bluuebunny/crossref_metadata_2025 huggingface dataset:
Ground‐based observations of subauroral energetic‐electron arcs
Authors: Vondrak R. , Harris S. , Mende S.
Published: February 2008

On March 1, 1981 the spatial distributions of ionization and luminosity were monitored at Chatanika, Alaska with the incoherent‐scatter radar, an all‐sky television system, and meridian scanning photometers. The radar detected discrete regions of enhanced E‐region ionization at subauroral latitudes, more than 3° equatorward of the diffuse aurora. The high‐resolution all‐sky television measurements at 427.8 nm showed that the luminosity pattern resembles multiple auroral arcs; they are narrow in latitudinal width and they extend from horizon‐to‐horizon in an east‐west direction. These observations indicate the existence of a subauroral source of electron precipitation that is both narrow in latitude and extended in longitude.
An observation of the surface circulation in a Gulf Stream frontal perturbation
Authors: Vukovich Fred M. , Maul George A.
Published: February 2008

In the period of 3‐16 June 1979, a satellite‐tracked, free‐drifting buoy passed through a Gulf Stream frontal perturbation and was entrained into a warm filament on the shoreward side of the perturbation. Significant speed convergence was noted as the buoy passed through the perturbation and approached the counterclockwise turn into the warm filament. In the warm filament, the buoy drifted to the southwest at speeds of about 0.1 to 0.3 m/sec. Eventually, the buoy drifted out of the filament and went westward in an apparent response to wind‐induced surface drift.
Electron acceleration by Landau resonance with whistler mode wave packets
Authors: Gurnett D. A. , Reinleitner L. A.
Published: February 2008

Recent observations of electrostatic waves associated with whistler mode chorus emissions provide evidence that electrons are being trapped by Landau resonance interactions with the chorus. In this paper we discuss the trapping, acceleration and escape of electrons in Landau resonance with a whistler mode wave packet. We show that acceleration can occur by both inhomogeneous and dispersive effects. The maximum energy gained is controlled by the points where trapping and escape occur. Large energy changes are possible if the frequency of the wave packet or the magnetic field strength increase between the trapping and escape points. Various trapping and escape mechanisms are discussed.
Photometric evidence of electron precipitation induced by first hop whistlers
Authors: Doolittle J. H. , Carpenter D. L.
Published: February 2008

Electron precipitation events induced by discrete VLF whistler mode waves have previously been detected by photometers at Siple Station, Antarctica. This paper presents the first observations of ionospheric optical emissions correlated with VLF waves at the conjugate location, near Roberval, Quebec. Since most whistlers recorded at Siple or Roberval originate in the north, Roberval affords a clear perspective on the direct precipitation induced during the first pass of the wave as it propagates southward. For such a wave the direct precipitation and that induced in the "mirrored mode" by the returning two‐hop wave should differ in arrival time by roughly twice the wave propagation time between hemispheres, while at Siple the effects of the direct and mirrored modes may overlap in time. A well defined series of observations of structured λ4278 optical emissions was observed on August 30, 1979 in the aftermath of an intense magnetic storm. The optical emissions were found to lead the arrival time of the two‐hop waves by about 0.7 s instead of lagging the local waves by about 1‐2 s as had been previously observed for whistler driven events at Siple. The observed arrival time relationships are consistent with the predictions of a cyclotron resonance interaction model, and thus support previous observations of x‐rays at Roberval. The importance of the first pass of the wave is further emphasized by an approximate proportionality between the amplitude of the VLF waves recorded at Siple and the intensity of the optical emission bursts at Roberval. Although structured optical emissions correlated with wave bursts can clearly be detected at Roberval, relatively large magnetospheric particle fluxes may be required to produce such events.
Pc 1 Pearl‐electron interactions on the L = 4.2 magnetic shell
Authors: Arnoldy R. L. , Kaufmann R. L. , Cahill L. J. , Lockheed S. B. Mende
Published: February 2008

A number of examples of auroral light bursts correlated with Pc 1 "pearl" wave packets have been recorded at Siple, Antarctica (L = 4.2). The events are unique in that an individual light burst occurs at Siple not when the wave packet is recorded at Siple but rather when the wave is measured to be at the conjugate point over Roberval, Quebec. Although one can fit the observations to a model where ions are precipitated from an interaction region near the equator via cyclotron resonance, the number of ions required to produce the light and the above mentioned light burst‐ULF wave phase relationship both make the precipitation of electrons a more plausible interpretation.

In an electron model, electrons are precipitated at Siple which have interacted with the Pc 1 wave packet over Roberval. Because of the South Atlantic magnetic anomaly, particle mirror points are nearly 200 km deeper in the atmosphere at Siple than at Roberval. Electrons of auroral energies (few keV) can be in longitudinal resonance with the Pc 1 waves over Roberval in the altitude range where the Alfvén speed rapidly decreases (2000 → 500 km). Low parallel velocities are possible for these electrons in this altitude range because the electrons are close to their mirror points. Those electrons in longitudinal resonance with the Pc 1 wave packet must have their mirror points lowered such that they do not reach the atmosphere at Roberval but are definitely precipitated at Siple. An interesting possibility is suggested in that these events represent the acceleration of electrons by a kinetic Alfvén wave.
Apparent electrostatic ion cyclotron waves in the diffuse aurora
Authors: Bering E. A.
Published: February 2008

Emissions that have properties consistent with electrostatic ion cyclotron (EIC) waves have been observed at low altitude in the diffuse aurora by a sounding rocket payload. Peaks were observed in the power spectrum of the electric field near the hydrogen and oxygen ion cyclotron frequencies. Doppler shift and polarization analyses have been performed using EIC wave parameters derived from linear theory. Both analyses indicated that these emissions had properties consistent with those expected for H+ and O+ EIC waves. The two analyses indicated that both emission bands were due to waves propagating eastward parallel to the poleward boundary of the diffuse aurora. The large local cold plasma density and resulting Landau damping require that the source be local. Magnetometer data indicated the presence of a downward parallel current density of 5μA/m². Sufficient free energy for the waves was available from this current, although the waves were observed frequently at altitudes where the ion‐neutral collision frequency exceeded the oxygen cyclotron frequency.
The mass dependence of wave particle interactions as observed with the ISEE‐1 energetic ion mass spectrometer
Authors: Sharp R. D. , Lennartsson W. , Peterson W. K. , Ungstrup E.
Published: February 2008

Simultaneous measurements of the O+ and H+ distributions from two transverse acceleration events in the high altitude auroral ionosphere are presented. The data were acquired from the energetic ion mass spectrometer on the ISEE‐1 satellite, in the dusk sector, on auroral field lines (L ≃ 8‐9), at geocentric radial distances of ∼ 3 RE. Temporal and/or spatial fluctuations during the measurement cycle resulted in some scatter of the data points, but the transverse velocity distributions are reasonably well represented by max‐wellians at energies in the few hundred eV range. The transverse temperatures were about 60 eV in both cases and no significant differences were observed between the temperatures of the O+ and H+. The flux intensities of the two ion species were also generally comparable.
Atmospheric sodium chemistry and diurnal variations: An up ‐ date
Authors: Kirchhoff Volker W. J. H.
Published: February 2008

Recent results for sodium reaction rates have led to a reassessment of the importance of atmospheric sodium constituents and their distribution with height. The largest changes occur at the bottom of the neutral atmospheric sodium layer. A much larger reaction rate coefficient for the three body production of NaO2 makes this constituent potentially much more dense below about 80 km, whereas the inclusion of photolysis produces a large diurnal variation in the NaOH loss frequency. Because many of the Na reaction rates are still uncertain static calculations for four different options on reaction rates have recently been offered in the literature. We show that only one of these choices is able to produce diurnal variations that are in agreement with recent measurements.
Uppermantle anisotropy and the oceanic lithosphere
Authors: Anderson Don L. , Regan J.
Published: February 2008

Rayleigh wave and Love wave dispersion data for oceanic paths cannot be satisfied by an isotropic uppermantle, and it is incorrect to invert these two datasets independently for separate isotropic structures. Available phase and group velocity data are inverted for oceanic structure as a function of age taking into account anelastic dispersion, sphericity, and anisotropy. The resulting models are quite different from previous results which ignore the above effects and the extra parameters involved in proper anisotropic inversion.

The models have a high‐velocity nearly isotropic layer at the top of the mantle that thickens with age, and an anisotropic low‐velocity zone with an age‐dependent anisotropy. The LID, or seismic lithosphere, reaches a maximum thickness of 50 km which is about one‐half the thickness obtained in previous isotropic or pseudo‐isotropic inversions. The seismic lithosphere therefore may be comparable in thickness to the elastic or flexural lithosphere, raising the possibility that both are controlled by effects other than temperature, stress and time, such as mineralogy, crystal orientation or partial melting. The velocities in the low‐velocity zone are higher than inferred by previous surface wave studies.
Effect of two different atmospheric models on the absorptive rate of excess atmospheric carbon by the sea
Authors: Higuchi K.
Published: February 2008

The effect of a well‐mixed atmosphere in a global carbon cycle model on the absorptive rate for excess CO2 by the ocean is investigated. It is found that Model I, in which the atmosphere is represented by a well‐mixed box, tends to overestimate the amount of carbon absorbed by the ocean, compared to Model II in which the atmosphere is more realistically represented by a two‐dimensional advective diffusive model.
The orientation of scatterers in noctilucent clouds
Authors: Gadsden M.
Published: February 2008

The scatterers which make up a noctilucent cloud have masses sufficiently small (< 10−14 kg) that they will show considerable Brownian agitation. The paths of the scatterers, as they fall from the region in which nucleation is occurring to the base of the cloud, will be irregular; their orientation, if the scatterers are nonspherical, will be continually changing direction. There will be no preferred orientation and all directions will be equally likely. This does not necessarily mean, however, that the assembly of scatterers cannot show a preferred direction of axial orientations when the assembly is studied by observing light scattered from it.
Very high latitude F‐region irregularities observed by HF‐radar backscatter
Authors: Baker K. B. , Greenwald R. A. , Tsunoda R. T.
Published: February 2008

In February and March, 1982, a coherent scatter HF radar was operated from Cleary, Alaska to observe 7‐ to 15‐m wavelength F‐region plasma irregularities near the poleward edge of the auroral zone and in the polar cap. The radar operated for five days from February 25 to March 1 and produced approximately 700,000 Doppler spectra during that time. Of those nearly 700,000 spectra, approximately 10% showed backscattered power 3 dB or more above the noise level. A ray tracing technique using electron densities determined by the Chatanika incoherent scatter radar was used to predict locations where the HF waves were approximately normal to the magnetic field. If those locations were also to contain small scale electron density structure, then one would expect them to backscatter the HF waves. Several comparisons were made between predicted and observed locations of radiowave backscatter and excellent agreement was obtained. In addition, comparisons of the Doppler velocities observed by the coherent scatter HF radar and those observed by the Chatanika radar showed good agreement, suggesting that the plasma irregularities observed by the HF radar drift with the ambient plasma. In addition, average vector velocities calculated for the entire 5‐day period show a flow pattern consistent with polar cap convection models. This again indicates that the irregularities drift with the plasma, as is predicted by a number of theories of F‐region plasma irregularities. In the summer of 1983, the research program begun with those measurements will be continued with a steerable phased‐array HF radar located at Goose Bay, Labrador, that will view the same ionospheric region as does the Sondre Stromfjord incoherent scatter radar.
Dimethyl sulfide in the Equatorial Pacific Ocean: A natural source of sulfur to the atmosphere
Authors: Cline Joel D. , Bates Timothy S.
Published: February 2008

The most abundant volatile sulfur compound found in the surface layers of the central equatorial Pacific Ocean (148°W to 170°E) was dimethyl sulfide (DMS). Concentrations of DMS ranged from 100‐400 ng DMS/L; the highest concentrations occurred at 2°N and 148°W. DMS accounted for more than 97% of the total volatile sulfur species present, and was significantly correlated with chlorophyll ‘a’. Elevated concentrations of DMS near the equator are related to nutrient eutrophication stimulated by equatorial upwelling and the horizontal transport from the east. Vertical profiles taken at 9 stations indicated that maximum DMS concentration occurred at 20‐40 m, with concentrations decreasing to < 1 ng DMS/L at 150‐200 m.

Flux calculations indicate that the central equatorial Pacific (6°N to 6°S between 148°W and 170°E) supplies about 1.0 Tg DMS/yr, assuming a mean surface concentration of 200 ng DMS/L and a piston velocity of 2.3 m/d.
Heater enhanced topside plasma line
Authors: Ganguly S. , Gordon W. E.
Published: February 2008

In a recent experiment at Arecibo, the ionospheric topside plasma line was enhanced by the high power, high frequency, radiowave, HF heater. The enhancement was a few orders of magnitude over the normal daytime photoelectron‐enhanced plasma lines. This is the first observation of an orders of magnitude enhancement of the plasma line in the topside ionosphere induced by the heater. The critical frequency of the F‐region (f0F2) was reasonably close to (approximately 10% higher than) the HF heater frequency of 5.1 MHz. Possible explanations include propagation via the magneto‐ionic Z‐mode with some unknown excitation mechanism, some severe inhomogenities in the ionosphere, or heater excited electrons streaming upward along the magnetic field lines to excite the plasma.
Stratospheric aerosol light absorption before and after El Chichon
Authors: Clarke A. D. , Charlson R. J. , Ogren J. A.
Published: February 2008

Direct in‐situ measurements of aerosol light absorption before, during and after the eruption of Mt. St. Helens and El Chichon reveal the presence of light absorbing species at all times. Large enhancements which appear to drop rapidly with time are found at certain locations immediatly following volcanic events. Although a general patchiness is present in the aerosol and its associated absorption coefficient, post eruption values appear to remain elevated in the mean when compared to early 1979 data prior to the El Chichon eruption. From the data collected for this period, lower bounds for the single scatter albedo are presented along with implications for associated radiative effects.
Balloon and aircraft measurements of stratospheric sulfate mixing ratio following the El Chichon eruption
Authors: Gandrud B. W. , Kritz M. A. , Lazrus A. L.
Published: February 2008

Profiles of sulfate mixing ratio versus altitude over the range 15‐28 km were obtained from filter samples collected aboard balloons and U‐2 aircraft. Observations were made in the summer, fall, and winter following the March‐April, 1982, El Chichon eruption. Observed sulfate mixing ratios were approximately two orders of magnitude greater than typical background (not volcanically augmented) mixing ratios. The sulfate mixing ratios obtained from the aircraft filter measurements were in good agreement with the results from a wire impactor and a particle counter flown simultaneously. Computations of the amount of sulfate contained in a vertical column of 1 m² were in agreement with similar calculations from airborne lidar, balloon‐borne particle counters, and Solar Mesosphere Explorer satellite radiance retrievals.
Higher harmonic effects of the Earth's gravitational field from post‐glacial rebound as observed by Lageos
Authors: Alexander J. C.
Published: February 2008

Recently, long‐term orbital data from the artificial satellite Lageos have been analyzed to determine the rate of post‐glacial rebound. Rubincam has compared the observed values against values derived from two realistic earth models (Wu‐Peltier L1,L2), working with the second harmonic mode of excitation. The data support model L1, with a uniform mantle viscosity of 1022 poise, over L2, with a lower mantle viscosity of 1023 poise. We find the higher degree harmonic contributions are significant, and considerably strengthen the support for model L1. We perform such calculations using the same parameter values for glaciation as Rubincam, and also values due to Peltier and coworkers. We also show that a similar analysis of data from the satellite Starlette is less likely to be as definitive as analysis of Lageos data, since there are significant contributions from very high harmonics, indicating that the behavior of the earth must be known in much greater detail.
On the effect of P‐S coupling on the apparent attenuation of elastic waves in randomly layered media
Authors: Menke William
Published: February 2008

As a pressure pulse propogates through a randomly layered, lossless fluid medium, it experiences an apparent attenuation due to pulse broadening by interbed multiples. This attenuation increases as the impedance contrast between layers is increased, for example, by making the angle of incidence more oblique. In elastic media, P‐S coupling affects the partitioning of energy between the interbed multiples and therefore leads to a different amount of apparent attenuation than the fluid case. In elastic media, both the impedance contrast and the amount of P‐S coupling increase as the angle of incidence is made more oblique. We explore the effect on apparent attenuation through numerical simulations. We find that: 1) the attenuation of the elastic P wave increases more slowly than the fluid P wave as the angle of incidence is made more oblique; 2) The attenuation of the elastic S wave decreases by a factor of about 2 as the angle of incidence is made more oblique; and 3) The coherent S wave pulse experiences a small (1%) apparent increase in propagation velocity.
Production of nitrous oxide and consumption of methane by forest soils
Authors: Keller M. , Goreau T. J. , Wofsy S. C. , Kaplan W. A. , McElroy M. B.
Published: February 2008

Soils in an Amazonian rainforest are observed to release N2O at a rate larger than the global mean by about a factor of 20. Emissions from a New England hardwood forest are approximately 30 times smaller than Brazilian values. Atmospheric methane is consumed by soils in both systems. Tropical forests would provide a major source of atmospheric N2O if the Brazilian results are representative.
Dependence of radiative properties of Arctic stratus clouds on cloud microstructure
Authors: Tsay Si‐Chee , Jayaweera Kolf , Stamnes Knut
Published: February 2008

Observations of cloud microstructure during the Beaufort Sea Arctic Stratus Cloud Experiments of June 1980 showed that the drop size distributions typically are nonuniform changing from monomodal near the base to bimodal near the top of the cloud. The observed drop size distributions are used to compute the reflection and transmission of solar radiation by Arctic Stratus Clouds in the visible part of the spectrum. Solutions of the radiative transfer equation using three different vertically uniform drop size distributions closely resembling those observed near the bottom, middle and top of the cloud, respectively, resulted in significant changes in the radiative properties even though the column liquid water content is kept constant. This finding implies that the shortwave optical depth of Arctic Stratus Clouds cannot be related to the column liquid water content (inferred from longwave satellite radiometry) unless realistic height‐varying drop size distributions are used. It also implies that in order to make reliable predictions concerning the clouds' effect on the surface heat balance, one needs not only the column liquid water content but also height profiles of the drop size distributions.
Raindrop axial and backscatter ratios using a collisional probability model
Authors: Beard K. V. , Johnson D. B.
Published: February 2008

The steady‐state distribution of oscillation energies for raindrops was computed for a balance between input energies from collisions and dissipation by viscosity. Calculations of the oscillation responses indicates that an appreciable fraction of large raindrops (≳ 3 mm diameter) in heavy rain showers are oscillating with axis ratio changes greater than 10%. Computations of the distribution averages for the axis ratio, backscatter ratio, and ZDR indicate increasingly significant deviations from values for static raindrop shapes with increasing rain rates.
Upper hybrid turbulence as a source of nonthermal continuum radiation
Authors: Christiansen P. J. , Etcheto J. , Rönnmark K. , Stenflo L.
Published: February 2008

Recent observations of very narrow band features in the terrestrial electromagnetic “continuum” spectrum indicate that at least part of the radiation is generated in comparatively small source regions, and that weak turbulence theory can account only for the average power. We point out that the structure of the dispersion relation of electrostatic waves near the upper hybrid frequency allows localized nonlinear collapse processes, which could be responsible for the observed narrow band radiation.
The mean life of continents is currently not constrained by Nd and Hf isotopes
Authors: Patchett Jonathan , Chauvel Catherine
Published: February 2008

The paper on crustal recycling by DePaolo (“The mean life of continents…”; Geophys. Res. Lett. 10, 705‐708, 1983) contains errors in the listing and plotting of published Hf isotopic data which materially affect the inferred pattern of mantle Hf isotopic evolution. More generally, the impression given in the paper that it is now possible to use Nd and Hf isotopic data to constrain the degree of crust‐to‐mantle recycling is misleading because exactly the same observed effects would be produced by mixing within the mantle itself. Existing Nd and Hf isotopic data allow either crustal growth with no recycling of crust to mantle, or a model of constant‐mass continental crust with extensive recycling. This implies that all intermediate growth plus recycling combinations are also permitted.
Hysteresis properties of sized dispersed monoclinic pyrrhotite grains
Authors: Clark D. A.
Published: February 2008

Monoclinic pyrrhotite (Fe7S8 with 4C superstructure) was magnetically separated from a massive pyrrhotitic ore for preparation of nine grain‐size fractions ranging from ∼ 80 µm (large multidomain grains) to < 3 µm (single‐domain grains). Grains smaller than 100 µm were found to be magnetically hard with coercive forces ranging from 135 oe for 83 µ grains to 920 oe for < 3 µm grains. For grain sizes between 83 µm and 7 µm the coercive force is given by Hc ⧜ d−0.79. Variations in hysteresis properties with grain size appear to be gradual, with no evidence of sudden changes associated with domain structure transitions.
Calculated anhysteretic susceptibility due to domain wall motion in two‐domain magnetite spheres
Authors: Veitch R. J.
Published: February 2008

It is important to palaeomagnetism to understand the processes of magnetization in submicron magnetite grains. The theoretical contribution of domain wall motion to the anhysteretic susceptibility of two‐domain magnetite spheres has been calculated. Comparison with experimental values shows that domain wall motion can account for the major part of the anhysteretic susceptibility of particles a little above the single‐domain size.
Depletion core in ionospheric depletion experiments: Snowplow effects or plasma recombination?
Authors: Yau A. W.
Published: February 2008

In F‐region ionospheric depletion experiments involving the explosive release of reactive molecular vapour such as H2O, CO2 and N2, a depletion core of ≳5 km diameter is formed within a few seconds of the release, where the plasma density is depleted by more than a decade. This paper examines the depletion core formation mechanism in the Lagopedo and Waterhole experiments. It is found that the "snowplow" model is inconsistent with observation. The core region is shown to be caused primarily by rapid three‐body ion recombinations during the initial, self‐continuum phase of the expansion. An analytic model is derived to estimate the extent of plasma depletion in the core region due to three‐body H3O+ ion recombination reaction, and the estimate is compared with experiment.
Magnetosonic waves adjacent to the plasma sheet in the distant magnetotail: ISEE‐3
Authors: Tsurutani Bruce T. , Smith Edward J.
Published: February 2008

Fast mode magnetosonic waves have been discovered in the distant plasma sheet boundary layers. The emissions have frequencies near the proton cyclotron frequency, are circularly or elliptically polarized in a right‐hand sense, and are propagating nearly along
(θkB <20°). The wave compressional component can be as large as 30‐90% of the wave amplitude. The emissions are substorm related. Several possible generation mechanisms are discussed, such as resonant interactions with ∼1 ‐ 2 keV streaming protons. In the firehose instability, energization of the protons would be caused by the adiabatic compression of plasma on freshly reconnected magnetic field lines. The role that the waves may play in the heating and expansion of the plasma sheet and as a component of internal pressure which keeps open the distant tail, are both briefly discussed.
Arctic haze and the Arctic Gas and Aerosol Sampling Program (AGASP)
Authors: Schnell R. C.
Published: February 2008

The Arctic Gas and Aerosol Sampling Program (AGASP) was conducted across the Arctic in the spring of 1983 to study the large scale air pollution phenomenon known as Arctic haze. A component of this program utilized a National Oceanic and Atmospheric Administration WP‐3D Orion research aircraft to study the haze in situ. The program and aircraft instrumentation are described.
Aerosol distributions and an Arctic aerosol front during AGASP: Norwegian Arctic
Authors: Raatz W. E. , Schnell R. C.
Published: February 2008

Vertical profiles of aerosol characteristics obtained near Svalbard, Norway, during the Arctic Gas and Aerosol Sampling Program (AGASP) indicate that high aerosol concentrations and strong visible haze were distributed throughout the troposphere. Layers of Arctic haze were observed in both dry air and moist air. A research flight on March 31, 1983, crossed a previously undocumented Arctic aerosol front structure. Condensation nucleus concentrations of 450 cm−3 within the polluted continental air mass south of the front decreased to 80 cm−3 within the clean Arctic air north of the front. Aerosols above the Aitken size range decreased one order of magnitude in both number and mass across this same air mass boundary.
Scattering of P‐waves beneath scarlet in Southern California
Authors: Powell Christine A. , Meltzer Anne S.
Published: February 2008

Previous studies have indicated that the crust and upper mantle beneath the Caltech‐USGS large seismic array, SCARLET, is extremely heterogeneous. In this study, Chernov theory has been applied to characterize the crust and upper mantle as a random medium. The data consist of travel‐time residuals from plane waves fit to teleseismic arrival times. Amplitude data were not available. Consistent results were obtained for events arriving from the NW, SW and SE and indicate a correlation distance for the inhomogeneities of 25 km and a maximum velocity perturbation of 3.26%. The random medium extends to a minimum depth of 119 km. Although these values are similar to those obtained for other arrays, they indicate that it may be improper to apply Chernov Theory to teleseismic P‐waves with dominant frequencies near 1 Hz.
Experimental evidence of non‐isotropic temperature distributions of ions observed by EISCAT in the auroral F‐region
Authors: Perraut S. , Bjørna N. , Brekke A. , Baron M. , Kofman W. , Lathuillière C. , Lejeune G.
Published: February 2008

Many theoretical studies using different collision models have been devoted to calculating ion velocity distributions in the high latitude ionosphere. In the presence of strong convection electric fields, the ions can be accelerated to drift speeds which exceed the thermal speed of the neutral gas leading to velocity distribution functions distorted from the Maxwellian shape.

With EISCAT we are able to measure three independent components of the ion velocity vector and temperature in the same scattering volume. The ion temperature observed at about 300 km during strong enhancements of the ion velocity is characterized by different temperatures parallel and perpendicular to the magnetic field with T⊥ > T⫽. For an electric strength of 50 mV/m, an anisotropy factor of about 1.5 was measured.
Measurements of thermal neutrons in the subsurface
Authors: Kuhn Mark W. , Davis Stanley N. , Bentley Harold W. , Zito Richard
Published: February 2008

Thermal neutrons are produced in the subsurface through (a) cosmic radiation interacting with material beneath the surface of the land, (b) alpha‐capture reactions with light elements, and (c) natural fission of uranium. Field measurements of thermal neutrons in mines deeper than 800 m yielded counts which varied between 1.1 and 33 neutrons per cm³ per year. These neutrons originated primarily from alpha capture and fission reaction sources. Larger counts, up to 116 neutrons per cm³ per year, were obtained from the shallow subsurface where neutrons associated with cosmic ray interactions probably accounted for a significant fraction of the neutrons detected. With only one exception, more thermal neutrons were detected than were predicted on the basis of the uranium and thorium concentrations and the overall chemical composition of rocks surrounding the measuring stations.
Paleomagnetism and rock magnetism of the Mississippian Leadville (carbonate) formation and implications for the age of sub‐regional dolomitization
Authors: Horton Robert A. , Geissman John W. , Tschauder Richard J.
Published: February 2008

The Mississippian Leadville Formation of Central Colorado is dolomitized near the Sawatch Uplift and hosts numerous Pb‐Zn‐Ag mineral deposits. Paleomagnetic and rock magnetic data from several dolomite types away from centers of Tertiary intrusive activity imply a late Paleozoic (Late Mississippian, ?) age for the dolomitization (e.g., D = 148°, I = −11°, k = 86, α95 = 8.6°, N = 3 localities, 31 samples in dolomitized units). The magnetization is of diagenetic origin and was probably acquired during or soon after dolomitization. Tertiary thermochemical activity has overprinted dolomites close to intrusive centers. Data indicate that limestones removed from igneous activity were also remagnetized at the same time.
First measurements of supersonic polar wind in the polar magnetosphere
Authors: Nagai T. , Waite J. H. , Green J. L. , Chappell C. R. , Olsen R. C. , Comfort R. H.
Published: February 2008

Measurements from the Retarding Ion Mass Spectrometer (RIMS) on Dynamics Explorer (DE) have, for the first time, revealed a supersonic polar wind (Mach number is greater than 1) along polar cap field lines. The observations reported were obtained on the nightside (22:30 to 23:30 MLT) from 65° to 81° invariant latitude and at altitudes near 2 RE. Fitting the data using a thin‐sheath model gives a range of temperatures of 0.1 to 0.2 eV with corresponding flow velocities of 25 to 16 km s−1 over the estimated range of spacecraft potential of +3 to +5 V. For these values the Mach number ranged from 5.1 to 2.6 (with a most likely value of 3). Characteristics of the H+ flow are in general agreement with those predicted by "classical" polar wind theory, but high variability of the He+/H+ ratio was observed.
How and why does olivine transform to spinel?
Authors: Green Harry W.
Published: February 2008

Recent conflicting results on the mechanism of the olivine‐spinel phase transition suggest that the mechanism varies with experimental conditions. Evidence for a shear‐induced mechanism is strong in experiments performed at temperatures far from the melting point or under conditions where very large shear stresses may be inferred. Where temperatures are closer to the melting point and stress concentrations probably less severe, the evidence favors a nucleation and growth mechanism. In one study, volume reduction accompanied anion restacking and significantly preceded cation reordering, suggesting a change in bonding between the two polymorphs.
Comparing tiltmeters for crustal deformation measurement – A preliminary report
Authors: Wyatt F. , Bilham R. , Beavan J. , Sylvester A. G. , Owen T. , Harvey A. , Macdonald C. , Jackson D. D. , Agnew D. C.
Published: February 2008

A collection of high‐precision tiltmeters is being operated at Piñon Flat Observatory, southern California, both to compare instruments and to measure tectonic deformation. We report on 1.2 years of data from four of these: two Michelson‐Gale long fluid tiltmeters, one long center‐pressure tiltmeter, and a shallow borehole tiltmeter. The three long‐base instruments are all located on the same baseline, with a precise leveling line running between their end‐monuments. At nontidal frequencies, only the two Michelson‐Gale instruments show some coherence (γ² = .3 for periods of 2 to 4 days), while the center‐pressure instrument is correlated with air temperature at periods from a few days to a few weeks. The most stable tilt record shows a secular rate of 0.28 µrad/a, which may be real. Over much longer times, leveling to specially stabilized benchmarks should confirm this. Comparing instruments has identified more and less successful measurement techniques; it appears that low‐noise data will most probably be produced only by relatively complex and expensive instruments, though even for these, the operating costs over any reasonable lifetime will exceed the capital cost. Even the best existing sensors must be improved to measure continuous tectonic motions.
Thermal infrared satellite data for the study of tectonic features
Authors: Andre Constance G. , Blodget Herbert W.
Published: February 2008

Multispectral thermal infrared data from the NOAA‐7 Advanced Very High Resolution Radiometer (AVHRR) have been processed to evaluate their potential for mapping tectonic features. Day/night ratio data from 3 thermal bands between 3.7 and 12.0 µm were used to construct a thermal infrared color image that emphasizes heat retention differences in surface materials as a function of wavelength. The study area is an arid region of the Arabian Peninsula where lithologic units are widely exposed to satellite detectors. In spite of the coarse resolution of 1.1 km at nadir, the image of emitted radiation data contains prominent features that appear to relate to fault systems, unmapped extensions of fault systems, and drainage patterns that are lacking in AVHRR reflected radiation data.
Henry's law constants for dimethylsulfide in freshwater and seawater
Authors: Dacey John W. H. , Wakeham Stuart G. , Howes Brian L.
Published: February 2008

Henry's law constants for dimethylsulfide were measured in several natural waters of varying salinity and in distilled water over a range in temperature from 0°‐32°C. Fitting our data to the equation: 1nH (atm L mol−1) = A/T(°K) + C yields A = −3463 (75) and −3547 (16), and C = 12.20 (0.26) and 12.64 (0.06), for distilled water and seawater respectively (standard errors in parenthesis). These solubilities support the concept that the concentration of dimethylsulfide in the atmosphere is far from equilibrium with seawater.
Power dissipation at slow‐mode shocks in the distant geomagnetic tail
Authors: Feldman W. C. , Baker D. N. , Bame S. J. , Birn J. , Hones E. W. , Schwartz S. J. , Tokar R. L.
Published: February 2008

ISEE‐3 plasma and field data were analyzed to estimate the power dissipated across slow‐mode shocks in the distant geomagnetic tail. A set of 26 unambiguous examples of slow‐mode shocks encountered by ISEE 3 near X(GSM) ≃ −200 RE was used for this purpose. The analysis yielded an average cross‐tail electric field of 1.6 ± 0.7 mV/m an upstream Alfvén Mach number of 0.19 ± 0.08 and a decrease in the Poynting flux at the shocks of 9.2 ± 7.4 × 10−3 ergs/cm²/s. Assuming a mean cross‐tail potential of 70 keV and a location of the neutral line near X(GSM) ≃ −100 RE, the average power dissipated tailward of the neutral line from lobe magnetic energy density to plasma sheet convection is 5 × 1018 ergs/s, a value comparable to the total power dissipated near the earth during moderate‐strength substorms.
Atomic oxygen concentrations in the auroral thermosphere: Application of a thermospheric temperature criterion
Authors: Shepherd G. G.
Published: February 2008

The quenching of N2(A³∑u+) by atomic oxygen in the auroral thermosphere offers an attractive method of determining atomic oxygen concentrations, using the emission rate ratio of the N2 Second Positive bands and the N2 Vegard‐Kaplan bands. In the first applications of this method it was necessary to derive the quenching rate constant, the production rate ratio and the 0 profile from the measurement of emission rate ratio versus altitude. Even with more recent laboratory measurements of the quenching rates, different analyses of the same datasets gave rise to conflicting results. In this paper the consequences of including a requirement of diffusive equilibrium are considered; it is concluded that at times the 0 concentration at 130 km can be lower than that of CIRA 72 by a factor of 5, while at other times it can agree with the CIRA model.
Periodicities in precipitation in north‐east China, 1470–1979
Authors: Clegg S. L. , Wigley T. M. L.
Published: February 2008

Claimed periodicities in northeastern Chinese rainfall are examined by comparing records spanning the period 1470–1979 from several sites near Beijing. Although a number of periodicities occur, they are generally unstable in both space and time. This suggests that they have little or no physical significance and that their predictive value is negligible.
Spectroscopic measurements of atmospheric HCN at northern and southern latitudes
Authors: Smith M. A. H. , Rinsland C. P.
Published: February 2008

A number of lines belonging to the ν3 fundamental vibration‐rotation band of hydrogen cyanide (HCN) have been identified in atmospheric infrared absorption spectra obtained on high‐altitude balloon flights at 32°N in 1976 and at 30°S in 1977. Quantitative analysis of these spectral features has resulted in the first determination of atmospheric HCN concentrations in the southern hemisphere, as well as an independent estimate of stratospheric HCN abundance in the northern hemisphere. Within the uncertainties of our own and previous measurements, our northern‐hemisphere result is consistent with those of other investigators, and southern‐hemisphere HCN concentrations appear to be similar to those in the northern hemisphere.
Generation of electrostatic shocks and turbulence through the interaction of conics with the background plasma
Authors: Pottelette R. , Treumann R. , Bauer O. H. , Lebreton J. P.
Published: February 2008

Experimental results, obtained during the PORCUPINE experiment and dealing with the interaction of an artificial ion conic with the background auroral plasma, are presented. In addition, these results are compared to the measurements performed by the S3‐3 satellite when natural ion conies are present. This comparison shows that the physical processes associated with the neutralization of conical ion distributions and with their interaction with the background plasma induce the same kind of electrostatic shocks and turbulence as those recorded by S3‐3.
Normal mode solutions for absorbing boundary conditions
Authors: Geller Robert J. , Noack Reinhard M. , Fetter Alexander L.
Published: February 2008

Wave propagation problems with radiation boundary conditions are non‐hermitian and therefore typically cannot be solved by expanding in terms of eigenfunctions that correspond to real eigenvalues. We present a method for solving such problems entirely in terms of a superposition of normal modes, using the "shifted eigenvalue" method outlined by Lanczos. In effect, the desired system with an outgoing radiation boundary condition is coupled to a system which is identical, but has an incoming radiation boundary condition. The combined system is hermitian, and thus has real eigenvalues. We present numerical computations for a one‐dimensional, semi‐infinite, homogeneous continuum.
Neutral motions in the polar thermosphere for northward interplanetary magnetic field
Authors: Killeen T. L. , Heelis R. A. , Hays P. B. , Spencer N. W. , Hanson W. B.
Published: February 2008

On 24th November, 1982, The North‐South (Bz) component of the Interplanetary Magnetic Field (IMF) became positive for a period of about 11 hours reaching a relatively large and steady value of ∼25 nT. During this rare occurrence, the Dynamics Explorer‐2 (DE‐2) spacecraft was in a configuration that enabled the dynamics of both ionic and neutral species of the high‐latitude F‐region to be measured simultaneously along the track of the polar‐orbiting satellite. Results from two Northern (winter) polar passes of DE‐2, extracted from a larger data set, are shown to illustrate the response of the neutral F‐region to ion drag forcing arising from a configuration of ion convection characteristic of strongly northward IMF. The measured neutral winds differ appreciably from those more commonly observed for periods of southward IMF. The multi‐cellular ion drift pattern associated with positive Bz is observed to drive a similar but less structured and weaker neutral wind configuration in the winter polar cap. Major features of the ion drift pattern are mimicked by the neutral circulation but smaller‐scale and more irregular structures of ion flow are not. This is ascribed to the relatively long time constant (few hours) for momentum exchange between the ion and neutral gases. The results demonstrate that sunward flow of neutral gas can be established and maintained by ion drag in the central polar cap for positive Bz.
Formation of dipole vortex in the ionosphere
Authors: Shukla P. K. , Yu M. Y.
Published: February 2008

It is shown that isolated dipole vortices can exist in the F‐region of the ionosphere. These are associated with the Rayleigh‐Taylor and
gradient drift instabilities. The vortices may be responsible for the rapid structuring of barium clouds as well as other phenomena observed in the upper ionosphere.
Complex resistivity of fault gouge and its significance for earthquake lights and induced polarization
Authors: Lockner David A. , Byerlee James D.
Published: February 2008

We have measured complex resistivity of 2 water‐saturated San Andreas fault gouges from 10−3 to 106 Hz and confining pressures of 0.2 to 200 MPa. Consistent with earlier observations of clays and common rocks, large low‐frequency permittivities were observed in all cases. Comparisons were made to induced polarization (IP) measurements by inversion of the data into the time domain, where we found that principal features of the IP response curves were due to these large low‐frequency permittivities. The results also suggest that following large earthquakes, significant electrical charge could remain for many seconds and could result in a variety of reported electromagnetic effects.
Magnetic anisotropy in the Trenton Limestone: Results of a new technique, anisotropy of anhysteretic susceptibility
Authors: McCabe Chad , Jackson Michael , Ellwood Brooks B.
Published: February 2008

A new method for determining magnetic anisotropy using anhysteric remanence susceptibility is described. The magnetic fabric of a collection of Trenton Limestone specimens has been determined using this method, as well as by conventional anisotropy of magnetic susceptibility. The results demonstrate the usefulness of the new method for finding the magnetic fabric of rock units such as the Trenton in which the bulk magnetic susceptibilities are low. A model is proposed to explain the observed foliated and lineated fabric as a consequence of overburden compaction and regional horizontal stresses. The original fabric is inferred to have been isotropic; the anisotropy resides in secondary magnetite of Late Paleozoic age. It is argued that the observed magnetic fabric must therefore be Alleghenian or younger in age. Our method has the potential to determine paleostress directions in carbonates elsewhere, provided our assumptions are correct.
Accelerogram evidence for southward rupture propagation on the Imperial Fault during the October 15, 1979 earthquake
Authors: Anderson John G. , Silver Paul G.
Published: February 2008

The 1979 Imperial Valley earthquake caused the Imperial fault to rupture 10 to 15 km southeast of the epicenter, in addition to the well documented rupture to the northwest. This is established from the properties of the initial S‐wave arrival at strong‐motion stations in Mexico at the southern end of the rupture zone. First, the amplitude of this S—velocity pulse is larger at stations 10 to 15 km southeast of the epicenter than at those within 2 km of the epicenter. Second, the pulse shapes and polarizations at three stations south of the epicenter are consistent with southeastward propagation. Third, travel time considerations rule out contributions to these pulses from faulting originating more than 4 km northwest of the epicenter.
Spectral comparisons between explosion P signals from the Tuamotu Islands, Nevada, and eastern Kazakh
Authors: McCreery Charles S. , Walker Daniel A.
Published: February 2008

A comparison is presented between explosion‐generated teleseismic P signals from single events of comparable magnitude in the Tuamotu Islands, Nevada, and E. Kazakh recorded by the Wake Island Hydrophone Array. Spectral analysis of these signals indicates that attenuation (presumably under the source) is greatest for the Tuamotu travel path and least for the E. Kazakh travel path. The high frequencies (> 3 Hz) present in E. Kazakh signals, which enhance the detectability of these signals on the ocean bottom near Wake (where noise levels are low in this range), are generally absent in signals from Nevada and the Tuamotus.