bluuebunny/crossref_metadata_2025 huggingface dataset:
Amalthea: Voyager imaging results
Authors: Veverka J. , Thomas P. , Davies M. , Morrison D.
Published: February 2008

Voyager images of Amalthea reveal a very irregular satellite with dimensions of some 270 × 165 × 150 km, in synchronous rotation relative to Jupiter. Amalthea is nearly as elongated and as large as the Trojan asteroid Hektor. Its surface is scarred by large craters, sharp ridges, and other prominent topography suggestive of a long history of cosmic battering. The largest crater on the satellite, Pan, is about 90 km across. The normal reflectance of the surface is very low (5–6%); the color is very red. We find that Amalthea's mean opposition magnitude is V=+14 and that the magnitude difference between eastern and western elongation does not exceed +0.1. The phase coefficient between phase angles of 0.8° and 42° of 0.042±0.004 mag/deg indicates that the phase integral does not exceed 0.3 and that the Bond Albedo is less than 0.02. Amalthea is redder than typical Trojan asteroids, but not quite as red as parts of Io. Laboratory simulations show that the combination of low albedo and red color probably requires contamination of the surface by sulfur the most likely source of which is Io. A noteworthy mystery concerning Amalthea is the composition of the material in several prominent bright spots. These isolated spots (typically 10–50 km across) occur preferentially on local slopes and ridges, have albedos several times higher than the background, and have a greenish color (the spectrum bends down beyond 0.56 µ m).
The carbon monoxide fourth positive bands in the Venus dayglow 1. Synthetic spectra
Authors: Durrance Samuel T.
Published: February 2008

Spectral observations of the Venus dayglow from 1200–1800 Å were made with the Pioneer Venus ultraviolet spectrometer (13‐Å resolution), a sounding rocket telescope and spectrometer (4‐Å resolution, and the International Ultraviolet Explorer (0.4‐Å resolution). Emissions due to H I, C I, O I, and the CO fourth positive system are identified. Emission rate factors for the fourth positive system are calculated using a high‐resolution solar flux. The importance of solar emission line excitation to this flourescence spectrum is shown. In particular, several bands of the υ′=14 progression are identified and their excitation mechanism is shown to be fluorescent scattering of solar Lyman α radiation. The CO (14, 5) band at 1392 Å is a prominent unblended spectral feature in the Venus dayglow. The (14, 3) and (14, 4) bands at 1317 and 1354 Å are blended with the O I 1304‐ and 1356‐Å features in lower‐resolution spectra. This identification resolves the problem of the interpretation of the ratio of the O I 1304/1356 Å emissions from Venus. It also provides an additional remote sensing technique to determine the density distribution of CO in the upper atmosphere of Venus.
Scaling of the beam‐plasma discharge
Authors: Rowland H. L. , Chang C. L. , Papadopoulos K.
Published: February 2008

It is shown that the scaling observed in a recent experiment of the beam‐plasma discharge is consistent with the assumption that triggering occurs when an instability threshold condition is exceeded for electron plasma waves with ω ≈ ωe, the electron plasma frequency.
Distant magnetic field effects associated with Birkeland currents (made possible by the evaluation of TRIAD's attitude oscillations)
Authors: Gustafsson Georg , Potemra T. A. , Favin S. , Saflekos N. A.
Published: February 2008

The magnetic field data acquired by the TRIAD satellite sometimes show variations with periods longer than 10 min and with amplitudes of a few thousand nanoTeslas due to attitude oscillations. From a study of 150 passes, the principal oscillations of TRIAD have been identified as the well‐known librations of a gravity‐stabilized satellite. The libration periods are approximately T0/2 and T0/(3)1/2, where T0 is the orbit period of about 100 min. The amplitude and phase of these librations appear to change over periods of a few days, and sometimes they vanish altogether. By use of data acquired over several consecutive TRIAD orbits, these attitude variations can be numerically evaluated and removed, leaving the disturbances associated with Birkeland currents. The establishment of a ‘base line’ for the TRIAD observations by using this technique has permitted, for the first time, a preliminary evaluation of the ‘current‐free’ magnetic field disturbance due to large‐scale Birkeland currents. Data acquired from three consecutive TRIAD passes (spanning more than 3 hours) show nearly the same magnetic disturbance profile, which extends as far as 10 degrees in latitude from a single (net) region 1 Birkeland current sheet. These observations confirm the permanent and global nature of large‐scale Birkeland currents.
A source of plasma turbulence at the ionopause of Venus
Authors: Daniell Robert E.
Published: February 2008

The simultaneous measurements of suprathermal ions and low frequency electric field signals at the ionopause of Venus by Pioneer Venus instruments suggests that they may be causally related. Linear Vlasov theory is used to examine both parallel and perpendicular propagating waves for instability in the presence of planetary ions added to the flowing ionosheath plasma. For the low β plasma conditions found near the ionopause, neither electrostatic (ion acoustic) nor electromagnetic (whistler) parallel propagating waves are found to be unstable. Perpendicular propagating electrostatic (Bernstein) waves are found to be quite unstable and to have the proper frequency‐wavelength relation to be Doppler shifted into the observed 100‐Hz frequency channel. The growth rates can be substantial, and the instability occurs for a wide range of ionosheath conditions. It is difficult for an electric field measurement to distinguish between these waves and electromagnetic waves such as whistlers. Planetary ions are probably thermalized only after several gyroperiods so that they may be easily observed only well downstream from the planet.
Study of tri‐diurnal variation of galactic cosmic radiation
Authors: Agrawal Sant P.
Published: February 2008

Using the experimental data of the high counting rate neutron and meson monitors, the solar tri‐diurnal anisotropy of galactic cosmic radiation has been investigated for the period 1962–79. The enhancement of the average tri‐diurnal amplitude observed by all the detectors during 1973–75 provides sufficient signal to noise ratio to obtain its variational characteristics. The observations are consistent with an interplanetary anisotropy having a power law rigidity spectrum exponent ≈ 1. The tri‐diurnal amplitude varies as cos³ λ, where λ is the effective asymptotic latitude of the detector. The annual average tri‐diurnal amplitude shows a significant positive correlation with the semi‐diurnal amplitude for the period 1968–79. The correlation, however, is poor for the earlier period 1962–67, which may be due to the presence of significant modulation of semi‐diurnal anisotropy with periods of 22‐year sunspot magnetic cycle. An analysis using groups of days with high and low solar wind speed shows greater amplitude of both the tri‐diurnal and semi‐diurnal waves for the group of days with high wind speed. This result coupled with the observation of a factor of 2 increase in both amplitudes during 1973–75, a period when high speed solar wind streams were prevalent, suggests that solar polar coronal holes may influence both the solar tri‐diurnal and semi‐diurnal variation of galactic cosmic ray intensity.
Plasma near Io: Estimates of some physical parameters
Authors: Kivelson Margaret G. , Southwood David J.
Published: February 2008

Models of Io's interaction with the Jovian plasma are examined to assess whether conditions hazardous to a spacecraft flying by Io at about 1000 km above its surface should be anticipated. Only two models are regarded as consistent with most of the presently available data. The ‘ionospheric’ model allows field‐aligned currents to close through Io and its ionosphere. The ‘magnetospheric’ model allows the currents to close on an Ionian magnetopause and across a tail neutral sheet. Although only the latter model provides an explanation for the pitch angle distribution of energetic electrons measured by the LECP detector on Voyager 1, the implications of both models for near‐Io plasma are explored. The plasma density is found to be roughly the same near Io and elsewhere in the torus. In Io's wake the plasma is hotter than elsewhere in the torus but in the extreme case the ion temperature is merely of order the temperature in the terrestrial ring current. No special problems are anticipated for a spacecraft subject to these plasma conditions.
A generation mechanism of narrow band hiss emissions above one half the electron cyclotron frequency in the outer magnetosphere
Authors: Hashimoto K. , Kimura I.
Published: February 2008

A mechanism of narrow band VLF hiss emissions above the local half cyclotron frequency observed in the outer magnetosphere by satellites is proposed. The proposed mechanism is a kind of Harris type electrostatic instability for whistler mode waves with short wavelengths and large wave normal angles in a bi‐Maxwellian hot plasma. The free energy of the instability originates from the anisotropy of the plasma whose temperature is as low as several electron volts. This wave mode has both an electrostatic and an electromagnetic nature. The growth rate of this instability and the frequency limit, below which the waves grow, are strictly dependent on the anisotropy factor A of the plasma. A type of narrow band hiss is considered to be generated in a region where A is maximum. When this hiss propagates from the source, the band of frequency becomes narrower because the upper limit frequency decreases due to a decrease of A. Extremely narrow band hiss observed by the satellite OGO 5 can be explained by a combination of the above instability and propagation effects.
About the parametric interplay between ionic Mach number, body‐size, and satellite potential in determining the ion depletion in the wake of the S3‐2 satellite
Authors: Samir Uri , Wildman P. J. , Rich F. , Brinton H. C. , Sagalyn R. C.
Published: February 2008

Measurements of ion current, electron temperature, and density and values of satellite potential from the U.S. Air Force Satellite S3‐2 together with ion composition measurements from the Atmosphere Explorer (AE‐E) satellite were used to examine the variation of the ratio α=[I+(wake)]/[I+(ambient)]| (where I+ is the ion current) with altitude and to examine the significance of the parametric interplay between ionic Mach number, normalized body size RD (=R0/λD, where R0 is the satellite radius and λD is the ambient debye length) and normalized body potential ϕN (=eϕS/KTe, where ϕs is the satellite potential, Te is the electron temperature, and e and K are constants). It was possible to separate between the influence of RD and ϕN on α for a specific range of plasma parameters. Uncertainty, however, remains regarding the competition between RD and S(H+) and S(O+) (where S(O+) and S(H+) are oxygen and hydrogen ionic Mach numbers, respectively) in determining the ion distribution in the nearest vicinity to the satellite surface. A brief discussion relevant to future experiments in the area of body plasma flow interactions to be conducted on board the Shuttle/Spacelab facility, is also included.
Preserved signatures of ion flux modulations observed by ATS 6
Authors: Su S.‐Y. , Konradi A. , Fritz T. A.
Published: February 2008

On August 13, 1974, for a few hours after local midnight, the ATS 6 NOAA instrument in geostationary orbit observed oscillations in the fluxes of ions from 24 keV to 150 keV (five channels) that had three striking characteristics: First, the starting times of the oscillations were observed to be different in different energy channels. The modulation was observed initially in the high‐energy channel and progressively later in the lower energy channels. Second, the oscillation frequency was higher for the highest energy ions and decreased with the ion energy; the multiple frequencies appeared to be discrete and harmonically related. Third, the duration of oscillations were energy dependent; the higher the ion energy, the shorter the duration of the oscillation in that channel. We conclude that the flux modulations did not start in the region where they were observed but were actually the preserved signatures drifting in longitude of flux modulations resulting from wave‐particle resonant interactions that occurred at an earlier time in a region east of ATS 6 probably associated with the onset of a substorm. Although flux oscillations of this kind are seldom observed, the drifting ions are apparently capable of preserving the signatures of the flux modulation after they leave the interaction region. The interaction region has been found to cover a wide magnetospheric local time sector from near midnight through the noon meridian, to the late morning hours.
On the half‐harmonic electrostatic emissions associated with shell‐like magnetospheric electron distribution functions
Authors: Cuperman S. , Gomberoff L.
Published: February 2008

The generation of half‐odd harmonic emissions by shell‐like electron distribution functions as recently observed by ISEE 1 is considered. The investigation includes (a) the analysis of the type of observed distributions and their representation by equivalent simplified forms consisting of a ‘shell’ in velocity space and a cold background at rest, (b) the possible generation by such distribution functions of almost perpendicular electrostatic emissions at half‐odd harmonics of the electron gyrofrequency, and (c) the possible enhancement of one (or more) particular emissions lines. We show that in a first approximation, neglecting temperature effects, a distribution of the type observed by ISEE 1 can be considered to be made up of an infinite number of monoenergetic beams characterized by different pitch angles and a cold background at rest. If these beams are considered in pairs, it is found that they support unstable electrostatic waves resulting from the resonant coupling of plasma (Cerenkov) modes and cyclotron modes; these waves occur at about odd, half‐harmonics of the electron gyrofrequency. The maximum growth rates caused by the interaction of the two‐electron beams may be strongly affected by the presence of a third, cold‐background component: under certain circumstances, a particular mode (at a given frequency, ω = (m + ½)Ω, m = 1, 2, …) can be enhanced in relation to the neighboring modes, thus dominating the discrete wave spectrum.
Electric field limitation of drift dissipative wave generation in ionospheric structures
Authors: Goldman S. R. , Sperling J. L.
Published: February 2008

Coupled background electric fields and density profiles exist across the sides of striations and other elongated ionospheric structures. The presence of the electric field profoundly modifies the behavior of drift dissipative waves by shifting the location of the waves away from the point where the relative density gradient is a maximum, consequently inhibiting the growth of the waves.
Modeling of high‐latitude currents in a substorm
Authors: Karty J. L. , Chen C.‐K. , Wolf R. A. , Harel M. , Spiro R. W.
Published: February 2008

A quantitative model is developed for computing currents and electric fields in the area covered by the poleward set of field‐aligned currents (region 1 Birkeland currents). The high‐latitude band considered carries most of the westward electrojet and lies just poleward of the region treated in the Rice University computer simulation (which covers the inner magnetosphere and corresponding ionosphere); the present high‐latitude‐current model supplements the inner‐magnetosphere simulations to make them nearly global. Birkeland current and aurorally enhanced conductivity are assumed to be uniformly distributed across the band. The area poleward of the band is taken to be an insulator, while boundary conditions at the low‐latitude edge of the band are derived from the results of the lower‐latitude computer simulations of the substorm event that occurred on September 19, 1976. The time‐dependent conductivity model used is based on electron fluxes and mean energies measured from the Air Force S3‐2 satellite. Ionospheric electric fields and currents are calculated; ionospheric neutral winds are neglected. Model predictions of the locations of the electric‐field reversal agree well with typical OGO 6 satellite observations. The model also agrees with S3‐2 data from September 19, 1976, on an important feature, namely, the electric field reversal usually occurs poleward of the bulk of region 1 current. Joule heating of the upper atmosphere, as inferred from calculation of currents and electric fields in the high‐latitude region considered here, was found to be about 2 × 1011 W during the substorm period, somewhat less than the value estimated for the lower‐latitude region (region 2 and below). Model values for the strength of the electrojet and the amount of Joule heating agree to within ∼ 20% with results based on a simple Cowling conductivity band (with no latitudinal current flowing into the band).
Is there an increase of geomagnetic activity preceding total lunar eclipses?
Authors: Fraser‐Smith A. C.
Published: February 2008

The possibility that there is a lunar modulation of geomagnetic activity around the time of total lunar eclipses is investigated. The modulation of activity, as seen in the Ap indices for the years 1932–1980, consists of a 4‐day increase starting 3 days before the eclipse day. This characteristic of the modulation suggests that it may be caused by entry of the moon into the magnetospheric tail and by the subsequent motion of the moon within the tail; it is not observed in conjunction with partial lunar eclipses. By using the aa indices, which are available back to 1868, it is possible to study the long‐term temporal characteristics of the modulation. It is found that the increase in activity after 1932 is not replicated in the data prior to 1932 (during the years 1870–1931), and it is concluded that the increase is most probably a statistical anomaly and that it would be inappropriate to conclude from it that the moon's entry into the geomagnetic tail enhances geomagnetic activity.
Ion distribution effects of turbulence on a kinetic auroral arc model
Authors: Cornwall J. M. , Chiu Y. T.
Published: February 2008

We extend an earlier plasma‐kinetic model of an inverted V auroral arc structure to include, in a phenomenological way, the effects of electrostatic turbulence with k∥/k⊥ ≪ 1. In the absence of turbulence, a parallel potential drop is supported by magnetic mirror forces and charge quasi‐neutrality, with energetic auroral ions penetrating to low altitudes; relative to the electrons, the ions' pitch angle distribution is skewed toward smaller pitch angles. The electrons energized by the potential drop form a current that excites electrostatic turbulence; we consider the specific case of the ion cyclotron mode. The turbulence heats the ions in T⊥ only, thus tending to reduce the differential pitch angle anisotropy between electrons and ions, which in turn reduces the potential drop—an effect of opposite sign to that associated with anomalous resistivity. In equilibrium the plasma is marginally stable, with growth rates and diffusion constants some 2 orders of magnitude below naive estimates. The conventional anomalous resistivity contribution to the potential drop is very small, because anomalous‐resistivity processes are far too dissipative to be powered by auroral particles; this is why growth rates and diffusion constants are so small. Under certain circumstances equilibrium may be impossible and relaxation oscillations set in; the time scale for such pulsating auroras is the ion transit time of 6–10 s.
Thermospheric molecular oxygen
Authors: Torr Marsha R. , Torr D. G. , Carter R. , Kayser D.
Published: February 2008

Thermospheric studies to date have relied heavily on model values of O2 concentration, which are in turn indirectly derived. This paper reports the results of a comparison of a large data base of directly measured O2 concentrations with the concentrations obtained from the MSIS model atmosphere. For concentrations of 1010cm−3 the direct measurements are larger than the model values by up to 50%. For concentrations of 108cm−3 the measured values are in agreement with the model to within 10%. A comparison is made of the computed major thermospheric species by using both the MSIS and the measured O2 concentrations. The impact is largest in the odd nitrogen species NO, N(4S), and N+, where the difference in concentration can be as much as 70%, and also on O2+.
Numerical simulation of the interaction of the plasma sheet with the lobes of the Earth's magnetotail
Authors: Swift Daniel W.
Published: February 2008

Codes involving one and two spatial dimensions and three velocity dimensions are used to model the earth's magnetotail. It is shown that the magnetotail can become inflated as a consequence of low‐energy plasma convection toward the neutral plane. The two‐dimensional code shows the development of small‐scale turbulence. However, the growth of the turbulence appears limited and does not lead to substantial dissipation. A one‐dimensional model was used to simulate a particle population consisting of plasma sheet ions and cold lobe plasma. An applied convection electric field causes plasma sheet thinning and later expansion, consistent with observed substorm morphology. During the course of a simulated substorm the cold particles are heated and merge with the plasma sheet population. The magnetic field energy shows a slight increase, followed by a more rapid decrease as all of the cold particles are swept into the magnetotail. The code exhibits a conversion of both magnetic field energy and energy supplied by the convection electric field into particle energy. The simulations suggest that much of the magnetotail substorm morphology may be a simple consequence of an increase, followed by a decrease, in the convection electric field, without the requirement of any magnetospheric size scale plasma instability or other disruptive processes. It is also concluded that the presence of the convection electric field and a continuing replenishment of low‐energy particles in the magnetotail lobes are both necessary for maintenance of the magnetotail.
Field‐aligned currents associated with Pc 5 pulsations: STARE and TRIAD observations
Authors: Poulter E. M. , Nielsen E. , Potemra T. A.
Published: February 2008

The resonance theory for monochromatic Pc 5 micropulsations predicts that the toroidal mode resonance should be accompanied by field‐aligned current systems. These currents close via Pedersen current in the ionosphere, and the drifting irregularities observed by the STARE radars are thought to be generated by the associated electric fields. Recent theoretical calculations by Walker (1980) are used to estimate the micropulsation current systems and accompanying magnetic perturbations. STARE radar observations of the pulsation electric field in the ionosphere are then compared with the corresponding magnetic perturbation observed with the TRIAD satellite magnetometer.
The contribution of singly scattered photons to the optically thick resonance radiation field of the helium geocorona
Authors: Fahr Hans J. , Smid Thomas
Published: February 2008

Analysis of the geocoronal He‐I 58.4‐nm resonance radiation field with rocket borne gas absorption cell photometers has revealed singly scattered photons to attain steadily increasing importance in the radiation signals if photons close to the line center are effectively suppressed. In order quantitatively to confirm this, we have reinvestigated the radiation transport problem and have given the spectral intensity in terms of contributions from different scattering orders. In the formulation of these contributions we have used the concept of angle‐dependent partial frequency redistribution in comparison with that of complete redistribution. The first and second order intensity contributions are studied in detail here with respect to their spectral profile, to their local and solar zenith angle dependence, and to their height profile. The second and higher order intensity contributions are shown to decrease steeply with increasing distance from the line center, such that for a specific observation a critical wavelength distance can be calculated beyond which only singly scattered photons contribute to the total intensity. The intensity due only to singly scattered photons is proven to be proportional to the helium column density on the line of sight within clearly determinable accuracies. Thus its height profile enables immediate deduction of local atmospheric parameters, as the atmospheric helium density and temperature, even under optically thick conditions.
Effect of parallel electric fields on whistler wave propagation at low latitudes
Authors: Singh Hari , Singh Birbal
Published: February 2008

Effect of parallel electric fields on whistler wave propagation at low latitudes is studied with the help of ray tracing computations. It is shown that in presence of such fields, whistler ray paths are defocused and their final wave normal directions at the base of the F region ionosphere in the opposite hemisphere are such that the waves would not be observed on the ground. In the absence of suitable ducts, horizontal density gradients existing in the low‐latitude ionosphere seem to play important roles in whistler propagations to ground stations.
Auroral nitric oxide concentration and infrared emission
Authors: Reidy W. P. , Degges T. C. , Hurd A. G. , Stair A. T. , Ulwick J. C.
Published: February 2008

Since 1972, the Air Force Geophysics Laboratory has launched a series of rockets to study emission in the 5.3‐µm and 2.7‐µm infrared bands of nitric oxide at high altitudes. The instrumentation varied from one probe to another; infrared fixed band radiometers and CVF spectrometers, narrow band photometers and instrumentation to measure the incident energy spectrum were each included on various occasions. Optical photometric data were also obtained with ground‐based instruments. We have used the available data to model the time history and chemistry of the auroral deposition, and have concluded that (1) the NO density is significantly enhanced over mid‐latitude values, (2) the measured NO emission in the fundamental band is due to resonance excitation by warm earth radiation, collisional excitation, principally with atomic oxygen, and chemiluminescence from N(²D) + O2 → NO‡ + O, and (3) the overtone band emission is due to chemiluminescence. We have also derived the NO density and the chemiluminescence efficiency. Furthermore, we believe we have a new technique for in situ and remote measurements of NO density both day and night.
Voyager 1 assessment of Jupiter's planetary magnetic field
Authors: Connerney J. E. P. , Acuña M. H. , Ness N. F.
Published: February 2008

A new estimate of Jupiter's planetary magnetic field is obtained from the Voyager 1 observations of the Jovian magnetosphere. An explicit model for the magnetodisc current system is combined with a spherical harmonic model of the planetary field with both sets of parameters determined simultaneously by using a nonlinear generalized inverse methodology. The resulting model fits the observations extremely well throughout the analysis interval (r < 20 RJ). The Jovian internal field model obtained from the Voyager 1 data is very similar to the octupole Pioneer 11 models. The best fitting magnetodisc lies in the centrifugal equator, 2/3 of the way between the rotational and magnetic equators, as is appropriate for centrifugal loading of the magnetosphere by a cold plasma. No statistically significant evidence is found for secular change of the equivalent dipole estimated from Pioneer 11 (1974.9) and Voyager 1 (1979.2) data.
Finite amplitude Alfvén waves in a multi‐ion plasma: Propagation, acceleration, and heating
Authors: Isenberg Philip A. , Hollweg Joseph V.
Published: February 2008

We derive an expression for the wave action flux of finite amplitude Alfvén waves in a multi‐ion plasma. The expression is valid in the presence of dissipative forces and allows an arbitrary angle between the average magnetic field and the wave vector. Applying the conservation of wave action and the first law of thermodynamics yields the following results for a multi‐ion plasma: (1) an expression for the spatial evolution of Alfvén wave amplitude in the absence of dissipation, (2) the relationship between the wave amplitude and the dissipative heating, and (3) an expression for the acceleration of an ion species by finite amplitude Alfvén waves. The acceleration consists of two terms: a nondissipative wave pressure that is identical to that derived previously under more restrictive conditions, and a new term giving the acceleration that must accompany dissipative heating. These results are discussed in the context of the observations of heavy ions in the solar wind.
Overview of the IMS July 29, 1977, magnetic storm analysis
Authors: Manka R. H. , Fritz T. A. , Johnson R. G. , Wolf R. A. , Teague M. J. , Vette J. I.
Published: February 2008

We review the physical characteristics and temporal development of a significant IMS magnetospheric event: the sudden commencement and multiple substorms of July 29, 1977. An interplanetary shock, superimposed on relatively high solar wind densities, forced the magnetopause at 0027 UT in past the position of GEOS 1 (∼6.7 RE). Following this compression, as well as periods of southward IMF, a series of substorms culminated in a very large substorm with peak electrojet current at 1230 UT, followed by a relatively quiet recovery phase. The ring current snowed a maximum at 0600 UT and a major perturbation at 1230 UT corresponding to the last substorm. A large suite of international data were analyzed for this event, concluding in a computerized coordinated data analysis workshop (CDAW 2) in October 1979. Included in the analysis are results from eleven spacecraft, seven ground arrays, several numerical models, and theoretical calculations. Emphasis of the analysis was on the physical processes of energy transfer and magnetospheric dynamics. We describe the CDAW analysis and present an overview description of the event, including the solar wind conditions and magnetospheric response, as an introduction to this series of papers.
Theoretical magnetograms based on quantitative simulation of a magnetospheric substorm
Authors: Chen C.‐K. , Wolf R. A. , Harel M. , Karty J. L.
Published: February 2008

Using substorm currents derived from the Rice computer simulation of the substorm event of September 19, 1976, we have computed theoretical magnetograms as a function of universal time for various stations. A theoretical Dst has also been computed. Our computed magnetograms were obtained by integrating the Biot‐Savart law over a maze of approximately 2700 wires and bands that carry the ring currents, the Birkeland currents, and the horizontal ionospheric currents. Ground currents and dynamo currents were neglected. Computed contributions to the magnetic field perturbation from eleven different kinds of currents are displayed (e.g., ring currents, northern hemisphere Birkeland currents). On the basis of comparison of theoretical results with corresponding observations, we make the following remarks. First, overall agreement of theory and data is generally satisfactory, especially for stations at high and mid‐magnetic latitudes. Second, model results suggest that the ground magnetic field perturbations arise from very complicated combinations of different kinds of currents and that the magnetic field disturbances due to different but related currents often cancel each other, despite the fact that complicated inhomogeneous conductivities in our model prevent rigorous application of Fukushima's theorem. Third, both the theoretical and observed Dst decrease during the expansion phase of the substorm, but data indicate that Dst relaxes back toward its initial value within about an hour after the peak of the substorm. This effect exists qualitatively in the computer simulation if we sharply reduce the assumed polar cap potential drop and conductivity at the end of the substorm. Fourth, the dawn‐dusk asymmetry in the horizontal component of magnetic field disturbance at low latitudes in a substorm is essentially due to a net downward Birkeland current at noon, net upward current at midnight, and generally antisunward flowing electrojets; it is not due to a physical partial ring current injected into the duskside of the inner magnetosphere.
Do E region plasma irregularities affect an auroral zone riometer?
Authors: Siren Jan C.
Published: February 2008

The suggestion by D'Angelo (1976) that E region field‐aligned ionospheric irregularities might be detectable by an auroral zone riometer is examined. Results of a study of rapid (≳60‐s period) variations of the Siple Station, Antarctica (L ≅ 4.2), 30‐MHz riometer signal are that the occurrence statistics of these variations are under control of universal time rather than sidereal time; there is a night‐day asymmetry and a quiet time afternoon secondary maximum in occurrence rate, and there is no significant difference in the occurrence rates of small variations initially deflecting above or below the background level of quasi‐steady signal. These conclusions are not in conflict with absorption, but cannot be explained by scattering from field‐aligned irregularities. A maximum of ≃30% of all rapid variations can be accounted for by the scattering interpretation, and the study results are consistent with a zero rate (null hypothesis). Calculations of the expected amplitude of variations due to scattering are derived by three different methods. All predict amplitudes lower than the 0.25‐ to 1.0‐dB range reported by Mehta and D'Angelo (1980), but not too low to render them undetectable by a sufficiently sensitive riometer.
Extremely quiet nighttime currents and magnetic baselines at Canadian observatories for the separation of external and internal fields
Authors: Walker John K.
Published: February 2008

The separation and delineation of external and internal current sources can be achieved by determining intervals of very quiet magnetic activity to ascertain the main field, which can then be used as a reference to obtain the magnetic variations of the sources. A new method is proposed and justified for determining periods of very quiet magnetic activity. The very quiet dark nighttime interval, when known magnetic activity and hence external ionospheric and magnetospheric sources are minimal, can be used to establish the baseline or reference level for the analysis of the sources. Magnetic fields were calculated at these times from typical very quiet nighttime ionospheric parameters and found to be a negligible 3 nT for the mid latitude and polar cap regions, and 10–20 nT for the auroral zone. At mid and low latitudes very quiet nighttime intervals often occur; however, at high latitudes significant magnetic activity is almost always present and it is difficult to obtain quiet intervals. Baselines determined from very quiet nighttime intervals were obtained from the Canadian magnetic observatories digital data base over the period from 1973 to 1980 by special selection and filtering techniques. The data were filtered to remove short period disturbances, and only intervals for which Dst was less than 10 nT and the regional and local activity were minimal were selected. The undisturbed field and its secular variation were determined and the standard deviation of the quiet levels about a quadratic function was 4–10 nT. An analysis of the residuals indicated little or no annual variation. This is a significant improvement in the delineation of the main field secular variation in high latitude regions. For some stations the secular variation determined from these undisturbed levels was systematically different from that obtained from the annual means, the difference being due to an equivalent net westward auroral current system of ∼40 kA. It is recommended that these undisturbed levels be systematically determined at observatories and used for a common reference level for the reduction of magnetic and repeat station surveys as well as for the analysis of internal and external sources.
Magnetosheath's parameters and their dependence on intensity and direction of the solar wind magnetic field
Authors: Pudovkin M. I. , Heyn M. F. , Lebedeva V. V.
Published: February 2008

The variations of the plasma parameters and of the magnetic field in the vicinity of the stream line passing the subsolar point at the magnetopause are calculated by using a special flow pattern of the plasma which is the result of the formation of a stagnation line at the nose part of the magnetopause. The calculations indicate a rotation of the direction of the magnetic field across the magnetosheath. The displacement of the magnetopause due to the penetration of the solar wind magnetic field into the magnetosphere is discussed.
A feedback model for the source of auroral kilometric radiation
Authors: Calvert W.
Published: February 2008

The self‐excited oscillations which result from positive wave feedback are believed to produce the discrete spectrum of auroral kilometric radiation. This would require a closed wave feedback path inside the source, having a length equal to a multiple of the wavelength, and it yields an emission model which is quite analogous to an optical laser oscillator. The end reflections for this feedback path, which would be comparable to those produced by the laser mirrors, are attributed to partial wave reflections at the source boundaries. However, in order to compensate for the wave refraction inside the source, the boundary reflection surfaces must converge with altitude, and this implies that the most likely auroral kilometric radiation source would be a thin, local density enhancement, since the refractive index contours at its boundaries would be expected to slope inward. The ISEE observations of multiple spectral components, which are attributed to separate oscillations at different altitudes in the same enhancement, suggest a source thickness as small as 25 km and an internal wave growth threshold of roughly 40 dB, rather than the 70‐120 dB previously believed necessary to account for auroral kilometric radiation without feedback. But more significantly, the feedback model accounts for numerous aspects of the auroral kilometric radiation behavior, predicts emission at the wave growth saturation level, and leads to the conclusion that auroral kilometric radiation originates at many compact sites, each emitting a nearly monochromatic wave.
Theory and observation of a dynamically evolving negative ion plasma
Authors: Mendillo Michael , Forbes Jeffrey
Published: February 2008

As part of the Project Firefly ionospheric modification campaigns conducted during the early 1960s, sulfur hexafluoride (SF6) was used to study the creation and consequences of artificially‐induced electron depletion regions via the attachment process (SF6 + e− → SF6−). Since those early experiments, a great many advances have occurred in theoretical, laboratory, and diagnostic techniques related to negative ion plasmas. This study examines the full range of negative ion chemistry in the upper ionosphere by using current reaction rate data to investigate the many chemical paths SF6 type injections might take in an F region environment. Particular attention is given to the conditions required to create heavy negative ions that persist long enough to affect the dynamical properties of the F region. The ambipolar diffusion characteristics of a three component plasma (O+, e−, SF6−) are described, and estimates of the incoherent scatter spectra obtained from such a plasma are presented. Model calculations using a first order chemical code are defined and tested to investigate the actual types of negative ion plasmas capable of being created under nighttime conditions. A versatile model for diffusion in an exponential atmosphere was used to simulate the evolution of 1026 SF6 molecules released at 222 km during a 1962 Firefly experiment. When examined in conjunction with the chemical model calculations, the results suggest that the ionospheric perturbations recorded at the time probably resulted more from molecular and atomic ion neutralizations involving SF6−, SF5+, O−, O+, and e−, rather than simple electron attachments, as had been expected. A similar use of SF6 diffusion scenarios for high‐altitude releases (h = 350–500 km) indicates that large‐scale, long‐lived negative ion plasmas could be produced by modest rocket or Shuttle‐borne payloads to study dynamical, chemical, and instability properties of space plasmas.
Association between magnetic field fluctuations and energetic particle bursts in the Earth's magnetotail
Authors: Lui A. T. Y. , Krimigis S. M. , Armstrong T. P.
Published: February 2008

The association between energetic protons (0.29–0.50 MeV) and simultaneous local fluctuations of magnetic field at 35 to 45 RE in the magnetotail is examined statistically with data from APL/JHU particle telescopes aboard IMP 7 and IMP 8. About four satellite years of 5.5 min averaged measurements are used in this study. In addition to confirming that the level of magnetic field fluctuations generally increases with the presence of energetic protons and their streaming anisotropy, it is found that increase in occurrence frequency of streaming of energetic protons are ordered far better by magnetic field fluctuations than by proximity to the neutral sheet. However, the presence of large magnetic field fluctuations (δB > 5 nT or δB/B > 50%) is neither a necessary nor a sufficient condition for the detection of large streaming in energetic protons.
Global dynamo simulation of ionospheric currents and their connection with the equatorial electrojet and counter electrojet: A case study
Authors: Hanuise Christian , Mazaudier Christine , Vila Paul , Blanc Michel , Crochet Michel
Published: February 2008

The interrelationship of equatorial and planetary scale ionospheric horizontal currents on quiet days is studied by means of a global ionospheric wind dynamo simulation. This simulation aims at reproducing magnetic and radar data first for a normal quiet day, and then for the strong counterelectrojet event of January 21, 1977, which was previously studied in detail on the basis of coherent backscatter radar data for the Addis‐Ababa location. For the reference quiet day (January 27, 1977), the pattern of low and middle latitude currents and electric fields can be roughly reproduced by a combination of the (1,−2) and (2,2) solar tides. Both the Sq current system, and the global electrostatic potential distribution as derived by Richmond et al. [1980] from incoherent scatter data are well simulated. Direct comparison of the computed electric field with the quiet‐day averages available for each radar site also show an excellent agreement on the east‐west component, but a poorer one on the north‐south component. The counterelectrojet simulation is performed by fitting the H component trace at the magnetic equator and the D trace at midlatitudes. The result appears to give a consistent solution to the problem of the electrical connection between the equatorial counterelectrojet and the planetary dynamo layer. Two horizontal current vortices of opposite directions are found to flow at low latitudes on each side of the noon sector, anticlockwise in the morning and clockwise in the afternoon. They both produce a poleward current flow at low latitudes at noon, a feature that is detected on the magnetic records. The counterelectrojet event is reproduced by a combination of the (2,2) and (2,4) solar tides, assuming that the contribution of the diurnal tide to the altitude‐integrated current flow cancels out. This result is in agreement with a previous simulation study of the counterelectrojet phenomenon.
Dynamics of magnetosphere‐ionosphere coupling including turbulent transport
Authors: Lysak Robert L. , Dum Christian T.
Published: February 2008

The dynamics of magnetosphere‐ionosphere coupling has been investigated by means of a two‐dimensional two—fluid MHD model including anomalous resistivity. When field‐aligned current is generated on auroral field lines, the disturbance propagates toward the ionosphere in the form of a kinetic Alfvén wave. When the current exceeds a critical value, microscopic turbulence is produced, which modifies the propagation of the Alfvén wave. This process is modeled by a nonlinear collision frequency, which increases with the excess of the drift velocity over the critical value. The system evolves toward an electrostatic structure, with the perpendicular electric field having a shorter scale than the field‐aligned current. The approach to a steady state is strongly dependent on the presence or absence of the turbulence and on the boundary conditions imposed in the generator. As current is increased or scale size is decreased, the turbulent region reflects and absorbs most of the Alfvén wave energy, decoupling the generator from the ionosphere.
On the injection of cosmic ray secondaries into the inner Saturnian magnetosphere: 1. Protons from the CRAND Process
Authors: Blake J. B. , Hilton H. H. , Margolis S. H.
Published: February 2008

The energy spectra and pitch angle distributions of energetic protons injected into the inner Saturnian magnetosphere by the cosmic ray albedo neutron decay (CRAND) process have been calculated using the nucleon transport code HETC. These calculations predict spectra and pitch angle distributions consonant with the Pioneer and Voyager observations for proton energies above ∼50 MeV assuming that the ring particles are ice, not rock, and that the mean mass seen by the cosmic rays is several tens to a few hundred grams per square centimeter.
Comparison of phase and amplitude structures of Pc 5 pulsations in the morning and afternoon sectors
Authors: Saka O. , Kim J. S. , Sugiura M.
Published: February 2008

Spatial phase and amplitude structures of the morning and afternoon Pc 5 pulsations are compared using the North American IMS magnetometer network data. Comparisons of phases and amplitudes between different stations were made by a cross spectral analysis. The magnetic local time (MLT) of the events analyzed extends from 0500 to 1100 for the morning and from 1200 to 2100 for the afternoon. All events were observed either during quiet periods or during the recovery phases of substorms. The following results are obtained: (1) The spatial phase structures are very similar in the morning and afternoon sectors for each of the three components. (2) The amplitudes are larger in X than in Y for both sectors, where X and Y are the magnetic north and east components, respectively. (3) The latitudinal variations of the amplitude and of the phase differences between X and Y show dissimilarities in the morning and afternoon sectors. These results suggest that the magnetic field oscillations in the compressional mode, which are believed to dominate in the afternoon magnetosphere, are not observed on the ground in this time sector. As seen from the ground observations, the pulsations in both time sectors are caused by oscillations of the magnetospheric field in the transverse mode. The theory of the resonant oscillation of the magnetic field lines, which successfully explains the pulsations in the morning sector, does not seem to be applicable to the pulsations in the afternoon sector.