bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of reflected and diffuse ions upstream from the Earth's bow shock
Authors: Paschmann G. , Sckopke N. , Papamastorakis I. , Asbridge J. R. , Bame S. J. , Gosling J. T.
Published: February 2008

The distinction between two types of upstream ion populations has been made on the basis of pronounced differences in their distribution functions. The ‘reflected’ ions represent a fast beam with temperatures typically 1 to 5 times 106 K and speeds up to five times the solar wind speed. An important feature of the reflected ion distributions in their strong temperature anisotropy, with T⊥ exceeding T∥ by a factor of two to three. In contrast, the ‘diffuse’ ions occupy a much larger region of phase space, both in energy and angle; their distribution function generally has the form roughly of a circular ridge in 2 dimensions and a spherical shell in 3 dimensions. Accordingly, their temperature is much larger (≳107 K), and their bulk speed typically is smaller than the solar wind speed. Both ion populations have densities of the order of 0.1 cm−3. At times transitions between the two extremes, represented by the reflected and diffuse ion populations, are observed. These ‘intermediate’ distributions are crescent shaped, with the center of curvature near the solar wind velocity. This property suggests that the intermediate distributions result from pitch angle scattering of the reflected beams in the solar wind frame and supports the idea that the reflected ions are the origin of the diffuse ions. At times the diffuse ion distributions exhibit considerable structure and rapid temporal variations. Reflected and diffuse ions can also be distinguished by their occurrence as a function of the angle θ between the local shock normal and the interplanetary magnetic field. Whereas the diffuse ions occur predominantly for small θ, the reflected ions are observed most frequently for θ ≳45°.
Plasma rest frame distributions of suprathermal ions in the Earth's foreshock region
Authors: Sentman D. D. , Kennel C. F. , Frank L. A.
Published: February 2008

We present rest frame ion distributions computed from three‐dimensional observations of upstream suprathermal ions gained by the University of Iowa Quadrispherical Lepedea on ISEE‐1. The observations are for a single inbound, midmorning pass starting upstream from the ion foreshock and continuing across the quasiparallel bow shock into the magnetosheath. The crossing of the ion foreshock boundary is marked by a several minute burst of ions of temperature 100–200 eV moving along the IMF away from the bow shock at 500 km/s relative to the solar wind. The observation of these ‘reflected’ ions is followed by an extended interval of ‘diffuse’ ions of temperatures 2‐3 keV flowing at ∼250 km/s relative to the solar wind and persisting until the bow shock is crossed. The diffuse ion β has a value of approximately 6 in the region of the suprathermal ions, exceeding the normal thermal ion β of the solar wind by roughly an order of magnitude. Both types of suprathermal ions constitute roughly 2% of the total ion density and carry a parallel heat flux of ∼2 × 10−2 ergs cm−2 s−1. When integrated over an assumed 10 × 10 RE bow shock emission area, this implies an upstream dissipation that may approach 1017 to 1018 ergs/s, comparable to a modest substorm.
Reflected and diffuse ions backstreaming from the Earth's bow shock 2. Origin
Authors: Bonifazi C. , Moreno G.
Published: February 2008

The morphology of the foreshock region and the origin of the ‘reflected’ and ‘diffuse’ ion populations are investigated for the first time through an extended statistical analysis. Data are supplied by the solar wind experiment on the satellite ISEE 2 in the period November 5 to December 20, 1977. It is confirmed, on a statistical basis, that quasi‐perpendicular shock structures generate beams of reflected ions which propagate along the interplanetary magnetic field lines against the incoming solar wind. Diffuse ions are at least in part originated by the disruption of the reflected beams due to some plasma instability, having a growth time of the order of a few tens of seconds. A preliminary energy balance appears to be consistent with the proposed picture of the phenomena occurring in the foreshock region.
The propagation of upstream protons between the Earth's bow shock and ISEE 3
Authors: Sanderson T. R. , Reinhard R. , Wenzel K.‐P.
Published: February 2008

We present a detailed analysis of a series of five successive upstream proton events observed within a 1‐hour time period on October 11, 1978. The observations were made by the low‐energy proton instrument on ISEE 3, which is designed to measure three‐dimensional anisotropies in the energy range 35–1600 keV. We have selected this particular series of events from the large number of upstream proton events observed at the position of ISEE 3, more than 200 RE upstream from the earth's bow shock, because the magnetic field at that time was quiet and the characteristics of the propagation of upstream protons were unusually clear. We examine in detail the intensity profiles and properties of the anisotropies. Of particular interest are effects in the anisotropy direction as the spacecraft enters or leaves a particle‐populated region. Analysis of the directions of the gradient anisotropies at the onsets and ends of the events reveals that upstream protons propagate in sheets or slabs from the earth's bow shock out to ISEE 3.
Propagation of energetic electrons in the magnetosheath and upstream solar wind
Authors: Palmer I. D.
Published: February 2008

The propagation of relativistic electrons through the magnetosheath and solar wind is investigated in the two extremes of scatter‐free motion and diffusive motion. For a source which is assumed on a field line close to the magnetopause, predictions are made of density U (or omnidirectional intensity) and anisotropy ξ at different points on the field line in the magnetosheath and upstream solar wind. Both extremes of motion predict in the solar wind a lower U than in the magnetosheath. However, while scatter‐free motion always gives greater anisotropy in the solar wind, in the diffusion case it depends on the locations of the comparison stations. The theory has been applied to observations of >200 keV electrons, and derived mean free paths in the magnetosheath are 3.8±0.6 RE and 8.7±0.6 RE on two separate traversals, while the average results over a 4‐year period give ≈ 1.0 RE. The latter value agrees with λ=1 RE obtained by an independent analysis of the same data set. The mean free path has also been computed from quasi‐linear theory and measured magnetic power spectra. These give λ varying from 0.27 RE for a typical high to 4.6 RE for a typical low level of disturbance in the magnetosheath, respectively. A particularly ‘quiet’ period gave λ=42.7 RE. The empirical results of λ=3.8 and 8.7 RE, obtained when Kp ≈ 2, are consistent with the low level of disturbance, while the average result of λ ≈ 1.0 RE lies right between the low and the high.
Upstream hydromagnetic waves and their association with backstreaming ion populations: ISEE 1 and 2 observations
Authors: Hoppe M. M. , Russell C. T. , Frank L. A. , Eastman T. E. , Greenstadt E. W.
Published: February 2008

Measurements from the Lepedea plasma instruments and the flux gate magnetometers on ISEE 1 and 2 are used to examine the nature of the hydromagnetic waves associated with the various classes of ions backstreaming from the earth's bow shock. The reflected ions, which are confined to a narrow energy and angular range, are accompanied by small amplitude (≲½γ peak to peak) left‐handed waves at frequencies close to 1 Hz in the spacecraft frame. Diffuse backstreaming particles with a broad energy spectrum are associated with low frequency (∼ 30‐s period) large amplitude (∼5γ peak to peak) waves. Intermediate particles are associated with a mixture of these two wave types. Often the waves associated with the diffuse beams steepen as if they were mini shocks. The leading edge (trailing edge in the spacecraft frame) frequently appears to break up into a whistler mode wave packet. These discrete wave packets are right‐hand polarized and have frequencies from below the proton gyrofrequency to well above it in the plasma frame and are blown back towards the earth by the solar wind.
Plasma waves associated with energetic particles streaming into the solar wind from the Earth's bow shock
Authors: Anderson R. R. , Parks G. K. , Eastman T. E. , Gurnett D. A. , Frank L. A.
Published: February 2008

In the upstream solar wind, three dominant types of plasma waves are observed associated with energetic particle streams coming from the earth's bow shock: ion acoustic waves, electron plasma oscillations, and whistler mode waves. The ion acoustic waves occur simultaneously with either ion beams or a dispersed ion population in the energy range from ∼0.5 to >45 keV. These short‐wavelength electrostatic waves are very impulsive, and the peak amplitudes increase with increasing ion flux and at spatial gradients in the energetic ion densities. The electron plasma oscillations are long‐wavelength nearly monochromatic electrostatic waves which are closely correlated with the flux of low‐energy electrons, especially in the 0.2–1.5 keV range. In the presence of only enhanced electron fluxes, the average amplitudes of the electron plasma oscillations approach the peak amplitudes. Amplitudes near 10 mV/m have been observed, although amplitudes from 0.1 to 1.0 mV/m are typical. In the presence of the dispersed ion component, electron plasma oscillations decrease in amplitude and become more impulsive. Electromagnetic waves with frequencies below 200 Hz are observed when either ion beams or dispersed ion distributions are present. These waves are usually weak and very impulsive. For these waves the refractive index determined from the wave B to E ratio is consistent with whistler mode radiation. Whistler mode waves also occasionally occur in association with electron plasma oscillations.
The modulation of low‐energy proton distributions by propagating interplanetary shock waves: A numerical simulation
Authors: Decker Robert B.
Published: February 2008

A numerical simulation has been developed to study the formation in the intensities of ≲0.1‐ to ∼10.0‐MeV protons of the long‐lived energetic storm particle (ESP) events observed in association with the passage of flare‐produced fast mode MHD shocks. Protons are traced numerically backward in time from a given observation point (i.e., particle detector), through their adiabatic scatter‐free motion along the assumed laminar spiral interplanetary magnetic field (IMF), and finally through the shock discontinuity to their pre‐shock interaction state. An ambient proton can undergo at most one shock encounter, during which, as seen in the shock frame, the proton is accelerated by its effective ‘grad‐B drift’ along the induced electric field each time it crosses the shock. The time‐reversed calculation reveals which of the observed protons interacted with the shock, where the shock interaction occurred, and by how much each interacting proton's kinetic energy was increased at the shock. Time profiles of the omnidirectional and unidirectional protons fluxes are formed from the trajectories by invoking Liouville's theorem and an ambient proton unidirectional flux j ∼T−γ, where T is the kinetic energy and γ the spectral exponent. Simulation predictions are shown for different observed proton energies under various assumptions concerning the shock speed and strength, the slope of the ambient proton energy spectrum, the variation of the angle β1 between the shock surface and the upstream IMF vector, and the heliocentric radial position r of the observation point. The simulation model correctly recovers the gross features of the intensity variations, flux anisotropies, and energy spectra time evolutions of many observed ESP events. Representative simulation results predict shock‐induced enhancements in low‐energy proton fluxes that are characterized by (1) long, steady preshock or upstream rises to peaks before the shock arrival and abrupt declines following the shock passage; (2) peak enhancement amplitudes that increase for lower‐energy protons, stronger and faster shocks, softer ambient proton spectra, decreased β1 and increased r, (3) large, highly field‐aligned preshock flux anisotropies directed away from the sun along the IMF, (4) small postshock flux anisotropies nearly perpendicular to the magnetic field and directed towards the sun along the IMF, and (5) steadily softening preshock energy spectra that are steepest at the peak flux enhancement and slightly softer than the ambient spectra after the shock passage.
Solar cycle modulation of galactic cosmic rays: Speculation on the role of coronal transients
Authors: Newkirk Gordon , Hundhausen A. J. , Pizzo V.
Published: February 2008

Coronal transients are believed to involve the expulsion of magnetic ‘bubbles’ or loops into interplanetary space. The close relationship of coronal transients with other forms of solar activity suggests a variation in their frequency of occurrence by a factor of 3–10 over the solar cycle. As magnetic ‘inclusions’ in the interplanetary magnetic field, transients should then lead to a solar cycle dependent scattering of cosmic rays entering the inner solar system. The power spectrum of a model of the transverse magnetic fluctuations and its solar cycle dependence is compared to the observed power spectra. Coronal transients are tentatively identified as the solar origin of the low‐frequency power in the interplanetary field and, as such, an important factor in cosmic ray modulation.
The solar origins of solar wind interstream flows: Near‐equatorial coronal streamers
Authors: Feldman W. C. , Asbridge J. R. , Bame S. J. , Fenimore E. E. , Gosling J. T.
Published: February 2008

Vela heavy ion and IMP solar wind data are used to identify the coronal origins of the interstream, low‐speed solar wind as well as to understand the causes of the long‐term trends in solar wind densities and electron temperatures observed at 1 AU. Several lines of evidence suggest a strong association between interstream flows and the extensions of the near equatorial band of coronal streamers into interplanetary space. This evidence includes (1) the moderate to high plasma density and oxygen freezing in temperatures measured at 1 AU which match similar conditions within coronal streamers close to the sun, (2) the strong association between sector boundaries and/or general field polarity reversals with both interstream flows at 1 AU and the photospheric footpoints of coronal streamers, and (3) the correlation between the long‐term trend in coronal morphology and the long‐term variation in the occurrence frequency of noncompressive density enhancements (NCDE's) which occur often within interstream flows. Our study further indicates that high electron temperatures at 1 AU result from a lower temperature gradient in the corona rather than an overall higher coronal temperature. Such conditions hold preferentially at the edges of NCDE's at 1 AU and hence by inference, the edges of coronal streamers near the sun. The observed flattening of the streamer belt about the solar equator near solar minimum, then led to a concurrent preferential sampling of streamer associated solar wind at 1 AU and hence a higher average density and electron temperature.
Interplanetary propagation of <1‐MeV protons in nonimpulsive energetic particle events
Authors: Zwickl R. D. , Roelof E. C.
Published: February 2008

A systematic analysis of low‐energy anisotropy data derived from nonimpulsive energetic (0.3–0.5 MeV) proton events has been carried out with the APL/JHU detectors on board the IMP 7 and 8 spacecraft during 1972–1975. After reducing to a minimum any magnetospheric influence by applying various selection criteria, 1289 hourly anisotropy averages survived for which we also had simultaneous hourly averaged solar wind and magnetic field observations. These anisotropy vectors were resolved into components parallel and perpendicular to the measured magnetic field. Analysis of the resulting anisotropy distributions leads directly to the following conclusions: (1) The average perpendicular anisotropy component is nearly entirely accounted for in terms of the E × B drift, and hence interplanetary transverse diffusion is negligible at these energies. (2) Application of diffusion‐convection theory to our data yields an estimate of a representative value for the ratio of mean free paths transverse and parallel to B which is consistent with zero but bounded above, i.e., 0 ≤λ1/λ∥ <0.05. (3) The parallel anisotropy component averages nearly to zero over many events, consistent with virtually no net particle streaming along the field line in nonimpulsive particle events at 1 AU. Therefore the net event‐averaged anisotropy of 0.3‐ to 0.5‐MeV protons observed by spacecraft located at 1 AU is outward away from the sun in a direction approximately perpendicular to the nominal magnetic field, implying that this population of protons is, on the average, being removed from the vicinity of 1 AU simply by ‘cross‐field convection,’ i.e., the E × B drift.
Nonlinear theory and experimental observations of the local collisional Rayleigh‐Taylor instability in a descending equatorial spread F ionosphere
Authors: Keskinen M. J. , Szuszczewicz E. P. , Ossakow S. L. , Holmes J. C.
Published: February 2008

The nonlinear evolution of the local collisional Rayleigh‐Taylor instability in downward‐moving equatorial F layers has been studied in a coordinated theoretical and experimental program dealing with actual conditions of bottomside spread F. For ambient bottomside electron density gradient scale lengths L=8 and 25 km, we find large percentage depletions and inverse power law spatial power spectra over the intermediate wavelength range λ=25 m‐1 km. In addition we outline a nonlinear theory of the collisional Rayleigh‐Taylor instability applicable to an upward‐ or downward‐moving equatorial F region ionosphere. The agreement between the experimental and theoretical results of this study lends further support to the belief that the collisional Rayleigh‐Taylor instability is responsible for large‐scale size irregularities that occur under conditions of equatorial spread F.
One‐dimensional models of quasi‐neutral parallel electric fields
Authors: Stern David P.
Published: February 2008

Parallel electric fields can exist in the magnetic mirror geometry of auroral field lines if they conform to the quasi‐neutral equilibrium solutions first suggested by Alfvén and by Persson. Such solutions may contain double‐layer discontinuities, reflecting the disparity between the two sources that contribute to their plasma population—the hot and rarefield magnetosphere, magnetically confined, and the cool dense ionosphere, held down by gravity. This study reviews previous results on quasi‐neutral equilibria and on double layers and then examines the effects on such equilibria due to nonunique solutions, potential barriers, and field‐aligned current flows, using as inputs monoenergetic isotropic distribution functions. Among the conclusions reached are the following: (1) Double layer solutions not involving any net current flow are readily constructed; (2) Such layers may occur naturally and may involve a significant fraction of the total field aligned voltage drop; (3) Nonuniqueness of quasi‐neutral solutions must be utilized to determine the position of such layers; (4) The gravitational potential barrier that confronts escaping ions plays an important role and must be taken into account; (5) Outbound field‐aligned currents are carried primarily by precipitating electrons and only a very small fraction of them is due to ionospheric positive ions; (6) Inbound field‐aligned currents require an appreciable voltage to drive them, and their density is no greater than that of outbound currents; (7) Precipitation with no net j∥ sets up a ‘thermoelectric potential’ similar to the one predicted by Hultqvist. Overall, the model suggests that quasi‐neutral equilibria can explain many of the observed features of field‐aligned currents and of their associated electric fields, though solutions at this stage do not extend to voltages exceeding 2.2 kV.
Mars satellite Deimos interaction with the solar wind and its influrence on flow around Mars
Authors: Bogdanov A. V.
Published: February 2008

Data are given indicating the possibility of strong solar wind Deimos interaction. Plasma measurements on board the Soviet interplanetary probe Mars 5 showed a drop in ion density and distortion of ion energy spectra in the region behind Deimos at a distance of about 20,000 km. The dimension of Deimos is smaller than the ion gyroradius, and the effect observed may exist in the case of Deimos outgassing. Ion spectra characteristics indicate that outgassing activity is probable. The existence of strong solar wind‐Deimos interaction may result in influence on the Martian magnetosphere and bow shock. The dimension of the magnetosphere is maximal when Mars is shaded by Deimos.
Radar measurements of high‐latitude ion composition between 140 and 300 km altitude
Authors: Kelly John D. , Wickwar Vincent B.
Published: February 2008

The Chatanika radar has been used to measure the ratio of atomic (O+) ions to molecular (O2+, NO+) ions in the high‐latitude ionosphere. The radar results agreed well with simultaneous in situ rocket data, giving confidence in the radar method of deducing ion composition. Measurements made over long periods of time show seasonal variations, diurnal variations, and variations due to auroral processes. The transition altitude, where the number densities of atomic and molecular ions are equal, is a convenient parameter for describing the composition variation with altitude or ‘composition altitude profile.’ The transition altitude occurs at ∼190 km at night and ∼170 km during the day, in agreement with midlatitude results. During the winter the daytime transition altitude is 15 km lower than in summer, a seasonal variation similar to that at midlatitudes. Energetic particle precipitation results in the lowering of the transition altitude, by 10 km in one case when energetic particles deposited ∼20 ergs/cm² s in the atmosphere. The largest variations in ion composition were found during periods of large joule heat input resulting from electric fields on the order of 50 mV/m. The transition altitude increased by 50 km in a case where the joule heat input rate was 30 ergs/cm² s. These observations were compared to calculations from a simple steady state model involving the principal consituents and reactions. The results indicate that the transition altitude during particle precipitation is most influenced by the increased ion production. There do not appear to be significant effects from possible increases of N2 vibrational temperature. A number of interrelated effects contribute to the increase in transition altitude during joule heating. The most important effect is the electric field contribution in raising the effective ion temperature. In addition, it appears that increased N2 density is also required to account for the observed change.
Characteristics of the instantaneous auroral oval in the 1200–1800 MLT sector
Authors: Murphree J. S. , Cogger L. L. , Anger C. D.
Published: February 2008

By using two‐dimensional optical images at 3914 Å and 5577 Å from the ISIS 2 satellite auroral imager, we have investigated the characteristics of auroras in the afternoon sector. The observed auroral configurations can be placed into three categories: diffuse aurora only, isolated discrete aurora, and discrete arcs connecting from the afternoon to the evening sector. Diffuse aurora only is observed when the By component of the interplanetary magnetic field is positive and no substorm processes are evident (Bz normally positive and AE values low). Isolated discrete features are observed when By is negative and are not dependent upon the presence of a substorm. The connected arcs category requires a substorm to have occurred with a pronounced westward electrojet. The average AE value of 240 γ is a factor of 3 higher than for the diffuse or isolated categories. During the expansion phase of a substorm these connecting arcs are identified with the latitudinally confined westward electrojet to the west of the auroral bulge.
Simultaneous measurements of meteor winds and green line intensity variations: Gravity waves and planetary waves
Authors: Teitelbaum H. , Massebeuf M. , Fellous J. L. , Petitdidier M. , Christophe J. , Blanco F.
Published: February 2008

We provide evidence of the influence of planetary waves on the intensity variations of the 557.7‐nm airglow emission. The comparison relies on simultaneous measurements at four different stations located between 37°N and 56°N in latitude, 36°E and 3°W in longitude: meteor wind observations in France and USSR and optical measurements at 557.7 nm in France and Spain, in July 1971. An oscillation of period near 2 days had been identified in the wind data; it is also apparent on the nightglow intensity variations. Its characteristics are well accounted for by the first symmetric mode of the 52‐ hour period planetary oscillation of horizontal wave number 3, described previously (Glass et al., 1975). A 4±1 hour period gravity wave apparently present in the data of the French stations is discussed.
Long‐term observations of the Arctic mesosphere with the MST radar at Poker Flat, Alaska
Authors: Ecklund W. L. , Balsley B. B.
Published: February 2008

In this report we summarize the results of 22 months of observations of Arctic mesosphere echoes with the 50‐MHz radar at Poker Flat, Alaska. Operation with a partially complete system began in February 1979 and has continued on a nearly continuous basis to the present time. The altitude range of the mesospheric echoes obtained during this period shows a pronounced seasonal variation. During summer months the mesospheric echoes are relatively continuous in time and extend from about 80 to 100 km with an unexpectedly strong peak in signal‐to‐noise ratio at about 85 km. In contrast, in nonsummer months, mesospheric echoes are less intense and occur at lower altitudes in the range from 55 to 80 km. These lower‐altitude nonsummer echoes are observed primarily during daytime hours when energetic auroral particle precipitation (as determined by the Poker Flat 30‐MHz riometer) is present.
Energetic particles in the predawn magnetotail of Jupiter
Authors: Schardt A. W. , McDonald F. B. , Trainor J. H.
Published: February 2008

A detailed account is given of the energetic electron and proton populations as observed with Voyager 1 and 2 during their passes through the dawn magnetotail of Jupiter. In general, the results of the Pioneer 10 pass at 90° to the Jupiter‐sun line have been confirmed and extended. The region between 20 and 150 RJ is dominated by a thin plasma sheet, and open field lines were observed at 42 RJ at a magnetic latitude of only 15°. Trapped energetic electron and proton fluxes reach their maximum in the plasma sheet and decrease rapidly even a few degrees away from it. The spectra of trapped protons can be represented by an exponential in rigidity and have a characteristic energy of ∼50 keV. Proton anisotropies in the plasma sheet were consistent with corotation even at 100 RJ, but the preliminary analysis is not yet conclusive. A major proton acceleration event and several cases of field‐aligned proton streaming were observed. Comparable proton fluxes were observed in the plasma sheet by Voyager 1 and 2. The flux of >0.4‐MeV protons decreases by 3 orders of magnitude between 20 and 90 RJ and then remains relatively constant from there to the boundary layer near the magnetopause. Between 20 and 30 RJ in the antisolar direction, the trapping region has a latitudinal extent which is comparable to that observed during the inbound pass at −30° solar aspect. The plasma sheet positions in the magnetotail can be represented by a distorted disk which rotates about the Jovian spin axis. Fine structure in the data indicates longitudinal asymmetries with respect to the dipole orientation. Electron spectra in the outer magnetosphere, the magnetosheath, and interplanetary space are modulated by the Jovian longitude relative to the subsolar point; this confirms the Pioneer 10 and 11 results.
Dispersive Doppler measurement of the electron content of the torus of Io
Authors: Levy G. S. , Green D. W. , Royden H. N. , Wood G. E. , Tyler G. L.
Published: February 2008

As Voyager 1 made its swing‐by of Io, it passed through and behind the satellite's plasma torus. The phase paths of the coherent 13 cm and 3.6‐cm wavelength signals transmitted from the spacecraft were shortened differentially by the plasma, resulting in the observation of a dispersive Doppler signature in the signals received at the NASA/Jet Propulsion Laboratory (JPL) deep space network (DSN) stations. Ray path integration through three different models of the electron distribution of the torus of Io (Warwick et al. 1979; Birmingham et al., this issue; Bagenal et al., this issue) have been performed. The results of the integrations are compared with the dispersive doppler data.
On the velocity distribution of ion jets during substorm recovery
Authors: Birn J. , Forbes T. G. , Hones E. W. , Bame S. J. , Paschmann G.
Published: February 2008

The velocity distribution of earthward jetting ions that are observed principally during substorm recovery by satellites at ∼15–35 RE in the magnetotail is compared quantitatively with two different theoretical models, the ‘adiabatic deformation’ of an initially flowing Maxwellian moving into higher magnetic field strength (model A) and the field‐aligned electrostatic acceleration of an initially nonflowing isotropic Maxwellian including adiabatic deformation effects (model B). It is assumed that the ions are protons or, more generally, consist of only one species. Both models can explain the often observed concave‐convex shape of isodensity contours of the distribution function. Model A, however, gives a somewhat better overall quantitative agreement with the observed distributions, leading us to conclude that field‐aligned electrostatic acceleration may not play the fundamental role in the energizing of the jetting ions that was suggested earlier (Frank et al., 1978; DeCoster and Frank, 1979). The two models imply different plasma conditions in the tailward source region. Model A requires a source in the far tail with plasma of kT ≈ 1 keV and density less than that at the observing satellite. Model B requires a source, probably closer to the satellite position, with plasma of kT ≈ 2–5 keV and density greater than that at the observing satellite. The conditions at the source region implied by model A are consistent with the plasma's having originated in the tail lobes and having been accelerated by a reconnection process in the far tail.
Gravity wave initiation of equatorial spread F: A case study
Authors: Kelley M. C. , Larsen M. F. , LaHoz C. , McClure J. P.
Published: February 2008

Jicamarca radar backscatter maps were made during four consecutive nights in March 1979. Two of these maps displayed single towering plumes extending to nearly 1000‐km altitude. On a third night, discussed in detail here, six plumes were generated in clear association with a nearly sinusoidal oscillation of the height of the bottomside of the F layer. The vertical amplitude of the oscillation was several hundred kilometers, and the period about 100 minutes. The plumes were generated either when the bottomside of the F layer was at the highest altitude or in the descending phase of the motion. Families of curves are presented which correspond to the solution of the dispersion relation for gravity waves capable of initiating the observed bottomside oscillations via the spatial resonance mechanism. We conclude that the solutions thus derived are reasonable and present a criterion for how well matched the gravity wave phase velocity and plasma drift have to be to produce a given perturbation in the ionization density. This criterion indicates that although initiation by a gravity wave seems likely, the gravity wave interaction cannot yield the large displacements observed without further amplification by the Rayleigh‐Taylor instability. Finally, we show that the preferential generation of plumes during the descending phase of the F layer height oscillation can be explained by a generalized Rayleigh‐Taylor instability operating on the distorted ionosphere with the destabilizing effects of gravity, a zonal electric field, and a zonal neutral wind included.
Plasma injection events at synchronous orbit related to positive DST
Authors: Arnoldy R. L. , Moore T. E. , Akasofu S.‐I.
Published: February 2008

Synchronous orbit measurements from the University of New Hampshire ATS 6 instrument have been compared with several other types of space and ground data in a study of the plasma effects related to SI and SC (positive excursions of Dst) magnetic perturbations. It is found that plasma injections at synchronous orbit, related to SI and SC, are very similar to plasma injections associated with substorms, except that the former occur at all local times. These injections can be interpreted as the co‐location of particle boundaries on an inward propagating front. The boundaries are those due to magnetospheric convection and precipitation losses and normally are spatially dispersed as a function of energy. The compression magnetic pulse associated with SI and SC events is apparently responsible for the co‐location of these boundaries and their inward propagation. The +Dst magnetic pulse plays a role similar to that of the magnetic tail reconfiguration pulse associated with substorms. Theories of convection in steady state magnetic fields cannot account for the dispersionless character of the injection front. The electron plasma behind the injection front is a hot Maxwellian for local evening +Dst plasma events as is the case for substorms. +Dst‐related injections observed on the dayside have enhanced low‐energy electron intensities, perhaps owing to an ionospheric component. The plasma observed behind the front appears to be hot tail plasma convected to its point of observation. We show evidence that +Dst enhances magnetospheric convection independent of interplanetary magnetic field direction. Since +Dst does not necessarily trigger substorms, enhanced convection is apparently not a sufficient condition for substorm generation.
On the relationships between interplanetary quantities and the global auroral electrojet index
Authors: Meloni A. , Wolfe A. , Lanzerotti L. J.
Published: February 2008

We have studied, using linear cross correlation and multilinear regression analyses, statistical relations between the magnetospheric auroral electrojet intensity index AE and various parameters characterizing the interplanetary plasma and magnetic field. We also consider the recently proposed ε parameter as an independent variable, the analyses were carried out separately for twenty‐eight days in mid 1975 and for each of five individual magnetic storm intervals that have been previously discussed extensively in the literature. We find that when the interplanetary data set is not distinguished as to the direction of the north‐south component Bz, the interplanetary electric field −VBz carried to the front of the magnetosphere correlates with AE substantially better than does ε. Considering only data during which Bz is negative gives a slightly better correlation of ε with AE than of the electric field with AE. The correlations are valid for the specific storm periods as well as for the unrestricted twenty‐eight days of data. Our results suggest that the physical processes involved in energy transfer to the nightside magnetosphere depend upon the direction of the north‐south component of the interplanetary magnetic field: the interplanetary electric field plays an important role during northward Bz and the ε parameter and the electric field both provide an indication of energy transfer and substorm activity during southward Bz.
The diurnal variation of atmospheric sodium
Authors: Clemesha B. R. , Simonich D. M. , Batista P. P. , Kirchhoff V. W. J. H.
Published: February 2008

Continuous measurements of the vertical distribution of atmospheric sodium, made over a number of complete diurnal cycles, show the existence of strong semidiurnal oscillations in total abundance and height. The amplitude of the abundance variation, about 15% of the mean, is about twice that predicted for the 2,2 mode of the semidiurnal tide, and its phase, with maxima at 0400 and 1400 LT, is in good agreement with tidal theory. The vertical oscillation, with an amplitude of 2 km at a height of 100 km, is about 3 times the expected amplitude, and the measured vertical wavelength of 38 km is in good agreement with theory, although the phase is not. A strong diurnal oscillation, observed only at heights below 82 km, is interpreted as being the result of photochemical reactions between sodium and other atmospheric constituents. The lack of any appreciable 24‐hour component in the total abundance variation implies either a residence time for total sodium of more than 3 days, or source and sink functions whose diurnal variations, unless identical, are very small.
The IMF sector pattern through the solar minimum: Two spacecraft observations during 1974–1978
Authors: Villante U. , Mariani F. , Francia P.
Published: February 2008

The hourly average values of the IMF as observed by Helios 1 and 2 in the period December 1974 through March 1978 have been examined to deduce how the sector pattern seems to evolve with time and heliographic latitude (±7.2° from the solar equator). The dominant two‐sector pattern observed after 1972 extends to the whole declining phase of solar cycle 20, and the corresponding source regions seem to corotate with an angular velocity smaller than the equatorial one. The latitudinal dependence of the IMF polarity (sunward field lines below the solar equator) is observed, with occasional deviations, through the whole period of time and becomes particularly clear in the first half of 1977. Gross scale implications for the shape and location of the sector boundary surface are discussed.
Plasma electron signature of magnetic connection to the Earth's bow shock: ISEE 3
Authors: Feldman W. C. , Anderson R. C. , Asbridge J. R. , Bame S. J. , Gosling J. T. , Zwickl R. D.
Published: February 2008

Enhanced fluxes of low‐energy electrons backstreaming from the earth's bow shock have been identified at ISEE 3. When present, these fluxes modify ambient solar wind electron velocity distributions f(υ) in characteristic ways that depends on whether ISEE 3 is near the edge of, or within the interior of the earth's electron foreshock. Near the edge, energy peaks in f(υ) are observed. Such distributions should be locally unstable to electron plasma oscillations. Well within the interior of the foreshock, enhanced fluxes of electrons with energies up to the maximum detected by the Los Alamos electron analyzer (∼1 keV) are observed over the full backward hemisphere. These electrons can be modelled with an asymptotic power law distribution having index in the range 4 ≲ pbs ≲ 6. At intermediate energies (∼20–50 eV), twin angular peaks are observed centered on the magnetic field direction
. Also observed at these times are depressions in f(υ) at energies less than ∼20 eV that are centered on
. Such distributions having a perpendicular temperature greater than their parallel temperature may be locally unstable to the generation of whistler waves. Analysis of a particularly clean example of connection to the bow shock is consistent with the possibility that the observed electron fluxes emerge from the forward foot of the electron heating region within the bow shock where the electron density and temperature are larger than that of the unperturbed upstream solar wind by a factor of ∼1.2. This analysis also indicates that the electrostatic potential within the forward foot of the shock is between ∼5 and 50 V more positive than that within plasma far upstream at ISEE 3. However, these interpretations depend on the assumption of nearly scatter‐free propagation, which may not hold. Using parameters derived from model fits to measured velocity distributions, we estimate ∼10−4 of the incident solar wind electrons are accelerated by the bow shock back into the upstream region with energies greater than 1 keV.
Characteristics of the ULF waves associated with upstream ion beams
Authors: Hoppe M. M. , Russell C. T. , Eastman T. E. , Frank L. A.
Published: February 2008

This report describes a new class of upstream wave with relatively high frequencies (∼1 Hz in the spacecraft frame of reference) and small amplitudes (1/2;γ peak to peak) compared with the more common larger amplitude (ΔB/B ∼ 1), low‐frequency (0.03 Hz) upstream waves. These waves were first noted in association with beams of ions reflected back upstream at the bow shock, appearing in conjunction with some but not all of such beams. Further work confirms the association of the waves with the beams: the presence of a beam appears to be a necessary condition for the observation of the waves. Beam presence is, however, not a sufficient condition for existence of the waves and no clear correlation has been found between beam properties and the presence or absence of the waves. We have used characterizations of the beams provided by the ISEE 1 and 2 LEPEDEA plasma analyzers along with wave profiles obtained by the ISEE 1 and 2 magnetometers in probing these relationships. In addition, measurements made by the magnetometers were used to determine the intrinsic properties of these waves, using the simultaneous two point measurements to calculate and eliminate Doppler shifting effects. Results demonstrate that these are right‐hand elliptically polarized whistler mode waves with plasma rest frame frequencies of 20–100 times the proton gyrofrequency and wavelengths ∼100 km. The waves tend to propagate in the plane formed by the local IMF direction and the solar wind at angles ∼45° with respect to the magnetic field direction. Group velocities estimated from cold plasma theory for waves of these frequencies traveling in the observed directions are often not sufficient to allow the waves to reach the spacecraft at the times of observation. This argues against the possibility that the waves could have propagated upstream to the spacecraft position from the bow shock itself.
The induced magnetosphere of Titan
Authors: Ness Norman F. , Acuna Mario H. , Behannon Kenneth W. , Neubauer Fritz M.
Published: February 2008

The Voyager 1 spacecraft had a close encounter (miss distance = 6970 km) with Titan (diameter = 5140 km) on November 12, 1980, while this large satellite was located within the Saturnian magnetosphere at a local solar time of 1330. No clear evidence was found for any intrinsic magnetic field nor for the development of a bow shock wave as the corotating Saturnian magnetoplasma convected past Titan. However, a strong electrodynamic interaction was evidenced with the observation of a very well developed, induced bipolar magnetic tail. Three thin current carrying regions were crossed, corresponding to the inbound and outbound tail magnetopause and an imbedded tail neutral sheet. An asymmetry in the tail axis orientation of 20° with respect to the corotation direction was observed. Also seen was an asymmetry in the structure of the two tail lobes. This interaction is unique among those in the solar system observed to date, being intermediate in the characteristic Mach numbers, both sonic and Alfvenic, when compared with Titan (or Venus) in the solar wind or Io in the Jovian magnetosphere. This paper presents the results of the analysis of the magnetic field data, which suggest an interpretation qualitatively described by the draping of the Saturnian magnetic field around the ionosphere of Titan.
Parametric excitation of Alfvén waves in the ionosphere
Authors: Papadopoulos K. , Sharma R. R. , Tripathi V. K.
Published: February 2008

A novel method for the excitation of ELF waves in the ionosphere is presented. It utilizes the nonlinear mixing of two ground‐ or satellite‐produced radio frequency waves with a compressional Alfvén wave. Parametric amplification thresholds are estimated to be between 10 and 20 MW peak power for 5‐MHz pumps producing waves in the ELF range. Potential applications to ELF communications are discussed.
Radar auroral observations during a burst of irregular magnetic pulsations
Authors: Haldoupis C. I. , Nielsen E. , Holtet J. A. , Egeland A. , Chivers H. A.
Published: February 2008

Micropulsation data from an auroral station are compared with concurrent STARE radar observations from the E region above the station during a substorm event. The substorm onset is marked by a strong burst of irregular pulsations (Pi B) accompanied by abrupt intensifications in the equivalent current, the backscatter intensity, and the riometer absorption. The magnetic Px and Py pulsation components have a reasonable degree of correlation and the polarization properties of the horizontal disturbance vector exhibit well‐defined changes during the first few minutes after onset. The radio signal undergoes deep quasiperiodic fading that is closely related to simultaneous Pi B amplitude variations. The radar Doppler data, which show normal fluctuations in the electron drift velocity, exclude modulation of radio backscatter by directional variations of the electric field. It is argued that the Pi B pulsations and the variations seen in the backscatter are reflecting changes of the ionospheric currents due to conductivity modifications dictated by variations in the field‐aligned currents flowing in the region. The possibility exists that the Pi B is closely related to precipitation pulsations as reported by Heacock and Hunsucker (1977).
Phase changes induced in a diagnostic radio wave passing through a heated region of the auroral ionosphere
Authors: Jones T. B. , Robinson T. , Kopka H. , Stubbe P.
Published: February 2008

Some results of recent high‐latitude ionospheric heating experiments are presented. Phase changes were induced in a diagnostic radio wave reflected from the lower F region of the ionosphere as it passed through a region of the ionosphere which was being illuminated by a high‐power electromagnetic wave. From the results obtained there are indications that anomalous absorption contributes much more than deviative absorption to ionospheric heating at high latitudes.
Mid‐latitude thermospheric neutral kinetic temperatures, 1. Solar, geomagnetic, and long‐term effects
Authors: Hernandez G.
Published: February 2008

The effects of solar activity and geomagnetic activity on the nighttime mid‐latitude thermosphere kinetic temperatures have been investigated by using measurements obtained from 1972 through 1979. This study has been made by using the kinetic neutral temperatures obtained from the Doppler widths of the [O I] 15867K (630 nm) emission at Fritz Peak Observatory, Colorado (39.87°N, 105.5°W). During the time span of the measurements solar activity, expressed as the 2.8‐GHz solar radio flux, varied nearly five‐fold, while the corresponding thermospheric temperature almost doubled. With these data a single variable simple power law relationship gives a high correlation with the temperature. A linear relationship between temperature changes and geomagnetic activity, expressed by the index Ap, has also been found. The residuals from the data and these relations show strong annual and semiannual components, with the former undistinguishable in phase with the annual variation of the solar declination angle. A comparison of these results with empirical models shows that most of the presently available empirical models do not adequately represent the observed dependence of temperature on solar activity, in particular during times of high solar activity. It is also found that on the basis of four parameters, namely solar activity, solar declination, geomagnetic activity, and a semiannual variation (and its associated phase), it is possible to obtain a better fit for our data than with the available empirical models.