bluuebunny/crossref_metadata_2025 huggingface dataset:
Upstream particle spatial gradients and plasma waves
Authors: Parks G. K. , Greenstadt E. , Wu C. S. , Lin C. S. , St‐Marc A. , Lin R. P. , Anderson K. A. , Gurgiolo C. , Mauk B. , Reme H. , Anderson R. , Eastman T.
Published: February 2008

The upstream electron and ion fluxes detected by our experiment on ISEE 1/2 spacecraft undergo frequent time variations, from a few seconds to minutes. Many flux variations correlate with directional changes of the interplanetary magnetic field (IMF). Particles propagating in the upstream region acted on by the solar wind electric field creates a quasi‐stationary particle pattern in space. Evidently, the spacecraft frequently crosses the boundaries of these particle patterns. Our analysis strongly suggests that the particle time variations are usually spatial variations that have been convoluted into our data. Estimates of the thickness of the particle boundaries deduced is ≳1 Larmor radius (for both the upstream electron and the ion events). Plasma waves are observed in association with the upstream particle fluxes and a correlation between the amplitudes and the particle boundaries is suggested. We will theoretically show that the ion and electron density gradients across the boundary play an important role in exciting the ion acoustic‐like and plasma waves.
Ion streams in the magnetotail
Authors: Sharp R. D. , Carr D. L. , Peterson W. K. , Shelley E. G.
Published: February 2008

Ion mass spectrometer observations of low‐temperature streaming plasmas in the earth's magnetotail are reported. Measurements in the energy per charge range 0 ≤E/q ≤17 keV/e were made at geocentric radial distances <23 RE from the ISEE 1 spacecraft. Ion streams of solar wind origin in the magnetotail boundary layer and of ionospheric origin in the tail lobes and plasma sheet are described. A statistical study of some of the characteristics of the streams allows us to infer that the central tail lobe plasmas are primarily constituted of ion streams of ionospheric origin and that the ionosphere is a significant contributor to the hot plasmas that form the plasma sheet.
Spectroscopy of the Cameron Bands in the Mars airglow
Authors: Conway Robert R.
Published: February 2008

Mars airglow spectra obtained by the ultraviolet spectrometer on board the Mariner 9 spacecraft were analyzed by using a high‐resolution synthesis of the observed emissions. These bright limb observations were made of altitudes between 88 and 180 km. the brightest features are the carbon monoxide Cameron bands in the wavelength region 1800–2600 Å The shape of these bands cannot be characterized by a single rotational temperature but is best described by temperatures of 1600°K for lower J values and 10,000°K for higher J values. The observed zenith intensity of 16.7 kR is in good agreement with an excitation theory in which electron‐impact dissociation is the most important mechanism. The observations suggest the value of the cross section for this process should be 7 × 10−17 cm². The first negative bands of CO+ are not identified in the Mariner 9 spectra. This is consistent with the excitation theory for these bands.
Ion temperature anisotropy and heat flow in the Venus lower ionosphere
Authors: Schunk R. W. , St.‐Maurice J.‐P.
Published: February 2008

Motivated by the recent observations of supersonic ion flow in the Venus ionosphere near the terminator, we have studied the extent to which such a flow can induce an ion temperature anisotropy and a diffusion‐thermal heat flow. Our calculations indicate that appreciable ion temperature anisotropies can be induced at altitudes below about 220 km. The temperature anisotropy is with respect to the ion‐neutral relative drift velocity vector, with the ion temperature parallel to the relative drift velocity greater than the perpendicular ion temperature. The parallel to perpendicular ion temperature ratio is likely to be in the range of from 2 to 4, depending on the ionospheric conditions. We have also found that in the same ionospheric region the ion neutral relative drift induces a diffusion‐thermal heat flow that is considerably more important than ordinary ion thermal conduction. Consequently, diffusion‐thermal heat flow could have an appreciable effect on the ion energy balance in the Venus lower ionosphere.
On the enhancement of the IMF magnitude during 1978–1979
Authors: King Joseph H.
Published: February 2008

The magnitude of the interplanetary magnetic field (IMF) exhibits an enhancement during 1978–1979 relative to all years back to 1963. It is shown that IMF magnitude variations over the 1966–1979 period represent the combined effect of variations in both the radial flux density of the IMF and the degree of spiraling of the IMF, consistent with the theoretical model of Parker. The 1978–1979 IMF magnitude enhancement is due to an enhancement of radial flux which was in turn related to an increase of magnetic flux leaving solar active regions. It is also shown that during the corotating stream dominated years 1973–1976, the IMF was less wound up than it was during other years, and that 1973–1974 were years of enhanced radial flux.
Observation of pronounced isotropic variations of cosmic ray intensity during August–September 1979
Authors: Venkatesan D. , Volk Kevin , Agrawal S. P.
Published: February 2008

A study of the cosmic ray intensity data from high‐latitude stations reveals an isotropic variation of ∼30‐day periodicity and a peak‐to‐peak amplitude of 10% during the two months August–September 1979. Such an unusual modulation of cosmic ray intensity has not been observed before. It is clear that the variation is worldwide and in view of no significant north‐south asymmetry, we have to visualize the modulation region responsible for the effect to be extremely large. The rigidity spectra of the variation is found to be similar to that of Forbush decreases. The results are discussed in terms of solar activity. No obvious physical mechanism is readily seen, to account for this intensity variation.
Chatanika Radar observations relating to the latitudinal and local time variations of Joule heating
Authors: Banks P. M. , Foster J. C. , Doupnik J. R.
Published: February 2008

Observations of plasma convection made with the Chatanika incoherent scatter radar have been analyzed to give latitude/local time plots of the electric field contribution (E²) to thermospheric Joule heating. The data, which span the latitude range 56° to 75°Λ, show the presence of strong heating throughout the auroral regions. Of special interest are brief interludes of intense heating (>50 mW m−2) that are observed at nearly all local times and latitudes in response to magnetospheric disturbances. Further, there seem to be particular regions of the auroral oval where Joule heating seems to be continually enhanced above the broad background. The results of six 24 hour experiments are presented to illustrate summer (5) and winter conditions (1). A shorter eight hour experiment is also given to show the characteristics of cleft heating, insofar as they are visible to the Chatanika radar.
Rocketborne observations of ion convection and electric fields in dayside and nightside visual auroral arcs
Authors: Yau A. W. , Whalen B. A. , Creutzberg F.
Published: February 2008

We present ionospheric ion convection measurements in a series of four rocket payloads in and near dayside and nightside auroral arcs—one at Cape Parry (75.4°N invariant latitude) near 1300 MLT and three at Churchill (70.0°N invariant latitude) between 1900 and 2200 MLT. Direct measurements were made of the ionospheric ion velocity distribution function, and the observed ion convection velocities and equivalent convective electric fields were correlated with the energetic particle precipitation, the optical morphology of the aurora, and the topology of the geomagnetic field. Both in the postnoon and premidnight sectors it was observed that (1) equatorward of the region(s) of precipitation the ion flow was predominantly westward, with velocity of about 1 km/s; (2) poleward of the region(s) the flow was predominantly eastward; (3) the change in the flow direction, where observed, occurred near though not exactly at the edges of the precipitation region; (4) the flow inside the precipitation region was lower; (5) the reversal of the ion flow, where observed, occurred on closed magnetic field lines; and (6) the convective electric field typically dropped from 40 to 80 mV/m outside the precipitation region to 10 to 30 mV/m within. In the dayside Cape Parry flight, where quantitative photometric measurements were available, detailed anticorrelation between the ion convection speed and the green line emission intensity was also observed.
Energetics of coronal hole expansion
Authors: Zhao Xue‐Pu
Published: February 2008

Based on the assumption of the undamped propagation of Alfven waves between 2 and 5 RS, the possible range of Alfven wave energy flux density at the base of a polar coronal hole has been deduced. It is concluded that extended heating above 2 RS is needed to maintain the temperature maximum above 2 RS and to supply energy for the formation of high‐speed wind streams. The energy contribution of extended heating to high‐speed wind streams might be greater than that of Alfven waves by direct momentum addition.
An analytic expression for the radial dependence of the diffusion coefficient for quiet time energetic helium and oxygen in the heliosphere
Authors: Hsieh K. C. , Richter A. K.
Published: February 2008

Taking recent observations of the differential radial gradients and energy spectra of quiet time energetic particles of different energies and masses and over a large heliocentric radial distance from 0.3 to 18 AU into account, we show that the transport equation for these particles (Fokker‐Planck equation) reduces to a first‐order differential equation for the radial diffusion coefficient, which then can be solved analytically. For energetic helium and oxygen nuclei we then discuss the radial dependence of their diffusion coefficient.
Visible aurora in Jupiter's atmosphere?
Authors: Cook A. F. , Jones Vallance , Shemansky D. E.
Published: February 2008

The darkside limb pictures obtained by the imaging experiment on Voyager 1 have been reexamined. It is concluded that the observed luminosity is very likely due at least in part to Io torus aurora. If the effective wavelength of the emission lies in the 4000‐ to 5000‐Å region, the slant intensity is estimated to be about 20 kR. The observed double structure may be due to a number of causes such as horizontal structure in auroral emission, aurora plus twilight or photochemical airglow plus aurora.
On the upper atmospheric chemiluminescent emission observed upon release of aluminum vapor and its compounds
Authors: Gole James L. , Kolb Charles E.
Published: February 2008

Upper atmospheric chemical releases of aluminum vapor and gaseous aluminum compounds have been used to determine a number of atmospheric properties in the 90 to 220‐km altitude range. Visible radiation from nighttime releases is due to a chemiluminescent reaction which has been traditionally identified as the radiative combination of AlO with atomic oxygen to form electronically excited AlO2. Atmospheric release data are reviewed which eliminate this traditional mechanism. Results from laboratory experiments are presented which indicate key roles for electronically excited HalOH formed in a direct insertion reaction of atomic aluminum with water vapor and AlO* (A²π) formed via the reaction of oxygen atoms with weakly bound aluminum adducts. These new mechanisms significantly influence the nature of input data for atmospheric models.
Joule Heating of the Jovian Ionosphere by Corotation Enforcement Currents
Authors: Nishida Atsuhiro , Watanabe Yukio
Published: February 2008

Heat is deposited to the Jovian ionosphere in the course of enforcement of corotation to the outer magnetosphere. The Joule heating rate is estimated for several possible causes of departure from the corotation by making use of a simple model of the magnetodisc. Following compression or expansion of the magnetosphere, the magnetospheric plasma superrotates or subrotates in consequence of conservation of the angular momentum, and thermal energy is deposited in the ionosphere at a rate of the order of 1012 W for about 105 s while rotational speed is adjusted toward the corotation with the planet. Outward diffusion of the Iogenic plasma at a rate of 1029 amu/s also causes ionospheric heating at a rate of 1013 W as the ionosphere acts to drive the plasma toward the corotation. Day‐night asymmetry in trajectory of rotational motion of plasma, owing to asymmetry in configuration of the magnetosphere, is also likely to produce energy dissipation of a similar magnitude as the rotational speed is adjusted continually. Thus the corotation enforcement current deposits as much heat as the dynamo current from Io and plays an important part in energetics and dynamics of the Jovian magnetosphere. The heating rate per unit area of the high‐latitude ionosphere is more than ∼10 erg/cm² s, namely, orders of magnitude greater than the rate of the energy supply by the solar UV radiation. These numbers depend on the adopted height‐integrated conductivity of 0.1 mho of the Jovian ionosphere.
The influence of the interplanetary magnetic field and thermal pressure on the position and shape of the magnetopause
Authors: Zhuang H. C. , Russell C. T. , Walker R. J.
Published: February 2008

An ellipsoidal model is used to represent the location of the dayside magnetopause and to study the influences of the interplanetary magnetic field and thermal pressure on its location. The position and shape of the dayside magnetopause in an unmagnetized cold solar wind can be approximately represented by an ellipsoid of revolution with a constant eccentricity. The size of the ellipsoid, its semilatus rectum l0, is inversely proportional to the sixth root of the stream pressure of the solar wind. The effects of the IMF and thermal pressure on the location of magnetopause are calculated analytically by using the Chapman‐Ferraro theory. When the IMF B0 is included in the boundary calculation, the changes in the magnetopause size, shape, and orientation are inversely proportional to the square of the Alfven Mach number of the solar wind (MA²) and depend on the direction of B0. For B0 directed along an Archimedian spiral and MA=7.3, the symmetry axis of the ellipsoid will deflect 0.6° from the sun‐earth line to the east of the sun. The changes in the magnetopause size, shape, and orientation caused by including the thermal pressure are inversely proportional to the square of the sonic Mach number of the solar wind (MS²). These effects are sufficient to explain the observed slight departure of the magnetotail from the expected aberration due to the earth's orbital motion. There is no requirement, based on the tail observations to invoke a nonradial solar wind component. Hence our results suggest that little angular momentum is presently being carried away from the Sun by the solar wind.
Modeling the ion chemistry of the D region: A case study based upon the 1966 total solar eclipse
Authors: Sears Robert D. , Heaps M. G. , Niles F. E.
Published: February 2008

The November 12, 1966, solar eclipse has been modeled by a large multispecies chemistry code and the results compared with the numerous experimental measurements that were made at that time. Measured preeclipse values of electron density and code‐predicted values agree closely if ionization by precipitating electrons from the radiation belts is included. Current gas‐phase ion chemistry does not predict the rapid decrease and subsequent reconstitution of electron density about totality in the 65‐ to 85‐km region, nor does it produce the large number of negative ions above 70 km that can be inferred from the experimental data. While basic constraints can be placed on the electron attachment processes because of the experimental data, an entirely new class of physical processes may need to be included to explain this phase of D region behavior.
Nitric oxide delta band emission in the Earth's atmosphere: Comparison of a measurement and a theory
Authors: Rusch David W. , Sharp William E.
Published: February 2008

The altitude dependent emission rate in the δ‐bands of nitric oxide has been measured in the earth's atmosphere at night by a scanning ultraviolet spectrometer. The reaction responsible is the two‐body association of nitrogen and oxygen atoms. The measurements reveal a vertical intensity beneath the layer for the δ‐band system of 19 R. The horizontal emission rate increases from 70 R at 117 km to 140 R at 150 km. The data have been analyzed with a one‐dimensional, time‐dependent, vertical‐transport model of odd nitrogen photochemistry. The calculated and measured intensities agree if the quenching of N(²D) by atomic oxygen is near 5 × 10−13 cm³ s−1. The diurnal variation of δ‐band emission, N(4S), and NO densities resulting from model calculations are presented and discussed.
4.5‐kHZ ground hiss and field‐aligned current in the dayside cusp
Authors: Dowden R. L. , Kleimenova N. G.
Published: February 2008

A slowly varying background noise in the 4.5‐kHz band observed at Lake Vanda, Antarctica (81°S, INV), has most of the features one would expect of Čerenkov radiation from the precipitating soft electrons that constitute the upgoing field‐aligned current from TRIAD measurements in the dayside cusp.
Variability of the diurnal anisotropy of the cosmic ray intensity during the interval 1973–1978
Authors: Agrawal S. P. , Venkatesan D.
Published: February 2008

The diurnal anisotropy of cosmic ray intensity has been investigated over the interval 1973–1978 by using neutron monitor data from Calgary, Deep River, Goose Bay, and Inuvik. It is observed that in general, the 27‐day variation in the diurnal anisotropy is greater for the component perpendicular to the nominal interplanetary magnetic field (IMF) in comparison with the parallel (or field aligned) component, which has very little ‘power’. However, the direction of the average anisotropy vector is aligned almost perpendicular (within the hour) to the IMF. The results are discussed in terms of alternate possibilities: the ‘power’ with 27‐day period and its harmonics arise from fluctuations in the amplitude aligned in the direction (a) of the total vector itself (≈ 16 hours) (b) perpendicular to the IMF.
Use of hydromagnetic waves to map geomagnetic field lines
Authors: Greenwald R. A. , Walker A. D. M. , Candidi M.
Published: February 2008

Quasi‐periodic oscillations in magnetospheric electric and magnetic fields are communicated to the ionosphere via guided Alfvén waves, propagating along magnetic field lines. Thus, if one could identify ionospheric and magnetospheric regions showing highly correlated temporal variations, one would, in effect, have determined the region in the ionosphere conjugate to a given location in the magnetosphere. In this paper we present a cross correlation analysis of Pc 5 magnetic field oscillations observed by GEOS 2 with drift velocity oscillations (electric field) observed with the STARE radars in the ionosphere. GEOS 2 is in geostationary orbit with its conjugate point nominally located in the STARE field of view. Several comparisons were made over a one hour period in the early afternoon sector and correlation coefficients reaching 0.84 over a limited area in the ionosphere were obtained. Between the beginning and end of the hour, the measured footpoint was displaced by ∼ 1° in latitude and ∼2.5° in longitude. Neither of the two determinations agreed with the predictions of the Mead‐Fairfield or Olson‐Pfitzer models, although the difference at the end of the hour was of the same order as the dispersion between the two models.
Hydromagnetic oscillations of the magnetopause
Authors: Tamao Tsutomu
Published: February 2008

Dispersion equations of hydromagnetic oscillations in the magnetopause‐magnetosheath region are derived in the two‐fluid approximation with the ion temperature higher than the electron temperature. In the derivation a finite thickness of the magnetosheath and the presence of the mean ion drift motion in the magnetosphere are taken into account, in addition to the tangential uniform flow in the magnetosheath. It is shown that there are two different kinds of oscillations in the region, which are in general coupled to each other. One is radial oscillations related to the nonuniform compressed flow in the magnetosheath and the other is the Kelvin‐Helmholtz instability of boundary waves due to the tangential flow. The fundamental mode of the former oscillation, taking a maximum displacement at the magnetopause, has an eigen period of 8 minutes, which is comparable with that of the observed oscillations obtained by particle data of ISEE 1 and 2 satellites. For a range of the tangential wavelength shorter than the thickness of the magnetosheath, dominant eigen oscillations are the boundary waves. The finite thickness has a tendency to reduce the boundary wave instability. The predicted relative phase differences between orientation angle and radial velocity of the moving magnetopause for the marginal state of oscillations are in phase in the morning and out of phase in the afternoon.
Magnetic field line reconnection experiments, 3. Ion acceleration, flows, and anomalous scattering
Authors: Gekelman W. , Stenzel R. L. , Wild N.
Published: February 2008

Extensive spatial and temporal measurements of plasma pressure nkTe, magnetic force density J × B, and ion velocities v have been performed in a laboratory experiment undergoing magnetic field line reconnection. The pressure is found to peak at the two edges of the neutral sheet. It exhibits large transverse gradients, causing space charge fields and Hall currents. The magnetic force density arises mainly from induced axial neutral sheet currents and transverse magnetic fields but also from transverse currents and a magnetic field component along the separator. The total force density on the fluid, J × B ‐ ▽p, is compared with direct measurements of the fluid acceleration by using differential particle detectors. It is found that the ion acceleration is strongly modified by scattering off wave turbulence. After several Alfvén times the fluid develops the classic flow pattern, with jetting from the edges of the neutral sheet to velocities close to the Alfvén speed.
Ion current in a magnetic neutral region: Generation of an incipient magnetopause
Authors: Whipple Elden C. , Silevitch Michael B.
Published: February 2008

We calculate the current contributed by ions trapped in the vicinity of a magnetic X line. The X line is formed from the superposition of a dipole and a uniform, antiparallel magnetic field. The system (Dungey's open model for the magnetosphere) has an electric field with equipotential magnetic field lines and with an asymptotic behavior such that at a great distance the electric field is uniform in the dawn‐to‐dusk direction. In the magnetic neutral region E is directed along the X line toward dusk. Ions incident within about one gyrolength from the X line are captured and accelerated along the X line to large kinetic energies by the electric field. Most ions escape from the neutral region by Speiser's ejection mechanism into spiral orbits along open magnetic field lines. The neutral region ion current is azimuthal and varies very nearly as cos ϕ on the dayside as predicted by Alfven, where ф is the GSM longitude, but is negligible on the nightside in this zero‐order calculation. Ion energization rates and escaping pitch angle distributions are estimated. The effect of the neutral region current is to extend the magnetic neutral line into a neutral sheet in the north‐south direction. This leads to a positive feedback mechanism whereby the greater vertical extent of the neutral region enhances ion capture, ensuring a still larger current. Thus a magnetopauselike structure will be rapidly formed for even very small incident plasma densities.
A simple kinetic theory calculation of terrestrial atomic hydrogen escape fluxes induced by charge exchange collisions
Authors: Shizgal Bernard , Lindenfeld Michael J.
Published: February 2008

A simple kinetic theory model is presented for the calculation of atomic hydrogen escape fluxes from earth induced by charge exchange collisions with hot protons. An analytical expression is derived for the nonthermal flux in terms of atmospheric and dynamical variables. The results, which indicate an increase in the nonthermal flux with decreasing exospheric temperature, are in good agreement with the earlier estimates by Bertaux (1975).
Test particle study of Landau damping of steepening magnetosonic waves
Authors: Matsumoto H. , Barnes A.
Published: February 2008

A test particle study of Landau damping of steepening large‐amplitude magnetosonic waves is carried out. Motions of test particles in a model steepening large‐amplitude magnetosonic wave are traced. The kinetic energy change of the ensemble of of test particles is computed to estimate an effective Landau damping rate of the magnetosonic wave. The numerical results are compared with the linear kinetic theory of Landau damping and interpreted in terms of a simple physical picture for particle trapping.
Long‐term variations in atomic nitrogen densities
Authors: Engebretson M. J. , Nygren J. B.
Published: February 2008

Thermospheric densities of atomic and molecular nitrogen were measured from February 1976 through December 1978 by the open source neutral mass spectrometer on the equatorial Atmosphere Explorer E satellite. During this period a significant increase in N densities was observed at altitudes of 250 km and above. We believe the increases can be explained by increased production of N due to enhanced solar extreme ultraviolet radiation but not by a simple rise in thermospheric temperature. Empirical modeling of N densities at 250 and 375 km by using stepwise regression techniques indicates that the increased solar EUV fluxes in the 800–1000 Å range are sufficient to account for the observed rise in N densities at 250 km from June 1976 to June 1977 and are the dominant factor in the density increase of a factor of 5 observed at 375 km altitude from June 1976 to late 1978.
Planetary radio astronomy observations during the Voyager 1 Titan flyby
Authors: Daigne G. , Pedersen B. M. , Kaiser M. L. , Desch M. D.
Published: February 2008

During the Voyager 1 Titan flyby, unusual radio emissions were observed by the planetary radio astronomy experiment in the 20‐ to 97‐kHz frequency range. In this paper we show that Titan itself is not the source of the observed radio emission. Rather, we attribute the emission features to modification of the normal Saturn kilometric radiation by propagation effects in enhanced density structures within the Titan wake. Furthermore, spiky emissions observed in the magnetic wake of Titan are interpreted in terms of local electrostatic instabilities at the electron plasma frequency. From these measurements we derive a range of electron densities in the wake region, and we discuss the consistency of the results.
Data processing for the Dynasonde: The Dopplionogram
Authors: Wright J. W. , Pitteway M. L. V.
Published: February 2008

Modern digital ionosondes can be programed to sound the ionosphere in more complicated patterns than by traditional radio experiments. In this paper we show how one such pattern, B mode, can be used to display Doppler information as a function of frequency. We show examples of ‘dopplionograms’, which follow a traditional ionogram format but with Doppler information added; these can be interpreted to reveal information on dynamic processes such as the effects of winds and waves in the plasma.
Reversal of the cosmic ray density gradient perpendicular to the ecliptic plane
Authors: Swinson D. B. , Kananen H.
Published: February 2008

Annual averages of the diurnal variation in cosmic ray intensity for neutron monitors in Deep River and Oulu and underground muon telescopes in Bolivia and at Embudo and Socorro, New Mexico, have been determined as a function of the sense of the interplanetary magnetic field for the years 1965–1975. These data point to a cosmic ray density gradient, perpendicular to the ecliptic plane, pointing southward prior to 1969 and changing to a northward pointing gradient after the reversal of the sun's polar magnetic field in 1969–1971. This result supports numerical calculations for the prereversal and postreversal field configurations at intermediate and high cosmic ray rigidities.
The fine structure of the front side magnetopause during two successive crossings
Authors: Formisano V. , Pedersen A. , Lindqvist P.‐A.
Published: February 2008

The fine structure of two magnetopause crossings observed on November 10, 1977, is studied in detail as representative of a class of magnetopause observations. A so‐called magnetopause layer is observed between the magnetosheath and the magnetosphere. Changes in the magnetic field indicate that there are current sheets on each side of this magnetopause layer, and therefore does not show the smooth features of a rotational discontinuity observed on other occasions. The magnetopause layer is characterized by an irregular and a magnetosheath‐like energy distribution, part of the time with increased flow and energy compared with the magnetosheath. The flow direction deviates considerably from that of the magnetosheath. No boundary layer plasma is observed on the magnetospheric field lines inside the magnetopause layer in the cases discussed. Electromagnetic energy is dissipated at the two edges of the magnetopause layer where the current layers are observed. The two crossings are tentatively interpreted to take place on the two sides of the X line that moved because of a change of the inclination of the magnetosheath magnetic field.
Unusual structure of the dayside low‐latitude magnetopause energetic electron layer
Authors: Scholer M. , Hovestadt D. , Ipavich F. M. , Klecker B. , Gloeckler G.
Published: February 2008

We have analyzed energetic electron measurements (E > 75 keV) with the Max‐Planck‐Institut/University of Maryland sensor system on ISEE 1 in the dayside magnetosheath just outside the magnetopause during an outbound orbit on November 6, 1977. An energetic electron layer was observed at 0800 LT to extend well into the magnetosheath. The electrons appear within the 8‐s time resolution of the instrument highly collimated at random in one of the eight sectors (instrument is sampling in the ecliptic plane). The most likely explanation is that the energetic electron layer has a sheetlike or filamentary structure with dimensions of a few electron gyroradii. These structures are convected with a magnetosheath plasma velocity perpendicular to the magnetic field of ≳100 km/s past the spacecraft. Since they are convected over the spacecraft within ∼0.4 s, which is about the measuring time in one sector of the instrument, they will be seen only in one or two sectors. The mean distance between structures is of the order of 1000 km. It can, however, not be excluded that the whole magnetopause acts as an intermittently particle‐ejecting source with ∼0.4‐s duration. The observed anisotropies could, in principle, also be real and constitute anisotropies in gyrophase. A structure of the energetic electron boundary layer as discussed here seems to be an exception rather than the rule.
Satellite observations of suprathermal electron bursts
Authors: Johnstone A. D. , Winningham J. D.
Published: February 2008

Data from the ISIS 2 satellite are used to study the spatial distribution of the suprathermal electron bursts discovered by high‐altitude sounding rockets. It is found that the bursts form an integral part of the boundary plasma sheet and are linked with the formation of discrete auroral arcs. The maximum energy of the bursts is always below the peak energy in neighboring discrete forms, and it appears that if the bursts fail to reach the minimum energy found to be necessary to sustain a discrete arc they collapse within a few seconds. It is suggested that in a pass across the auroral oval the overall envelope of the maximum energy in bursts and the peak energy in discrete auroral forms reflects the variation of the available acceleration (perhaps a parallel electric potential) across the auroral oval while the energy structure in individual forms is a function of the nonlinear processes which sustain them. This explanation appears to resolve the apparent discrepancy in scale thickness between rocket and satellite inverted V's.
The electron content and its variations at Natal, Brazil
Authors: Tyagi T. R. , Yeh K. C. , Tauriainen A. , Soicher H.
Published: February 2008

The Faraday rotation and amplitude data for the period September 1978 through August 1979, recorded from the geostationary satellite SMS 1 (90°W) at Natal (5.9°S, 35.2°W), have been utilized to study the behavior of total electron content (TEC). Apart from diurnal and seasonal behavior of TEC, two characteristic features of the nighttime ionosphere are discussed: (1) a postsunset enhancement in TEC which lasts for several hours following the rapid sunset decrease and (2) the sharp, isolated changes in TEC. In particular, relating to phenomenon 2, the depletions in TEC are usually accompanied by a simultaneous increase in fading rate, scintillation index, and amplitude level, while the enhancements are accompanied by a simultaneous decrease in fading rate, scintillation index, and amplitude level. The statistics of their occurrence and nature are described. The average behavior of the signal amplitude after propagating through either a depleted or an enhanced ionosphere is modeled theoretically and shown to be in agreement with the observed experimental behavior.
Field‐aligned currents in high latitudes estimated from Millstone Hill Radar observations of ion drifts
Authors: Yasuhara F. , Kamide Y. , Holt J. M.
Published: February 2008

A simple scheme has been developed to estimate the global distribution of field‐aligned currents by using electric field measurements by an incoherent scatter radar at Millstone Hill. The combination of the electric field data and a realistic, quiet‐time model of the ionospheric conductivity gives horizontal currents in the ionosphere. The divergence of the ionospheric currents then yields the distribution of the field‐aligned currents. This method is applied to two quiet days in May and July 1978. The field‐aligned currents obtained are consistent with TRIAD satellite observations. The peak location of the global field‐aligned current intensity and the spatial distribution of field‐aligned currents near midnight appear to vary between these two magnetically quiet days.
A model of propagation of solar flare particles and its application to cosmic ray ground level events
Authors: Lockwood J. A. , Debrunner H. , Flückiger E. , Neuenschwander H. , Schubnell M.
Published: February 2008

A Monte Carlo simulation of the propagation of relativistic solar flare protons in the interplanetary magnetic field was used to understand the intensity‐time profiles and anisotropies for the GLEs on November 22, 1977 and May 7, 1978. Mean free paths for pitch angle scattering of 0.5 AU and 5 AU, respectively, were deduced. The injection of the solar flare protons had an extended time structure that was found to be of similar shape as the x ray burst profiles in the bands 1–8 Å and 0.5–4 Å, respectively.
Coordinated measurements of slot region electron precipitation by plasmaspheric wave bands
Authors: Imhof W. L. , Anderson R. R. , Reagan J. B. , Gaines E. E.
Published: February 2008

It has been hypothesized by Lyons et al. that electrons in the slot region are precipitated by cyclotron resonance interactions with the plasmaspheric whistler mode wave bands. The energy spectra and the variations with L shell of the energy bands of the precipitating electrons have been found by Imhof et al. (1974) to be consistent with cyclotron resonance by waves in the few hundred Hz to few kHz range. Now, for the first time, simultaneous measurements have been made of the precipitating electron spectra, the wave frequency distributions, and the plasma density profiles. The electron measurements were performed from the P78‐1 low‐altitude satellite, whereas the wave and plasma density observations were made with the plasma wave experiment on the ISEE 1 spacecraft. Broad bands are often observed in the electron energy spectra with a well‐defined low‐energy cutoff that decreases in energy with increasing L value in a manner consistent with that calculated for first‐order cyclotron resonance with waves at the high‐frequency cutoff of the band. On the basis of the electron spectra from P78‐1 and the plasma densities obtained from the upper hybrid resonance frequencies measured on ISEE 1, the hiss cutoff frequencies are calculated for an assumed first‐order cyclotron resonance interaction and compared with the wave spectral density profiles measured on ISEE. Overall, the plasma wave and the electron measurements are consistent with each other, supporting the earlier hypothesis for the precipitation mechanisms.
On the origin and spatial extent of high‐latitude F region irregularities
Authors: Kelley Michael C. , Vickrey James F. , Carlson C. W. , Torbert R.
Published: February 2008

Further evidence is presented that structured soft‐electron precipitation is an important source of large‐scale (λ ≳ 10 km ) F region ionization irregularities in the high‐latitude ionosphere. We show that large amplitude, 20‐km to 80‐km structured plasma exists in both the dayside and nightside auroral oval. In the latter case, the structured F layer plasma has been observed to convect into and through the field of view of the Chatanika radar. Here, and in a companion paper, we hypothesize that this soft electron precipitation is the primary source of high‐latitude structure and that convection acts to distribute the irregular plasma throughout the polar ionosphere. Indeed, at the observed production scale (20–80 km), irregularities can easily convect throughout the high‐latitude region with negligible decay from classical or anomalous diffusion, including the effects of a conducting E region. Our convection/decay model also explains the following observed features of published high‐latitude irregularity data: (1) The steep gradient in irregularity intensity at the equatorward edge of the nighttime magnetospheric convection zone. (2) The existence of irregularities throughout the polar cap. (3) The reduction of irregularity intensity in the central polar cap. (4) The dawn‐dusk asymmetry in the equatorward boundary of the high‐latitude irregularity zone. On the other hand, if classical theory is applied to a 100‐m scale structure, diffusion should rapidly limit the irregularities to an area within a few degrees of the production zone, a prediction not upheld by experimental data. Thus, plasma instabilities must operate on the large‐scale structures to produce the observed intermediate scale (100 m < λ < 10 km) power law irregularity spectra. Calculations of the
instability growth rate in its generalized form, which includes field‐aligned currents (the current convective instability), shows that growth should occur. The universal drift instability should then operate on these intermediate scale features. We suggest that this latter instability maintains the shorter scale plasma structure at the expense of a more rapid decay of the intermediate scale irregularities in a cascade‐like process. Enhanced, turbulent diffusion can reduce significantly the lifetime of the intermediate scale irregularities but not of the larger structures, which can therefore still transit the polar cap.
Ion temperature variations in the daytime high‐latitude F region
Authors: Schunk R. W. , Sojka J. J.
Published: February 2008

We improved our high‐latitude ionospheric model by including thermal conduction and diffusion‐thermal heat flow terms in the ion energy equation so that we could study the ion temperature variations in the daytime high‐latitude F layer in a region poleward of the auroral oval for steady state conditions at local noon. From our study we found that (1) The variation of Ti with solar cycle, season, and geomagnetic activity closely follows the Tn variation. The general trend is for higher temperatures in summer than in winter, at solar maximum than at solar minimum, and for active magnetic conditions than for quiet conditions. However, Ti changes by less than 600°K over the range of conditions considered; (2) Meridional electric fields act to heat the ion gas, and electric fields greater than 40 mV m−1 can cause a larger Ti change than that due to solar cycle, seasonal, and geomagnetic activity variations; (3) In the presence of meridional electric fields, there is an upward flow of heat from the lower ionosphere that acts to raise Ti at high altitudes; (4) Zonal electric fields affect Ti indirectly through changes in the electron density, but the effect can be larger than that associated with solar cycle, seasonal, and geomagnetic activity variations; (5) Diffusion‐thermal heat flow affects Ti by at most 500°K; (6) Typically, Te has a much smaller effect on Ti at high latitudes than at middle and low latitudes.
Spatial variation of electric fields in the high‐latitude ionosphere
Authors: Zi Minyun , Nielsen Erling
Published: February 2008

The patterns of ionospheric electron drift velocities at high latitudes have been determined during 18 magnetically disturbed days using observations made with the STARE system. These patterns have been compared with those which are characteristic for magnetically quiet days determined from 11 days of STARE measurements. The changes from magnetic quiet to active times are (1) the electric field magnitude increases, (2) the average location of the field maximum moves to lower latitudes, (3) the maximum field occurs closer to noon in both the morning and afternoon cell, (4) the maximum electric field, which is observed after midnight during quiet days, is observed during the afternoon instead, (5) the morning convection cell increases, and (6) the reversal from westward to eastward directed electron drifts and vice versa occurs earlier in local time. All these trends become increasingly clear as the Kp index increases. Comparisons with model predictions suggest that variations in the spatial distribution and intensities of ionospheric conductivities as well as variations of the relative strength of the intensities of the field‐aligned current pair flowing in the morning and dusk sector are closely associated with the observed phenomena.
SO2 ionization and dissociation in the Io plasma torus
Authors: Cheng Andrew F.
Published: February 2008

Escape of SO2 from Io may be driven by corotating ion impact and energy deposition by the Io flux tube current. The yield of O I per SO2 is estimated in steady state ionization and dissociation of SO2. An average SO2 injection rate of 1028 s−1 is found to be consistent with O I observations in the hot plasma torus. The average densities of S I and SO2 are estimated, but the expected oxygen to sulfur ion ratios from SO2 ionization and dissociation are uncertain. There is substantial loss of neutrals from charge exchange and electron impact on molecular and negative ions (Io plasma torus, mass injection, neutral densities).
Observations near the magnetopause at the onset of the July 29, 1977, sudden storm commencement
Authors: Knott K. , Fairfield D. , Korth A. , Young D. T.
Published: February 2008

Observations by GEOS 1, supported by data collected by IMP 7, IMP 8 and ATS 6 during the July 29, 1977, sudden storm commencement (SSC) have been used to derive the magnetopause's position (7.8 RE before and 6.1 RE after the SSC), velocity (inward speed of about 95 km/s by two independent methods) and thickness (∼500 km measured by the change in drift pattern). Particle, field and wave data from GEOS 1 have been used to establish the satellite's position with respect to the magnetopause. After the initial crossing of the magnetopause, the satellite remained in the magnetosheath for most of the interval considered, occasionally encountering what are interpreted as ‘open magnetic field lines.’ When the spacecraft was in the magnetosheath, duskward plasma flows tangential to the magnetopause are derived from our electric field measurements. The flow velocity was higher during periods when the interplanetary magnetic field assumed a southward component as compared to periods when a northward component was present. On three occasions, an environment was encountered which was neither typical magnetospheric or magnetosheath‐like. It is argued that in these instances GEOS 1 either reentered the magnetosphere or encountered a ‘magnetic island,’ caused by a tearing mode instability at the magnetopause. The electric field dropped to zero or very small values in these instances.
Sunward convection in both polar caps
Authors: Reiff Patricia H.
Published: February 2008

The geomagnetic storm of July 29, 1977 has been the object of concentrated study. The latter part of the day (1800–2300 UT) is particularly interesting because it is a period of extremely strong, almost directly northward interplanetary magnetic fields (IMF). Such northward IMF's have been related to periods of reversed (i.e., sunward) convection in the polar cap, and this day is no exception. Zanetti et al. [1981], using Triad magnetometer data, show magnetic perturbations implying reversed convection in the northern polar cap, while the Birkeland currents in the southern polar cap are very weak. They give two possible interpretations: (1) merging occurs preferentially in the northern cusp region, and therefore reversed convection is restricted to the northern polar cap or (2) the currents flow predominantly in the sunlit northern polar cap because its conductivity is higher. This paper shows convection data from both the northern polar cap (S3‐3) and the southern polar cap (AE‐C). In both cases, regions of reversed convection are seen. Therefore the asymmetry of the Birkeland currents is more likely caused by a conductivity asymmetry than a convection asymmetry. It is likely that the low‐energy ions seen deep in the polar cap may be trapped on closed field lines after merging on both tail lobe boundaries.
On the relationship of the plasmapause to the equatorward boundary of the auroral oval and to the inner edge of the plasma sheet
Authors: Horwitz J. L. , Cobb W. K. , Baugher C. R. , Chappell C. R. , Frank L. A. , Eastman T. E. , Anderson R. R. , Shelley E. G. , Young D. T.
Published: February 2008

ISEE 1 observations of the plasmapause are compared with simultaneous observations of the electron plasma sheet and also the auroral oval observed in DMSP photographs. Only a limited amount of appropriate data was available for the comparisons: the plasmapause/plasma sheet inner edge comparisons were restricted to the early and late morning sectors, while there were two satisfactory comparisons of the plasmapause and the equatorward boundary of the auroral oval in the evening sector. However, these examples indicate that the plasmapause location often coincides to within ΔL ∼ 0.1–0.2 with both the plasma sheet inner boundary and the field line threading the equatorward boundary of the auroral oval. This co‐location of the plasmapause and the plasma sheet inner edge may be due to shielding of the magnetospheric convection electric field by an Alfvén layer located at the inner edge of the plasma sheet as discussed by Jaggi and Wolf (1973) and others.