bluuebunny/crossref_metadata_2025 huggingface dataset:
Substorm‐associated pulsations and magnetopause‐magnetosheath fluctuations
Authors: Heacock R. R. , Chao J. K.
Published: February 2008

Substorm‐associated fluctuations in magnetopause position were observed on October 8, 1974, as the Hawkeye satellite approached the magnetopause outbound. On October 4, while Hawkeye was well within the magnetosheath, substorm activity was accompanied by a significant increase in the magnetic field fluctuation level at the satellite and on the ground in the polar cap and nightside sectors. Several mechanisms for producing the pulsations observed in the magnetosheath are considered. Some fluctuations of magnetopause position are produced internally by substorms, while others are produced externally by interaction of the interplanetary medium with the magnetosphere. Reconnection on the dayside together with invasion of the inertia current into the magnetosheath may account for the wave activity observed in the magnetosheath during the October 4 substorm.
A study of the outer limits of ducted whistler propagation in the magnetosphere
Authors: Carpenter D. L.
Published: February 2008

The outer limits of propagation of ducted magnetospheric whistlers have been estimated by analysis of whistlers recorded at Byrd (longwire) Station, Antarctica (L ∼7) during two 3‐day periods of magnetic calm (July 2–4 and July 8–10, 1967). Path radii in an IGRF/Olson‐Pfitzer geomagnetic field model were determined from the nose frequencies of observed whistlers. On the nightside, the path radii typically extended to about 5 RE geocentric distance. The dayside radii were generally larger; on 3 of the days they were observed in the 6–8 RE range in the afternoon sector and during periods of 1 or more hours in duration. It was also found that on most hours in the 6 days, the outer propagation limits were located within ΔR <0.3 RE of a plasmapause‐type density falloff, usually on its inner side. From these results and earlier results on path radii, it is concluded that the distribution of ducted whistlers near 80°W longitude tends to reflect the instantaneous distribution of disturbance processes such as perturbing substorm electric fields. The path limits tend to fall well within the plasmapause following disturbance onset, but move beyond it during the early stages of recovery and then approach coincidence with the larger plasmasphere limits during prolonged quiet periods.
Tearing modes at the magnetopause
Authors: Greenly J. B. , Sonnerup B. U. Ö.
Published: February 2008

This paper examines the possible occurrence of tearing modes in the dayside magnetopause. First, the expected magnetic signature of tearing, as obtained from existing theory, is reviewed. Magnetometer data from one terrestrial magnetopause crossing and one crossing of Jupiter's magnetopause are then examined in detail. Magnetic field oscillations are found in three subsegments of the terrestrial crossing at a frequency of 0.1–0.2 Hz and with peak amplitudes of 5‐10 nanotesla (nT), and in one segment of the Jovian crossing, at 0.05–0.1 Hz and with 2‐nT amplitude. The frequency range, as well as the orientation of the magnetic field perturbation vectors, agrees with a model in which tearing‐produced magnetic islands are convected past the satellite with the plasma flow in the current layer. In both cases the magnetopause structure was of the rotational discontinuity type with a nonvanishing normal magnetic field component. Hence, if the tearing structures were active, i.e., growing, at the observation site, ion tearing (or perhaps resistive tearing, with the resistivity provided by microturbulence) must be invoked. But it is also possible that the structures were passive, consisting of ‘debris’ from active tearing elsewhere on the magnetopause surface, this debris being convected along the magnetopause past the observation site.
Infrared emission from NO (Δυ=1) in an aurora: Spectral analysis and kinetic interpretation of HIRIS measurements
Authors: Rawlins W. T. , Caledonia G. E. , Gibson J. J. , Stair A. T.
Published: February 2008

High‐resolution NO (X²Π, Δυ=1) emission data, obtained in an aurora between 100 and 125 km by the rocket‐borne HIRIS cryogenic interferometer spectrometer, have been analyzed by a spectral simulation/least squares technique. The vibrational state population distributions determined by this method exhibit significant population of up to six vibrational states of NO and a multimodal behavior with vibrational quantum number that is not predicted by present models. This result is interpreted in terms of direct auroral formation of NO(υ) by the chemiluminescent reaction of N(²D) with O2, coupled with excitation of NO(υ=1) by collisions between thermal atomic oxygen and aurorally enhanced NO(υ=0). The distribution shapes and their apparent invariance between 100 and 125 km suggest that collisional relaxation of NO(υ), probably by atomic oxygen, prevails over radiative cascade at these altitudes; this result is not in keeping with the present understanding of the kinetics and component densities in this region. The apparent auroral photoefficiency for NO(Δυ = 1) radiation deduced from these measurements is 1.1±0.4% over the range 100–125 km, with a calibration uncertainty of a factor of 2.5; approximately 70–90% of the observed radiation is directly excited via the N(²D) precursor.
The statistical character of Pc 4 magnetic pulsations at synchronous orbit
Authors: Arthur C. W. , McPherron R. L.
Published: February 2008

A statistical study of 215 magnetic pulsation events identified on the basis of waveform and period as Pc 4 (45‐ to 150‐s period) observed at synchronous orbit by ATS 6 is reported. The study was designed to be similar to that done with Pc 3 (10‐ to 45‐s period) by Arthur et al. (1977). These Pc 4 are found to occur most often near 1800 local time but are observed at all local times. The dominant period is ∼100 s, but a secondary peak in the distribution occurred at ∼53 s. They tend to be nearly linearly polarized, principally transverse to the ambient magnetic field. The Pc 4 are found to divide naturally into two classes (radial and azimuthal) on the basis of the azimuth of the major axis of polarization. These classes divide further into low‐frequency (≤0.015 Hz) and high‐frequency (≥0.015 Hz) classes. These four classes organize the remaining wave characteristics quite well. Division of the Pc 4 events into these classes does not lead to identification of a single source mechanism as it did with Pc 3. However, some correspondence between the classes and various proposed mechanisms does exist.
Timing of energetic proton enhancements relative to magnetospheric substorm activity and its implication for substorm theories
Authors: Belian R. D. , Baker D. N. , Hones E. W. , Higbie P. R. , Bame S. J. , Asbridge J. R.
Published: February 2008

Enhancements of the fluxes of protons having energies of several hundred keV are commonly observed at synchronous orbit and in the magnetotail during geomagnetically active periods. In many cases these flux enhancements have been shown to be closely associated with individual magnetospheric substorms. Using energetic proton data (Ep >0.3 MeV) from synchronous orbiting satellites and from Vela satellites in the magnetotail, we find that the timing of proton enhancements relative to substorm onsets and recoveries (derived from ground magnetic records) and relative to plasma sheet thinnings and recoveries (measured with plasma probes on the Imp 7, Imp 8, and Vela satellites) can be understood in terms of a neutral line model of substorms in which the protons are impulsively accelerated, possibly near the neutral line(s), during a brief period at substorm onset. The energized particles subsequently appear to stream both sunward and antisunward as discrete particle bunches with those flowing sunward observed in the inner magnetosphere as ‘drift echoes’ and those flowing antisunward seen in the magnetotail as single short, intense ’impulsive’ bursts. The more commonly observed rapid‐rise slow‐decay type of plasma sheet proton enhancements occur during the substorm recovery phase and are, in the present model, attributed to envelopment of the observing satellite by the recovering (i.e., expanding) plasma sheet into which have leaked protons previously injected into the outer radiation zone. We find that many of the energetic proton bursts reported by other research groups, when examined together with concurrent plasma measurements, are also consistent with this model. This paper describes events from our own records and from the published reports of others and offers a unified view of such energetic proton flux enhancements.
Seasonal variation of ozone in the mesosphere
Authors: Kirchhoff V. W. J. H. , Clemesha B. R. , Simonich D. M.
Published: February 2008

The mesospheric ozone density at a height of 88 km has been deduced from simultaneous ground‐based observations of neutral sodium density and sodium nightglow intensity, using a photochemical equilibrium model. The data have been obtained at São José dos Campos (23°S, 46°W). Sodium densities are measured as a function of height between 76 and 106 km by laser radar, and the nightglow intensities by a tilting filter photometer. The ozone density shows a strong seasonal variation with well defined maxima at the equinoxes, and a mean annual value of 8 × 107 cm−3. The average nocturnal variation shows a factor of 2 increase between sunset and sunrise.
Difference in quenching of N(²D3/20) and N(²D5/20) by atomic oxygen
Authors: Sivjee G. G. , Deehr C. S. , Henriksen K.
Published: February 2008

The ratio of auroral [N I] (²D3/2, 5/20 → 4S3/20) 5198.5 Å to 5200.7 Å emissions at Svalbard (Λ=75°N) is found to vary between 1.56±0.06 and 1.20±0.08. The observed variations can be explained if quenching of N(²Dj0) by atomic oxygen is constrained by the conservation of total angular momentum as follows: N(²D3/20) + O(³P2,1,0) → N(4S3/20) + O(³P2,1,0); N(²D5/20) + O(³P1,0) → N(4S3/20) + O(³P2,1). The ratio ΣJ=0¹ n(O(³PJ))/ΣJ=0² n(O(³PJ)) in the atmosphere, which affects steady state populations of N(²D3/20) and N(²D5/20) through the above quenching reactions, depends on kinetic temperature; the latter varies with atmospheric height. Consequently, the ratio of the steady state populations of N(²D3/20) and N(²D5/20) and hence the intensity ratio I(5198.5 Å)/I(5200.7 Å) would vary in an aurora as changes in particle characteristic energy lead to auroral emissions from different heights in the atmosphere. We have calculated the ratio of the volume emission rates of 5198.5 Å and 5200.7 Å lines over the altitude range 100–350 km, taking into account the quenching effects of O, O2, and e interacting with N(²DJ0), the variation in [O(³P1,0)]/[O(³P2,1,0)] with height and the radiative transitions of N(²DJ0). This ratio decreases from 1.5 at 100 km to around 1.1 at 250 km and then increases to 1.45 at 350 km.
The aurora inferred from S3‐3 particles and fields
Authors: Mizera P. F. , Fennell J. F. , Croley D. R. , Vampola A. L. , Mozer F. S. , Torbert R. B. , Temerin M. , Lysak R. , Hudson M. , Cattell C. A. , Johnson R. J. , Sharp R. D. , Ghielmetti A. , Kintner P. M.
Published: February 2008

Measurements from the University of California at Berkeley electric field experiment are combined with electron and ion measurements from the Lockheed and Aerospace experiments flown on the S3‐3 satellite for two dusk auroral acquisitions on September 6 and September 18, 1976. For the first time, the diverse measurements obtained by experiments on S3‐3 are combined in an attempt to describe the auroral morphology at ∼1 RE altitude. A detailed picture of several electrostatic shocks, plasma wave emissions, and particle distributions are presented with auroral precipitation boundaries. Comparisons between estimated electric potentials above and below the satellite with those potentials measured at the satellite are made for a broad inverted ‘V’ structure.
High‐resolution spectral features observed in the inner radiation belt trapped electron population
Authors: Imhof W. L. , Gaines E. E. , Reagan J. B.
Published: February 2008

Fine resolution measurements from the P78‐1 satellite of 68‐ to 1120‐keV electrons trapped at the lower L shell edge of the inner radiation belt have provided additional information on the previous discovery (Imhof and Smith, 1965) of the occurrences of peaks in the energy spectra. In some cases the data have yielded upper limits on the widths of the peaks as small as 26 keV. The energies of the peaks decrease slowly with increasing L value at a rate such that the calculated longitude drift periods remain nearly the same over the full L shell range for which they appear: often from ∼1.2 to ∼1.4 but occasionally up to L shells as high as ∼2.2. These peaks are frequently observed at ∼600‐km altitude in the more durably trapped electron population having minimum drift altitudes of 100 km or greater and are to be contrasted with peaks in the quasi‐trapped electrons precipitating from the inner belt at L ≃(1.5–1.85) that decrease in energy much more rapidly with increasing L value (Imhof et al., 1974, 1978; Vampola and Kuck, 1978). The spectra at the lower edge of the inner belt often contain sharp features which are continually changing, perhaps as a result of new injections and/or redistributions and the rapid loss of trapped electrons due to atmospheric scattering. For the narrow peaks the observed small but significant changes in central energy with L value that maintain a constant longitude drift period are consistent with the previous interpretation of the nearly monoenergetic electrons trapped on a given L shell resulting from a redistribution of electrons trapped on somewhat higher L shells (Imhof et al., 1966; Cladis, 1966). In that hypothesis the energy selectivity was postulated to result from a quasi‐resonance process whereby the electrons were accelerated as a result of the geomagnetic fluctuations that had periods comparable to the azimuthal drift periods of the electrons. In one case presented here, narrow peaks were observed over a broad L shell interval on only one satellite pass but were not present 24 hours earlier or later, suggesting that the peaks might have been observed as a result of drift dispersion from an impulsive event.
Reinterpretation of flux structures of solar protons and their use as probes of an open and closed magnetosphere
Authors: Gall Ruth , Bravo Silvia
Published: February 2008

In this article we question the capacity of higher energy solar protons to distinguish between open and closed magnetospheres, propose a new interpretation of flux structures detected at low altitudes, and develop a method that allows to infer from the structures observed the anisotropy of the flux in the interplanetary medium. This research is based on and extensive study of particle motion in closed and open magnetospheres, using the method of trajectory simulation with the help of mathematical models. Applied to the solar cosmic ray flux detected by Esro II during the February 28, 1969, event, the simulation showed that tens to hundreds of MeV protons cannot distinguish between an open and a closed field topology. From the flux structures observed at low altitude and the computed viewing angles of the satellite‐borne detectors, the anisotropic distribution function of cosmic ray flux in the interplanetary medium is derived; it presents a bidirectional anisotropy, from solar and antisolar directions, that agrees with flux anisotropies observed in the interplanetary medium and clearly account for the structures observed.
Observations of quasi‐periodic flux variations of energetic ions and electrons associated with Pc 5 geomagnetic pulsations
Authors: Kremser G. , Korth A. , Fejer J. A. , Wilken B. , Gurevich A. V. , Amata E.
Published: February 2008

Simultaneous quasi‐periodic variations of electrons (Ee >22 keV), ions (Ei >27 keV), and the geomagnetic field in the Pc 5 period range were observed on board the geostationary satellite GEOS 2. Fifty‐four events occurred between August 1978 and July 1979. Two types of events could be distinguished. During the first type, electrons and ions reached their flux maxima and minima simultaneously (‘in‐phase events’). During events of the second type the electron flux had minima at the ion flux maxima and vice versa (‘out‐of‐phase events’). During all events the total magnetic induction had minima at the time of the ion flux maxima and vice versa. The in‐phase events occurred preferentially around noon. They had longer average periods and durations than the out‐of‐phase events that appeared around dusk. The phase relationship between electrons and ions was found to depend on the slope of the electron pitch angle distributions. For pitch angles α ≷90° the variations of the electron intensity J were in phase with the ion intensity variations for dJ/dα ≶0 and out of phase for dJ/dα ≷0. The ion intensity variations were associated with azimuthal asymmetries that can be interpreted as the east to west movement of regions of intense ion fluxes. The observations are in reasonable agreement with the predictions of the drift mirror instability theory. In terms of this theory the two different types of quasi‐periodic events can be regarded as the result of different responses of the electrons to the disturbance conditions around noon and dusk. The drift mirror instability is associated with drifting energetic proton bunches that generate Alfvén waves. An estimate of the wave amplitudes yielded values similar to those actually observed.
Morning sector ion precipitation following substorm injections
Authors: Sauvaud J. A. , Crasnier J. , Mouala K. , Kovrazhkin R. A. , Jorjio N. V.
Published: February 2008

The auroral ion measurements (0.4–30 keV) made from the polar satellite Aureol 1 have revealed two types of precipitation with different energy characteristics in the auroral and subauroral nighttime zone: (1) In the entire nighttime auroral zone a proton precipitation with an average energy ranging from ≃5 keV to at least 25 keV, which coincides with the region of auroral Balmer series lines emission as observed from the ground (Crasnier et al., 1974). The large scale characteristics of this precipitation reflect the adiabatic acceleration of the protons in the plasma sheet and their drift motions in the outer magnetosphere (Galperin et al., 1976, 1978). (2) A subauroral precipitation of ions with energy less than 12 to 15 keV limited to the morning sector between approximately 0000 and 0500–0600 MLT. This newly observed structure is sporadic and takes place in the hours following the injections of plasma sheet particles into the inner magnetosphere at the onset of magnetospheric substorms. The ionospheric region affected by this precipitation corresponds, in the equatorial plane, to the zone in which Alfvén layers result from the ion drift pattern (from the added effects of convection and corotation electric fields and from magnetic field gradient). It is shown that the electric and magnetic field models derived by McIlwain (1972) from the energy dispersion of the particles injected at 6.6 RE at the substorm onset accounts for the main spatial and energy characteristics of these low‐energy ion subauroral precipitation. This result is obtained by extending the logic used to study the proton ‘noses’ (Smith and Hoffman, 1974; Konradi et al., 1976) from the evening side to the morning side of the inner magnetosphere, and this makes it possible to obtain, from the injection boundary concept, a coherent approach to the substorm injection features at different local time sectors.
An analytic formulation for heating source memory in the thermospheric composition
Authors: Porter H. S. , Mayr H. G. , Hedin A. E.
Published: February 2008

We utilize numerical calculations from a spectral circulation model to construct an analytic Green's function formulation describing the meridional, time dependent thermospheric composition and temperature response during magnetic storms. Our purpose is to develop a formulation that embodies source memory while being sufficiently simple to serve as a heuristic guide for empirical modeling. By passing from the discrete Fourier series representation, utilized for the numerical circulation model, to a continuous Fourier integral representation, we obtain explicit values for the thermospheric response times. The response times are altitude and species dependent and can exceed two days below 200 km. Thus, for certain storm scenarios, pronounced source memory signatures for the composition and temperature are predicted. Response times obtained from the formulation are shown to give a response consistent with previously published neutral composition data from AE‐C for the February 1974 storm when an ap dependent heat source is employed.
Winter nighttime ion temperatures and energetic electrons from OGO 6 plasma measurements
Authors: Sanatani S. , Breig E. L.
Published: February 2008

This paper presents and discusses ion temperature and suprathermal electron flux data acquired with the retarding potential analyzer on board the OGO 6 satellite when it was in solar eclipse. Attention is directed to measurements in the 400‐ to 800‐km height interval between midnight and predawn in the northern winter nonpolar ionosphere. Statistical analysis of data recorded during a 1‐month time span permits a decoupling of horizontal and altitude effects. A distinct longitudinal variation is observed for ion temperature above 500 km, with a significant relative enhancement over the western North Atlantic. Altitude distributions of ion temperature are compatible with Millstone Hill profiles within the common region of this enhancement. Large fluxes of energetic electrons are observed and extend to much lower geomagnetic latitudes in the same longitude sector. Both a direct correlation in magnitude and a strong similarity in spatial extent are demonstrated for these ion temperature and electron flux data. The location of the limiting low‐latitude boundary for observation of the electron fluxes is variable, dependent on local time and season as well as longitude. Variations in this boundary are found to be consistent with a calculated conjugate solar zenith angle of 99°±2° describing photoproduction of energetic electrons in the southern hemisphere. The OGO 6 data are considered to be indicative of an energy source originating in the sunlit summer hemisphere and providing heat via transport of photoelectrons to a broad but preferential segment of the winter nighttime mid‐latitude ionosphere. Ions at other longitudes are without access to this energy source and cool to near the neutral temperature at heights to above 800 km in the predawn hours.
Polar cap plasma flow entry region
Authors: Primdahl F. , Primdahl I. S. , Spangslev F.
Published: February 2008

In an earlier paper [Primdahl et al, 1980] we presented the daily distribution for the slant E condition (SEC) occurrences seen on ionograms from Thule (86° invariant latitude), from Godhavn (77.5° invariant latitude), and from Narssarssuaq (68° invariant latitude). The data was divided into two groups: one for A days and one for T days corresponding on the average to IMF By >0 and IMF By <0, respectively.

At Thule the distribution shifted toward morning hours on A days and toward afternoon hours on T days, in accordance with the expectation that SEC should follow the region of high plasma flow velocity and thus the region of high electric field. (For further discussion see the reference).
The distribution function of upstream energetic particle populations
Authors: Stevens G. A. , van Rooijen J. J.
Published: February 2008

In constructing the proton distribution function at low energies, one usually applies Compton‐Getting corrections to the observed anisotropies. This implies, among other things, that the spectrum as far as its functional form is concerned has to be defined with respect to a moving frame (solar wind). The justification for applying such corrections, in particular in case of the upstream events, will be discussed. Tools to investigate this ‘frame problem’ will be described, and some appropriate examples, taken from the many burst events as observed with the low energy proton spectrometer aboard ISEE 3, will be presented. It is found that none of the directional characteristics can be properly accounted for by Compton‐Getting effects.
Electron precipitation induced by VLF noise bursts at the plasmapause and detected at conjugate ground stations
Authors: Dingle Bruce , Carpenter D. L.
Published: February 2008

A new type of wave‐induced electron precipitation event has been identified. During observations at conjugate stations Siple, Antarctica, and Roberval, Canada (L ∼4.2), VLF noise bursts were found to be associated on a one‐to‐one basis with amplitude perturbations of subionospheric radio propagation. The amplitude perturbations are attributed to patches of enhanced ionization that extended below ∼80 km in the nighttime ionosphere and that were produced by precipitating electron bursts. Similar amplitude perturbations seen previously were correlated with whistlers that propagated within the plasmasphere. For the new events the driving waves were structured collections of rising elements that propagated just beyond the plasmapause at roughly 5‐min intervals over a several‐hour period. These noise bursts were of relatively long duration (∼10 s) and strong intensity (inferred to be >30 pT at the equator). Triggering of the noise bursts appears to have been mostly by whistlers but changed in character with time. Some later bursts had narrowband precursors at constant frequencies possibly locked to power line harmonic radiation. The burst initiation characteristics suggest the existence of a variable threshold for rapid temporal growth in the magnetosphere controlled by the trapped electron dynamics. The temporal signatures of the amplitude perturbations show that precipitation was maintained over multiple bounces of the trapped magnetospheric electrons. In some cases these signatures included a new undershoot effect during the recovery phase lasting 2–5 min. This effect may have been related to cutoff of background drizzle precipitation. Precipitation effects were observed on both long (∼10 Mm) and short (∼½ Mm) subionospheric paths and were monitored simultaneously at the conjugate stations. Similarities in the perturbation signatures on long and short paths suggest that the form of the signatures was governed by ionospheric changes and was not distorted by the subionospheric propagation mechanism. Some differences in the conjugate perturbation signatures are believed to be caused by the difference in loss cone widths for precipitation in the northern and southern hemispheres. Existence of this loss cone gap produced an estimated ∼30‐pT noise amplitude threshold for significant northern precipitation and possibly caused saturation of southern precipitation.
Field‐aligned current, convective electric field, and auroral particle measurements during a major magnetic storm
Authors: Shuman B. M. , Vancour R. P. , Smiddy M. , Saflekos N. A. , Rich F. J.
Published: February 2008

The S3‐2 polar‐orbiting satellite has provided simultaneous measurements of the transverse component of the ambient magnetic field, the trajectory component of the electric field, and the auroral electron flux during the very intense substorm period of March 26, 1976. Using orbits that traversed the midnight, dawn, and noon local time sectors of the low‐altitude polar magnetosphere during extremely active times, we have calculated field‐aligned current densities, compared them with precipitating auroral electron fluxes, and by utilizing the direction (forward or backward) of the electric field component, identified the regions to which they map down. Our principal results from two such orbits, subject to the limitations of single‐axis measurements, include the following: (1) The observed direction of the electric field component indicated closure of the major field‐aligned current pattern by Pedersen current flow in the ionosphere, consistent with a magnetospheric current source. (2) Values of the height‐integrated Pedersen conductivity, calculated from the gradients of the electric and magnetic field components, were typically in the range 10–30 Ω−1 in the current‐carrying regions during active times. At such times, particle precipitation on the nightside became the major factor in controlling the magnitude of the ionospheric conductivity, outweighing the influence that sunlight has in quiet times. (3) In regions of increased fluxes of precipitating electrons in the nightside auroral oval, current densities calculated from electron fluxes in the energy range 0.08‐ to 17‐keV accounted for up to 50% of the upward currents, increasing to better than 70% during the most intense substorm period. (4) In each of the three auroral oval crossings on the nightside, an intense upward current sheet was observed at the equatorward side of the westward electrojet, just poleward of the electric field reversal associated with the Harang discontinuity. (5) During the most intense current period, the region of field‐aligned currents was compressed down to L shell values 2.2 to 5.1, within the trapping region, indicating that the equatorial source of these currents was the inner magnetospheric plasma inside the outer Van Allen radiation zone rather than the distant plasma sheet or the boundary layer.
Morning IPDP events observed at high latitudes
Authors: Fukunishi Hiroshi , Toya Takeshi
Published: February 2008

From continuous f‐t spectra of magnetic pulsations observed at Syowa and Mizuho stations in Antarctica, a special type of magnetic pulsation event characterized by a gradual midfrequency rise throughout the entire duration of one hour or so has been found in the magnetic local morning hours. Here these events are named as ‘morning IPDP’ events. The f‐t spectrum consists of irregularly spaced discrete emissions whose midfrequency rises almost linearly with time. The events occurred mostly in the magnetic local time interval of ∼3–7 hours and also in the frequency range of ∼0.1–0.6 Hz. It is also seen that the discrete elements which form a morning IPDP event are observed simultaneously at the Syowa‐Husafell conjugate pair of stations. The relationship between occurrences of morning IPDP events and magnetic disturbances in the auroral zone suggests that these events are closely associated with substorm activity.
Rocket measurements of O2 atmospheric and OH Meinel Bands in the airglow
Authors: Watanabe Takashi , Nakamura Masatoshi , Ogawa Toshihiro
Published: February 2008

Altitude distributions of the (0, 0) 7619‐Å band of O2 atmospheric system (b¹Σg+ ‐, X3Σg−) and the (7, 2) 6863‐Å band of OH (X²Π) in the night airglow emissions were measured at 31°N latitude. In spite of the different seasons and local times of the observations, all three measurements presented the peak emission rate occurring at an altitude of 94±1 km for the O2 band and at 90±2 km for the OH band. The former emitting altitude is in basic agreement with the atomic oxygen density profile as measured by using an O I 1300‐Å resonance lamp, but the latter is considerably higher than expected from relevant theoretical models. After examining various possible causes for this discrepancy, it seems that the continuum airglow may contaminate our observations of the OH airglow.
Detailed study on acceleration and propagation of energetic protons and electrons in the magnetotail during substorm activity
Authors: Kirsch E. , Krimigis S. M. , Sarris E. T. , Lepping R. P.
Published: February 2008

High time resolution measurements of energetic particles (Ep >0.29 MeV, Ee >0.22 MeV) obtained by the Applied Physics Laboratory, Johns Hopkins University, detector along with magnetic field measurements obtained simultaneously by the Goddard Space Flight Center magnetometer, both aboard the IMP 8 satellite in the distant magnetotail (XSM ≈ −26, YSM ≈ +18, ZSM ≈ +1.6 RE) are presented for November 26, 1973, when several of the highest‐intensity particle bursts were detected in nearly ∼9 years of observations by the IMP 7 and IMP 8 spacecraft. The AE index and magnetograms of auroral stations indicate that this day was moderately disturbed magnetically. The energetic particle bursts were associated with rapid changes in the magnetic field, including both positive and negative excursions in the Bz component. One of the particle bursts was accompanied by a quasi‐periodic north‐south fluctuation of the tail magnetic field. The onset of the most intense burst was associated with a rapid change (∼28 γ in ∼4 s) in the Bz component; during this burst the intensity of ∼1‐MeV protons increased ∼20 s later than for ∼0.3‐MeV protons. The spectral index for protons and electrons varied from ∼3 to ∼6. The appearance of α particles at >2.4 MeV and the absence of >2.0‐MeV protons suggest the presence of electric fields capable of accelerating particles up to ∼1 MeV/charge. During the onset of the most intense burst as well as during other times, oppositely directed anisotropies of protons and electrons parallel to the tail field lasting up to ∼60 s have been observed, possibly indicating the presence of field‐aligned electric fields. Some of the bursts revealed that protons and electrons reached comparable maximum energies of ∼1 MeV, but the electron fluxes were mostly smaller by a factor of ∼10 to ∼100 than the proton fluxes. The intense bursts showed spatially separated beams of protons and electrons exhibiting large tailward anisotropies (∼104 ∶1 and ∼10² ∶1 front‐to‐back ratio for protons and electrons, respectively). Other bursts showed both earthward and tailward directed proton anisotropies in association with negative Bz components. Negative Bz components were observed to be associated with both closed and open field lines as determined from electron anisotropies. The particle and field observations are discussed in the context of proposed mechanisms for the acceleration of particles during various dynamical magnetospheric processes.
The atmospheric neutral sodium layer 1. Recent modeling compared to measurements
Authors: Kirchhoff V. W. J. H. , Clemesha B. R. , Simonich D. M.
Published: February 2008

Atmospheric sodium distributions derived according to the recent Liu and Reid model for the sodium photochemistry, which includes reactions leading to the formation of NaOH, are compared with lidar measurements, and good agreement is found. Attempts to reproduce the observed vertical distribution of atmospheric sodium by photochemical models are hampered by a lack of precise knowledge of the appropriate reaction rates. It is easy to show, however, that on the basis of the usual Chapman photochemistry only a most unreasonable choice of rate coefficients would lead to the observed vertical distribution, even when a source is included in the model. Models of this sort, apparently compatible with the observations, have invariably contained the implicit assumption of an unexplained sink, unreasonable distributions of the reacting species, or have not been in equilibrium. A number of these models also suffer from the defect of leading to values of the sodium airglow emission much smaller than that observed. It is concluded that, unlike previous models, the Liu and Reid model for the sodium photochemistry is capable of explaining both the observed vertical distribution of sodium, and the intensity of the sodium nightglow.
Cosmic ray power spectral variations 1. Simulation study
Authors: Lanzerotti L. J. , Maclennan C. G. , Agrawal S. P. , Venkatesan D.
Published: February 2008

Studies of the daily variation of cosmic ray intensity by power spectral techniques have been essentially limited in the past to demonstrating the existence of peaks at frequencies corresponding to the 24‐hour (diurnal) wave and its harmonics. The Fourier analysis technique has largely been used in many detailed investigations of the daily variation. A recent comparative study of both techniques over five solar rotations has revealed the correspondence between the two techniques and the suitability of the power spectral method in relating cosmic ray observations to interplanetary parameters. The study of the daily variation of the cosmic ray intensity over a long interval, extending, for example, over the 11‐year solar cycle, is complicated by other types of superposed variations. An analysis of real data can be considerably facilitated by a power spectral study using simulated input incorporating different artificial but physically based variations. The present study utilizes, in the simulation data, the known average characteristics of the daily variation as well as other variations present in real data. Power spectra are then calculated from a series of test data sets, each of which consists of hourly values for an interval of 27 days. The essential parameters relating to the peaks of the daily variation are tabulated. The study demonstrates the effects of superposed variations (starting from the simple case of a pure sinusoid) on power spectral features. The ambient power (background power level under the diurnal peak) is found to be dependent on the day‐to‐day phase changes in the daily variation. The realistic magnitude of the random noise is observed to have large observable effects in the power at the high frequencies only.
Plasma sheet motions inferred from medium‐energy ion measurements
Authors: Andrews M. K. , Keppler E. , Daly P. W.
Published: February 2008

Medium‐energy ions (E >25 keV) measured by the ISEE 2 satellite are used to provide information on plasma sheet motions during expansions following substorms. We show that the upward speed of the plasma sheet edge measured locally is commonly ∼50 km/s, a value high in comparison with two‐satellite measurements. It is thought that waves in the form of field‐aligned corrugations of the sheet boundary may be responsible for the high speeds measured in some cases. The boundary between the lobe and plasma sheet intensity fluxes is about 2 Rg thick at the ion energies looked at, or 1000–3000 km. After the passage of the plasma sheet boundary, particle fluxes drifting downward toward the neutral sheet are often encountered. This is interpreted as an E × B drift, in which case the electric field is about 1 mV/m. This could imply high cross‐tail potentials. At the outer boundary of the plasma sheet, it is found that the streaming ion layer recently reported by Möbius et al. [1980] and Spjeldvik and Fritz [unpublished manuscript, 1980] shows a peaked spectrum that softens as the plasma sheet is approached. The observation of a rising plasma sheet boundary, downward‐drifting flux tubes, and the behavior of the streaming ion layer are consistent with the tailward motion of a source region together with a cross‐tail electric field. The data can be interpreted to show that the source region when the plasma sheet 20 RE downtail has expanded to about 6 RE is ∼50 RE down the tail.
Radio Jupiter after Voyager: An overview of the planetary radio astronomy observations
Authors: Boischot A. , Lecacheux A. , Kaiser M. L. , Desch M. D. , Alexander J. K. , Warwick J. W.
Published: February 2008

We present an overview of Jupiter's low‐frequency radio emission morphology as observed by the planetary radio astronomy (PRA) instrument onboard the Voyager spacecraft. The PRA measurement capabilities and limitations are summarized following over two years of experience with the instrument. As a direct consequence of the PRA spacecraft observations, unprecedented in terms of their sensitivity and frequency coverage, at least three previously‐unrecognized emission components have been discovered: broadband and narrow‐band kilometric emission and the lesser‐arc decametric emission. Their properties are reviewed here. In addition, the fundamental structure of the decameter wavelength and hectometer wavelength emission, which is now believed to be almost exclusively in the form of complex but repeating arc structures in the frequencytime domain, is described here for the first time. Dramatic changes in the emission morphology of some components as a function of the sun‐Jupiter‐spacecraft angle (local time) are described. Finally, the PRA in situ measurements of the Io plasma torus hot‐to‐cold electron density and temperature ratios are summarized.
Ion anisotropies in the outer Jovian magnetosphere
Authors: Carbary J. F. , Krimigis S. M. , Keath E. P. , Gloeckler G. , Axford W. I. , Armstrong T. P.
Published: February 2008

We present results from the Voyager 1 and 2 low‐energy charged particle measurements of ion anisotropies in the outer Jovian magnetosphere (R ≳20 RJ). These anisotropies represent the first observed from an instrument rotating in the spin plane of Jupiter. For the several ion species investigated the first‐order anisotropies are all strongly in the corotational sense throughout most of the Jovian magnetosphere and out to the magnetopause on the dayside. There is some evidence for a small component of outward flow in the corotating region. Beyond ∼ 130–150 RJ along the Voyager outbound trajectories the anisotropies indicate a magnetospheric wind flowing outward from Jupiter. The change from corotational to tailward flow on the nightside occurs well inside the magnetopause. The anisotropy amplitudes increase linearly with radial distance and, in the disc regions, decrease with distance from the magnetodisc midplane. In one case examined in detail using separately identified H, He, and O/S ions the convection speed at 58 RJ is found to agree with the corotation speed (ΩR) to within ∼3%. A linear Compton‐Getting analysis reveals that the convective speeds in the dayside magnetosphere are in agreement with rigid corotation whenever the plasma flow direction is approximately in the corotation sense, while at other times the convection speeds are substantially less than corotation.
Voyager observations of Jupiter's distant magnetotail
Authors: Kurth W. S. , Gurnett D. A. , Scarf F. L. , Poynter R. L. , Sullivan J. D.
Published: February 2008

Observations of nonthermal continuum radiation by Voyager 1 and 2 at large distances from Jupiter have led to the identification of brief encounters with the Jovian magnetosphere at distances greater than 700 RJ and in directions substantially far from the Jupiter‐sun line. In addition, a number of examples of continuum radiation apparently trapped in local density depressions in the solar wind are observed. Simultaneous measurements by the Voyager plasma instrument have verified the distant magnetotail crossings and are used to correlate the occurrence of trapped continuum radiation events within solar wind density rarefactions. The Voyager observations of the distant Jovian magnetotail are compared with observations in the distant terrestrial magnetosphere and also with observations of the plasma tails of comets. Viable explanations of the observations are that the Jovian tail consists of filamentary structures, some of which extend to large distances in the predawn direction, or that the Jovian tail may be offset in the dawn direction by a combination of corotation angular momentum and forces associated with high‐speed streams in the solar wind. The observations of continuum radiation trapped in low‐density regions of the solar wind suggest that Voyager may at times be connected to the distant tail by a low‐density trough which acts as a wave guide and allows radiation from the tail to reach the spacecraft. This may provide an indirect method of detecting the tail extending more than 2 AU downstream from Jupiter.
Ion and electron angular distributions in the Io torus region of the Jovian magnetosphere
Authors: Lanzerotti L. J. , Maclennan C. G. , Armstrong T. P. , Krimigis S. M. , Lepping R. P. , Ness N. F.
Published: February 2008

Angular distributions are presented of ion (∼0.5–2 MeV) and electron (>10 Mev) fluxes measured during the Voyager 1 spacecraft passage through the inner regions of the Jovian magnetosphere (radial distances from the planet ≲10 RJ). In the regions of peak flux intensities, just outside the orbit of Io, the ion angular distributions are most sharply peaked at 90° local pitch angle, a configuration consistent with diffusion of the particles inward from larger radial distances. Inside the orbit of Io the lower‐energy ions exhibit angular distributions depleted at 90° local pitch angles, suggesting the possibility of charge‐exchange scattering loss of these particles. In the vicinity of the Io flux tube, no significant effect is observed in the flux or pitch angle distributions of the ions. The relativistic electrons are depleted in the flux tube region and exhibit an asymmetrical pitch angle distribution, with more electrons appearing to arrive from the equatorial region (the direction of Io) than from the low‐altitude mirror point.
Ray tracing in the Io plasma torus: Application to the PRA observations during Voyager 1's closest approach
Authors: Lecacheux Alain
Published: February 2008

An attempt is made to simulate propagation of the low‐frequency radio waves in the vicinity of the Io plasma torus near Jupiter. In absence of a definitive and detailed electron density model for this torus, a number of minimal hypotheses were used. Nevertheless, the anomalous radio dynamic spectrum observed during the day of Voyager 1's closest approach could agree with an emission source situated around the planet in the southern hemisphere and related to the local gyrofrequency.

The major conclusion is that the entire low frequency (up to a few megahertz) dynamic radio spectrum of Jupiter could be modified by refraction inside and around the Io torus. The magnitude of the effects depends on the location of the source and on the plasma parameters distribution inside the torus.
Oscillations and velocity structure of a long‐lived cyclonic spot
Authors: Hatzes Artie , Wenkert Daniel D. , Ingersoll Andrew P. , Danielson G. Edward
Published: February 2008

Dark brown cyclonic spots (‘barges’) at 14°N were studied by using Voyager 1 and 2 images of Jupiter. Movie sequences were made to study the spots' behavior over intervals of 50 days and longer. These movies revealed that the length and width vary by ±9% with a period of about 15 days, while the area remains approximately constant. The horizontal velocity field was investigated for an interval of about 1 day. Flow around the largest barge (feature 6) occurs as a ring current. The vorticity inferred is about 2½ times that of the ambient cyclonic zonal circulation, and about one‐half the value of the local planetary vorticity. Length and width variations appear to be associated with a nonzero horizontal divergence field. If the oscillations are a natural mode of the system, the 15‐day period will provide an important datum for testing models of stable closed vortices.
A fireball in Jupiter's atmosphere
Authors: Cook A. F. , Duxbury T. C.
Published: February 2008

One fireball was photographed during two encounters with Jupiter. Its total luminosity was 1.2 × 105 0 mag s (at standard range 100 km). If we employ the luminous efficiency proposed by Cook et al. (1981) for slip flow of a meteoroid in its own vapors we obtain an estimated mass of 11 kg. A rough absolute magnitude is −12.5. If we note that we searched for a total of 223 s during two exposures, we estimate a number density near Jupiter of 7 × 10−28 cm−3 for masses of meteoroids of 3 kg and greater. This value is about a factor of 6 smaller than a rough upper limit reached from an extrapolation from terrestrial observations of meteors and comets.
Coronal density and the solar wind speed at all latitudes
Authors: Sime D. G. , Rickett B. J.
Published: February 2008

Data from essentially all heliographic latitudes (50°S to 60°N) are used to demonstrate directly the anticorrelation between the solar wind speed and the coronal density to which it maps. The data, coronameter observations of density and interplanetary scintillation measurements of wind speed, are well suited for comparison, since they have similar selection effects, both responding most accurately to large‐scale structures. Their relationship is demonstrated on time scales from 2 days to 1 year for the years 1972–1975, during which the structures were corotating or slowling evolving. This study makes a quantitative point‐by‐point comparison of coronal density and solar wind velocity, in contrast to earlier comparisons where holes were parameterized by their area and streams by their maximum speed.