bluuebunny/crossref_metadata_2025 huggingface dataset:
Short‐term variability in the HF‐enhanced plasma line
Authors: Ganguly S.
Published: February 2008

Plasma lines enhanced by HF radio waves have been used as a tracer of electron density fluctuations in the ionosphere. Both the intensity and the altitude of these plasma lines have been measured with very short time and range resolution. The power spectrum of the range variations indicates a power law dependence with a spectral index of −2.0 over periods of a few minutes to about 8 s; corresponding amplitudes are greater than 500 m to ∼70 m. Instability and turbulent mechanisms seem to be responsible for the dissipation of large‐scale irregularities to form continuously smaller scale sizes. Furthermore, isolated peaks of about 2‐ to 6‐s periods with amplitudes of about 15–90 m have been observed on several occasions. The possible source of these fluctuations could be sound waves ducted in the ionosphere.
The role of vibrationally excited oxygen in auroral excitation of O2(¹Δg)
Authors: Monchick L. , Parker J.G. , Potemra T.A.
Published: February 2008

Several early auroral observations of enhanced radiation in the 1.27‐µ band of O2 were suggested as being due to the tapping of a reservoir of vibrational energy. The cross section for the process
is here estimated by elementary compound state theory and found to be much larger than that predicted by the first Born approximation formula but still too small for this mechanism to be a dominant feature in 1.27‐µ radiation in aurorae. Appreciable populations of higher vibrational states of O2(1Δg) are predicted by compound state theory, and these can be a significant feature of auroral infrared radiation before they are relaxed by further collisions.
Isee 1 charged particle observations indicative of open magnetospheric field lines near the subsolar region
Authors: Williams D.J. , Frank L.A.
Published: February 2008

On November 20, 1977, at 0230–0300 UT, Isee 1 encountered unusual charged particle distributions within the magnetosphere. The three‐dimensional distribution observations for energetic (>24 keV) ions and plasma show the development of field‐aligned asymmetries in the energetic ion distributions simultaneously with a marked change in plasma flow. We conclude that the most likely explanation for these observations is that Isee 1 encountered open magnetospheric field lines at its position within the magnetosphere (∼1030 LT and ∼1200 ±300 km from the magnetopause). Field lines were open near the geomagnetic equator, and the geometry was spatially or temporally variable. Other features of the field line topology are presented.
Nitric oxide delta band absorption measurements in the lower thermosphere
Authors: Massie S.T.
Published: February 2008

The first successful measurements of nitric oxide band absorption in the earth's atmosphere have been made by using the high‐resolution ultraviolet spectrometers on Orbiting Solar Observatory 8. These measurements were conducted between January and August 1977 and between 30° north and south latitudes. The nitric oxide absorption data, at the (1, 0) delta band wavelength of 1829.41 Å, are numerically inverted to produce nitric oxide density profiles between 85 and 145 km. The major finding of the observations is that for altitudes below 95 km there is more nitric oxide at sunrise than at sunset. A numerical model, incorporating time‐dependent ionospheric chemistry and vertical diffusive transport (both eddy and molecular), is used to simulate the Oso 8 nitric oxide profiles. The peak of the model sunset profile lies at 95‐km altitude, in agreement with observation, if the vertical component of the eddy diffusion coefficient is 107 cm2 s−1 near 100 km. The model specifies a sunrise to sunset density ratio of 1.9 at 85 km, while the observed value is 4.2−2.7+7.3. Vertical and horizontal transport processes are probably responsible for the observed diurnal variation.
Interplanetary sector boundaries 1971–1973
Authors: Klein L. , Burlaga L.F.
Published: February 2008

Eighteen interplanetary sector boundary crossings observed at 1 AU during the period January 1971 to January 1974 by the magnetometer on the Imp 6 spacecraft was discussed. The events were examined on many different time scales ranging from days on either side of the boundary to high‐resolution measurements of 12.5 vectors per second. Two categories of boundaries were found, one group being relatively thin (averaging ≈ 104 km) and the other being thick (averaging ≈ 106 km). In many cases the field vector rotated in a plane from one polarity to the other. Only two of the transitions were null sheets. Using the minimum variance analysis to determine the normals to the plane of rotation and assuming that this is the same as the normal to the sector boundary surface, it was found that the normals were close to (≤45°) the ecliptic plane. The high inclination of the sector boundary surfaces during 1971–1973 verifies a published prediction and may be related to the presence of large equatorial coronal holes at this time. An analysis of tangential discontinuities contained in 4‐day periods about our events showed that their orientations were generally not related to the orientations of the sector boundary surface, but rather their characteristics were about the same as those for discontinuities outside the sector boundaries. Magnetic holes were found in thick sector boundaries, at a rate about 3 times that elsewhere. The holes were especially prevalent near stream interfaces, suggesting that they might be related to the convergence and/or slip of adjacent solar wind streams.
ELF sferic occurrences in the Antarctic during a solar proton event: Case study of occurrences at Byrd Station during the event of June 9, 1968
Authors: Fraser‐Smith A.C. , Helliwell R.A.
Published: February 2008

Electromagnetic waves with frequencies above the extremely low frequency range (ELF; frequencies in the range 5 Hz to 3 kHz) are susceptible to a variety of solar proton event (SPE) effects when propagating through a polar region in the earth‐ionosphere wave guide. These effects appear to become less severe as the frequency of the waves becomes smaller and approaches the ELF range. Although measurements have been lacking, it would be expected that ELF wave propagation through the polar regions would be comparatively stable. To investigate polar ELF wave propagation during an SPE, we have carried out a series of measurements of the properties of ELF sferics (75 Hz) at a polar location (Byrd Station, Antarctica) during a moderately large SPE. These measurements suggest that an SPE can significantly alter the characteristics of ELF signals propagating through the polar regions: during the first 24 hours of the SPE there was a reduction of about 50% in the median amplitudes of the sferics, compared with their amplitudes before the SPE, and there were substantial changes in their rates of occurrence. However, there was no polar cap ‘blackout’ of the sferics, and their amplitude reduction appeared to be no greater than the reductions occasionally observed at lower latitudes in experiments with man‐made ELF signals. Thus our measurements provide support for the view that ELF signal propagation through the polar regions during an SPE is comparatively stable. At frequencies below the ELF range we note the appearance of Pc 3 pulsations at the start of the SPE. Further study of the possible stimulation of these pulsations by SPE's and additional measurements of the SPE‐related changes of ELF sferic characteristics at polar locations are desirable.
The volume emissivity of type III radio bursts
Authors: Tokar Robert L. , Gurnett Donald A.
Published: February 2008

The volume emissivity has been calculated for thirty‐six type III solar radio bursts obtained from approximately 6.5 years of Imp 8 and ISEE 1 satellite data. Although the emissivities for these events vary over a large range, all the emissivities decrease rapidly with increasing heliocentric radial distance. The best fit power law for the emissivity, using the average power law index for all events analyzed, is J=J0R−6.0, with J0=1.5 × 10−24 W m−3 sr−1. This best fit emissivity is used to estimate the expected radial variation of the plasma oscillations responsible for the type III radio emission.
Rocket‐borne wave measurements in the dayside auroral oval
Authors: Temerin M. , Kelley M.C.
Published: February 2008

VLF and ELF waves were measured on two rocket payloads launched into the dayside auroral oval on December 18, 1974, and on January 11, 1975. The correlation of the VLF hiss intensity with the fluxes of precipitating electrons above 500 eV on short spatial and time scales was often poor, even when a positive slope existed in the electron phase space density. During the flight of January 11, 1975, distinct features were observed at the lower hybrid frequency. The frequency of this emission was used together with an independent density measurement to determine the relative concentration of O+ to the heavier ions NO+ and O2+. It was found that the density of NO+ or O2+, which could not be distinguished, is enhanced over expected values between 150 and 400 km altitude. This may be due to conversion of O+ to NO+ by large dc electric fields as observed in the experiments. Broadband electrostatic and electromagnetic waves were observed shortly after the barium‐shaped charged explosion on January 11, 1975. The observed lowering of the auroral VLF hiss cutoff due to the barium is consistent with either ducting of VLF hiss emissions along the enhanced density duct produced by the barium or with local generation VLF hiss during the barium injection. ELF hiss observations were consistent with previous results, indicating that it is limited to latitudes equatorward of the dayside auroral oval.
Coincident particle observations from AE‐C and ATS 6 during the October 28, 1977, geomagnetic storm
Authors: Zanetti L.J. , Potemra T.A. , Doering J.P. , Lee J.S. , Arnoldy R.L. , Hoffman R A.
Published: February 2008

Ion and electron energy spectra (<30 keV) were recorded simultaneously by the AE‐C (at ∼400‐km altitude) and ATS 6 (at 6.63 RE) spacecraft during the intense geomagnetic storm of October 28, 1977 (Kp → 7+). Observations were acquired in the evening sector, when the two spacecraft were nearly on the same L shell. The orbit of AE‐C provides wide longitudinal coverage of the auroral oval, whereas ATS 6 remains relatively stationary near the equatorial plane. An unusual particle injection event that was characterized by a series of periodic (∼12 min) bursts of electrons was observed by ATS 6. During this time a variety of phenomena could be identified in the AE‐C particle data, including a widespread low‐energy ‘inverted V’ that extended over 1‐1/2 hours of local time. Distinct from this region are precipitating electrons which have monoenergetic peaks of variable intensity. These electron spectra are similar to those normally observed coincident with discrete arc aurora. The coincident electron energy spectra acquired by AE‐C and ATS 6 match well above 5 keV. The spectra of electrons peak near 1 keV at ionospheric altitudes (typical of this event), whereas no peaks in energy appear at synchronous altitude.
The latitudinal variation of the charge exchange induced atomic hydrogen escape flux
Authors: Maher Louis J.
Published: February 2008

Using plasma data from the Isis 2 spacecraft and Arecibo radar, diffusive equilibrium models of the ionosphere were constructed for equinox conditions. These plasmaspheric models were combined with models of the neutral atmosphere to calculate the atomic hydrogen escape flux due to charge exchange between thermal protons and to calculate cooler hydrogen and oxygen atoms as a function of dipole latitude and local time. These calculations showed that the daytime escape flux increases as the absolute value of the dipole latitude decreases, reaching its maximum value at the magnetic equator. At 15 hours local time (LT) on March 23, 1972, the calculated escape flux varied from an insignificant amount at 55° dipole latitude, to 3 × 108 atoms cm−2 s−1 at the magnetic equator. In addition, the relative importance to the total charge‐exchange escape flux of the component due to charge exchange between protons and atomic oxygen is discussed. The contribution to the escape flux of plasma at high L values, and the effect of newly produced hot hydrogen upon the neutral temperature are also discussed.
Rocket‐borne auroral EUV measurements
Authors: Fischer F. , Schmidtke G.
Published: February 2008

The measurements of two rocket spectrometers on January 22, 1977, and February 8, 1977, over Andoya, Norway are described. While five channels recorded height profiles of selected emissions such as O II 83.4 nm, O I 98.9 nm, N I 120 nm, H I 121.6 nm, and O I 130.4 nm, two channels repeatedly scanned the wavelength range from 50 to 135 nm. Results are discussed and compared with other measurements.
Rocket observations of stimulated electron acceleration associated with the Trigger Experiment
Authors: Lundin Rickard , Holmgren Gunnar
Published: February 2008

Evidence for a strong enhancement of the electron flux associated with a cesium cloud release from the ‘Trigger’ rocket payload, launched from Esrange on February 11, 1977, will be presented. The up to three orders of magnitude enhancement of the electron flux first appeared some ˜150 ms after the cesium injection and prevailed for about 1 s. A remarkable feature of this enhancement is that it was not only field aligned (at 2 keV) in the downward direction, but also in the center of this electron ‘burst’, field‐aligned in the upward direction. A possible interpretation for the quasi periodic modulation of the 2 keV electron flux in the center part of the ‘burst’, may be that a ‘bunch’ of electrons was locally trapped between two potential barriers. From the bouncing period, the velocity of the 2 keV electrons, and the time dispersion versus pitch angle, the altitude as well as the relative thickness of these potential barriers could be estimated. The altitude and the average parallel electric field strength of the upper (accelerating) potential drop was estimated to be around 500 km and ∼60 mV/m, respectively. The strong field alignment of the upward directed electrons suggests that a reflecting potential barrier was located below the rocket altitude (∼162 km). Although the most evident consequence of the cesium release from particle point of view was the very intense and short‐lived burst of accelerating electrons, there were also indications of a more prolonged effect on the high energy particle population (>40 keV).
The results from the X Ray Bremsstrahlung Experiment of Project Trigger
Authors: Bering E. A. , Benbrook J. R. , Stansbery E. G. , Sheldon W. R. , Roeder J. L.
Published: February 2008

An ionospheric cesium cloud release experiment, Project Trigger, was conducted at ESRANGE, Kiruna, Sweden, on February 11, 1977. A rocket‐boosted, parachute‐borne X ray bremsstrahlung detector was included in the overall project to accomplish three objectives: (1) an assessment of the preexplosion background precipitation from a slowly moving platform, (2) a measurement that would allow the effective radius of the triggered precipitation region to be determined, and (3) detection of any long‐duration precipitation effects. Analysis of the data produced the following conclusions: (1) with some slight exceptions, the counting rate observed before the explosion was the normal quiet background expected for the experimental circumstances; (2) the counting rate below 20 keV observed after the explosion was considerably in excess of that predicted by existing theoretical calculations of atmospheric X ray production and known cosmic ray sources; there is a possibility that this excess was an effect of the explosion; (3) a 0.13‐Hz peak in the power spectral density of the X ray flux was observed; this observation is interpreted as evidence for a particle‐wave‐particle interaction involving a bounce resonance between 1.5‐keV electrons accelerated by the explosion and 1.7 kHz whistler mode waves, which in turn pitch angle scatter higher‐energy electrons; (4) no prompt effect of the cesium release was seen in the X ray data; and (5) this result sets an upper limit of ∼2.8 km on the effective radius of the triggered prompt precipitation flux tube. This article contains supplementary material.
Cloud forms on Saturn
Authors: Burke J. J. , Gehrels T. , Strickland R. N.
Published: February 2008

The imaging photopolarimeter (IPP) on Pioneer Saturn provided spin‐scan images of Saturn's cloudtops. Only subtle departures from a uniform brightness distribution were apparent, except in the polar regions. At other latitudes the images show only a few features; they primarily support the conclusion that the visible atmosphere is a deep haze. Belts and zones are seen, and some detail in a zone near ±60° latitude. The North Equatorial Belt consists of two dark belts separated by a brighter zone exhibiting longitudinal structure.
Graphical measurement of Saturn's oblateness and the radius of the Encke Gap
Authors: Burke J. J.
Published: February 2008

The geometric distortions attendant to spin‐scan imaging were extraordinarily manifest in the Pioneer encounter with Saturn. By overlapping graphical predictions of these distortions with raster scans of the raw intensity data, both displayed to the same scale on a Versatec printer‐plotter, we are able to determine the precise geometry of a data‐taking sequence. The predictions are quite sensitive to the assumed dimensions of Saturn and its rings. We accordingly conclude that the ratio of polar to equatorial radius is 0.91 and that the Encke gap is 133,500 km from Saturn's center.
An extraordinary view of Saturn's rings
Authors: Burke J. J. , KenKnight C. E.
Published: February 2008

We report a unique set of photometric and polarimetric observations made by the imaging photopolarimeter aboard the Pioneer spacecraft shortly after it penetrated the ring plane from above on its way to closest approach. The bright planet limb is observed through the rings, which themselves weakly reflect direct sunlight. Polarizations range from 41% (16%) at the extreme planet limb to 2% (1.5%) at the darkest part of the B ring in the blue (red) channel. Detailed structure of the A ring is evident, most notably the Encke gap.
Dynamical response of the dayside ionosphere of Venus to the solar wind
Authors: Hartle R. E. , Taylor H. A. , Bauer S. J. , Brace L. H. , Russell C. T. , Daniell R. E.
Published: February 2008

Dayside ion composition measurements made by the orbiter ion mass spectrometer and the orbiter electron temperature probe on the Pioneer Venus orbiter are used to infer the dominant processes involved in the dynamic response of the Venus ionosphere to the solar wind. The analysis is confined to the topside ionosphere in the vicinity of the subsolar point, where the ionosphere‐solar wind interaction is expected to be maximized. Height profiles of the ion composition and plasma temperatures in the main body of the topside ionosphere, lying between the ionopause and chemical equilibrium regions, reveal that the ionosphere is in a compressed state. This region of the ionosphere is interpreted in terms of a stationary equilibrium where the compression is derived from the ponderomotive force j × B. The estimated magnitude of this force is confirmed by the magnetic field measurements made by the orbiter magnetometer.
Mass spectrometric measurements of the neutral gas composition of the thermosphere and exosphere of Venus
Authors: Niemann H. B. , Kasprzak W. T. , Hedin A. E. , Hunten D. M. , Spencer N. W.
Published: February 2008

The neutral gas composition and density in the thermosphere of Venus is being measured with a quadrupole mass spectrometer on the Pioneer Venus orbiter. Data are obtained near periapsis once per day approximately 150–250 km above the surface. The principal gases in the thermosphere are CO2, CO, N2, O, N, and He. Atomic oxygen is the major constituent above 155 km on the dayside and also on the nightside up to 180 km when helium becomes the major constituent. The average values of CO2, CO, N2, O, and N remain nearly constant during day and night, but an abrupt change occurs across the terminator from a high dayside value to a low nightside value. The helium density varies in the opposite way, and a distinct bulge was observed at night near the morning terminator. The data have been used as the basis of an empirical model. Large orbit to orbit variations in densities were also observed on the nightside, suggesting perhaps strong turbulent motion in the atmosphere below. Kinetic temperatures inferred from scale heights are approximately 285°K on the dayside and 110°K at night. The average global temperature obtained from the model is 199°K.
Ion‐cyclotron heating and acceleration of solar wind minor ions
Authors: Dusenbery Paul B. , Hollweg Joseph V.
Published: February 2008

The resonant acceleration and heating of solar wind minor ions via interactions with a spectrum of dispersive or nondispersive undamped ion‐cyclotron waves are investigated. The principal goal is to determine how the dimensionless parameters of the problem affect the heating and acceleration processes. In addition, simple physical interpretations of the heating and acceleration are given. The exact numerical evaluations of the heating and acceleration rates imply that (1) the total heating rate is roughly proportional to the mass of the ion; (2) dispersive waves should lead to νi >να >νp, where i refers to ions heavier than He++; (3) dispersive waves have a slight tendency to yield ∂Ti/∂t >(mi/mα) ∂Tα/∂t, while non‐dispersive waves have a slight tendency to yield ∂Ti/∂t <(mi/mα) ∂Tα/∂t. The predictions of this model are compared with observations and may offer an explanation for some observed properties of minor ions.
Distribution of the field‐aligned currents, ionospheric currents, and electric fields in the polar region on a very quiet day and a moderately disturbed day
Authors: Akasofu S.‐I. , Ahn B.‐H.
Published: February 2008

The comparison of the distribution of field‐aligned currents and ionospheric currents on a very quiet day and a moderately disturbed day, obtained on the basis of the International Magnetosphere Study Alaska meridian chain of magnetometers, reveals that the field‐aligned currents (region I and II currents) consist of two systems: the part I system in the dayside and the part II system in the nightside. On a very quiet day the part II system is either absent or very weak. On the other hand, on a moderately disturbed day the part II system becomes a dominant feature. It is also shown that both the ionospheric currents and the electric fields on quiet and disturbed days can be understood in terms of the response of the ionosphere to changes of the part I and II systems.
DMSP/F2 electron observations of equatorward auroral boundaries and their relationship to magnetospheric electric fields
Authors: Gussenhoven M. S. , Hardy D. A. , Burke W. J.
Published: February 2008

Energetic electron measurements from a particle detector on the DMSP/F2 satellite have been used to determine the corrected geomagnetic latitude ΛCGM of the equatorward boundary of the auroral oval. The satellite was launched into a nearly sun‐synchronous, polar orbit centered on the 0700–1900 MLT meridian. Because of the wobble of the dipole and a very slow precessional motion of the orbit more than 6000 boundary crossings could be studied in the 1600–2300 and 0400–1000 MLT sectors. The detectors, which have large geometric factors, look radially away from the earth and detect precipitating electrons with energies between 50 eV and 20 keV. In the evening sector the equatorward boundaries are precisely determined from the rise in the total electron flux. The morningside boundary cannot always be clearly delineated. Data were divided into 1‐hour magnetic local time bins with ∼400 samples per bin. In each of the MLT bins, ΛCGM was found to be linearly correlated to the KP index. Regression values of ΛCGM were projected to the magnetic equatorial plane by using the Mead‐Fairfield magnetic field model. The projected boundaries are not in good agreement with the injection boundaries of Mauk and McIlwain (1974). They are best fit to boundaries derived by using Volland‐Stern type electric fields with the axis of symmetry rotated into the evening sector for KP <2 and into the afternoon sector for KP ≥2.
Magnetic field of the average substorm current system in middle and low latitudes
Authors: Kamide Y. , Ahn B.‐H. , Corrick G. K. , Akasofu S.‐I.
Published: February 2008

The distribution of magnetic disturbance vectors in middle and low latitudes produced by the average three‐dimensional current system which is obtained by using magnetic records from the IMS Alaska meridian chain is computed. It agrees fairly well with the observed distribution obtained by Akasofu and Meng [1969] by rotating the latter counterclockwise by about 15°, although, the distribution obtained by Silsbee and Vestine [1942] must be rotated by as much as 30°‐45°. The results suggest that there is no significant leakage of ionospheric currents from the auroral oval to middle and low latitudes.
Laboratory investigations of the ionospheric N2+ (X, ²Σg+, ν≠0) reaction with O2
Authors: Alge E. , Lindinger W.
Published: February 2008

Laboratory measurements of the charge transfer reaction of N2+ (X, ²Σg+, ν≠0) and N2+ (X, ²Σg+, ν=0) with O2 have been carried out with various mixtures of these N2+ species in the energy range from near thermal to 0.12 eV. No difference in the reactivities of vibrationally excited and nonexcited N2+(X)—both present in the ionosphere—with O2 was observed.
On the use of electron data to infer the structure of parallel electric fields
Authors: Greenspan M. E. , Silevitch M. B. , Whipple E. C.
Published: February 2008

We investigate the use of electron data to probe the structure of parallel electrostatic fields. Low‐energy electrons can be trapped between their magnetic mirror points below an observer and the upward directed electric field above. The shape of the trapping region in phase space gives information about the field structure. We use equivalent potential diagrams and plots of phase space boundaries in (µ, E) space both to explain our results and to demonstrate the utility of these formalisms for studying particle motion in time‐independent electric fields. A comparison of theoretical boundaries in (ν∥, ν⊥) space with S3‐3 data shows that it is difficult to determine the shape of the low‐energy trapping boundary with present particle experiments. We discuss the instrumentation required to measure the low‐energy electron population with sufficient detail to resolve these boundaries.
Magnetohydrodynamic interaction of high‐speed streams
Authors: Whang Y. C. , Chien T. H.
Published: February 2008

Numerical solutions of a magnetohydrodynamic model are carried out to describe the nonlinear interaction of corotating high‐speed streams near the solar equatorial plane. Two problems are studied. The first problem is to simulate the evolution of an idealized high‐speed stream. Numerical solutions are obtained to represent the variations of flow velocity, magnetic field, plasma density, temperature, and conduction heat flux in the interaction region. They demonstrate that the dynamical interaction and heat conduction process are responsible for the thermal structure of a high‐speed stream. The second problem deals with the formation of corotating shock waves near the leading edge of a broad stream resulting from the merging of characteristic curves. Corotating shocks do not necessarily occur in pairs; a reverse shock can be formed without a forward shock nearby.
A comparison of radio data and model calculations of Jupiter's synchrotron radiation 2. East‐west asymmetry in the radiation belts as a function of Jovian longitude
Authors: de Pater Imke
Published: February 2008

On the basis of a comparison of radio data and model calculations of Jupiter's synchrotron radiation the ‘hot region’ or east‐west asymmetry in the planet's radiation belts is proposed to be due to the combined effect of an overabundance of electrons at jovicentric longitudes λJ ∼240°–360° and the existence of a dusk to dawn directed electric field over the inner magnetosphere, generated by the wind system in the upper atmosphere. The model calculations were based upon the magnetic field configurations derived from the Pioneer data by Acuna and Ness [1976] (the O4 model) and Davis, Jones and Smith (quoted in Smith and Gulkis [1979]) (the P11 (3,2)A model), with an electron distribution derived in the first paper of this series [de Pater, this issue]. We would infer from the calculations that the O4 model gives a slightly better fit to the data; the relatively large number density at λJ ∼240°–360°, however, might indicate the presence of even higher order moments in the field.
O2 (c¹Σu− → X³Σg−) emission in the terrestrial nightglow
Authors: Slanger T. G. , Huestis D. L.
Published: February 2008

Synthetic spectra have been calculated incorporating three O2 emission systems, A³Σu+ → X³Σg−, A′³Δu → a¹Δg, and c¹Σu− → X³Σg−, and matched to the 3100‐ to 4500‐Å nightglow spectrum of Broadfoot and Kendall (1968). The synthesis necessitated the inclusion of the c¹Σu− → X³Σg− system, which has never been previously identified in the airglow, although it is a dominant system in the Venusian nightglow. The emissions from the extremely metastable A′³Δu and c¹Σu− states account for half the radiation in the 3100‐ to 4500‐Å region, from which it may be deduced that the mesospheric concentrations of O2(A′³Δu) and O2(c¹Σu−) are much higher than that of O2(A³Σu+). The vibrational distributions are quite unrelaxed for all three states.
Alfven wave resonances in a realistic magnetospheric magnetic field geometry
Authors: Singer H. J. , Southwood D. J. , Walker R. J. , Kivelson M. G.
Published: February 2008

The notion of magnetic field line resonance has been very effective in explaining many features of long‐period geomagnetic pulsations. To date the decoupled transverse wave equations have been solved in a magnetic dipole field, whereas only WKB approximate solutions have been used in more general geometries. We have developed a solution of the decoupled equations that includes both a general magnetic field geometry and the effects of density and mass composition. The aim of this paper is to isolate and examine the effect on eigenfrequencies of only the field geometry by keeping density constant along all field lines. We review the diurnal variations in wave period predicted on the ground and in space by using the recent Olson‐Pfitzer magnetospheric magnetic field model in our solution. For example, on the ground at 67° magnetic latitude the diurnal variation in period caused by field geometry is larger than a factor of 2. At 6.6 RE, where the dipole field line from 67° crosses the magnetospheric equator, there is negligible diurnal variation in period. Significant diurnal variations in period (≳10%) at fixed radial distance in the equatorial plane in space occur only at distances ≳10 RE. Knowledge of the field geometry is shown to be important for the determination of mass density in space from ground pulsation observations. We discuss the impact of our results in interpretation of experimental data.
Ion composition and energy distribution during 10 magnetic storms
Authors: Lennartsson W. , Sharp R. D. , Shelley E. G. , Johnson R. G. , Balsiger H.
Published: February 2008

Data from the plasma composition experiment on ISEE 1 were used to investigate the relative quantities and energy characteristics of H+, He++, He+, and O+ in the near‐equatorial magnetosphere at R ≤15 RE during magnetic storms, principally during the early main phase. The ions included in this study had energies in the range of 0.1 ≤E/Q ≤17 keV/e. The number densities were characterized by a large to dominant fraction of terrestrial ions throughout this energy window. Terrestrial O+ ions were most clearly identified, but strong evidence for a significant contribution of terrestrial H+ ions was also found. On occasions, the O+ alone contributed 50% or more of the integral number density, as well as the energy density, over distances of several earth radii along the orbit. The largest fractions of O+ (≲75%) and He+ (≲25%) were found at R <3 RE (L <5). In general, the He+ only represented a few percent, however. Small fractions of O+ (<10%) and He+ (<1%) were mostly found in the 0100‐0600 LT sector, at R ≳7 RE. The He++ was often obscured by background and rarely exceeded 2%, except in the 0100–0600 LT sector, at R ≳7 RE, where it reached several percent relatively frequently, suggesting a larger solar wind component here. It is argued, based on certain signatures in the energy spectra, that solar wind ions may enter the inner magnetosphere through this region and thereby contribute a larger portion of the high‐energy ring current population (50–100 keV). The data do not suggest, however, that the solar wind is always the dominant source of ions for the high‐energy ring current.
Solar wind pickup of ionized Venus exosphere atoms
Authors: Curtis S. A.
Published: February 2008

Previous calculations of electrostatic and electromagnetic growth rates for plasma instabilities have neglected the thermal spread of the distribution function of the planetary ions. We consider the effects of finite temperatures for exospheric ions born in the solar wind. Specifically, growth rates are calculated for electromagnetic instabilities in the low‐frequency case for Alfven waves and the intermediate frequency case for whistlers. Also, electrostatic growth rates are calculated for the intermediate frequency regime. From these growth rates, estimates are derived for the pickup times of the planetary ions. The electromagnetic instabilities are shown to produce the most rapid pickup. In the situation where the angle between the local Venus magnetic field and the plasma flow direction is small, the pickup times for both electromagnetic and electrostatic instabilities become very long. A possible consequence of this effect is to produce regions of enhanced planetary ion density in favorable Venus magnetic field‐solar wind flow geometries.
The effect of MHD waves on the threshold wave field for initiating VLF nonlinear growth and emissions
Authors: Dowden Richard L.
Published: February 2008

VLF nonlinear wave growth can only be initiated by signals above some threshold amplitude. Current theories do not predict this for a uniform or smoothly varying geomagnetic field. It is shown here that if near‐resonant electrons see fluctuations in the total field of sufficient frequency and amplitude, cyclotron wave trapping and thus nonlinear growth cannot occur. MHD waves in the VLF interaction region have sufficient amplitude (>2γ) on rare occasions to raise the threshold above VLF growth saturation level, while MHD background levels of around 0.05γ would produce a base level threshold only a little below an estimate made from a VLF event and described here.
A study of Pi 2 pulsations at Canadian Magnetic Observatories
Authors: Gupta Jagdish Chandra
Published: February 2008

The analysis of the Pi 2 pulsations for the period May 15, 1970, to May 14, 1971, from Ottawa, Meanook, Baker Lake, and Resolute Bay observatories reveals the following: (1) Pi 2 pulsations occur most frequently near midnight at Ottawa, Meanook, and Baker Lake and near 15±1 h LT at Resolute Bay; the 18±1 h LT peak at Baker Lake was found to be quite strong, especially during winter. Also at Baker Lake and Resolute Bay, Pi 2's occurred at later hours during magnetically quiet conditions but at earlier hours during magnetically disturbed conditions. (2) The amplitude of Pi 2 is found to be largest before midnight at Ottawa and Meanook and at midnight at Baker Lake. (3) The period of Pi 2 is noted to be minimum in the morning and maximum in the evening at Ottawa and Meanook. Also, Ottawa results indicate that Pi 2 periods undergo a nonseasonal annual variation. (4) Both the occurrence and amplitude of Pi 2 are found to increase with incrasing magnetic activity to a certain level of Kp, which varied among the stations. (5) Some evidence of a 27‐day recurrence tendency in the period of Pi 2 is found. A lunar influence on the occurrence of Pi 2 is also noted, and this effect deserves further attention.
Ionospheric total electron content behavior at a pair of mid‐latitude conjugate stations
Authors: Essex E. A. , Klobuchar J. A.
Published: February 2008

A correlation study of the geomagnetic conjugate effects in the ionospheric total electron content was carried out between Shemya, Alaska, and Beveridge, Australia. The seasonal, diurnal, and magnetic activity dependence of the correlation was determined. It was found that for equinoxes during low magnetic activity the correlation is positive during local afternoon and negative during local night to local morning hours. For the early winter‐summer conjugate study, the correlation is generally positive during the local daytime and negative during local nighttime. For later winter‐summer the correlation is generally low, oscillating about zero throughout the day. For higher magnetic activity the correlation is generally positive throughout the day during equinoxes, dropping below zero for about 3 hours around local sunrise. A similar result holds for late winter‐summer. However, early winter‐summer only shows significant positive correlation during local afternoon hours. A study of equinoctial and winter‐summer geomagnetically conjugate storm effects shows that while equinoctial storm effects can occur simultaneously in both hemispheres, the seasonal differences between winter and summer storms tend to dominate during solstice storms. Local winter nighttime variations in total electron content appear to occur simultaneously in the summer hemisphere at the magnetically conjugate station for high levels of magnetic activity, but not for low levels of magnetic activity.
Three‐dimensional structure of ionospheric currents 2. Currents caused by semidiurnal tidal winds
Authors: Takeda Masahiko , Maeda Hiroshi
Published: February 2008

Ionospheric three‐dimensional currents caused by semidiurnal tidal winds are examined by a magnetic field line coordinate system, assuming infinite parallel conductivity. Electrostatic potential generated by (2,2) tidal mode is mainly distributed in the low‐latitude region, compared with that by (2,4) mode. Height integrated currents obtained by using the authors' assumed wind field are too strong and not similar to a normal Sq current system, unlike that of (1,−2) mode. Therefore these currents do not seem to flow normally, but their structure resembles that of equatorial counterelectrojet in the afternoon, and their variation may be one of the causes of day‐to‐day changes in Sq currents.
What causes the warp in the heliospheric current sheet?
Authors: Wilcox John M. , Scherrer Philip H.
Published: February 2008

Thomas and Smith [1980] give an excellent description of the observations of the interplanetary magnetic field by the spacecraft Pioneer 10 and 11. Our purpose in this note is to discuss one aspect of their interpretation of their observations.

They suggest that the fast solar wind streams associated with interaction regions may move the current sheet to higher heliographic latitudes. We have recently shown [Wilcox et al., 1980] that observations of the interplanetary magnetic field polarity in early 1976 obtained at several locations in the heliosphere at Helios 1, Helios 2, and earth show a rather detailed agreement with a warped heliospheric current sheet calculated from the observed photospheric magnetic field using a potential field method. It appears that at least in early 1976 the observations of the warped heliospheric current sheet are adequately explained using the observed photospheric magnetic field, and it is therefore not necessary to postulate that fast streams associated with interaction regions may move the current sheet to higher heliographic latitudes.
Auroral electron beams: Stability and acceleration
Authors: Kaufmann R. L. , Ludlow G. R.
Published: February 2008

Electron beams are identifiable groups of electrons that occasionally are seen streaming along the magnetic field over active auroral arcs. High‐energy beams appear at the outer edges of the plateaus in distribution functions. Low‐energy beams are imbedded well within a broad distribution function and usually are seen when the rocket is near the edge of an arc. The present analysis shows that the observed distribution functions containing low‐energy beams are unstable to upper hybrid waves in the immediate vicinity of the rocket. The most unstable waves have growth lengths and perpendicular wavelengths of 0.3 km. Electrostatic whistlers with wavelengths and growth lengths of several kilometers may grow well above the rocket. These growth lengths are too long to destroy the observed beams through quasilinear or nonlinear processes. It is concluded that electrons are accelerated in a parallel electric field associated with closed or U‐shaped equipotentials. The electrons become unstable during or after acceleration and form plateaus plus residual high‐energy beams. Low‐energy beams involve acceleration of cold ionospheric electrons that enter the acceleration region above open equipotentials at the edge of an arc.
Remote sensing of muon variation spectra and interplanetary inhomogeneities
Authors: El‐Raey M. , Gaber S.
Published: February 2008

The similarity between the general remote sensing integral equation and Dorman's integral equation relating secondary to primary muon variation spectra has been pointed out and exploited. Primary muon variation spectra and parameters of interplanetary field inhomogeneities are remotely sensed by a nonlinear inversion technique, using two different coupling functions. Results are compared to those obtained by the spectrographic technique and interpreted in terms of interplanetary field fluctuations. Based on relationships among kernels of the integral equation, optimization of location and orientation of measuring stations become possible.
Properties of whistler mode waves between 0.3 and 1.0 AU from Helios observations
Authors: Beinroth H. J. , Neubauer F. M.
Published: February 2008

A study of magnetic fluctuations in the solar wind in the distance range from 0.3 to 1 AU and the frequency range 4.7 Hz‐2.2 kHz by the Technical University of Braunschweig search‐coil magnetometer experiment onboard Helios 1 and 2 during the time intervals from December 1974 to April 1975 for Helios 1 and January 1976 to May 1976 for Helios 2 yields the following results: (1) Near 1 AU electromagnetic wave modes are restricted to frequencies less than 220 Hz for 99% of the time. Inside 0.5 AU the waves are restricted to less than 470 Hz in 94% of all cases. (2) For a spectral density [P(f)]1/2; ∝ fα with the quantity √P measured in nT/√Hz the spectral index α varies between −1.4 and −2.0 with a most probable value of −1.7 and a slight tendency toward steeper spectra towards the sun. (3) No clear correlation between simple plasma parameters and magnetic field magnitude F on one side and spectral densities on the other side is found. The proportionality between spectral density and F is simply attributed to the radial variation. (4) High wave intensities occur in the vicinity of stream interfaces with a decrease in wave intensity with increasing distance from the stream interaction region. (5) Magnetic field energy density above 4.7 Hz varies between 5 × 10−18 erg/cm³ and 10−14 erg/cm³ with a maximum of occurrence of 5 × 10−17 erg/cm³ near 1 AU and 1.6 × 10−15 erg/cm³ near 0.3 AU. The values are therefore orders of magnitude below the total magnetic field energy density. (6) The fluctuations are tentatively interpreted as locally generated whistler waves.
Observations of the Ca+ twilight airglow from intermediate layers of ionization
Authors: Tepley C. A. , Mathews J. D. , Meriwether J. W. , Walker J. C. G.
Published: February 2008

Application of complementary optical and incoherent scatter radar techniques has detected the presence of Ca+ in lower thermospheric intermediate layers over Arecibo. The altitude distribution and density of the calcium ion is inferred from the variation of twilight resonant scattering with solar depression angle while the Arecibo 430Mhz radar measured electron densities. Comparison between the Ca+ and electron column densities indicates that the composition of low‐altitude intermediate layers was 2% Ca+. This value is consistent with both rocket mass spectrometer measurements and with the relative concentration of calcium expected for meteoric debris. These results have implications regarding both possible nighttime tropical E region ionization sources and metal ion circulation in the tropical thermosphere.
Determination of Jupiter's electron density profile from plasma wave observations
Authors: Gurnett D. A. , Scarf F. L. , Kurth W. S. , Shaw R. R. , Poynter R. L.
Published: February 2008

This paper summarizes the electron density measurements obtained in the Jovian magnetosphere from the plasma wave instruments on the Voyager 1 and 2 spacecraft. Three basic techniques are discussed for determining the electron density: (1) local measurements from the low‐frequency cutoff of continuum radiation, (2) local measurements from the frequency of upper hybrid resonance emissions, and (3) integral measurements from the dispersion of whistlers. The limitations and advantages of each technique are critically reviewed. In all cases the electron densities are unaffected by spacecraft charging or sheath effects, which makes these measurements of particular importance for verifying in situ plasma and low‐energy charged particle measurements. In the outer regions of the dayside magnetosphere, beyond about 40 RJ, the electron densities range from about 3 × 10−3 to 3 × 10−2 cm−3. On Voyager 2, several brief excursions apparently occurred into the low‐density region north of the plasma sheet with densities less than 10−3 cm−3. Approaching the planet the electron density gradually increases, with the plasma frequency extending above the frequency range of the plasma wave instrument (56 kHz, or about 38 electrons cm−3) inside of about 8 RJ. Within the high‐density region of the Io plasma torus, whistlers provide measurements of the north‐south scale height of the plasma torus, with scale heights ranging from about 0.9 to 2.5 RJ.
Standing Alfvén wave current system at Io: Voyager 1 observations
Authors: Acuña M. H. , Neubauer F. M. , Ness N. F.
Published: February 2008

The enigmatic control of the occurrence frequency of Jupiter's decametric emissions by the satellite Io has been explained theoretically on the basis of its strong electrodynamic interaction with the corotating Jovian magnetosphere leading to field‐aligned currents connecting Io with the Jovian ionosphere. Direct measurements of the perturbation magnetic fields due to this current system were obtained by the Goddard Space Flight Center (GSFC) magnetic field experiment on Voyager 1 on March 5, 1979, when it passed within 20,500 km south of Io. An interpretation in the framework of Alfvén waves radiated by Io leads to current estimates of 2.8 × 106 A. A mass density of 7400–13,600 proton mass units per cm³ is derived, which compares very favorably with independent observations of the torus composition characterized by 7–9 proton mass units per electron for a local electron density of 1050–1500 cm−3. The power dissipated in the current system may be important for heating the Io heavy ion torus, inner magnetosphere, Jovian ionosphere, and possibly the ionosphere or even the interior of Io.