bluuebunny/crossref_metadata_2025 huggingface dataset:
Correlated electric field and low‐energy electron measurements in the low‐altitude polar cusp
Authors: Kintner P. M. , Ackerson K. L. , Gurnett D. A. , Frank L. A.
Published: February 2008

Correlated electric field and low‐energy electron measurements are presented for two passes of Hawk‐eye 1 through the south polar cusp at 2000‐km altitude during local morning. In one case the electric field reversal coincides with the boundary of detectable 5.2‐keV electron intensities and the equatorward boundary of the cusp. In the other case the electric field reversal and the 5.2‐keV electron trapping boundary coincide, but the equatorward edge of the cusp as determined from the presence of 180‐eV electron intensities is 5° invariant latitude equatorward of the electric field reversal. We conclude that in the second case, electron intensities associated with the polar cusp populate closed dayside field lines, and hence the corresponding equatorward edge of these electron intensities is not always an indicator of the boundary between closed dayside field lines and polar cap field lines.
Comparison of satellite self‐contamination experiments and scattering return flux calculations
Authors: Scialdone John J. , Hedin A. E. , Rice Carl J.
Published: February 2008

Gaseous emissions from a spacecraft modify the orbital environment and degrade the observations of distant radiation sources. These emissions also provide contamination fluxes induced by self‐scattering and scattering with ambient particles. Experiments were carried out on the orbiting Atmosphere Explorer D satellite (AE‐D) to verify the calculated return fluxes of a neon source. Known rates of neon were emitted in the direction of the velocity vector on command from the MRMU (molecular return measurement unit). At 250 km the neutral mass spectrometer indicated a total neon return flux of 2.46 × 10−2 times the emitted flux. The calculated fraction was 1.23 × 10−2, including 9.14 × 10−3 for the ambient scatter and 3.54 × 10−3 for the altitude‐independent self‐scatter. The pressure gages indicated pressures less than 7 × 10−6 torr at altitudes from 161 to 210 km. The maximum pressure for 161‐km orbit was calculated as 7.4 × 10−7 torr.
Longitudinal extension of the substorm‐associated long‐period hydromagnetic waves
Authors: Wang C. S. , Lee T. , Kim J. S.
Published: February 2008

A recent study has shown that long‐period hydromagnetic (hm) waves (T ∼ 30 min) exist at middle‐ and low‐latitude stations prior to and/or simultaneous with the polar substorm. The latitude‐independent characteristic of waves has led to the suggestion that the plasmasphere oscillates as a resonant cavity (Wang et al., 1977) and this makes it necessary to examine their longitudinal extension to see if their activities are spatially localized. Magnetograms recorded at 19 stations in an east–west chain situated along a geomagnetic latitudinal circle of about 49° in the northern hemisphere were collected for the study. The following results have been found. (1) For waves occurring prior to the substorm of a period T ∼ 30 min the longitudinal range is about 240°, starting clock‐wise from the 0400 meridian to the noon meridian. It is likely that this prestorm activity covers a much larger spatial extent than that of a polar substorm. (2) For waves with a longer period, of the order of 2 hours, which occurred simultaneously with the substorm a much smaller longitudinal range (∼90°–100°) is observed in the nightside. This localized character of long‐period hm waves suggests that it is a result of magnetotail oscillations. (3) The disturbed magnetic field sometimes exhibits sector structure.
The effect of negative ions on collision‐dominated Thomson scattering
Authors: Mathews John D.
Published: February 2008

An expression for the collision‐dominated Thomson scatter power spectrum is derived from the fluid or continuum equations. This expression includes the possibility of multiple ion species of arbitrary charge. The total power and power spectral shape are investigated for scattering from a plasma composed of negative ions, positive ions, and electrons. The results indicate that total scattered power is modified by negative ion presence and that a limited amount of information about the negative ion content of the ionospheric D region may be found from Thomson scatter experiments. In particular, negative ions are found to increase the width of the power spectrum as would increased ion temperature or decreased ion neutral collision frequency. Spectra over a wide range of parameter values display the property of ‘scaling’: however, this effect may be sorted out such that negative ion presence is deduced from anomalously small ion‐neutral collision frequencies.
Ozone measurements in the stratosphere, mesosphere, and lower thermosphere during Aladdin 74
Authors: Weeks L. H. , Good R. E. , Randhawa J. S. , Trinks H.
Published: February 2008

Four different rocket techniques provided data on ozone at Wallops Island, Virginia, during the Aladdin 74 program. The entire altitude region from 19 to 108 km was covered, the different techniques providing overlapping profiles that included the afternoon of June 29 and the early morning of June 30 (local time). There were systematic differences between the chemiluminescent sonde and UV absorption techniques, the sonde giving the greater densities. These differences became larger with increasing altitude up to the maximum common altitude, 62 km. Both airglow and absorption techniques indicate a density minimum at 81 km of 1–3 × 107 cm−3 and agree within the experimental errors in the overlap region down to 72 km. Above 90 km the airglow experiment shows a relatively constant but structured density profile. The mass spectrometer measured a considerably higher ozone density at 90 km with a rapidly decreasing scale height up to 108 km. The experimental results are compared with photochemical‐transport models.
Ionospheric effects of the gravity wave launched by the September 18, 1974, sudden commencement
Authors: Roble R. G. , Richmond A. D. , Oliver W. L. , Harper R. M.
Published: February 2008

A sudden commencement of a geomagnetic storm occurred at 1434 UT on September 18, 1974. A traveling ionospheric disturbance was detected about an hour later by the incoherent scatter radar at Millstone Hill, Massachusetts (42.6°N, 71.5°W), and still later by the incoherent scatter radar at Arecibo, Puerto Rico (18.3°N, 66.7°W). Measurements of the vertical distribution of electron temperature, ion temperature, and electron density made during the passage of the disturbance at both stations showed significant perturbations in comparison to the geomagnetic quiet time values obtained on the previous day. We calculated characteristics of the thermospheric gravity wave from a time‐dependent dynamic model of the thermosphere. The wave source is assumed to be enhanced electric currents and particle heating over the polar cap region. The gravity wave generated by the impulsive heating propagates equatorward, and its characteristic structure changes as it progresses to lower latitudes. The calculated neutral temperature and wind perturbations are added to the quiet time variations in a diurnal model of the mid‐latitude ionospheric F region to calculate the time‐dependent properties of the ionosphere during the passage of the wave over both incoherent scatter radar stations. By requiring agreement between the calculated and observed ionospheric structure we estimated the magnitude of the gravity wave energy source. For the event on September 18, 1974, we obtained reasonably good agreement between the calculated and observed ionospheric structures for a total energy input of about 2 × 1015 J, occurring over a period of 3 hours.
On the poleward expansion of ionospheric absorption regions triggered by sudden commencements of geomagnetic storms
Authors: Brown R. R.
Published: February 2008

A review of riometer data from the south pole (74.2° invariant latitude) for a 7‐year period (1967–1973) indicates the occurrence of sc‐triggered poleward expansions of auroral absorption regions. For 15 such events the average AE index in the hour before the sc's was twice as large as that for 30 sc's that did not trigger substorm events at auroral latitudes. This result indicates that the triggering of substorms involves the enhancement of processes already in progress by the compression of the magnetosphere.
The winter polar ionosphere
Authors: Whitteker J. H. , Shepherd G. G. , Anger C. D. , Burrows J. R. , Wallis D. D. , Klumpar D. M. , Walker J. K.
Published: February 2008

An unusually comprehensive set of ionospheric, particle, optical, and magnetic measurements were made during simultaneous Isis 1 and 2 passes on December 14, 1971, at about 0520 and 0720 UT, when the northern magnetic polar ionosphere was in darkness to almost the maximum possible extent. During the first part of the day, magnetic activity was very low, but substorm activity began between the two sets of observations, and a westward surge is seen in the optical data of the second set. The results show that while particle precipitation plays a role in controlling the density of the F layer and the topside ionosphere, the details of the horizontal drift associated with magnetospheric convection must also be important. Before the substorm activity there was a region of low F layer density in the central polar cap which must have been in a stagnant part of the convection pattern. This region was subsequently filled in with ionization, evidently by convection that penetrated more poleward than before. In the topside the height of transition between O+ and light ions was found to be much lower in winter than in summer, and it was found to be lower equatorward of the polar cap boundary than in the polar cap. A detailed correspondence between electron precipitation and optical emissions was found.
The Tordo 1 Polar Cusp Barium Plasma Injection Experiment
Authors: Wescott E. M. , Stenbaek‐Nielsen H. C. , Davis T. N. , Jeffries R. A. , Roach W. H.
Published: February 2008

In January 1975, two barium plasma injection experiments were carried out with rockets launched from Cape Parry, Northwest Territories, Canada, into the upper atmosphere where field lines from the dayside cusp region intersect the ionosphere. One experiment, Tordo 1, took place near the beginning of a worldwide magnetic storm. It became a polar cap experiment almost immediately as convection perpendicular to B moved the fluorescent plasma jet away from the cusp across the polar cap in an antisunward direction. Convection across the polar cap with an average velocity of more than 1 km/s was observed for nearly 40 min until the barium flux tubes encountered large E fields associated with a poleward bulge of the auroral oval near Greenland. Prior to the encounter with the aurora near Greenland there is evidence of upward acceleration of the barium ions while they were in the polar cap. The three‐dimensional observations of the plasma orientation and motion give an insight into convection from the cusp region across the polar cap, the orientation of the polar cap magnetic field lines out to several earth radii, the causes of polar cap magnetic perturbations, and parallel acceleration processes.
A fluid description of a hot collisionless plasma and limits to the double‐adiabatic approximation associated with the presence of Birkeland currents
Authors: Hruška A.
Published: February 2008

The large‐scale structure of a slowly moving plasma is discussed, a modified Chew‐Goldberger‐Low approximation being used. The double‐adiabatic relations for pressure components fail if there is a nonzero current flowing perpendicularly to the binormals to field lines.
Spectrum of mean free paths near Earth in the solar cosmic ray event of April 29, 1973
Authors: Palmer I. D. , Zwickl R. D. , Webber W. R. , McDonald F. B.
Published: February 2008

The Ground Level Event of April 29, 1973, was recorded by Pioneer 11 at 1.07 AU and 6° west of the earth‐sun line. The anisotropy and the omnidirectional intensity of protons between 1 MeV and a few GeV, and of relativistic electrons, were consistent with (1) an impulsive‐like injection of electrons and 20‐ to 56‐MeV protons, (2) a long‐lived injection of 1‐MeV protons lasting ≈13 hours, (3) mean free paths near 1 AU of 0.35 AU at a few GeV and 1‐MeV proton energies, but only 0.1 AU at 10‐ to 50‐MeV proton energies, and 0.03 AU for 1‐MeV electrons. The rigidity dependence of λ11 is anomalous in the 1‐ to 50‐MeV proton region, according to current scattering theory. By invoking a radial dependence in κ(r) that is radically different for 1‐MeV and 10‐ to 50‐MeV protons, the anomaly can be reduced but not removed. Although an azimuthal dependence may be inherent in the results, observations of B, V, and σy² do not discount the anomalous λ11(R) dependence. A possible interpretation, at least for protons, is that as rigidity is decreased, propagation changes from diffusive to a ‘supercoherent’ mode where focusing by the diverging field is dominant. However, the small 0.5‐MeV electron mean free path does not fit the extension of such a scheme to lower rigidities. Finally, later in the event a rapid intensity decrease in 1‐MeV protons reflects a strong spatial gradient across the solar surface, which is due to poor access of particles across magnetic field lines of an ‘open’ region and also possibly across the leading edge of a magnetic cell of opposite polarity.
Quiet‐time plasma irregularities at 1400 km in the cleft region
Authors: Kayser Susan E. , Maier Eugene J. , Brace Larry H.
Published: February 2008

The quiet north polar cleft at 1400 km has been found to contain many small‐scale irregularities in the density of the thermal plasma. Data from the retarding potential analyzer and the cylindrical electrostatic probe on board Isis 2 have shown that these density fluctuations are distributed in a region between 75° and 82° invariant latitude and approximately dawn to dusk. Their presence is interpreted as a signature of the cleft. The low‐latitude edge of this region was not symmetric about noon. The shape and position of the cleft were somewhat influenced by the interplanetary field sector and by season (spring and autumn). Irregularity amplitudes were usually 10% or less, although density changes of a factor of 2 or more have been seen. The typical scale size is 0.7 km. Irregularities were also seen in the superthermal (>20 eV) electrons. However, although the thermal ions and thermal electrons usually fluctuated together, the superthermal electrons fluctuated independently, implying that energy transfer between the superthermal and thermal particles is indirect. Comparison of thermal plasma data with data from other Isis experiments shows that irregularities correlated fairly well with observations of soft particles and auroral optical emissions and not as well with measurements of high‐energy particles. This is an additional indication that the energy source for the thermal irregularities is associated with soft particles and that precipitating high‐energy particles do not drive the thermal plasma at these altitudes. The position of the cleft determined by plasma irregularities thus agrees best with those cleft descriptions derived from low‐energy particle observations.
Harmonic generation of acoustic gravity waves
Authors: Stenflo L. , Dysthe K. B.
Published: February 2008

We have found that a wave at a particular frequency, which is approximately 0.8 times the Brunt‐Väisälä frequency, may play an outstanding role in second‐harmonic generation of acoustic gravity waves.
An analysis of the Venus thermal infrared temperature maps
Authors: Ainsworth J. E. , Herman J. R.
Published: February 2008

We have performed a detailed analysis of the published Venus IR maps and have obtained a number of new results. The global contour map of the average temperature variations in the vicinity of 6120 km reveals the existence of saddle points along the equator at dawn, at noon, and just before sunset. The hot spots observed at 4:30–4:40 A.M. at 65°–68°S latitude appear to be in the vicinity of the coldest region from which the 8‐ to 14‐µm emissions originate. At large earth zenith angles the limb darkening curves show a hump which is attributed primarily to a single patchy haze layer in the vicinity of 6123 km and with a thickness of the order of 3 km. We obtain an average IR source region temperature of 250°K at the equator. At the poles the same altitude region is 8°K cooler.
A hydromagnetic dynamo of the atmosphere
Authors: Volland H. , Grellmann L.
Published: February 2008

Conventional dynamo theories start from wind fields which are considered as external forces independent of the ionospheric plasma. These dynamos are called kinematic dynamos. Coupling between the neutral wind and the ionospheric plasma in a self‐consistent manner results in a hydromagnetic dynamo. In this paper a theory of a hydromagnetic dynamo of the geomagnetic Sq current is developed assuming a thin shell model with constant elements of the electric conductivity tensor. Coupling between neutral gas and plasma is described by the Ampere force j × Bo (j being electric current density and Bo geomagnetic field) which depends not only on the velocity difference between neutrals and plasma (ion drag) but also on the electric polarization field. The electric polarization field includes a source free component which is not negligibly small at dynamo layer heights, so that the electric field cannot be represented by an electric potential. This theory leads to a modified Laplace equation of tidal theory which can be solved numerically. Calculations are presented for the diurnal and the semidiurnal tidal wave modes. Their equivallent depths, their vertical wavelengths, and their attenuation factors are discussed as functions of a plasma parameter δ which is proportional to a Cowling conductivity. The horizontal structures of pressure and electric current of the dominant symmetric tidal waves are determined for different values of δ representing the lower atmosphere (δ = 0), the dynamo region (δ ≃ 1), and F layer heights (δ ≃ 10). It is shown that waves with positive equivalent depths at δ = 0 are heavily attenuated at δ > 1 and drastically change their horizontal structure there. On the other hand, waves with negative equivalent depths at δ = 0 are only weakly affected by the Ampere force. From our calculations we suggest that tidal wave theory at thermospheric heights should be reconsidered taking into account electric coupling between the modes. In particular, we predict that the semidiurnal (2, 2) wave so far considered as the dominant semidiurnal mode above about 200 km height may have lost its significance and may in fact be replaced by the symmetric (2, ‐3) wave.
Microturbulence and the solar wind 1. Analytical results for fast mode instability growth rates
Authors: Schwartz Steven J.
Published: February 2008

Analytical expressions for the growth rates of unstable low‐frequency ‘fast’ modes are derived here in the low‐frequency, low‐βi limit for a plasma obeying classical linear transport theory. The results indicate that at the onset of instability (∼10 Rs from the sun) the first growing mode in the solar wind has a frequency of ∼0.1 times the proton gyrofrequency and propagates at an appreciable angle to the background magnetic field. Substantial inhomogeneity is required for the growth to overcome competing processes. These modes may have consequences for thermal conduction, proton and helium heating, the observable wave spectrum, and other facets of solar wind theory, though considerable additional theory will be required.
The magnetopause energetic electron layer, 1. Observations along the distant magnetotail
Authors: Baker D. N. , Stone E. C.
Published: February 2008

Observational features of the magnetopause energetic electron layer have been studied along the distant magnetotail (− 10 RE ≳ XSM ≳ −40 RE) using California Institute of Technology instrumentation aboard Imp 8. On the basis of 101 layer crossings obtained on 60 spacecraft orbits it is concluded that the layer of electrons (E ≳ 200 keV) was present on 97% of the magnetopause crossings during 1973–1975. The inner edge of the layer is typically found to correspond to the magnetopause boundary as determined from concurrent plasma analyzer and magnetometer data. Energetic electrons within the layer are observed to be persistently streaming tailward along local magnetosheath field lines. Pitch angles of electrons along the dusk magnetopause are often restricted to values of ≲40°, whereas along the dawnside of the tail somewhat larger pitch angles are normally seen. Differential energy spectra of electrons in the layer are typically fit by power law forms with spectral indices 2 ≲ γ ≲ 4, and intensity enhancements often extend to energies of ≳1 MeV. Average directional intensities (E ≳ 200 keV) flowing through the layer are remarkably constant, ranging from ∼1 to ∼5 (cm−2 s−1), but apparent ‘hot spots’ are found along the dawn flank of the magnetotail. It is suggested that these hot spots are near a source region for energetic electrons.
Cooling of slow solar wind protons from the Helios 1 Experiment
Authors: Eyni Menashe , Steinitz Raphael
Published: February 2008

In a recent survey of initial results of the Helios experiment, Rosenbauer et al. [1977] suggested that there could be two types of solar wind, characterized by a ‘slow’ and a ‘fast’ component. This idea is based mostly on two distinct ranges of observed flow speed and on a preliminary analysis of data showing that the protons in the slow component expand nearly isothermally.

Contrary to this result, we have found from the same data that the slow protons in the solar wind do clearly exhibit cooling, compatible with adiabatic expansion. For the analysis we used the data published by Rosenbauer et al. [1977] and treated them as we did in our previous analysis of the Mariner 2 data [Eyni and Steinitz, 1978]. The essence of our analysis is twofold: (1) the reduction of the strong dependence of temperature T on velocity u by the definition of a reduced temperature τ ≡ T/u2 and (2) the choice of samples which are as uniform as possible in velocity u and in (distance) normalized density n.
Quiet time observations of equatorially trapped megaelectronvolt radiation belt ions with nuclear charge Z ≧ 4
Authors: Spjeldvik Walther N. , Fritz Theodore A.
Published: February 2008

The equatorial satellite Explorer 45 was equipped with a heavy ion solid state ion detector system in which four of the detector channels were sensitive to heavy ions like oxygen ions but not to protons or helium ions. Of these, only the lowest energy passband covering 1.82–4.8 MeV per ion for oxygen showed sufficiently high count rates to give meaningful statistics in a single satellite pass through the radiation belts. All measurements were carried out close to the equatorial plane, 1 ≤ B/B0 ≲ 1.4 at L shells below the spacecraft apogee of 5.24 RE, and the scope of this report is restricted to geomagnetically quiescent conditions during the period June 1–15, 1972. Fluxes of these ions are interpreted as oxygen ions and are found to maximize in the L shell range 3–3.5 with a peak equatorially mirroring flux of 0.38 ions/cm² s sr keV. This peak is not as sharply confined in L shell as the one previously reported for helium ions.
The electric field of a time‐dependent Alfven‐type neutral sheet
Authors: Murphy Charles H.
Published: February 2008

The behavior of the total electric field in an Alfven‐type neutral sheet is considered for the time‐dependent case. By assuming that the characteristics of the neutral sheet can be represented by an effective capacitance and inductance, a differential equation describing the behavior of the electric field is derived. The parameters for the neutral sheet system are its magnetic field strength, plasma density, and width. The numerical solution of this equation is found for two cases, one where the energy source of the neutral sheet is removed and the electric field decays away and a second where energy is pumped into the system as a pulse. In both cases the characteristic time scale of the electric field changes was of the order of the transit time of an Alfven wave across the system. This time constant agrees fairly well with the time constants of the earth's magnetotail and magnetopause but is shorter than what is commonly accepted for solar flares. The case where the neutral sheet is subjected to a pulse in energy from an external source shows a response that depends on the ratio of the time constant of the neutral sheet to the rise time of the pulse. This ratio, which measures the importance of the inductive component of the electric field, characterizes the different response of the neutral sheet to an external energy input.
Neutral thermospheric winds deduced above Millstone Hill, 1. Mathematical model, uncertainties, and representative results
Authors: Emery Barbara A.
Published: February 2008

Incoherent scatter radar measurements from Millstone Hill have been combined with mass spectrometer/incoherent scatter (MSIS) model neutral densities to derive exospheric temperatures and the neutral wind component at 300 km parallel to the magnetic field. These quantities have been used to determine the neutral horizontal pressure gradients and winds in a dynamical model of the thermosphere above the radar site. The model can be extended in latitude with further assumptions to find the vertical velocity via the continuity equation. The uncertainties involved in these neutral wind determinations are examined. Representative summer and winter results are presented and compared with results of calculations in which the pressure gradients were taken from the global Ogo 6 and MSIS models. Zonal velocities derived from the Millstone Hill results were found to be larger than those for the empirical models because the zonal pressure (diurnal temperature) gradients were much steeper over parts of the day.
A case study of the aurora, high‐latitude ionosphere, and particle precipitation during near‐steady state conditions
Authors: Winningham J. D. , Anger C. D. , Shepherd G. G. , Weber E. J. , Wagner R. A.
Published: February 2008

An Isis 2 pass is singled out for a detailed examination of the particle fluxes, optical emissions, and ionospheric parameters observed during a quiescent period (late recovery) between two substorms. This pass was chosen because it was part of a coordinated data acquisition period between the Air Force Geophysics Laboratory (AFGL) Airborne Ionospheric Observatory, Isis 2, and DMSP (Defense Meteorological Satellite Program). As a result, both long‐duration measurements (aircraft) and transient, snapshot (spacecraft) data are available. This allows, on a macroscopic level, the separation of space and time effects.

On the basis of the joint data set it was established that the latitudinal morphology observed by the satellite is basically spatial in nature. It is concluded that the observed particle fluxes are most easily understood in terms of precipitation from the quiet time plasma sheet without intervening acceleration. The observed optical emissions and ionospheric parameters are found to be in good qualitative and quantitative agreement (within experimental error) with the electron fluxes, although establishment of this point has required careful determination of the viewing direction of the optical instruments, removal of scattered light (albedo) from underlying cloud and snow, and consideration of the effects of photon‐counting statistics on contour plots of the optical data.
Collisionless effects on the spectrum of secondary auroral electrons at low altitudes
Authors: Papadopoulos K. , Rowland H. L.
Published: February 2008

It is shown by use of particle computer simulations that Collisionless interactions, due to energetic electron precipitation in the auroral zones, can be responsible for the break from the E−α (2.2 < α < 2.5) dependence of the secondary electron spectrum expected on the basis of collisional models, even at very low altitudes (< 180 km).
Low‐altitude measurements of precipitating protons, alpha particles, and heavy ions during the geomagnetic storm on March 26–27, 1976
Authors: Scholer M. , Hovestadt D. , Hartmann G. , Blake J. B. , Fennell J. F. , Gloeckler G.
Published: February 2008

During the geomagnetic storm of March 16–17, 1976, observations were made of precipitating protons, alpha particles, and heavy ions by two counter telescopes aboard the low‐altitude S3‐2 satellite. These observations are presented in this paper and their significance discussed. Briefly, a two‐zone precipitation region is observed on the nightside, at L ≈ 2.7 and L ≈ 4.0 with an α/p ratio ∼8 × 10−3 in the low‐latitude region and ∼9 × 10−4 at higher latitude at 0.4 MeV/nucleon. The heavier ions, CNO nuclei, are seen in the low‐latitude zone with a CNO/α ratio of ∼5.6 × 10−2 at 0.25 MeV/nucleon.
Observations of plasma depletion in the magnetosheath at the dayside magnetopause
Authors: Crooker N. U. , Eastman T. E. , Stiles G. S.
Published: February 2008

In a set of 17 low‐ to mid‐latitude crossings of the dayside and near‐dayside magnetopause, Imp 6 plasma measurements show 11 cases of decreases in magnetosheath density just outside the boundary which are consistent with plasma depletion owing to magnetic flux tube compression as the field becomes draped against the magnetopause. Pressure anisotropies in the sense p⊥ >p∥ are a predicted result of the plasma depletion and field compression, and such anisotropies are observed. Application of the mirror instability criterion, which predicts growth of slow mode magnetoacoustic waves for values of p⊥/p∥ greater than a critical value, suggests that dayside magnetosheath plasma is usually unstable. One of the seventeen cases shows long‐period waveforms in the 100‐s density data that are 180° out of phase with simultaneous waveforms in the magnetic field strength. We interpret these data as the signature of slow mode magnetoacoustic waves.
Geomagnetic pulsation signals and hourly distributions of IMF orientation
Authors: Greenstadt E. W. , Olson J. V.
Published: February 2008

Hourly distributions of the angle θXB=arccos (X · B), where X is the solar ecliptic earth‐sun axis and B is the interplanetary magnetic field (IMF), have been compared with hourly Pc 3 and Pc 4 signal activity at Calgary for 198 hours in September, October, and November 1969. Hours whose distributions were concentrated above or below θXB = 50° were correlated with a clear separation of inactive from active micropulsation intervals. The correlation was stronger for the Pc 3 than for the Pc 4 band, and hours with significant fractions, say 10–20% of their θXB distributions below 30°, corresponded particularly well with high amplitudes of micropulsation signals. Signals in the Pc 3 period range on the ground can therefore be used as a crude monitor of certain extremes of IMF orientation.
Auroral origin of medium scale gravity waves in neutral composition and temperature
Authors: Chandra S. , Krankowsky D. , Lämmerzahl P. , Spencer N. W.
Published: February 2008

The kinetic temperature and neutral composition data obtained from the Aeros B neutral atmosphere temperature experiment and the neutral and ion mass spectrometer show spatial structures characteristic of medium scale gravity waves with a wavelength in the range of several hundred kilometers. These waves are associated with auroral activity, and their spatial structure reflects the time history of the auroral electrojet. The medium scale gravity waves tend to propagate to mid‐latitudes on the nightside. On the dayside their range is limited to high latitudes. Gravity waves are carriers of auroral energy to middle and low latitudes where they may cause irreversible changes in temperature via viscous dissipation. Since auroral activity occurs frequently, it is suggested that this energy reaches the mid‐latitude region of the thermosphere much more frequently than is indicated by planetary magnetic indices.
The seasonal‐latitudinal variation of exospheric helium from He 584‐A Dayglow emissions
Authors: Anderson D. E. , Meier R. R. , Weller C. S.
Published: February 2008

The transport of solar 584‐A photons through the spherical, asymmetric helium geocorona is discussed in detail. The analysis shows that with a favorable geometry and a moderately optically thick atmosphere it is possible to determine the helium abundance from dayglow observations without knowing the incident solar flux or the instrument calibration. Comparison of theoretical intensities with 584‐A airglow observations made from the STP 72‐1 satellite shows that recent satellite‐drag and mass spectrometer‐incoherent scatter empirical models predict helium densities which have seasonal‐latitudinal dependences which approximate the airglow‐determined densities in shape, but in general are high by as much as a factor of 2 in absolute density. Airglow‐determined densities in the polar regions suggest a decrease in the exospheric helium density relative to the empirical model estimates.
Energetic particle precipitation into the high‐latitude ionosphere and the auroral electrojets, 1. Definition of electrojet boundaries using energetic electron spectra and ground‐based magnetometer data
Authors: Winningham J. D. , Kawasaki Koji , Rostoker Gordon
Published: February 2008

Data from the University of Alberta meridian line of magnetometers are utilized to define the poleward and equatorward borders of the eastward electrojet in the evening sector. Soft particle spectrometer data from the Isis 2 polar‐orbiting satellite are organized in the framework of the eastward electrojet for cases where the satellite orbital path took it close to the meridian line of ground‐based magnetometer stations. It is shown that in the late evening hours the equatorward border of the eastward electrojet coincides with the equatorward edge of the central plasma sheet (cps) as marked by electrons of E >1 keV. The boundary plasma sheet (bps) spans the poleward portion of the eastward electrojet and a region up to a few degrees poleward of the eastward electrojet where the westward electrojet is known to penetrate on average. A level shift in the Y′ component of the ground magnetometer data exists across the portion of the electrojet region marked by bps; this level shift is interpreted as net upward field‐aligned current flow. In the hours between noon and dusk the correlation between the equatorward border of the eastward electrojet and the equatorward edge of the cps deteriorates completely, and the magnetic latitude profiles exhibit anomalous behavior. This problem will be discussed in paper 2 of this series. On the basis of this study we conclude that in the evening sector the cps is threaded by field lines carrying current flowing into the ionosphere, while the bps is threaded by field lines carrying current flowing out of the ionosphere. The electric field transition from the auroral oval to the polar cap must occur in the heart of the bps under average conditions.
Propagation characteristics of low‐latitude whistlers
Authors: Ondoh T. , Kotaki M. , Murakami T. , Watanabe S. , Nakamura Y.
Published: February 2008

Whistler observations at Okinawa (geomagnetic latitude 15.3°N), Japan, have been carried out as one of the IMS projects since October 1974. Whistlers and their echoes following Eckersley's law have been observed mainly during winter night. The diurnal variation of whistler occurrence at Okinawa has no evening peak, while that at mid‐latitudes has an evident peak. This may be due to the evening D region absorption resulting from the late sunset in the subtropical region, a lack of field‐aligned ducts, and the whistler absorption by the ion‐electron Coulomb collision in the ionospheric equatorial anomaly. The whistler dispersion at Okinawa varies, on the average, from 20 s1/2 in the evening to 9 s1/2 in the dawn and has little seasonal variation. Observed dispersions fit well‐computed ones along the International Geomagnetic Reference Field (IGRF) line passing through Okinawa for the Chapman distribution of the electron density. The IGRF line enters into an active area of thunderstorms east of Java island. The whistler activity at Okinawa is less than about one fifth of that at Kagoshima (20.7°N) and increases with increasing local geomagnetic activity. Most durations of whistler activities (>5/min) at Okinawa are no more than 2 hours which are close to theoretical lifetimes of field‐aligned irregularities over Okinawa. Whistlers at Okinawa are associated with weak ionospheric irregularities of foEs=2.0‐2.4 MHz. These suggest ducted propagation of low‐latitude whistlers along field‐aligned irregularities. The ducted propagation of low‐latitude whistlers and duct formation models which function effectively at night and in equatorial region are discussed, especially on the ionization enhancement factor for trapping whistlers in field‐aligned irregularity and the electrostatic field in the irregularity. Some results of direction finding of whistlers at Okinawa support the ducted propagation of low‐latitude whistlers.
A correlative study of magnetic flux transfer in the magnetosphere
Authors: Holzer Robert E. , Slavin James A.
Published: February 2008

The applied magnetic flux (Φap) of the southward component of the interplanetary magnetic field in GSM coordinates (Bz−) which impinges upon the sunward magnetopause has been compared with the time integral of the auroral AL index during 56 intervals within a 3‐month period in 1969 when interplanetary records from Heos 1 and Explorer 35 were available. The periods of magnetic activity chosen were those for which Bz > 0 and AL < 20 γ at the beginning and end of the interval. It was found that for these intervals, ∫ AL dt ∝ Φap with a correlation coefficient of 0.94. In addition, the empirical relationships between magnetic flux transfer, the applied southward flux, and ∫ AL dt arrived at by Holzer and Slavin (1978) on the basis of expansions and contractions of the forward magnetosphere observed with Ogo 5 are reexamined and improved. With these expressions describing the bulk rates of magnetic flux transfer within the magnetosphere a lower limit of 0.2±0.1 on the local reconnection efficiency at the magnetopause is calculated.
Mesopause temperature from the [NO+ · H2O]/[NO+] ratio
Authors: Chakrabarty Purobi , Chakrabarty D.K.
Published: February 2008

On the basis of the present status of positive ion chemistry, reliable laboratory measurements of reaction rates, and in situ measurements of electron density and positive ion composition an attempt has been made to estimate the atmospheric temperature at the mesopause region for different geophysical conditions. It is found that at high‐latitude mesopause, when the ionosphere is quiet, the temperature is about 130 K during summer and about 200 K during spring, consistent with the Cira (1972) model. During winter anomaly, a temperature larger by about 70 K than that of the normal level is estimated, also in agreement with the observation. But at mid‐latitude during quiet conditions a temperature unexpectedly higher by about 60 K than its normal value is obtained from the ion composition data of August 12, 1976, at Wallops Island.
DMSP calibration
Authors: Eather R.H.
Published: February 2008

Although DMSP satellite data are widely used, there has been no reliable absolute calibration. Coordinated data with ground‐based photometers allow a calibration curve of film density versus 4728 N2+ intensity to be derived. The DMSP satellites (5C series) record airglow and can detect auroral forms of intensities ≥50 R of 4278 N2+. It is estimated that the 5D series satellites are capable of detecting auroras with ∼25 R of 4278 N2+.
The motion of depleted plasma regions in the equatorial ionosphere
Authors: Anderson D.N. , Haerendel G.
Published: February 2008

Depleted plasma regions in the equatorial ionosphere and their associated motions have been observed by a variety of ground‐based, rocket‐borne, and satellite instruments. Various theories, based primarily on the Rayleigh‐Taylor instability mechanism, have been proposed for the formation and motion of these bubbles. Numerical studies in the past have incorporated local electron density depletions, with Pedersen conductivities involving local ion‐neutral collision frequencies. Realizing that bubbles are actually depleted magnetic flux tubes, we investigate the vertical E × B motion of these depleted regions, incorporating flux tube integrated quantities of electron content and Pedersen conductivity. A simple expression for the polarization electric field E1 inside the depleted flux tube is used. The resulting calculations show that the vertical bubble velocity as a function of time critically depends on the background ionospheric electric field and that this dependence extends to much greater heights than was previously thought. Bubbles which are initiated at 350‐km altitude (1900LT) with a 5% depletion in electron content attain an upward velocity of 200 m/s at 1920 LT when the background electric field is 0.6 mV/m. Bubble altitude at this time is 447 km with an 88% depletion in electron content. In the absence of an ambient electric field, 1 hour is required for the vertical bubble velocity to reach 200 m/s.
Nearly simultaneous observations of field‐aligned currents and visible auroras by the Triad and Isis 2 satellites
Authors: Kamide Y. , Murphree J.S. , Anger C.D. , Berkey F.T. , Potemra T.A.
Published: February 2008

Magnetic field data from the Triad satellite at 800‐km altitude are utilized to define the poleward and equatorward boundaries of field‐aligned currents in the premidnight sector when auroral luminosity along the same meridian was scanned by another polar‐orbiting satellite, Isis 2. It is found that the latitudinal boundaries of the major portion of the field‐aligned currents line up very well with the auroral luminosity boundaries at both the poleward and equatorward sides of the auroral distribution. The boundary between the upward and downward field‐aligned currents generally occurs at a minimum in the auroral luminosity profiles. Poleward of this minimum, the current is upward, and the aurora is characterized by the discrete auroral component with intensities at the boundary of 1–2 kR. Equatorward, in the region of the downward current, the aurora is essentially diffuse, and the auroral intensity at the boundary is 0.5–1 kR.
Electromagnetic noise and radio wave propagation below 100 kHz in the Jovian atmosphere 1. The equatorial region
Authors: Rinnert K. , Lanzerotti L.J. , Krider E.P. , Uman M.A. , Dehmel G. , Gliem F.O. , Axford W.I.
Published: February 2008

The Galileo satellite program includes the delivery of an entry probe to the Jovian equatorial atmosphere in mid‐1985. Optical and RF sensors for a lightning detection system are included as a part of the probe experimental payload. In this paper we present calculations of the RF wave propagation and reflection characteristics of the equatorial Jovian atmosphere and ionosphere for frequencies less than 100 kHz. We show that the wave propagation is limited to line‐of‐sight and one‐hop from the ionosphere. We also present results of a statistical treatment of the RF wave power densities for the case of a finite number of events and for the case of a uniformly distributed source. The results can be applied to specific RF experiment configurations concerned with establishing the statistical characteristics of Jovian lightning.
Comparison of three different types of VLF direction‐finding techniques
Authors: Tsuruda K. , Ikeda M.
Published: February 2008

Three different types of VLF direction‐finding techniques (goniometer, tracker, and University of Tokyo type) were tested by using whistler mode VLF signals from Siple. The tests were carried out by simulating each type of direction finder (DF) in a digital computer. The results are as follows: (1) the difference between the azimuth angle obtained by the tracker DF and that obtained by the University of Tokyo type DF is smaller than the difference between the azimuths given by the goniometer and by the University of Tokyo type DF; and (2) in some periods all three DF techniques give nearly equal azimuth angles, and the wave polarization agrees with that expected from the full wave calculations, but in other periods all three techniques give considerably different azimuth angles, and the wave polarizations do not agree with the theoretical ones.
polar cap electron acceleration regions
Authors: Burch J.L. , Fields S.A. , Heelis R.A.
Published: February 2008

The characteristics of polar cap electron acceleration regions and the relationship of their occurrence to the interplanetary magnetic field (IMF) have been investigated by using data from Atmosphere Explorer D and Imp J. It was found that electron energy spectra and angular distributions within the acceleration regions are generally consistent with models of acceleration of auroral primaries and reflection of atmospheric secondaries by field‐aligned electrostatic potential differences. However, localized strongly field‐aligned fluxes are also observed at energies below the spectral peak. It is suggested that these transient beams of field‐aligned low‐energy electrons result from the acceleration of thermal electrons from within the acceleration regions and that this thermal electron population may be partially replenished by small pitch angle atmospheric secondaries. The occurrence of the polar cap acceleration regions in the northern hemisphere is strongly correlated with IMF vectors which project into the (−X, +Z) sector of the solar magnetospheric X‐Z plane; that is, with northward ‘away’ IMF polarities.
Energetic particle activity at 5‐min and 10‐s time resolution in the magnetotail and its relation to auroral activity
Authors: Carbary J. F. , Krimigis S. M.
Published: February 2008

Using data from the JHU/APL experiments on the Imp 7 and 8 spacecraft, we have examined several energetic (Ep ≳ 0.3 MeV, Ee ≳ 0.2 MeV) particle bursts associated with substorm events in the magnetotail. During these events the spacecraft were within ∼10 RE of the nominal neutral sheet (ZSM ≈ 0) and within ∼20 RE of each other. Individual proton and electron bursts observed by both spacecraft do not always coincide nor does magnetotail activity correlate strongly with auroral activity on time scales less than ∼1 hour. This may be a consequence of the magnetic connection of the spacecraft to the region producing the energetic particles. Strong proton anisotropies are observed during most events. Several of the bursts exhibit rapid onsets and slow, near‐exponential decays with repetitive injections. Combining magnetic field and particle measurements on Imp 8, we can determine the pitch angle distributions with a time resolution of ∼10 s. During intense particle bursts the 0.3‐MeV protons exhibit unidirection or bidirectional anisotropies along the magnetic field. At other times, the protons exhibited anisotropies indicating motion from dawn to dusk across field lines. Both types of proton anisotropies persist for minutes, suggesting that the mechanism generating them must be active for at least as long. The energetic electrons tend not to be anisotropic, at least to the same degree as the protons. The data suggest the presence of small localized acceleration regions in the magnetotail which are observable when magnetically connected to the spacecraft. Little convincing evidence is found for a single neutral line extending across the width of the magnetotail.
Field‐aligned currents in the magnetospheric boundary layer
Authors: Lee L.C. , Kan J.R.
Published: February 2008

A self‐consistent magnetopause‐boundary layer model is constructed which contains two current layers, one for the magnetopause and one for the magnetosphere‐boundary layer transition region. Field‐aligned sheet currents in the boundary layer are generated by the plasma flow along the boundary layer. The magnitude of these boundary layer field‐aligned currents is about 10−8 A/m², which can be scaled along field lines to about 5 × 10−6 A/m² near the ionosphere and therefore can be identified as a possible source for the auroral sheet currents. The cross‐field current density in the model is also about 10−8 A/m², which is sufficient to excite the lower‐hybrid‐drift waves to produce the observed electromagnetic fluctuations in the magnetopause‐boundary layer region.