bluuebunny/crossref_metadata_2025 huggingface dataset:
Distribution of energetic positive ion species above a diffuse midnight aurora
Authors: Moore Thomas E. , Evans David S.
Published: February 2008

Observational approaches to the problem of magnetospheric plasma origin usually depend upon mass‐discriminating measurements of ion distribution functions. A new instrument for this purpose has been developed and flown via sounding rockets above a diffuse midnight aurora during geomagnetically quiet conditions. The instrument combines wide mass and energy ranges (2.5 ≤ME ≤160 amu · keV), high mass resolution with good sensitivity, and superior rejection of undesired particles. The rocket payload (29.008) was launched on February 2, 1978, from Chatanika, Alaska, and reached an apogee of 615 km at approximately 0900 UT (2300 LT), traversing invariant latitudes from 65.5° to 67.4°. Only ions identified as H+ and He++ were detected, and the He++ was not clearly above background, having an upper limit of 2–4% of the H+ intensity. All other ions, including the ionospheric species He+ and O+, had upper limits at a similar or smaller level. This situation contrasts sharply with a number of recently reported observations of large intensities of O+ during magnetic storms and may be characteristic of undisturbed periods. Though these results suggest a solar wind source for the ions, an admixture including an appreciable fraction of polar wind material (predominantly H+) is not precluded. The measured proton distribution was nearly isotropic over downcoming pitch angles at all energies and showed a depleted atmospheric source cone. The proton energy distribution had a best fit temperature of 4.5 keV and a number density of 0.17 cm−3, corresponding to a peak intensity just over 105 cm−2 s−1 sr−1 keV−1. The energy flux carried into the atmosphere by such a distribution (0.032 erg cm−2 s−1) is consistent with ground‐based Hβ measurements (⪝10 R) of patches of aurora linked to the rocket by magnetic field lines. Altitudinal variations observed during the flight are consistent with the theory of charge exchange of a time steady incident proton population. These ion observations, taken together with electron observations reported in a companion paper, appear to be consistent with the model of diffuse auroras in which trapped plasma precipitates owing to strong pitch angle diffusion on auroral field lines linking the near‐earth plasma sheet.
ISEE 1 and 2 particle observations of outer plasma sheet boundary
Authors: Parks G.K. , Lin C.S. , Anderson K.A. , Lin R.P. , Rème H.
Published: February 2008

Observations of particle structures by a medium‐energy particle experiment on ISEE 1 and 2 spacecraft at ∼20‐RE distance in the geomagnetic tail are presented. Comparison of our data with plasma data indicates the existence of a layer of energetic electrons and ions just outside the plasma sheet. The region outside the plasma sheet in the high‐latitude lobe is permeated with low‐intensity, low‐energy (∼1.5 keV) ions. These particle structures have velocities of a few kilometers per second to ≳60 km/s. Large‐scale motions are observed with onset and recovery of substorms. The dimensions of the particle structures are estimated to range from ∼200 to 10,000 km at 20 RE. The particle structures are dependent upon the energy as well as on the species of the particles.
F layer positive response to a geomagnetic storm – June 1972
Authors: Miller Nathan J. , Grebowsky Joseph M. , Mayr Hans G. , Harris Isadore , Tulunay Yurdanur K.
Published: February 2008

A circulation model of neutral thermosphere‐ionosphere coupling is used to interpret in situ spacecraft measurements taken during a topside mid‐latitude ionospheric storm. The data are measurements of electron density taken along the circular polar orbit of Ariel 4 at 550 km during the geomagnetically disturbed period June 17–18, 1972. We infer that collisional momentum transfer from the disturbed neutral thermosphere to the ionosphere was the dominant midday process generating the positive F layer storm phase in the summer hemisphere. In the winter hemisphere the positive storm phase drifted poleward in apparent response to magnetospheric
drifts. A summer F layer positive phase developed at the sudden commencement and again during the geomagnetic main phase; a winter F layer positive phase developed only during the geomagnetic main phase. The observed seasonal differences in both the onsets and the magnitudes of the positive phases are attributed to the interhemispheric asymmetry in thermospheric dynamics.
Self‐modulated VLF wave‐electron interactions in the magnetosphere: A cause of auroral pulsations
Authors: Davidson G.T.
Published: February 2008

A model is developed for self‐modulated pulsations in the outer trapped electron belts. The pulsations are a consequence of growth of VLF waves and removal of trapped electrons following an electron injection event. If too many electrons are removed by wave interactions, the system restores itself by building up the flux again to values exceeding the equilibrium flux, repeated through many cycles. Pulsations are shown to be possible for both broadband VLF wave generation and narrowband wave generation. The resulting electron precipitation pulses are consistent with observations of pulsating aurorae on the morningside following a substorm injection event. The conditions for pulsations are quite stringent and favor trapped particle fluxes near the stable trapping limit. Individual pulses may be in or near strong diffusion.
Relationships between auroral particle distributions and magnetic field perturbations associated with field‐aligned currents
Authors: Klumpar D.M.
Published: February 2008

Simultaneous measurements of magnetic fields and soft particle distributions in the topside auroral ionosphere reveal the relationships between field‐aligned currents and primary and secondary auroral particles. In the evening MLT sector the region 2 field‐aligned currents, which are directed into the ionosphere, are found to extend on the average 2.4° of invariant latitude equatorward of the low‐latitude boundary of 1‐keV electron precipitation from the magnetospheric plasma sheet. This current system is found to lie within the mid‐latitude total ion trough, as defined by its topside density depletion. This is a region predominantly void of particles between 5 eV and 15 keV. The current carriers are inferred to be upward flowing cold ionospheric electrons. At higher latitudes in the premidnight sector the region 1 field‐aligned current system lies within the region of particle precipitation and terminates at its high‐latitude boundary coincidently with the termination of energized precipitating particle fluxes. The primary reversal from downward to upward flowing field‐aligned currents may be quite sharp or may occur over several degrees of latitude. The current reversal is not necessarily associated with any particular particle precipitation structure.
The structure and parameters of flare streams
Authors: Pudovkin M.I. , Zaitseva S.A. , Benevolenska E.E.
Published: February 2008

The structure and parameters of flare streams in relation to the location of the flare and to the configuration of the large‐scale magnetic field on the sun are considered. The following results are obtained: (1) The flare streams spread in a rather wide angle (λm ≈ ±60°). (2) The velocity of the streams ejected by the flares in the sun’s western hemisphere is 1.5 times higher than that of the streams ejected by eastern flares. (3) The sign of Bz being fixed, the sign of Bx within the stream is determined by the location of the flare with respect to the solar equator. (4) The exponent of the polytrope for the solar wind plasma (γ = 1.4–1.7) is close to or less than the adiabatic one.
Correlation of Pc 3, 4, and 5 activity with solar wind speed
Authors: Greenstadt E.W. , Olson J.V. , Loewen P.D. , Singer H.J. , Russell C.T.
Published: February 2008

Positive correlations of magnetic pulsation amplitude with solar wind speed are found for Pc 3, 4, and 5 at both Calgary and Leduc. The data, obtained in September and October 1970, confirm and extend similar results found in an earlier interval for Pc 3, 4 at Calgary alone, thus adding further evidence for a velocity‐controlled contribution, such as the Kelvin‐Helmholtz instability, to pulsation activity.
Strong plasma acceleration by slow shocks resulting from magnetic reconnection
Authors: Sato Tetsuya
Published: February 2008

An externally driven magnetic reconnection is simulated for two two‐dimensional MHD models with anomalous resistivity: a closed boundary model where an O‐type neutral point is formed between two X‐type neutral points and an open‐ended model where only an X‐type neutral point is formed. Computer runs have shown the following: (1) X‐shaped (Petschek type) slow shocks are formed. Upon examination of their fine structure it is found that the Rankine‐Hugoniot shock conditions are extremely well satisfied. (2) In the closed boundary case the plasmas entering into the magnetic island through the X‐type neutral points are moderately accelerated along the magnetic island boundaries. Two pairs of vortices are formed internally in such a way that the plasmas are confined. Consequently, the region of the island expands as the pressure increases. As reconnection proceeds, another set of vortices is generated in the expanding island causing the plasma to become turbulent. (3) In the open‐ended case the plasma acceleration is intensified, and strong jet streams are generated on the downstream side of the slow shocks, with the speed approaching the Alfvén speed of the upstream region. Interestingly, the jet streams tend to concentrate preferentially along the plasma sheet boundaries (shock fronts). This is attributed to sharp pressure gradients along the magnetic field lines as a result of slow shocks whose fronts obliquely intersect the field lines. These features of strong jetting of plasmas along the plasma sheet boundaries can explain the recent observations of high‐velocity proton flows in the earth's magnetotail during substorm expansions. (4) Examination of the energy conversion rate has shown that the externally driven magnetic reconnection acts as a powerful magnetic energy converter.
Acceleration of energetic protons by interplanetary shocks
Authors: Pesses M. E. , Tsurutani B. T. , Van Allen J. A. , Smith E. J.
Published: February 2008

The University of Iowa instrument aboard Pioneer 11 detected 69 energetic proton events (EPE) (0.6 ≤Ep ≤3.4 MeV) during 1973–1974 in the heliocentric radial range 1–5 AU. Sixty percent of the EPE peak within ±5 hours of a corotating interaction region (CIR) boundary, while 19% peak inside and 21% peak outside the interaction regions. Of the CIR boundaries at which an EPE peaks within ±5 hours, 80% have associated shocks. The observed intensities and pitch angle distributions of protons near shock fronts are consistent with a theoretical simulation of the acceleration of protons by a ▽|B| drift in a V × B electric field at the shock front.
Cross sections for asymmetric charge transfer and collisional dissociation reactions of Atmospheric ions at keV energies
Authors: Sheridan J. R. , Merlo T. , Enzweiler J. A.
Published: February 2008

Electron capture and ion loss cross‐section measurements are reported for the reactants N+ + O2, N2+ + O2, N2+ + H2, N+ + H2, and O+ + N2. Ion loss cross‐section measurements are presented for the reactants N2+ + He. Measurements of cross sections for collisional dissociation of the incident molecular ion are reported for the reactants N2+ + O2 and N2+ + H2. The measurements span the projectile energy range from 2.4 keV to 24.3 keV. Good agreement is found with the results of other investigators for those energies and reactions for which comparisons are possible.
Seasonal and diurnal variation of Ps 6 magnetic disturbances
Authors: Rostoker Gordon , Barichello Joan C.
Published: February 2008

Ps 6 magnetic variations are quasi‐periodic perturbations of the auroral zone magnetic field found in the morning sector during periods of strong magnetospheric activity. The disturbance affects mainly the D and Z components of the perturbation field and amplitudes can reach several hundred nanoteslas. In this report we show that Ps 6 activity has a peak in occurrence frequency around magnetic local dawn and that there are significantly more Ps 6 variations detectable in the months around summer solstice than during the months around winter solstice. Our results suggest that the electric field configuration is the most crucial factor in the control of the generation of Ps 6 magnetic disturbances.
On the spatial relationship of 1‐m equatorial spread F irregularities and plasma bubbles
Authors: Tsunoda Roland T.
Published: February 2008

A radar experiment was conducted on August 18, 1978, at Kwajalein Atoll, Marshall Islands, to investigate the spatial relationship of 1‐m equatorial spread F irregularities to plasma bubbles (localized depletions in F layer plasma density). East‐west scans were made with Altair, an incoherent scatter radar, to spatially map (1) the backscatter produced by field‐aligned irregularities and (2) the electron density distribution of the background F layer. Plasma bubbles were spatially mapped for the first time with an incoherent scatter radar. By assuming invariance along the magnetic field lines (over distances of less than 100 km) we show that 1‐m field‐aligned irregularities are directly related to plasma bubbles.
Correlated observations of the equatorward diffuse auroral boundary
Authors: Slater D.W. , Smith L.L. , Kleckner E.W.
Published: February 2008

The equatorward boundary of the diffuse auroral zone, as viewed via the 6300‐Å (O(¹D)) emission line, has been examined by using ground‐based photometer data. These observations are supplemented with in situ measurements of ionospheric parameters by satellite‐borne instrumentation within the photometer field of view. We find high spatial correlation among 6300‐Å emission, low‐energy (E <1 keV) electron precipitation, and the high‐latitude recovery of ambient electron density which constitutes the poleward cliff of the main ionospheric trough. Time resolution afforded by this ground‐based optical method is especially suited for monitoring the ionospheric signature of this low‐energy particle precipitation over broad longitudes. A model is developed of the statistical equatorward boundary of the diffuse aurora as a function of magnetic local time and magnetic activity (as monitored by Kp index). The local time dependence of this boundary exhibits a latitudinal morphology similar to that of the earthward equatorial plasma sheet—that is, asymmetric about local midnight and skewed toward lesser invariant latitude values within the morning sector.
The excitation and collisional deactivation of metastable N(²P) atoms in auroras
Authors: Zipf E.C. , Espy P.J. , Boyle C.F.
Published: February 2008

The concentration and altitude distribution of metastable N(²P) atoms has been measured in a diffuse IBC II+ auroral arc. The dominant N(²P) source is shown to be the dissociative excitation of N2 by electron impact with a minor contribution from the dissociative recombination of N2+ ions. The possibility that an ion‐molecule process involving atomic oxygen and vibrationally excited N2+ ions, (N2+)vib + O → NO+ + N(²P), is a significant N(²P) source is also explored. Atomic oxygen is found to be the principal N(²P) quenching agent, with O2 contributing significantly below 120 km. By combining these observational results with recent laboratory studies on N2 dissociative excitation the proportional yield of N+, N(²P), N(²D), and N(4S) atoms from electron‐impact dissociation of N2 under optically thick conditions is found to be 0.135∶0.165 0.30∶0.40, respectively, at 100 eV.
Comparison between the 30‐ to 80‐keV electron channels on ATS 6 and 1976‐059A during conjunction and application to spacecraft charging prediction
Authors: Garrett H.B. , Schwank D.C. , Higbie P.R. , Baker D.N.
Published: February 2008

The ATS 6 satellite, during an orbital maneuver in September 1976, passed within a few hundred kilometers of the geosynchronous satellite 1976‐059A. Analysis of the 30‐ to 80‐keV electron data from the University of California at San Diego (UCSD) electrostatic analyzers on ATS 6 and the 30‐ to 300‐keV electron data from the Los Alamos Scientific Laboratory instrument on 1976‐059A during this period reveals good agreement between the two instruments even when the separation is ±7°. The low‐energy UCSD ion data from ATS 6 allow a simultaneous determination of the potential difference between ATS 6 and the ambient medium. Use of the 1976‐059 A electron data to approximate the ambient plasma electron density and temperature during these charging periods indicates sufficient information exists in order to estimate the maximum potentials to which ATS 6 charges in sunlight and eclipse. As data from 1976‐059A and similar satellites are potentially available in real time, the information therefore exists to create a satellite charging index for the geosynchronous regime that would be valid within at least ±7° longitude of the position of each measurement.
Type Pi Magnetic field pulsations at very high latitudes and their relation to plasma convection in the magnetosphere
Authors: Heacock R.R. , Chao J.K.
Published: February 2008

Type Pi (broadband) magnetic field pulsation activity near the dayside cusp and in the polar cap has been investigated using data recorded at Sachs Harbour (76.2°N, IL (invariant latitude)) and at Thule, Greenland (86.3°N, IL). Most of the pulsation activity observed at these sites must be classsified as type Pi, and this activity occurs mainly in midday hours. In summer, the midday Pi intensities are on the same order as at auroral oval sites in the night sector. Pi amplitudes are smaller in winter at Thule than in summer in the ratio 1∶3. Pi activity is always present at these very high latitudes in day hours in summer, with a minimum observed amplitude of 14 nT at Sachs and 5 nT at Thule in June–July, 1977. A study of isolated substorms having sharp onsets revealed a clear tendency for Pi activity to appear in the polar cap preceding the substorm, with a median lag between onset of Pi at Thule and onset of substorm near 1½ hours. We believe that this class of Pi activity indicates the presence of plasma convecting antisunwards over the polar cap. Polar cap and cusp Pi activity also tends to be seen during the substorms. The Pi pulsations appear to be caused by three‐dimensional current loops that are driven by the magnetospheric electric field at times of enhanced plasma convection. The response of the current loop is closely related to the conductivity of the E region portion of the loop, and this characteristic explains the tendencies for larger Pi amplitudes to be observed in the dayside and summer time polar cap and at locations where auroral precipitation increases the E region conductivity.
Non‐WKB Alfvén waves in the solar wind
Authors: Heinemann M. , Olbert S.
Published: February 2008

We treat, both analytically and numerically, small‐amplitude, undamped, toroidal Alfvén waves in a model of axisymmetric solar wind flow in which solar rotation is neglected. There is no restriction to WKB waves; the waves may have any frequency. By transforming in simple ways the equations governing the waves we are able to obtain exact formal solutions to the general time‐dependent problem as well as to the Fourier‐analyzed problem. We discuss the equations and their solutions in terms of coupled inward and outward propagating waves. One integral of the equations for the Fourier amplitudes is obtained; it relates the amplitudes of the ingoing and outgoing waves. The integral is a special case of a general law of conservation of wave action, which we show to hold for finite wavelengths. The statement of the conservation of wave action is shown to be analogous to the conservation of particle‐antiparticle pairs in relativistic quantum theory. We obtain the condition required for WKB waves and show that it depends on the coupling of waves in a flowing medium. The solar wind problem is discussed in terms of the Fourier amplitudes. It is shown that there is a singularity in the equations, at the Alfvén point, which determines physically acceptable solar wind solutions. A qualitative account of the amplitudes far from the sun is given based on an exact solution for a model with constant solar wind flow speed. A conservation equation for the wave energy is obtained, and the relations among the wave energy density, energy flux density, force, and acceleration are stated. Numerical solutions, based on realistic solar wind profiles, are given. We show that non‐WKB waves with wave periods of about a day or two have somewhat greater wave energy densities, up to a factor of 2 or so, in the corona than do WKB waves with the same amplitude at 1 A.U. On the other hand, non‐WKB waves of any wave period are no more effective in accelerating the plasma than are WKB waves; they are much less effective for wave periods of a day or more. We conclude that, for conditions actually existing in the corona, WKB estimates quite accurately account throughout the corona for the wave energy density, energy flux density, and wave acceleration of the plasma for Alfvén waves with periods less than about 0.05, 1, and 0.01 day, respectively; the corresponding periods in the solar wind are about 1, 1, and 0.5 day.
Power density of equatorial electric field at L=2.3
Authors: Andrews M.K.
Published: February 2008

Records of the Doppler shift on signals from a VLF transmitter received in the whistler mode are converted to fluctuation electric fields in the equatorial plane at L=2.3 and presented as power spectral densities. The 200 hours of data examined show 2 orders of magnitude variation in the power level as magnetic activity rises, though there is a considerable range of values at a given level of activity. Median values are an order of magnitude below the levels found by balloon extrapolations at what were generally higher latitudes. Simultaneous whistler mode records of azimuthal electric field at longitudes spaced by about 7 hours show such correlations that the electric fields near 1‐hour period must be composed mainly of low order spatial modes. With this assumption a diffusion coefficient at L=2.3 for radially diffusing particles is calculated which shows that at energies up to ∼0.5 MeV, electrostatic diffusion must be very important.
High‐latitude ion convection in the nighttime F region
Authors: Heelis R.A. , Hanson W.B.
Published: February 2008

A large data base of Atmosphere Explorer C measurements of the bulk ion velocity vector in the high‐latitude F region has been examined. The concept of shear and rotational flow reversals is expanded upon to determine the extent to which the boundary between antisunward and sunward convection (i.e., a polar cap boundary) is an electrostatic equipotential. A most important factor in characterizing the nature of the large‐scale geometrical configuration of the nighttime F region convection is the location and extent of quasi‐equipotential regions of the convection reversal boundary.
Micropulsations in the electric field near the plasmapause, observed by Isee 1 (paper 80A0033)
Authors: Moe T.E. , Maynard N.C. , Heppner J.P.
Published: February 2008

Based on 1 year of data from the double‐probe electric field instrument on Isee 1, a survey of occurrence of micropulsations near and inside the plasmapause has been made. The observed pulsations are classified as Pc 3 and Pi 2. In addition one single event of Pc 1 is observed. Pc 3 events are common during the local day, with a maximum percentage of occurrence as high as 72 in the morning hours. They occur on all frequencies in the Pc 3 band, but the most dominant frequencies are 30–50 mHz (20–33‐s period), and the amplitudes range from 0.1 to 4–5 mV/m peak to peak. The strongest Pc 3 events are nearly linearly polarized. Based on the azimuth angle of the polarization, the orientation is usually either radial from the earth or east‐west. The direction of rotation for the electric field vector is most often left‐handed in the morning sector and right‐handed in the afternoon sector. The Pi 2 events are concentrated on the local nightside. The amplitude for these pulsations is typically of the order of 2 mV/m peak to peak but can range as high as 20 mV/m peak to peak. These pulsation events are usually composed of several frequency components, with the dominant frequency most often in the band 10–16 mHz (62–100‐s period).
Diurnal, seasonal, and nighttime variations of atomic nitrogen in the equatorial thermosphere
Authors: Engebretson M.J. , DeFreese J.A. , Mauersberger K.
Published: February 2008

The open source neutral mass spectrometer on board the equatorial Atmosphere Explorer E satellite (AE‐E) measured atomic nitrogen densities at frequent intervals during both the elliptical and circular orbit phases of satellite operations. Elliptical orbit data presented here by means of empirical models at 225‐ and 300‐km altitude provide diurnal and seasonal profiles at altitudes lower than previously possible. Data from individual circular orbits later in the AE‐E mission confirm essential features of these models, particularly the diurnal density profile. At lower altitudes, considerable variation is evident near midnight, with density enhancements correlated with increasing levels of geomagnetic activity.
Particle diffusion in the geomagnetosphere: Comparison of estimates from measurements of magnetic and electric field fluctuations
Authors: Lanzerotti L.J. , Wolfe A.
Published: February 2008

We present a comparison of particle radial diffusion in the earth's magnetosphere that is determined from measurements of fluctuating magnetic and electric fields. We show, for a day when simultaneous satellite and ground‐based magnetic field data and published electric field data are available, that estimates of the radial diffusion from these fluctuating fields are comparable. We also show that the fluctuating fields at high latitudes, in the auroral zone, produce radial diffusion coefficients a factor of ten larger than would be expected by the extrapolation of subauroral latitude observations to higher latitudes.
A coherent nonlinear theory of auroral kilometric radiation 1. Steady state model
Authors: Grabbe Crockett L. , Papadopoulos Konstantinos , Palmadesso Peter J.
Published: February 2008

A theory of auroral kilometric radiation due to the nonlinear interaction between negative energy electromagnetic waves and coherent electrostatic ion cyclotron waves is developed. The theory predicts that such radiation produced must have X mode polarization and must have a frequency that lies in a narrow band between the right‐hand cutoff and the Doppler‐shifted beam cyclotron frequency for each local point of origin. The basic requirement for free space accessibility is the presence of high‐energy beams in the inverted V events and a density‐depleted cavity of the type observed by Isis 1 measurements. Beam densities of the order of 10−3 of the (depleted) background density appear to be necessary for the instability producing the radiation. Under ideal conditions, paths of wave growth of the order of 100 km may be adequate to produce observed radiation levels from electromagnetic noise at the appropriate frequency in the source region.
Spaced lidar and nightglow observations of an atmospheric sodium enhancement
Authors: Clemesha B.R. , Kirchhoff V.W.J.H. , Simonich D.M. , Takahashi H. , Batista P.P.
Published: February 2008

On the night of August 25–26, 1979, a large enhancement was observed in the density of atmospheric sodium at a height of 95 km. The enhancement, lasting about 15 min and extending over a height range of about 2 km, was observed at three positions about 50 km apart. Increases in sodium airglow occurring almost simultaneously were observed at two points separated by 107 km. From the time lags between the occurrence of the enhancement at the various measuring points it is concluded that it was caused by the horizontal motion of a cloud of sodium with a density about 10 times the normal density at the peak of the sodium layer. The cloud appears to have been moving in an approximately SW direction with a velocity of the order of 200 m s−1. On the assumption that the sodium was of meteoric origin, it is concluded that a minimum of 10 kg of meteoric material was necessary for its formation. From the magnitude of the observed increases in sodium abundance and sodium airglow a value of 3 × 1013 m−3 is derived for the ozone density at 95 km.
The observation and production of ion acoustic waves during the Trigger Experiment
Authors: Kintner P. \M. , Kelley M. \C. , Holmgren Gunnar , Bostrom Rolf
Published: February 2008

A cesium ion cloud was created by an explosive release about 1 km from the instrumented section of the Trigger payload. Band‐limited electric field and density waves were observed shortly after the ion cloud was detected. Since the electric field and density components had similar spectral shape and the wave electric field was oriented parallel to the ambient magnetic field, we identify the waves as collisionless ion acoustic waves. Ion‐ion streaming between Cs+ and the ambient ions is suggested as a source of free energy for the ion acoustic waves, and this hypothesis is tested using the linear dispersion relation. Ion‐ion streaming is found to be a plausible mechanism if Te/Ti is large. Te was measured to be elevated over the ambient value briefly, and modeling indicates that the Cs ion temperature may have been greatly depressed from the ambient value, thereby implying that within the explosive cloud, Te/Ti ≥10.
Saturn's magnetosphere and its interaction with the solar wind
Authors: Smith Edward J. , Davis Leverett , Jones Douglas E. , Coleman Paul J. , Colburn David S. , Dyal Palmer , Sonett Charles P.
Published: February 2008

Pioneer 11 vector helium magnetometer observations of Saturn's planetary magnetic field, magnetosphere, magnetopause, and bow shock are presented. Models based on spherical harmonic analyses of measurements inside 8 Rs reveal that the planetary field has a high degree of symmetry about the rotation axis. The vector dipole moment of 0.2 G Rs³ has a tilt angle less than 1° and is offset along the polar axis 0.04±0.02 Rs. Equatorial offsets derived from the models show substantial variability and could be consistent with a very small offset. Beyond 10 Rs, near the noon meridian, the field topology is characteristic of a dipole field being compressed by high‐speed solar wind. There is no evidence of plasma outflow, i.e., a planetary wind. Near the dawn meridian the field lines in the outer magnetosphere are stretched‐out into a nearly equatorial orientation. Crossings of a thin current sheet are observed, apparently caused by motions driven from outside the magnetosphere. The field above and below the current sheet spirals out of the magnetic meridian plane at large distances to point tailward and parallel to the magnetopause. The location of the magnetopause is consistent with a shape that is similar to that of the earth but perhaps more blunt, as suggested by the attitude of the magnetopause near dawn. Near both the noon and dawn magnetopause the field in the magnetosheath equals or exceeds the field in the magnetosphere. The noon observations suggest a piling‐up of magnetosheath field lines adjacent to the magnetopause. Large impulsive field compressions are observed in the magnetosheath near noon. Multiple crossings of the bow shock are observed, and the absence of significant changes in field direction shows that it is quasi‐perpendicular. The speeds of motion of the shock toward and away from Saturn are estimated to be 150 and 50 km/s, respectively. A shock thickness of ∼2000 km is inferred.
Sources and sinks of energetic electrons and protons in Saturn's magnetosphere
Authors: Van Allen J. A. , Randall B. A. , Thomsen M. F.
Published: February 2008

This paper reports the results of continuing analysis and interpretation of energetic particle observations obtained by the University of Iowa instrument on Pioneer 11 during traversal of Saturn's magnetosphere in August–September 1979. On the basis of the radial dependence of the phase space density of very energetic protons (Ep >80 MeV) and estimates of the necessary source strength, it is reasonably certain that cosmic ray neutron albedo from the planet's atmosphere and Rings A and B is the source of such particles. At radial distance r=2.7 Rs and for Ep >80 MeV, the ratio of source strength 𝒮 to radial diffusion coefficient D is ∼2 × 10−24 cm−5. A reasonable pair of values is 𝒮 ∼7 × 10−15 cm−3 s−1 and D ∼1 × 10−10 Rs² s−1. The spectrum of electrons 0.040< Ee <(few MeV) and the radial dependence of the phase space density of such electrons are derived. The source of these electrons is at the magnetosheath. The source of protons Ep ∼1 MeV is also at the magnetosheath and may be either thermalized solar wind or energetic interplanetary protons which were unusually abundant at the time of Pioneer 11's encounter. Low energy electrons and protons experience strong losses inward of r ∼10 Rs, apparently attributable to the large inner satellites Rhea, Dione, Tethys, Enceladus, and Mimas and to a broad tenuous ring of particulate matter (Ring E) and/or gas. There were important temporal changes in the distributions of low energy electrons and protons within a period of ∼10 hours between inbound and outbound passes, probably caused by unusually disturbed interplanetary conditions.
Charged particle anisotropies in Saturn's magnetosphere
Authors: Bastian T. S. , Chenette D. L. , Simpson J. A.
Published: February 2008

We report observations of anisotropies and pitch angle distributions for 0.5–1.8 MeV protons, 7–17 MeV electrons and ⪞3.4 MeV electrons in Saturn's magnetosphere made with the University of Chicago experiments on Pioneer 11. In the outer magnetosphere (L >6) there is clear evidence for corotation of the proton flux, and the proton pitch angle distribution shows maximum flux perpendicular to the magnetic field (‘pancake’ distribution). Observed changes in the amplitude and shape of the pitch angle distributions suggest the existence of significant temporal variations in the outer magnetosphere. From L=6 to L=4, the proton intensity decreased by more than two orders of magnitude, and the pitch angle distribution shifted to a ‘dumbbell’ form (maximum flux parallel to magnetic field). The shift in pitch angle distribution most likely results from preferential absorption of large pitch angle particles by the tenuous E‐ ring found in the equatorial plane out to at least R=5 Rs. For L <4, the proton intensity increased inwards, implying an inner edge for the E ring at R ≈4 Rs. Except for regions where the flux was reduced by satellite absorption, the pitch angle distributions remained dumbbell. In absorption regions, pancake distributions were found. The observations are consistent with the suggestion by McKibben and Simpson (this issue) that inward diffusion and acceleration at Saturn may proceed primarily via large, infrequent disturbances. Electron anisotropies were measurable only for L ⪝4.5, and the pitch angle distributions were found to be pancake for the entire region L <4.5, suggesting that the absorbing particles in the E ring have radii that lie between the range of ∼1 MeV proton and ∼10 MeV electrons, or of the order of millimeters.
Results of Pioneer 10 and 11 Meteoroid Experiments: Interplanetary and near‐Saturn
Authors: Humes D. H.
Published: February 2008

The meteoroid penetration detectors on Pioneer 10 (channel 0) recorded 95 penetrations through the 25‐µm stainless steel test material while the spacecraft was between 1 and 18 AU. The spatial density of 10−9g meteoroids is found to be essentially constant between 1 and 18 AU. The meteoroid penetration detectors on Pioneer 11 recorded 87 penetrations (55 on channel 0 and 32 on channel 1) through the 50‐µm stainless steel test material while the spacecraft was between 1 and 9 AU. It is found that the meteoroids between 4 and 5 AU are not in direct circular or near‐circular orbits near the ecliptic plane. The Pioneer 11 data obtained between 4 and 5 AU are best explained by the meteoroids being in randomly inclined orbits of high eccentricity. If meteoroids are in these cometlike orbits, the great increase in penetration flux previously measured near Jupiter with the Pioneer 10 experiment cannot be attributed to gravitational focusing unless the size distribution of meteoroids changes substantially between 1 and 5 AU. At Saturn encounter, the penetration flux increased by about three orders of magnitude, probably as the result of impacts from ring particles. Saturn's ring E is estimated to be 1800 km thick with an optical thickness greater than 10−8.
The radius of Titan from Pioneer Saturn data
Authors: Smith Peter H.
Published: February 2008

The radius of Titan has been determined from Pioneer Saturn observations taken September 2, 1979. The data sets, one in the red (0.64 µm) and one in the blue (0.44 µm), yield radii of 2840±25 km and 2880±22 km, respectively. The discrepancy between the radius values in the two colors is felt to be the consequence of an optically thin submicron haze above the nominal haze layer. The altitude difference between the red and blue limb is 40±20 km. Using a cloud model derived from the Pioneer Saturn data, the lunar occultation radius (Elliot et al., 1975) has been revised to 2845±40 km, in good agreement with the present result. A lower limit of 1.37 g cm−3 can now be set on Titan's bulk density, using the red radius at the haze top. The actual bulk density probably falls in the range 1.65–1.85 g cm−3 for an atmosphere of 150‐ to 250‐km thickness below the red limb.
Charge transfer of doubly charged oxygen ions in helium
Authors: Dalgarno A. , Butler S. E. , Heil T. G.
Published: February 2008

The charge transfer reaction O++ + He → O+ + He+ is analyzed. It is argued that the measured upper limit of 10−14 cm³ s−1 for the rate coefficient at 300 K is close to the actual value and that the rate coefficient is a rapidly increasing function of temperature. A value between 4 × 10−14 cm3 s−1 and 4 × 10−13 cm3 s−1 is predicted at 1000 K and between 2 × 10−11 and 1 × 10−10 cm3 s−1 at 10,000 K.
Multispacecraft observations of energetic electron flux pulsations at 6.6 RE
Authors: Baker D. N. , Higbie P. R. , Belian R. D.
Published: February 2008

This paper reports observations of highly periodic flux pulsations in >30‐keV electrons measured by essentially identical Los Alamos National Scientific Laboratory charged particle analyzers on board spacecraft 1976‐059, 1977‐077, and 1979‐053 at geostationary orbit. Oscillations with periods in the range from ∼1 min to ∼10 min (Pc 4 and Pc 5) have been studied. Statistical analyses were performed using ∼4.5 years of data obtained at magnetic latitudes of 4.8°, 9.4°, and 11.4°. The statistical occurrence probabilities have been evaluated for measurements made at each of the various magnetic latitudes and for all local times. Substantial magnetic latitude and seasonal dependences are found for the flux pulsation occurrence frequency versus local time. These results are discussed in terms of previous observations and present theories of magnetic pulsation generation.
Superthermal electrons and Bernstein waves in Jupiter's inner magnetosphere
Authors: Barbosa D. D. , Kurth W. S.
Published: February 2008

A theoretical model for generation of banded electrostatic emissions by low density, superthermal electrons is developed for application to Jupiter's magnetosphere. The model employs a power law form for the energy dependence and a loss cone pitch angle distribution of the superthermals to drive convective instability of Bernstein modes. We concentrate on instability in the upper hybrid band and on lower harmonic bands below the upper hybrid frequency. A direct correspondence between spectral features of the 3/2's band and resonant superthermal electrons is found. The concept of a critical flux j⊥* of resonant electrons able to provide 10 e‐foldings of electric field amplification yields an explicit relation j⊥* ∼p in terms of the background thermal electron pressure. This result is used to construct a theoretical/empirical model of thermal electron density and temperature from 6–20 RJ in the Jovian magnetosphere which suggests that the ion and electron temperatures satisfy Te <Ti ∼10Te in this region. Finally, wave ray paths are computed for propagation in the magnetic equator and in the magnetic meridional plane of a dipole magnetic field. These ray paths suggest that intense wave activity is tightly confined to a small latitudinal extent, Λ≲±4°, about the magnetic equator.
Conjugate observation of electron microburst groups by Bremsstrahlung X ray and riometer techniques
Authors: Siren J. C. , Rosenberg T. J. , Detrick D. , Lanzerotti L. J.
Published: February 2008

The first evidence is reported of simultaneous conjugate electron microburst group precipitation. Groups of bremsstrahlung X ray microbursts (E >25 keV) were observed during a substorm recovery phase by a balloon‐borne scintillation counter over Roberval, Quebec, Canada. The microburst groups were accompanied one‐to‐one by time‐delayed and broadened pulses of ionospheric absorption measured by a high sensitivity 30‐MHz riometer at Siple Station, Antarctica (L ≈ 4.1). For the interval of highest correlation, the absolute lag between the two data sets was 4±1 s, to the limit of the relative timing accuracy. Approximately 2 s of the observed lag had been introduced by a low‐pass filter in the riometer data acquisition unit. The remainder (2 s) was due to the ionospheric recombination process, which evidently had a response time (τ∼5 s) during this event much shorter than that ordinarily associated with the D region of the ionosphere. Model calculations of the ionospheric response to time‐varying precipitation, derived from the profile of the measured X ray flux, provide a consistent picture of simultaneous microburst group precipitation at conjugate points, absolute absorption and the electron spectrum derived from X rays, the degree of variation in absorption and X ray fluxes, and the characteristic ionospheric time constant at the altitude of maximum energy deposition.
Turbopause internal gravity waves, 557.7 nm airglow, and eddy diffusion coefficient
Authors: Battaner E. , Molina A.
Published: February 2008

A study of the properties of internal gravity waves by means of observations of the 557.7‐nm emission line has been carried out. Special emphasis was put on the determination of the kinetic energy density of the waves, which have maxima in winter and in summer, and on the determination of the enhanced diffusion tensor K. Values of Kzz, the zz component, important in theoretical models, of the order of 3 × 106 cm² s−1 were obtained, and its seasonal variation exhibits a winter maximum. The enhanced diffusion due to internal gravity waves is highly anisotropic, being the two eigenvalues corresponding to the horizontal degeneration plane of the order of 4 × 109 cm² s−1. The possible relation between K and D region winter anomalous absorption has been also examined.
The spatial anisotropy, rigidity spectrum, and propagation characteristics of the relativistic solar particles during the event on May 7, 1978
Authors: Debrunner H. , Lockwood J. A.
Published: February 2008

The data from the worldwide network of neutron monitors have been used to deduce the spatial distribution, rigidity spectrum, and propagation characteristics of the GLE on May 7, 1978. The large magnitude of the GLE and hard rigidity spectrum enabled an analysis to be made utilizing both high‐latitude and mid‐latitude stations. A straightforward method of analysis could not be used to determine the source function, probably owing to the influence of external magnetospheric currents upon the asymptotic directions of high‐latitude neutron monitors and on the asymptotic directions of all stations at rigidities near cutoff. Consequently, we used measurements from the mid‐latitude neutron monitors sensitive to high rigidity particles from the solar flare. The apparent source of the solar particle flux near earth was located in a region around 20°N, 87.5°E, which is approximately 40° west of the sun. The functional form of the pitch angle distribution was given by exp (−δ²/2θ²), θ≈ 25° during the first 30 minutes and then became flatter. The observed anisotropy was ∼1 until 0410 UT, then decreased to <0.7 at 0430 UT when the enhancement of the counting rate was ≲10% of the maximum increase at neutron monitors that were ideally situated to observe the GLE. The rigidity spectrum for P >3 GV was an exponential exp (−P/Po) with Po=1.45 near the onset, changing to Po=0.7 GV later. An analysis using the telegraph equation [Fisk and Axford, 1969] yields a scattering mean free path λ∥≳3 AU. The analysis indicates that the propagation was scatter‐free for about one hour and that the intensity‐time profile of the solar injection was observed for particles with P >1 GV.
On the three‐dimensional nature of the modulation of galactic cosmic rays
Authors: Venkatesan D. , Agrawal S. P. , Lanzerotti L. J.
Published: February 2008

Recent results, on two different time scales, of the influence of solar polar coronal holes on the galactic cosmic ray intensity appear on the surface to be inconsistent. We show, in the context of present knowledge of the effects of high‐speed solar wind streams on energetic particles, that the results are indeed mutually consistent and they support the view that coronal holes are influential in determining the three‐dimensional modulation of galactic cosmic rays in the solar system.
Electron temperature and heat flow in the nightside Venus ionosphere
Authors: Hoegy W. R. , Brace L. H. , Theis R. F. , Mayr H. G.
Published: February 2008

The electron energy budget of the nightside Venus ionosphere is analyzed by comparing two‐dimensional solutions of the heat conduction equation with an empirical model of the electron temperature based on Pioneer Venus measurements. The theoretical and empirical models are confined to a narrow latitude band at low latitudes. The energy calculation includes solar EUV heating at the terminator, electron cooling to ions and neutrals, and heat conduction within the ionospheric plasma. Heating at the ionopause by the shocked solar wind is included through an upper boundary condition. Several simple, uniform magnetic field models are found to be inconsistent with the empirical temperature model. An optimum magnetic field for the equatorial region is derived by solving for the heat flux directions which force energy conservation while constrained by the observed temperatures within the range of 80° to 170° SZA (solar zenith angle) and 160 to 700 km. The resulting heat flux vectors suggest a magnetic field that connects the lower nightside ionosphere (less than 300 km) to the dayside ionosphere and connects the upper ionosphere (greater than 300 km) to the ionosheath. Thus the lower ionosphere is heated through conduction of heat from the dayside, and the upper ionosphere is heated by the solar wind in the ionosheath, heat flowing downward and from the nightside to the dayside. The suggested magnetic field appears to be consistent with the magnetic field directions observed by the Pioneer Venus magnetometer.