bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes of mean magnitude of Parkfield seismicity: A part of the precursory process?
Authors: Wyss Max
Published: February 2008

The average magnitude of earthquakes produced along the Parkfield segment of the San Andreas fault was decreased significantly between late 1986 and late 1988 along with the seismic quiescence [Wyss et al., 1990a]. The change corresponds to an increase of the b‐value from 1.1 to 1.4. During the last year (1989) however, the average magnitude produced was approximately normal again. This same phenomenon had been identified before several other mainshocks. Therefore it may be interpreted as a precursor to the predicted Parkfield mainshock.
A joint nitric oxide measurement by rocket‐borne ultraviolet photometer and mass spectrometer in the lower thermosphere
Authors: Trinks H. , von Zahn U. , Barth C. A. , Kelly K. K.
Published: February 2008

On June 29, 1974, at 1514 local solar time a nitric oxide photometer and a cryogenic neutral gas mass spectrometer were flown aboard the same rocket above Wallops Island, Virginia, as part of the NASA/Air Force Cambridge Research Laboratories Aladdin 74 program. Altitude profiles of the nitric oxide density between 100 and 220 km were obtained by both experiments. The profiles agree within the experimental errors, this agreement proving the reliability of both methods. Nitric oxide emission from the rocket motor can be excluded as a perturbation source for the measurements.
The cooling of solar wind protons from Mariner 2 data
Authors: Eyni Menashe , Steinitz Raphael
Published: February 2008

We examine the possibility that cooling of solar wind protons has escaped detection in the Mariner 2 data. After dividing the data into two velocity ranges and introducing an intermediate quantity τ to decrease the strong dependence of temperature on velocity, we find that the low‐velocity data exhibit cooling.
A technique for mass spectrometer measurements of atomic and molecular oxygen in the lower thermosphere
Authors: Kayser D. C. , Potter W. E.
Published: February 2008

A neutral mass spectrometer with a quasi‐open ion source was flown on each of the Atmosphere Explorer (AE) C, D, and E satellites. The three instruments provided an opportunity to study the effects of different source insert materials on the source surface chemistry. It was found that, after a period of conditioning in space, the recombination coefficient of atomic oxygen on gold appears to be substantially lower than it is on Nichrome V. The lower recombination coefficient on gold allows the spectrometer to directly measure a significant fraction of the incident atomic oxygen, making it possible to distinguish between ambient O and O2. Equations are developed to calculate the atomic and molecular oxygen densities. Preliminary measurements of molecular oxygen densities obtained by this technique agree well with measurements taken in the fly‐through mode of operation.
Extended Rankine‐Hugoniot relations for collisionless shocks
Authors: Sanderson J. J. , Uhrig Richard A.
Published: February 2008

The hydromagnetic Rankine‐Hugoniot relations are extended to allow for separate ion and electron temperatures and arbitrary degrees of freedom for ion and electron heating; when the degrees of freedom are unequal, this comprises an unclosed set of equations. The system is reduced to one equation in two unknowns containing the usual one‐fluid model as a special case. Closure is achieved by means of empirical arguments for both subcritical and large Mach number shocks, and a general parametric solution is also presented. Analytic expressions for the fluid and field jumps are obtained and compared with various experimental observations.
Mercury's helium exosphere after Mariner 10's third encounter
Authors: Curtis S. A. , Hartle R. E.
Published: February 2008

From a comparison of the Mariner 10 third‐encounter UV spectrometer data with intensities generated from a newly constructed model exosphere, we have derived a new value of 4.5 × 10−4 for the fraction of the solar wind He++ flux to be intercepted and captured by Mercury's magnetosphere if the observed He atmosphere is maintained by the solar wind. If an internal source for He prevails, the corresponding upper bound for the global outgassing rate is estimated to be 4.5 × 1022 s−1. These values differ from those given earlier because of the present use of a surface temperature distribution satisfying the heat equation over Mercury's entire surface which employs Mariner 10 determined mean surface thermal characteristics. We also use the mean standoff distance of Mercury's magnetopause averaged over Mercury's orbit. We find the agreement between the observed and calculated intensities to be good and believe that the minor discrepancies that exist on the nightside of the terminator are explicable in terms of differences between actual and computed surface temperatures and the resulting scale height structure changes. We attribute these temperature differences to the inhomogeneity of the physical properties of the surface of Mercury.
Numerical simulation of MHD shock waves in the solar wind
Authors: Steinolfson Richard S. , Dryer Murray
Published: February 2008

The effects of the interplanetary magnetic field on the propagation speed of shock waves through an ambient solar wind are examined by numerical solutions of the time‐dependent nonlinear equations of motion. The magnetic field always increases the velocity of strong shocks. Although the field may temporarily slow down weak shocks inside 1 AU, it eventually also causes weak shocks to travel faster than they would without the magnetic field at larger distances. Consistent with the increase in the shock velocity, the gas pressure ratio across a shock is reduced considerably in the presence of the magnetic field. The numerical method is used to simulate (starting at 0.3 AU) the large deceleration of a shock observed in the lower corona by ground‐based radio instrumentation and the more gradual deceleration of the shock in the solar wind observed by the Pioneer 9 and Pioneer 10 spacecraft.
Quiet time interplanetary cosmic ray anisotropies observed from Pioneer 10 and 11
Authors: Ip W. ‐H. , Fillius W. , Mogro‐Campero A. , Gleeson L. J. , Axford W. I.
Published: February 2008

The University of California at San Diego Cerenkov counters on the Pioneer 10 and Pioneer 11 spacecraft are capable of detecting protons and alpha particles with kinetic energy T ≥ 480 MeV/nucleon and electrons with T ≥ 6 MeV. With these instruments we have made measurements of cosmic ray anisotropies in interplanetary space, using the Pioneer 11 detector between April 17 and November 31, 1973 (during which interval the spacecraft moved from 1.1 to 2.7 AU), and the Pioneer 10 detector between March 1 and November 31, 1974 (during which interval the spacecraft moved from 6.0 AU to 6.8 AU). From the Pioneer 11 data the east‐west anisotropy has been determined to be ξϕ* ≈ 0.41 ± 0.11%, and the north‐south anisotropy ξθ* ≈ 0. The ratio of the perpendicular and parallel components of the diffusion coefficient (κ⊥/κ∥) is on this basis estimated to be ≈ 0.26 ± 0.08%. From the Pioneer 10 data, ξϕ* ≈ 0.59 ± 0.18%, ξθ* ≈ 0.25 ± 0.08%, and we estimate that κ⊥/κ∥ ≈ 0.13 ± 0.04. The large value of ξθ* obtained from Pioneer 10 suggests that there was a substantial component of cosmic ray streaming from north to south. A comparison of the anisotropy and magnetic field data suggests that such a north‐south anisotropy could be due at least in part to the gradient drift effect and perhaps in part to an additional streaming independent of the magnetic field polarity. To produce the observed value of ξθ* from the gradient drift effect the radial gradient at this distance should have a value of ≈0.3 ± 0.3%/AU, which is not incompatible with the radial gradients obtained from direct measurements.
The localized origin of equatorial F region irregularity patches
Authors: Aarons Jules , Buchau Jürgen , Basu Santimay , McClure J. P.
Published: February 2008

An intensive study of nighttime irregularities of electron density in the equatorial ionosphere was performed in October 1976 by making 50‐MHz radar backscatter measurements at Jicamarca, Peru, and scintillation measurements of 249‐MHz transmissions from Les 9 at two ground stations (Ancon and Huancayo, both in Peru) as well as by aircraft flying in the vicinity of the stations. The 137‐MHz scintillations from the orbiting Wideband satellite were also recorded at Huancayo. The results of such measurements made on October 16–17, 1976, are discussed in this report. We find that on this particular night a large‐scale irregularity patch evolved first in the west, as was detected by the radar at Jicamarca, and drifted eastward to cause successive onsets of scintillation activity on propagation paths from Ancon and Huancayo. The observations indicate the east‐west dimension of the large‐scale structure to be 400 km drifting eastward at a speed of approximately 100 m/s, having a lifetime of several hours, and containing a hierarchy of irregularity scale sizes in the range of kilometers to meters causing both scintillations at 249 MHz and radar backscatter at 50 MHz.
Shear instability: Auroral arc deformation and anomalous momentum transport
Authors: Miura Akira , Sato Tetsuya
Published: February 2008

Temporal evolution of a two‐dimensional electrostatic shear instability is numerically studied with special attention to rotational deformation of auroral arcs and momentum transport across the magnetospheric boundary. It is found that the spatial structure of the growing vortex is in good agreement with the small‐scale auroral deformation called ‘curl.’ An anomalous viscosity arising from the shear instability is found to be given approximately by 0.08 aV0, where a is the characteristic distance over which the flow velocity changes by V0. If we assume that a = 200 km and V0 = 250 km/s at the magnetospheric boundary, the anomalous viscosity becomes 4 × 1013 cm² s−1, which is comparable to, or even larger than, the value estimated by Axford (1964) from energy requirements of a typical magnetic storm. Spectral energies of fully developed electrostatic turbulence are also studied. It is found that the observed power spectral energies can well be represented by a power law of the form k−4.
Low‐latitude E region ionization by energetic ring current particles
Authors: Lyons L. R. , Richmond A. D.
Published: February 2008

Energetic neutral particles resulting from the charge exchange of ring current ions with geocoronal hydrogen are known to strike the atmosphere at low latitudes. We have evaluated the ionization rates caused by these particles in the low‐latitude upper E region ionosphere. We find that these particles are an important quiet time source of E region ionization at night and that they can account for the observed increases in nighttime ionization that correlate with geomagnetic activity. This ionization has previously been attributed to 1‐ to 10‐keV electron precipitation. However, sufficiently intense precipitating electron fluxes have not been measured at low latitudes, and we know of no source of such electrons.
Association of ULF magnetic variations and changes in ionospheric conductivity during substorms
Authors: Lanzerotti L. J. , Maclennan C. G. , Evans C.
Published: February 2008

Quantitative determinations are made of the correlation coefficients and their standard deviations between variations in the cosmic noise absorption by the ionosphere and variations in magnetic field in the period range ∼20–100 s, as measured at Siple, Antarctica. Several intervals during four magnetic storms were identified where the correlations were significant at the 3–4σ level. During a number of these intervals the correlations between the magnetic field fluctuations in the northern and the southern hemisphere are <2σ and often <1σ. The magnitudes of the magnetic field fluctuations together with the absorption variations are consistent with changes in the ionospheric conductivity at ∼100 km produced by particle precipitation. The particle precipitation may at times be evidence of the modulation of particle pitch angle distributions by highly localized hydromagnetic waves in the earth's magnetosphere.
A self‐consistent model of a corotating Jovian magnetosphere
Authors: Carbary J. F. , Hill T. W.
Published: February 2008

A rotation‐dominated model of the Jovian magnetosphere is constructed in which the plasma current distribution is dynamically consistent with the magnetic field. We assume an ionospheric plasma source with no pitch angle scattering, magnetically aligned rotation, loss‐free radial transport through flux tube interchange diffusion, and a static balance between centrifugal force and magnetic stress. From these assumptions a dynamical equation is derived for a self‐consistent magnetic field configuration having a single adjustable parameter that is related to the plasma source strength. An iterative numerical method is used to solve this equation. The self‐consistent field resembles a radially distorted dipole field and does not resemble the flat ‘magnetodisc’ configuration that has often been inferred from the Pioneer data. The implication is that such a magnetodisc field would require an equatorial plasma source (for example, the Galilean satellites) rather than a source at the feet of the field lines. The centrifugal force opens the field at a radial distance approximately 10% greater than that expected for a pure dipole field for a given source strength. For expected source strengths this opening radius is found to lie in the range 40–75 RJ.
(U, B, K) Coordinates: A natural system for studying magnetospheric convection
Authors: Whipple Elden C.
Published: February 2008

A coordinate system consisting of the electric potential U, the magnetic field intensity B, and the modified longitudinal invariant K forms a natural system for the analysis of plasma convection in the magnetosphere. In the absence of parallel electric fields the bounce‐averaged drift motion of a particle mirror point follows a straight line trajectory in this representation. The steady state equations of motion for particle mirror points are given by dB/dt = W, dU/dt = ‐(µ/e)W, and dK/dt = 0, where W is a generalized velocity function given by W = [(▽U × ▽B) · nK]/(B·nK) and nK is a unit vector perpendicular to the local constant K surface. W depends only upon position in the magnetosphere, independent of any particle properties. However, W is proportional to the rate of transformation between potential energy and particle kinetic energy. The surfaces on which W vanishes form natural boundaries between accelerator regions (W > 0) and dynamo regions (W < 0) of the magnetosphere. The occurrence of forbidden zones for particles and the distinction between various types of particle trajectories are determined by the topology of these boundaries and can be easily visualized. The coordinate system is particularly useful in sorting out trajectory‐dependent from source‐ or sink‐dependent effects. The representation is illustrated by applying it to the analysis of the nose structure protons observed by Smith and Hoffman (1974).
Characteristics of the equatorward auroral boundary near midnight determined from DMSP images
Authors: Sheehan R. E. , Carovillano R. L.
Published: February 2008

The latitude of the equatorward auroral boundary near local midnight has been determined for 162 Defense Meteorological Satellite Program (DMSP) images in November‐December 1972. When grouped according to Kp and AE, these observations show approximate linear decreases in the average boundary latitude with increasing values of these magnetic indices. There appears also to be a slight diurnal variation in the boundary location. Mapping of the appropriate McIlwain injection boundaries to auroral latitudes shows good agreement with the average DMSP equatorward auroral boundary latitude. Similar analyses at 2000 and 2200 CGLT (corrected geomagnetic local time) using a different set of DMSP images yield similar results, with somewhat poorer agreement under quiet conditions.
The high‐latitude winter F region at 300 km: Thermal plasma observations from AE‐C
Authors: Brinton H. C. , Grebowsky J. M. , Brace L. H.
Published: February 2008

Ion composition and electron temperature data obtained from AE‐C during a magnetically quiet period centered on the June 1976 solstice have been used in a statistical study of the southern winter F region poleward of ‐50° Λ at 300‐km altitude. Prominent ionospheric features revealed by topographic maps of O+, NO+, and O2+ concentration and Te include the nightside main trough, an ionization ‘hole’ poleward of the nightside auroral zone, and ionization and Te enhancements in the dayside auroral zone‐cusp region. The main trough, in which O+ was the dominant ion, extended throughout the night between ‐60° and ‐70° Λ, the lowest trough densities, ∼1 × 10³ cm−3, being detected near dusk. We attribute these low concentrations to the opposition, in the dusk sector, of plasma corotation and solar wind induced plasma convection velocities, leading to long plasma residence (and decay) times. That the distributions of NO+ and O2+ in the trough region exhibited little correlation with O+ suggests that drift‐enhanced O+ loss via reactions such as O+ + N2 → NO+ + N played a minor role in the formation of the trough during this period. A band of enhanced electron temperature coincided with the trough throughout the night; this Te peak, which has been observed previously in the topside ionosphere, is attributed to heat conducted downward from the protonosphere. The ionization hole, a region poleward of the nightside auroral zone between ‐70° and ‐80° Λ, was characterized by depletions in all the measured ion densities and by a minimum in Te. The total ion concentration measured in this region exhibited extreme temporal variability, ranging from values as low as 2 × 10² to 6 × 10³ cm−3. We have concluded that the hole forms as a result of slow antisunward plasma drift across the dark polar cap and attendant ion recombination; an average drift velocity of ∼0.1 km/s, corresponding to a convection electric field of less than 5 mV/m, could produce the deepest holes observed. The ion density variability in the hole is attributed to changes in the transpolar plasma convection configuration and the distribution of energetic particle fluxes. The dayside auroral zone‐cusp region was characterized, in general, by enhanced levels of ionization and electron temperature associated with energetic particle precipitation. On some passes through this region, however, localized O+ depletions and corresponding molecular ion increases were detected; we attribute these features to the reactions O+ + N2 → NO+ + N and O+ + O2 → O2+ + O, whose rates are enhanced by the high‐speed plasma drifts observed in the cusp region.
Recurrent geomagnetic disturbances and coronal holes as observed in Fe XIV λ5303 Å
Authors: Musman Steven , Altrock Richard C.
Published: February 2008

We present data obtained with the Fe XIV λ5303‐Å coronal photometer of the Sacramento Peak Observatory for the period October 3 to December 22, 1976. During this period there was a pattern of three coronal holes and three emission regions near the solar equator. Recurrent geomagnetic disturbances were associated with two of these three holes. We propose a simple method for predicting recurrent geomagnetic disturbances at times of low solar activity based on coronal brightness and test it on our data. We show that the method gives correct results 72% of the time, compared with 64% for 27‐day recurrence.
Identification of mixing frequency components in ionospheric electron content data by multiplicative homomorphic filtering
Authors: Bernhardt P. A.
Published: February 2008

Ionospheric electron content data contain frequency components which are produced by nonlinear processes in the solar‐terrestrial environment. Nonlinear analysis, known as multiplicative homomorphic filtering, is used to identify these components in the data. The homomorphic analysis is used on electron content data taken at Honolulu and Stanford. Mixing frequencies produced by solar rotation, by tidal winds, and by unknown sources have been isolated.
Lower‐hybrid‐drift wave turbulence in the distant magnetotail
Authors: Huba J. D. , Gladd N. T. , Papadopoulos K.
Published: February 2008

Recent satellite observations of electrostatic and magnetic noise in the distant magnetotail (Gurnett et al., 1976) can be explained by the excitation of the lower‐hybrid‐drift instability. In particular, it is shown that (1) existence conditions for the lower‐hybrid‐drift instability can be met, (2) the observed frequency spectra and polarization are in good agreement with the predictions of linear theory, and (3) the observed amplitudes of fluctuations are consistent with the nonlinear theory of this mode. Moreover, the observation of this instability suggests that the anomalous transport properties associated with these waves, which are important in many laboratory devices, may play a crucial role in the macroscopic evolution of magnetotail processes such as field line merging, tearing instabilities, or ‘fireballs.’
Aeronomical reference spectrum for solar UV below 2000 Å
Authors: Heroux L. , Hinteregger H. E.
Published: February 2008

The solar reference spectrum named R74113 announced at the 1975 International Association of Geomagnetism and Aeronomy symposium in Grenoble refers to the solar conditions of April 23, 1974, and covers the wavelength range 14–2000 Å. The fluxes for R74113 between 250 and 1940 Å were based on a preliminary evaluation of data obtained from a rocket experiment flown on April 23, 1974. The fluxes outside of the wavelength range covered by the rocket experiment were estimated values for the solar condition of April 23, 1974. This reference spectrum has been revised because of refined evaluation of the rocket data and detailed experience gained from many scans of the solar spectrum for the entire wavelength range 140–1850 Å obtained from the extreme ultraviolet spectrometer experiment on the AE‐E satellite. Although numerous changes have been made in the revised spectrum named F74113, summarized here, these changes have only a small effect on aeronomical calculations that have been based on the original reference spectrum.
Anisotropies in the fluxes of Pioneer 10 protons
Authors: Northrop Theodore G. , Birmingham T. J. , Schardt A. W.
Published: February 2008

One‐hour‐averaged fluxes of 1.8‐to 2.15‐MeV protons observed by the LET2 detector on Pioneer 10 on the inbound trajectory showed anisotropies attributable to corotation of Jupiter’s magnetodisc only when Pioneer was near the dipole equator. Most of the time the anisotropy greatly exceeded the value expected from corotation. Gradients in the distribution function can be used to account for this excess anisotropy, but the amount of gradient required is unacceptably large by 1–2 orders of magnitude. If they were taken as real, these gradients would predict almost complete disappearance of these protons from Jupiter's magnetosphere in a matter of hours. The remedy is to introduce into the model of the distribution function proton flow along field lines away from the equator into both the southern and the northern hemisphere. The parallel flux at the southernmost latitudes reached by Pioneer can reach 25% of the product of proton density and velocity, i.e., 25% of the maximum possible.
Voyager observations of the interstellar medium in the 500‐ to 1700‐Å spectral region
Authors: Shemansky D. E. , Sandel B. R. , Broadfoot A. Lyle
Published: February 2008

Observations of the interstellar medium have been obtained in the 500‐ to 1700‐Å spectral region by the ultraviolet spectrometers installed on the Voyager spacecraft. A preliminary analysis of the least complex of the spectra obtained to date indicates measurable emission in spectral lines at 584, 1026, and 1216 Å. These emissions are identified with resonance scattering of solar radiation in transitions of helium and atomic hydrogen. The observations in the direction α 324°, δ −23° contain no measurable direct emission or scattering of stellar radiation by the interstellar medium to an upper limit of 5 × 10−4 R/Å at 975 Å. Spectra obtained in other directions indicate measurable sources of apparent continua having relatively broad spatial extent.
The polar thermospheric temperature behavior during the 11‐year solar cycle
Authors: Chanin M. L. , Tulinov G. F.
Published: February 2008

Results of neutral temperature measurements in the polar thermosphere between 1968 and 1976 show a large variation as a function of the solar cycle. A very cold thermosphere associated with a high altitude for the mesopause is found at the maximum of solar activity. The amplitude of variation of neutral temperature at 165 km is 500°K, and the mesopause is observed to move from 120 to 90 km. Those results are attributed to the variation of both the amplitude and the altitude of turbulent processes as a function of solar activity. Theoretical calculations and experimental facts are in support of that explanation.
Precipitation fluxes of energetic electrons at Jupiter: An estimated upper limit
Authors: Thomsen M. F. , Sentman D. D.
Published: February 2008

Using Divine's (1976) model for the observed energetic electron intensity distribution in the inner Jovian magnetosphere to calculate phase space density profiles, we estimate the loss term for steady state radial diffusion in which the first and second adiabatic invariants are conserved, namely ℒ = L² ∂/∂L (D0Ln−2 ∂f/∂L), where a radial diffusion coefficient of the form DLL = D0Ln is assumed. The assumption that all of the losses are due to precipitation into the ionosphere yields an upper limit for the precipitation flux at ionospheric altitudes. We find that for a given electron energy, the ionospheric precipitation flux rises steeply with L between ∼3 and ∼10. For example, the precipitation flux of 1 MeV electrons is ∼105 cm−2 s−1 MeV−1 at L = 9.1 but diminishes to ∼50 cm−2 s−1 MeV−1 at L = 3.6. Using our calculated precipitation profiles, we estimate the total energy deposition in the ionosphere due to the precipitating particles and find it to be less than a few tenths of an erg cm−2 s−1, which is of the same order as the energy deposited by energetic (Ee > 100 keV) electrons during the recovery phase of a terrestrial geomagnetic storm. The estimated flux of X rays that would be produced by bremsstrahlung of the precipitating particles is several orders of magnitude below the observational upper limit at earth. We further estimate that the total rate at which electrons with first invariants between a few tens and a few thousands of MeV/ Gauss are lost from the range 2.8 < L < 10.2 is ∼1024 electrons/s. This is of the same order as the rate at which electrons of this energy range diffusively enter this region, indicating that the loss processes are quite efficient. Finally, we estimate the lifetimes of the particles against precipitation and find them to be more than two orders of magnitude longer than the minimum lifetime against strong pitch angle diffusion. The losses therefore occur near the weak limit. We discuss the effects of varying D0 and n and of the distortion of the magnetic field at the ionospheric level due to higher order moments.
The solar cycle variability of diurnal and semidiurnal thermospheric temperatures
Authors: Forbes Jeffrey M. , Garrett Henry B.
Published: February 2008

Diurnal and semidiurnal components of exospheric temperature derived from midlatitude incoherent scatter measurements corresponding to 100 ≤F10.7 ≤200 between 1969 and 1972 are interpreted in the light of recent theoretical results. Diurnal temperature amplitudes are in excellent agreement with theoretical calculations previously calibrated with equatorial temperature variations inferred from satellite drag data. Present evaluation of the semidiurnal temperature component indicates that semidiurnal temperatures in the upper thermosphere are primarily due to thermal excitation above 100 km, except during very quiet solar conditions, when contributions due to upward propragating tides are comparable. Current theoretical estimates of the (2, 2) tidal mode propagating into the thermosphere are inferred to be approximately a factor of 2 too large; thus excitation and damping mechanisms affecting the (2, 2) tidal mode below 150 km require continued examination.
Rapid changes in the hydromagnetic wave coupling region in the magnetospheric plasma
Authors: Lanzerotti L.J. , Maclennan C.G. , Webb D.C.
Published: February 2008

We present evidence for the occasional observations of rapid (few minute) changes in the localization region of hydromagnetic waves in the earth's magnetosphere. These changes in the wave localization region, which can last for several hours, can be used to deduce the cold plasma density distributions in the magnetosphere in the L range of observations of the wave resonance location. We find that the plasma density distribution can vary as L−8 in the range L = 3.2 to L = 4.4 during these periods. The plasmapause is likely to be in the vicinity of the observing stations at these times. The cause of these variations in the wave resonance location remains unknown.
Electron precipitation of evening diffuse aurora and its conjugate electron fluxes near the magnetospheric equator
Authors: Meng C.‐I. , Mauk B. , McIlwain C.E.
Published: February 2008

A more precise and definitive relation between diffuse auroras and their particle source region was determined by examining simultaneously the particle observations at the geosynchronous orbit and the auroral display as well as the auroral electron precipitations near its field line conjugate observed by the polar‐orbiting DMSP 32 satellite. It is found that the spectral shape and differential fluxes of precipitated auroral electrons of diffuse auroras are very similar, and sometimes almost identical, to those of the trapped plasma sheet electrons located simultaneously in the conjugate magnetospheric equator. The characteristics of auroral electron precipitations are determined by the particle features in the conjugate magnetospheric equator, and diffuse auroras are produced by the direct dumping of the plasma sheet electrons.
Simulation studies of ionospheric electric fields and currents in relation to field‐aligned currents, 2. Substorms
Authors: Kamide Y. , Matsushita S.
Published: February 2008

The computer simulation scheme for calculating the electric fields and currents in the global ionosphere in relation to field‐aligned currents for quiet periods that we previously developed is extended to disturbed conditions. In a series of numerical simulations representing various substorms we take into account our current knowledge of characteristics of auroral enhancement in the ionospheric electric conductivities as well as changes in the intensity and location of field‐aligned currents. The possible effects of these variable parameters in producing the observed complexity of the electric field and current patterns are studied, with the following main results: (1) The conductivity inhomogeneity in the auroral belt can reproduce the observed local time dependence of the electric fields and currents. (2) The amount of the ‘return’ currents from the auroral electrojets flowing within the ionosphere is small, an indication that the major part of the electrojets is connected directly to the field‐aligned currents. Therefore the ground magnetic perturbations in the polar cap and also in the middle and low latitudes during substorms can be ascribed mainly to the magnetic effects of the field‐aligned currents. (3) Even when the intensities of the field‐aligned currents and the associated auroral electrojets do increase considerably during substorms over their values of quiet times, the total potential difference across the polar cap does not increase very much, because of a simultaneous increase in the ionospheric conductivities along the nightside auroral oval. (4) No special field‐aligned current system in the Harang discontinuity region is required to reproduce this feature. (5) The distribution pattern of the equivalent ionospheric current differs significantly from that of the real ionospheric current vectors. The maximum electrojet intensity seen in the equivalent current system is weaker than that of the real auroral electrojets.
Sunlit cleft and polar cap ionospheric currents determined from rocket‐borne magnetic field, plasma, and electric field observations
Authors: Primdahl F. , Walker J.K. , Spangslev F. , Olesen J.K. , Fahleson U. , Ungstrup E.
Published: February 2008

Intense Pedersen and Hall currents in the sunlit cleft and polar cap ionosphere are determined from rocket‐borne plasma, electric field, and magnetic field magnitude measurements and from recordings at nearby magnetic observatories. The ionospheric conductivities are calculated from a model atmosphere, the international geomagnetic reference field, and the E and F1 region electron density and temperature observations. Current densities are calculated from these conductivities and the observed dc electric fields by Ohm's law. The height profile of the polar cap Hall current density is compared with the current density determined from the perturbations of the magnetic field magnitude along the downleg part of the rocket trajectory. These two independently derived polar cap current densities agree in peak magnitude and height, and they indicate a peak Hall current of 34 µA/m² at 107‐km altitude. A significant Pedersen current flows above this Hall current. The magnetic field at the earth's surface of the height‐integrated current system is calculated; only the Hall component compares favorably in magnitude and direction with that obtained from local magnetic observatories. Field‐aligned currents are estimated, and they may be present at the polar edge of the cleft coincident with a discontinuity in the electric field and the influx of ≃500‐eV electrons. Joule heating of the sunlit polar cap upper atmosphere is determined and found to be very intense and comparable to that of a disturbed auroral zone.
Simultaneous observations of sodium density and the NaD, OH (8, 3), and OI 5577‐Å, nightglow emissions
Authors: Clemesha B.R. , Kirchhoff V.W.J.H. , Simonich D.M. , Takahashi H. , Batista P.P.
Published: February 2008

Simultaneous observations of the vertical distribution of sodium density and the intensities of the OI 5577‐Å, NaD, and OH (8, 3) airglow emissions show that the nocturnal variations of the emissions are well correlated with those of the sodium at 91, 87, and 84 km, respectively. In the case of NaD and OH (8, 3) these heights correspond closely to expected heights of peak airglow emission, although in the case of OI 5577 Å, maximum emission would be expected from about 4 km higher. The correlated variations appear to be caused by atmospheric waves having vertical wavelengths between 10 and 15 km whose phases propagate downward with velocities between 1 and 2 km hr−1. The amplitude of the correlated nocturnal variations in sodium density on the bottom side of the layer is normally too large to be explained as the direct result of atmospheric density changes. These large variations could be the result of vertical motions of the layer or might be caused by changes in the equilibrium between sodium and its oxide. On a number of occasions, large nocturnal changes in sodium density were seen to be closely correlated with changes in OH rotational temperature, suggesting a temperature effect on the chemical equilibrium. Enhanced sodium density, observed on days of exceptionally high OH (8, 3) band rotational temperature, could either be the result of increased sublimation from sodium‐bearing aerosols or again might be caused by a temperature dependence of the sodium photochemistry.
New insights into the variability of the cosmic ray diurnal anisotropy
Authors: Duggal S.P. , Tolba M.F. , Pomerantz M.A. , Owens A.J.
Published: February 2008

A new study of the variation of the diurnal anisotropy has unambiguously confirmed the reality of a recurrence tendency that is related to the period of rotation of the sun. Data recorded at two equatorial viewing stations with essentially similar responses to the primary anisotropy (Swarthmore and Deep River) were analyzed by using three different techniques: power spectral analysis, harmonic analysis, and superposed epoch analysis. The following experimental results were obtained: (1) The variance of day‐today changes in the diurnal anisotropy is greater for the component that is perpendicular to the interplanetary magnetic field than that which is parallel to it. (2) The 27‐day variation is maximum for the component of the diurnal anisotropy in the direction perpendicular to the interplanetary magnetic field. In contrast, there is no correlation between the sun’s rotational period and the field‐aligned component. Unlike the first result, the second, which was quite unexpected, cannot be accounted for by current theoretical models. This suggests that a new approach to this problem—probably including quasi‐stationary corotating structure and particle drifts—is required.
Polarization of Pc 1 and IPDP pulsations correlated with particle precipitation
Authors: Arnoldy R. L. , Lewis P. B. , Cahill L. J.
Published: February 2008

The correlation of Pc 1 and IPDP pulsations with particle precipitation shows that the waves are left (L) polarized when observed simultaneously with precipitation. This is consistent with theoretical understanding of the generation of the pulsations as an L wave in the magnetosphere and the L wave propagation through the ionosphere with horizontal ducting of the R wave. It is suggested that L polarization of Pc 1 and IPDP locates the ULF source field line. Three events studied were IPDP correlated with riometer absorption. The observations strongly support the inward convecting source model for the generation of IPDP. On the other hand, the origin of the particles (presumably electrons) responsible for the riometer absorption is still an open question. Finally, a very long duration Pc 1 (HM emission) event is presented where L polarized wave packets were very closely correlated with auroral light bursts measured at 4278 Å wavelength.
Cosmic ray intensity pulses
Authors: Duggal S. P. , Pomerantz M. A.
Published: February 2008

Pulse variations in the galactic cosmic ray intensity, extending over intervals of several hours, have often been observed during cosmic ray storms as well as during other periods. On some occasions, these pulses appear in the data recorded at polar stations during epochs characterized by enhanced diurnal anisotropy at low latitudes. The short‐term intensity increase at polar stations cannot be ascribed solely to the azimuthal anisotropy, and it is demonstrated that the cosmic ray transport during a pulse displays both azimuthal and north‐south anisotropies. Furthermore, it is found that the magnitude of the pulse height recorded by a station i is proportional to eμi where μi=cos θi and θi, is the angular separation between the mean asymptotic direction of viewing of station i and the direction of anisotropy in three‐dimensional space. The relationship between pulse modulations and transient disturbances in the interplanetary magnetic field, and especially their location, remain to be investigated.
The equatorial total electron content and shape factor
Authors: Donnelly R. F. , Davies K. , Anderson D. N.
Published: February 2008

The diurnal variations of electron content NT and shape factor ℱ observed at an equatorial station during sunspot minimum are shown to be consistent with the electron density profiles Ne(h), observed at Jicamarca during sunspot minimum. The rapid increase in NT and ℱ at sunrise results from the EUV production of ionization in the E and F regions. Day‐to‐day variations in daytime NT are observed to be quite small at the equator. The evening decrease in ℱ results from an upward drift of the F region at sunset and the evening decay of the E and bottomside F regions. The nighttime peak or plateau in ℱ is produced by the slow downward drift of the electron density profile. The deep predawn dip in ℱ is caused by the main peak of the F layer reaching low altitudes where high loss rates cause a large reduction in ionization below 300 km and a very flat Ne(h) profile.
Simultaneous observations of field‐aligned currents and plasma drift velocities by Atmosphere Explorer C
Authors: Bythrow P.F. , Heelis R.A. , Hanson W.B. , Power R.A.
Published: February 2008

A three‐axis flux gate magnetometer was included in the Atmosphere Explorer C (AE‐C) payload for engineering functions. The instrument was activated during the last half of AE‐C's life, and its output appears to be useful only during approximately one‐half of the data gathering time when the vehicle was spinning. Still, the addition of even a partial magnetic field data set to the already broad spectrum of AE‐C measurements is an exciting prospect. The high telemetry rate (128 bits/s per axis) could produce a spatial resolution in B of ∼½ km, but the 8‐bit word size yields an amplitude resolution of only 562 nT. A large modulation (15,000 nT) of the output from the spin axis (Z) magnetometer occurs during sunlit orbit segments. Application of a spin‐averaging technique to the modulated output signal has enabled us to improve the amplitude resolution of the signal to ∼40 nT (rms), although a corresponding loss in spatial resolution from ∼½ to ∼15 km results from the averaging procedure. By taking the difference between the spin‐averaged signal and a model magnetic field in a manner similar to that used by McDiarmid et al. (1978) we deduce a resultant magnetic perturbation ΔBZ. Attributing ΔBZ to field‐aligned current (FAC) sheets, we arrive at typical values of ∼1 µA/m² for sheet current densities. The amplitudes and distributions of these FAC’s are observed to be consistent with those measured by Triad (Iijima and Potemra, 1976a, b). Simultaneously measured Z components of the plasma drift velocity (Vz) show correlations with magnetometer measurements indicating that the positions of FAC's correspond to the gradients in the component of the electric field along the satellite track (X component). By using the current continuity equation for the ionosphere (▽ · I⊥=J∥), values of height‐integrated Pedersen conductivity Σp from 2.5 to 17.5 mhos are calculated.
Observations of lower ionospheric wind by the Kyoto Meteor Radar
Authors: Aso Takehiko , Tsuda Toshitaka , Takashima Yosuke , Ito Rei , Kato Susumu
Published: February 2008

This paper describes the results of meteor radar observations which have been carried out at Kyoto University since December 1977. The radar, a coherent pulse Doppler radar with transmitting frequency of 31.57 MHz and nominal peak power of 10 kW, measures wind fields at meteor heights of 80–110 km. The solar semidiurnal tide generally dominates the wind oscillations at these heights. The less regular diurnal tide has comparable magnitude. The variability of the tidal structure suggests the possibility of interaction between respective waves or winds, particularly the influence of disturbed conditions in the lower atmosphere. Other components of winds as mean flow or a quasi 2‐day planetary wave have also been observed. The combination of meteor wind radar and other observational techniques will further the understanding of the global dynamics of atmospheric waves.
Anomalous vibrational distribution of N2+ 1 NG emissions from a proton aurora
Authors: Sivjee G.G.
Published: February 2008

The relative vibrational population of N2+ (B²Σu+) in a rare proton aurora, observed on March 8 (UT), 1978, was twice as high as the values found in almost all nighttime auroras. On the basis of various laboratory measurements the proton aurora observations point to precipitation of ∼1.2‐keV protons, carrying an energy flux of ∼14 ergs cm−2 s−1. Simultaneous measurements of N2+ 1 NG (0, 1), (1, 2), (0, 2), and (1, 3) bands as well as Hβ and [O I] 6300‐Å emissions from this rare, low‐energy proton aurora yield Hβ/N2+ 1 NG (0, 2) ≃ 3 and [O I] 6300/N2+ 1 NG(0, 1) ≃2.4. The corresponding values in the auroras excited predominantly by electrons are generally low (e.g., <0.7 and 0.6, respectively). Most of the N2+ 1 NG emissions from proton auroras are excited by protons (and not hydrogen atoms which constitute the bulk of the charge equilibrated auroral particle beam) interacting with N2.
Permanent magnetic trapping
Authors: Michel F. Curtis
Published: February 2008

We show that the global nature of trapped particle motion in phase space makes it entirely plausible that particles with pitch angles near 90° are trapped for extremely long times, probably indefinitely. The long observed lifetimes of trapped particles can immediately be accounted for by this former population. For particles with low pitch angles an ‘overstability’ develops which serves to produce rapid variations in pitch angle and, presumably, random walk into the loss cone. Numerical calculations are needed to assess how this transition to overstability depends on particle rigidity.
An empirical determination of the production efficiency for auroral 6300‐Å emission by energetic electrons
Authors: Shepherd G.G. , Winningham J.D. , Bunn F.E. , Thirkettle F.W.
Published: February 2008

Auroral data from the soft particle spectrometer and the red line photometer on the Isis 2 spacecraft have been selected to form an electron energy flux and optical auroral emission data base. The energy fluxes are stored as integrated fluxes over four energy bands, and the corresponding stored optical emission rates are corrected for airglow and for albedo. Because of the variety of electron energy spectra represented in the data base, it was possible to perform a regression analysis that yielded the production efficiency for the production of emission for each of the four bands. While the results of this analysis are interesting to compare with theoretical predictions of 6300‐Å excitation processes, these statistical results are not as precise as the comparisons of individual experiments where all parameters, such as the atmospheric composition and temperature profiles, are measured. The significance of this approach is that it permits a multiparameter description of an electron energy spectrum, and its relationship to a specific optical emission, by purely empirical means. This is particularly useful in the interpretation of Isis 2 data from the instruments which provided the results, but should find further application in optical‐particle auroral studies.
The total cross section for incoherent scattering: An analytical result and a clarification
Authors: Fejer J.A. , Kohl H.
Published: February 2008

An analytical result for the total scattering cross section as a function of the electron to ion temperature ratio is derived. The result is valid for large values of the temperature ratio and for small values of the ratio of the Debye length to the wavelength. A comparison with the results of numerical integration and with previous analytical results is made.
The dependence of ion density in the wake of the AE‐C satellite on the ratio of body size to Debye length in an [O+]‐dominated plasma
Authors: Samir Uri , Kaufman Y.J. , Brace L.H. , Brinton H.C.
Published: February 2008

Measurements of electron temperature, satellite potential, ion density and ion composition from the cylindrical electrostatic probe and the Bennett ion mass spectrometer on board the AE‐C satellite were used to investigate the influence of the body size paramter RD = R0/λD (where R0 is the satellite radius and λD is the ambient Debye length) on ion distribution in the very near wake. The investigation focused on [O+] plasmas. It was found that the ratio (β) of density in the wake to ambient density varies with RD and that the variation can be described by a simple exponential relationship of the form β = a0 exp (a1RD) for 37 ≤RD ≤ 47 and a0 = 0.06, a1 = −0.009. The present study extends that of Samir et al. [1979a].