper we present evidence for a corresponding change in the ACR helium spectrum. We find that the energy spectra of ACR helium and oxygen and galactic cosmic ray (GCR) 4He and ³He can be reproduced both before and after the field reversal using a simple solar modulation model in which the effects of curvature and gradient drifts are arbitrarily neglected.
The phase diagram of iron to 430 kbar
Authors: Boehler Reinhard
Published: February 2008

The ε ‐ γ transition and the melting curve of pure iron have been measured in an internally heated diamond cell to 430 kbar. The sample, an iron wire with 0.02‐mm diameter, was resistively heated in a sandwiched gasket arrangement, using alumina as the pressure medium. The phase transitions were determined by discontinuities in the resistance‐temperature curves of the heated wire. Temperatures were measured with an optical multi‐channel analyzer (OMA) by fitting a black‐body radiation function to the emission spectrum of the hot wire. Pressures were measured at room temperature using the ruby scale. New data on the α ‐ ε transition by Huang et al. (1986) and the present result on the ε ‐ γ transition yield a α ‐ ε ‐ γ triple point of 116 kbar and 810 K. The slope of the ε ‐ γ transition is 2.9 K/kbar. At 500 kbar the present melting temperatures of iron are about 1000 K lower than those calculated by Anderson (1986). From this data, one would expect a ε ‐ γ ‐ 1 triple point at 750 kbar and 2500 K. The solid‐solid transition found in shock wave experiments at 2 Mbar could therefore be the appearance of a new iron phase, which would be the phase of the inner core of the Earth.
An observational study of the final warming in the Southern Hemisphere stratosphere
Authors: Farrara John D. , Mechoso Carlos R.
Published: February 2008

The final warming in the Southern Hemisphere stratosphere during the period 1 September ‐ 30 November for the years 1978‐1983 is studied. The change in zonally averaged temperatures during that period is almost the same for each year. However, there is substantial interannual variability in the time evolution of the warming as events of enhanced wave, mean‐flow interaction associated with bursts of upward propagating planetary waves develop at different times in different years. Polar temperatures in the middle stratosphere can increase as much as about 20 K in 4 days during these events. Such dynamical processes can play a significant role in the interannual variability of stratospheric ozone and other constituents.
Stratospheric nitrogen dioxide observed by ground‐based and balloon‐borne techniques at Syowa Station (69.0°S, 39.6°E)
Authors: Shibasaki K. , Iwagami N. , Ogawa T.
Published: February 2008

Seasonal variation of vertical column density of stratospheric NO2 was determined for the period of March 1983 to January 1984 by means of ground‐based visible absorption spectroscopy at Syowa Station (69.0°S, 39.6°E), Antarctica. The winter minimum of about 1×1015 cm−2 and the summer maximum of 7×1015 cm−2 were observed. These values are nearly equal to, or a little bit smaller than, those observed at northern high latitudes. The nighttime decay of column density was small from autumn to early spring. A rapid increase in column density occurred at the end of September before the minimum of total ozone content in mid‐October. This behavior suggests that both dynamical and photochemical processes may be involved in the Antarctic ozone depletion. The vertical profile of stratospheric NO2 in early summer in Antarctica was revealed by three balloon‐borne measurements over Syowa Station in November 1982 and 1983. Above 25 km altitude, these profiles are basically identical to those observed at middle and high latitudes in the northern hemisphere. In the lower stratosphere below 25 km, variability in NO2 density seems to be large due to dynamical effects.
Condensation of HNO3 and HCl in the winter polar stratospheres
Authors: Toon Owen B. , Hamill Patrick , Turco Richard P. , Pinto Joseph
Published: February 2008

Nitric acid and hydrochloric acid vapors may condense in the winter polar stratospheres. Nitric acid clouds, unlike water ice clouds, would form at the temperatures at which polar stratospheric clouds (PSCs) are observed and would have optical depths of the magnitude observed suggesting that HNO3 is a dominant component of PSCs. ClO, N2O5 and ClNO3 may react on cloud particle surfaces yielding additional HNO3, HCl, and HOCL. In the vicinity of PSCs these reactions could deplete the stratosphere of photochemically active NOx species. The sedimentation of PSCs may remove these materials from the stratosphere. The loss of vapor phase NOx might allow halogen‐based chemistry to create the ozone hole.