bluuebunny/crossref_metadata_2025 huggingface dataset:
Particle pitch angle diffusion due to nonadiabatic effects in the plasma sheet
Authors: Gray P. C. , Lee L. C.
Published: February 2008

In order to understand certain aspects of the plasma sheet dynamics, a numerical study of the nonadiabatic behavior of particles in a model field geometry is performed. The particle's magnetic moment as a function of time is calculated for various initial parameters, corresponding to various particle energies and degrees of field curvature. It is shown that the magnetic moment changes as the particle passes through the plasma sheet and that the magnitude of the change is related to the curvature of the field at the middle of the plasma sheet. The relation of the magnitude of the change in magnetic moment to the particle's pitch and phase angles as it passes through the sheet is numerically resolved. The nature of the change may be considered as a mechanism for pitch angle diffusion, and the diffusion coefficient is calculated. This scattering mechanism is significant for plasma sheet ions (1–10 keV) as well as energetic electrons (⩾100 keV).
Recurrent fast motions of pulsating auroral patches: 1. A case study on optical and quantitative characteristics during a slightly active period
Authors: Yamamoto Tatsundo , Oguti Takasi
Published: February 2008

Observations of pulsating auroras with all‐sky TV cameras during the Canadian pulsating aurora campaign (January–February 1980) have revealed that fast motions occurring within auroral patches with direction predominantly parallel to the long axis of elongated auroral structures (termed streaming pulsations) are one of the most prevalent conditions in the pulsating auroral displays. An example of a typical period on a slightly active day, February 15, 1980, is described in detail by analyzing the fast motion of and within auroral forms. Some initial results of studies on their motional characteristics, derived from studying the spatial coherence of luminosity fluctuations, are presented. The dominant direction of the streaming pulsations within E‐W elongated structures was westward with speeds in the range of 10–100 km/s. The extent of movement was normally between 10 and 150 km, but sometimes longer than 1000 km. These characteristics are briefly discussed in relation to wave‐particle interactions, by referring to the previously proposed models.
First evidence for a Europa plasma torus
Authors: Intriligator D. S. , Miller W. D.
Published: February 2008

This paper summarizes the evidence from the Pioneer 10 plasma analyzer that plasma derived from Europa was present in the Jovian magnetosphere in December 1973. Plasma detected between 1900 UT and 2100 UT on December 3, 1973, shows a number of significant phenomena near the expected position of Europa's L shell. Mass addition to the magnetospheric plasma is suggested by a local increase in density apparently superimposed on the density gradient of Iogenic plasma. This increase in plasma density is unlike any phenomenon observed when the spacecraft is not close to a lunar L shell. The density shows fluctuations which allow an estimate of the net outflow speed of magnetospheric ions per Jovian rotation. We estimate a radial flow speed in 1973 of 0.37 km/s from the Pioneer data and we estimate 1 km/s in 1979 from Voyager 2 data, thus indicating a significant change. The mass addition from Europa is consistent with the expected derivation of oxygen ions (or OH+ or H2O+) from the icy surface of Europa by sputtering or other processes or with the derivation of recycled sulphur ions from Europa. Evidence from other peaks in the plasma spectra also argues for the identification of the most prominent peak in these spectra as having M/Q in the range of 16–18. The estimate of the bulk plasma speed obtained by combining this identification with the absolute energies of the peaks and the spacecraft trajectory information indicates that at this time the corotation speed is substantially higher than the expected corotation speed for a large number of spectra. If the most prominent peak in the spectra were associated with M/Q values of 32, then the corotation speed would be consistent with rigid corotation. These results contrast with the Voyager 1979 observations and are more evidence for a large change in magnetospheric conditions between the 1973 and 1979 observations. We can account partially for the increased corotation speed of the plasma during the Pioneer 10 encounter by use of momentum conservation and compression of the magnetosphere by the solar wind.
ULF geomagnetic power near L = 4: 7. A conjugate area study of power controlled by solar wind quantities
Authors: Wolfe A.
Published: February 2008

Geomagnetic energies are computed at hourly intervals for three period bands (in the Pc 3–5 range) from horizontal component magnetometer data recorded at Pittsburg, New Hampshire (L ∼ 3.5), Girardville, Quebec (L ∼ 4.4), and their approximate conjugate location at Siple, Antarctica (L ∼ 4.0). The data were recorded during September 23–29, 1977, a relatively quiet to moderately disturbed geomagnetic interval. High correlations are found at all three stations between day side ground magnetic energies and the solar wind kinetic energy flux density by using multivariate analysis techniques. The interplanetary quantity ε, whose values did not exceed 4×1018 erg/s for this data set, is found not to have a significant association with day side magnetic activity. The similar results found at the conjugate stations indicate that the solar wind kinetic pressure variations are important to control dayside broadband magnetic fluctuations in the Pc 3–5 frequency range measured on the ground.
Case studies of the storm time variation of the polar cusp
Authors: Meng Ching‐I.
Published: February 2008

The latitudinal variations of the polar cusp region were examined during three intense geomagnetic storms. The variations were compared with the intensity of storm time ring current inferred from the Dst index, with the magnitude of the north‐south component Bz of the interplanetary magnetic field and with substorm activity. The common feature is that the rapid equatorward shift occurred during the increase of the ring current growth and during the southward turning of the interplanetary magnetic field orientation. The equatorwardmost latitude of the cusp was reached before the peak of the ring current intensity, by a few to several hours, coinciding with the occurrence of the largest magnitude of the southward interplanetary magnetic field component. However, details of the polar cusp latitudinal movement differ from storm to storm. During the three storms studied, the poleward recovery commenced at the peak magnitude of the negative IMF Bz component, but the recovery proceeded without a clear relation to variations of the interplanetary Bz component, to the ring current intensity, or to the substorm activity. The lowest cusp latitude observed was at ∼61.7°, and the magnitude of this shift seems to be related to the magnitudes of −Bz. It is further observed that the approximate rates of the cusp macroscopic equatorward and poleward movements are about 3° and 1.5° per hour, respectively.
Differences in near UV (∼3400–4300 Å) optical emissions from midday cusp and nighttime auroras
Authors: Sivjee G. G.
Published: February 2008

Our ground‐based spectrophotometric observations of nighttime auroras over Fairbanks (Λ = 64.6°N), Alaska, and from dayside cusp auroras over Longyearbyen (Λ = 75°N), Svalbard, show that while molecular bands contribute most of optical radiation from nighttime auroras, atomic line emissions, particularly from metastable atmospheric species, dominate midday cusp auroral spectra. In the near UV (∼3400–4300 Å) nighttime auroral optical emissions (excited by electrons with average energy of a few keV) consist mostly of N2+ first negative group (1 NG), N2 2P and N2 Vegard‐Kaplan (VK) bands; the only prominent atomic feature is [N I] 3466A line and its intensity is about 1/300 of N2+ 1 NG (0, 0) band; the [O II] 3726‐3729 Å lines are very weak (<2R). In midday cusp regions, where magnetosheath electrons with average energy <100 eV precipitate, the N2 2P and the N2 VK bands are extremely weak (<2R), on the other hand [N I] 3466 Å and [O II] 3726–3727 Å lines are relatively intense. N2+ 1 NG bands are observed in midday cusp auroras, but unlike night auroras, where these bands are excited by electron impact ionization of N2, in cusp auroras most of the N2+ 1 NG band emissions come from resonant scattering of sunlight by N2+ ions; these ions are formed mostly through charge exchange reaction: N2(X¹Σu+) + O+[²D]→ N2+ (A²π) + O (³P). The vibrational rotational distributions of these bands vary with shadow height but on the average they are approximately similar to bands excited by electron impact ionization of N2 thermalized at ∼2500°K. In midday cusp auroras, the ratio of [N I] 3466‐Å line intensity to particle‐excited component of N2+ 1 NG (0, 0) band intensity is ∼1/10. Relatively more energetic (average energy ∼1 keV) electrons precipitate equatorward of the cusp, exciting both atomic and molecular emissions; the optical spectra of these auroras, which occur temporally coincident with but spatially separated from the cusp auroras, are similar to those observed on the nightside. Even in the cusp region, the average energy of precipitating particles can be higher during pre and post local magnetic noon periods; cusp auroral spectra observed during these periods contain molecular bands. Hence, major differences in auroral optical emissions are most noticeable when nightside spectroscopic observations are compared with similar measurements from the cusp region made around (±1 hour) local magnetic noon.
Solitary waves and double layers on auroral field lines
Authors: Hudson M. K. , Lotko W. , Roth I. , Witt E.
Published: February 2008

Time stationary solutions to the Vlasov‐Poisson equations for ion holes and double layers are examined along with particle simulations that pertain to recent observations of small amplitude eϕ/ Te ∼1 electric field structures on auroral field lines. Both the time stationary analysis and the simulations suggest that the observed double layers evolve from holes in ion phase space. Multiple small amplitude double layers, as seen in long simulation systems, are observed to propagate past the spacecraft and may account for the acceleration of plasma sheet electrons to produce inverted‐V precipitation.
Turbulence analysis of the Jovian upstream ‘wave’ phenomenon
Authors: Smith Charles W. , Goldstein Melvyn L. , Matthaeus William H.
Published: February 2008

As Voyager 2 approached Jupiter's bow shock, large‐amplitude fluctuations were seen in both the magnetic field and plasma fluid velocity. These fluctuations generally coincided with the occurrence of long‐lived energetic particle events similar to the upstream waves often observed near the earth's bow shock. In this paper we present an analysis of the magnetic field and plasma observations using spectral methods. The characteristic spectral features related to the upstream waves are generally seen near 1 mHz. The measured correlation lengths of these fluctuations suggest that they are coherent over only a few wavelengths. Our analysis is consistent with the hypothesis that these fluctuations are driven by streaming ions, possibly protons. No evidence for the existence of whistler waves is found. We argue that some of the observed spectral features suggest that dynamical turbulent processes are occurring in the upstream wave region, including a possible observation of an inverse cascade of magnetic helicity to large spatial scales.
On the rotation of the polar cap potential pattern and associated polar phenomena
Authors: Yasuhara F. , Greenwald R. , Akasofu S.‐I.
Published: February 2008

Geomagnetic and radar observations indicate that the potential and convection pattern in the northern polar cap are significantly rotated clockwise with respect to the noon‐midnight meridian. On the basis of simple models, some of the basic roles of the highly conductive belt (the auroral oval) on the rotation is examined. It is shown that it develops a space charge distribution along the boundaries in such a way as to rotate the potential pattern clockwise. The rotation angle is estimated as a function of the ratio of the conductivity in the auroral oval to that in the polar cap for a given set of conditions for an assumed conductivity ratio of ΣH/ΣP = 2.0.
Electron precipitation and related aeronomy of the Jovian thermosphere and ionosphere
Authors: Waite J. H. , Cravens T. E. , Kozyra J. , Nagy A. F. , Atreya S. K. , Chen R. H.
Published: February 2008

Voyager ultraviolet spectrometer (UVS) measurements provided the first unassailable evidence for particle precipitation in the Jovian atmosphere. Strong Lyman and Werner band emissions at high latitudes indicate particle precipitation energy fluxes of about 10 ergs cm−2 s−1. On the other hand dayglow Lyman and Werner emissions at mid‐ and low‐latitudes may indicate additional particle precipitation fluxes on the order of 0.3 ergs cm−2 s−1 at all latitudes. Such particle precipitation can have significant aeronomical effects on the Jovian thermsophere and ionosphere. A one‐dimensional theoretical model is used to study these effects for the case of electron precipitation, although ion precipitation produces similar effects. Diffusion equations are solved for all the major neutral species and for H+, and photochemical solutions are given for the short lived ions. These neutral and ionospheric components of the model are coupled with the electron and ion energy equations and a two‐stream electron transport code that calculates the energy deposition of precipitating electrons (considered to be the precipitating particles) and photoelectrons. An independent calculation of the vertical neutral temperature is also obtained. The results of the model calculations can be broadly categorized as effects of electron precipitation (1) on the neutral composition and temperature of the thermosphere, and (2) on the composition and structure of the ionosphere. Auroral electron precipitation by 10‐keV electrons with a total energy flux of 10 ergs cm−2 s−1 produces 4.7×1011 H atoms cm−2 s−1 and 5 ergs cm−2 s−1 of heat, over 2 orders of magnitude larger than solar EUV processes that produce 3.3×109 H atoms cm−2 s−1 and 0.03 ergs cm−2 s−1 of heat. Thus, Jovian auroral H production coupled with aurorally driven meridional winds in the thermosphere can possibly explain the high concentration of atomic hydrogen in the low‐latitude Jovian upper atmosphere. Furthermore, aurorally produced changes in composition can create important feedback which affects the relative airglow efficiencies and heating rates in the high‐latitude thermosphere. In addition, ionization and vibrational heating of H2 from precipitation processes appear to play a central role in determining the structure of the high‐latitude ionosphere. Theoretical fits to the Voyager radio occultation electron density profiles at high latitudes suggest a 10‐keV electron aurora with an energy flux of 10 ergs cm−2 s−1 coupled with a height‐dependent H2 vibrational temperature that reaches 3000 K in the topside ionosphere.
Altitude and structure of an auroral arc acceleration region
Authors: Paschmann G. , Papamastorakis J. , Sckopke N. , Haerendel G. , Shelley E. G.
Published: February 2008

During a rocket flight in the dayside auroral oval on December 17, 1974, several examples of velocity dispersions of precipitating electrons were observed. It is shown that the commonly employed interpretation of such dispersions as resulting from a purely temporal modulation of the source is not unique: the same dispersion effects can also be caused by a moving source of finite width and constant intensity. This spatial model is further improved by adding the dispersion originating from a superimposed convection velocity. In general the source altitudes implied by the two models (temporal and spatial) differ. For one of the events analyzed the temporal model yielded a source altitude of ∼3000 km. Because of special circumstances this did not differ significantly from the result obtained with the spatial model. The second case analyzed was inconsistent with the temporal model and required further modification of the spatial model to include an energy dependent source width, in line with expectations from an acceleration in a V shaped electric field pattern. Applying the latter model we derive a source altitude of ∼3500 to ∼5000 km.
Implications of Voyager data for energetic ion erosion of the icy satellites of Saturn
Authors: Lanzerotti L. J. , Maclennan C. G. , Brown W. L. , Johnson R. E. , Barton L. A. , Reimann C. T. , Garrett J. W. , Boring J. W.
Published: February 2008

The possible production of a neutral particle “torus” by magnetosphere particle sputtering of the icy satellites (Enceladus, Tethys, Dione, Rhea) of Saturn is discussed. Particle spectra from the Voyager low‐energy charged particle experiment are used together with laboratory‐derived erosion rates and velocity distributions for the ejected species. An extended torus region in the inner magnetosphere of Saturn is expected, with H2O escape fluxes in the vicinities of the satellites varying from ∼2 to 7×107 mol/cm²/s for incident protons and from ∼6 to 14×109 mol/cm²/s if the incident ions are all oxygen.
Corotation anisotropies in Saturn's magnetosphere
Authors: Carbary J. F. , Mauk B. H. , Krimigis S. M.
Published: February 2008

Ion data from the Voyager 1 and 2 low‐energy charged particle (LECP) experiment are fit to a second‐order harmonic expansion to determine anisotropies within the Saturnian magnetosphere. Anisotropies from the low‐energy channels (28–130 keV) are often consistent with those expected from corotation (generally with a small radial component on the dayside) but are at times distinctly different from corotation. On the dayside, near the noon meridian, first‐order anisotropies often depart significantly from the corotation direction. On the nightside, amplitudes are consistent with full corotation but begin to drop below corotation values at a dipole L of ∼27 Rs (corresponding to a velocity of ∼265 km/s). Second‐order anisotropies are significant, even dominant at times, on the dayside where a relatively broad range of pitch angles is sampled by the instrument. In all cases there is a departure of ∼180° from the first‐order anisotropies expected due to corotation beginning outside the Rhea L shell and continuing through at least the orbit of Dione. This is the region where the cold and hot plasma tori have been observed. We have computed the anisotropies expected from rigid corotation of the observed flux distributions and conclude that parts of the Saturnian magnetosphere are not rigidly corotating. Calculations based on the combined effects of corotation plus solar wind generated convective electric fields appear to provide insights into the anisotropies along the dawn meridian. However, on the dayside near noon, turbulence and/or time variations seem necessary to explain the departure from simple convection models.
Nitrogen escape from Mars
Authors: Fox J. L. , Dalgarno A.
Published: February 2008

The escape rate of nitrogen from Mars is calculated to be 2.3×105 s−1 for low solar flux conditions and 8.9×105 s−1 for high solar flux conditions. The major source of energetic atoms is dissociative recombination of ground state and vibrationally excited N2+ ions. The measured 15N/14N isotope ratio can be reproduced by postulating an early dense atmosphere during which little differentiation occurred.
Solar irradiance variations: 2. Analysis of the extreme ultraviolet measurements onboard the Atmosphere Explorer E satellite
Authors: Oster L.
Published: February 2008

Five of the extreme ultraviolet channels (Lα, Lβ, He I, He II, Fe XV) measuring irradiance fluctuations on board the AE‐E satellite between 1977 and 1980 have been studied in detail. It is shown that the daily variations correspond very closely to the daily variations in solar radio emission (F10.7), but that the UV data are afflicted with serious and to date unrecognized calibration changes during the period of operation of the instruments. In order to correct for these changes, a statistical analysis is carried out, and a set of corrections to the raw data is suggested. We then compare the resulting, now uniform, data with rocket measurements (Lα) and data acquired onboard the AE‐C satellite (Lβ). Finally, we discuss the remaining discrepancies. After concluding that they are below the overall level of uncertainties, we propose a first‐order 10‐year run of EUV irradiances derived from F10.7 data. This estimate includes the ratio of irradiance levels between the maxima of solar cycles 20 and 21 and the intervening minimum.
Possible observation of a disconnected magnetic structure in a coronal transient
Authors: Illing R. M. E. , Hundhausen A. J.
Published: February 2008

We present SMM coronagraph/polarimeter observations of the coronal transient of March 15–16, 1980, which show a bright front convex toward the sun propagating out through the corona at 175 km s−1. A fan‐shaped bright region connecting this front to the inner corona collapses into a narrow bright ray over the next few hours. We interpret these observations as resulting from the disconnection of magnetic loops from the underlying prominencelike loop structures seen rising earlier in the event. Other similar “inverted arches” exist in the C/P data but are usually seen with poorer temporal resolution.
The radial distribution of radiation belt protons: Approximate solution of the steady state transport equation at arbitrary pitch angle
Authors: Jentsch V.
Published: February 2008

We present quasi‐analytic solutions to the proton diffusion equation, with energy degradation and charge exchange losses included. The transport mode is modeled as D ∝ M−l Lg(K,l), where M, K, and L are the adiabatic invariants, and l refers to the spectral index of the fluctuating electric field. At the outer boundary, say L = 7, a distribution function of the form f ∝ exp −[M/M0(K)]v is maintained; at the inner boundary (L ≈ 1), f is required to vanish. We find that (1) the diffusion flux is directed outward, when energy loss and charge exchange are in approximate balance, (2) the shape of the proton flux is strongly affected by the spectral index of the fluctuating fields, (3) the proton flux exhibits both positive and negative gradients with respect to energy, and (4) the anisotropy of the proton flux increases with decreasing L value, and may pass through a minimum with respect to energy.
Velocity spike at the poleward edge of the auroral zone
Authors: de la Beaujardiere O. , Heelis R. A.
Published: February 2008

Data from coordinated observations of the Chatanika incoherent scatter radar and the Atmosphere Explorer C satellite are examined to study the poleward edge of the auroral zone for one pass in the morning sector. A very intense, spikelike electric field is seen at the boundary between the auroral zone and the polar cap, coincident with the convection reversal. The particle detector data are consistent with the presence of a pair of oppositely oriented potential drops parallel to the magnetic field. These potential drops are of a few hundred electron volts, and their direction is such that the precipitating electrons are accelerated on the poleward side and decelerated on the equatorward side of the electric field spike. These observations are examined in the light of recent theoretical investigations that have shown that parallel acceleration can indeed be expected to occur in the regions of large velocity shear. The Chatanika data suggest that such spikes may occur repeatedly at the poleward edge of the diffuse aurora, but that they are confined in either time or space.
The effects of interplanetary magnetic field orientation on dayside high‐latitude ionospheric convection
Authors: Heelis R. A.
Published: February 2008

The Atmosphere Explorer C data base of northern hemisphere ionospheric convection signatures at high latitudes is examined during times when the interplanetary magnetic field orientation is relatively stable. It is found that when the interplanetary magnetic field (IMF) has its expected garden hose orientation, the center of a region where the ion flow rotates from sunward to antisunward is displaced from local noon toward dawn irrespective of the sign of By. Poleward of this rotation region, called the cleft, the ion convection is directed toward dawn or dusk depending on whether By is positive or negative, respectively. The observed flow geometry can be explained in terms of a magnetosphere solar wind interaction in which merging is favored in either the prenoon northern hemisphere or the prenoon southern hemisphere when the IMF has a normal sector structure that is toward or away, respectively.
Analysis of chorus emissions at Jupiter
Authors: Coroniti F. V. , Scarf F. L. , Kennel C. F. , Kurth W. S.
Published: February 2008

On the Voyager 1 inbound pass through the Jovian magnetosphere, the frequent acquisition of wide band data from the plasma wave instrument has permitted a quasi‐continuous survey of the waves which occur in the frequency band below the electron cyclotron frequency, the chorus band. Structured, rising frequency chorus was observed just outside the dense Io plasma torus but inside the low‐density middle magnetosphere. A quasi‐continuous, very narrow band emission occurred just above one‐half the electron cyclotron frequency. Power spectra, which were constructed from the wide band data, showed that the half‐cyclotron emission is unaffected by the simultaneous occurrence of chorus at lower frequencies and is separated from the chorus by a deep spectral gap just below one‐half the cyclotron frequency. Within the rising chorus band, a hisslike emission was observed which consisted of two quasi‐continuous, very narrow band tones located near the upper and lower frequency limits of the rising chorus band. Sequential power spectra showed that these twin‐frequency tones persisted during rising chorus bursts. Chorus occurs in the spatial regions where whistlers have cyclotron resonant interactions with the suprathermal population of ∼keV electrons. A possible interpretation of the twin tones is that these signals are electrostatic or resonance cone whistlers. Growth rate calculations show that the electrostatic whistler is destabilized by a loss cone distribution with the same pitch angle anisotropy which is needed to excite the electromagnetic chorus whistlers. A speculative hypothesis is presented to explain the half‐cyclotron emission. The Landau absorption of oblique chorus whistlers results in the spectral gap just below one‐half the cyclotron frequency and in the formation of a quasi‐linear plateau in the parallel velocity distribution of the suprathermal electrons. The plateau alters the Landau and cyclotron resonant interactions and permits the unstable growth of electrostatic and electromagnetic whistlers in a narrow range just above one‐half the cyclotron frequency.
The entry of AMPTE lithium ions into a magnetically closed magnetosphere
Authors: Olson W. P. , Pfitzer K. A.
Published: February 2008

In a magnetically closed magnetosphere, none of the geomagnetic field lines intersects the magnetopause. Solar wind particles incident upon such a field topology are normally thought to be specularly reflected and therefore none gains entry to the magnetosphere. Strictly speaking, however, specular reflection occurs only when the incident charged particle encounters a uniform magnetic field. Although the geomagnetic field at the magnetopause does appear quite uniform to incident particles (its scale size is much greater than the gyroradii of solar wind particles), it possesses a small gradient parallel to the magnetopause. When this gradient is taken into account, a fraction of the incident particles can gain access to the magnetosphere. This gradient drift entry (GDE) process is a feature of the basic structure of the geomagnetic field and should occur at all times. It is therefore expected that the Active Magnetospheric Particle Tracer Explorers (AMPTE) lithium ion releases will penetrate certain regions of the magnetopause. An excellent test of the GDE process could be made by initiating a lithium release during a northward interplanetary magnetic field (when the magnetosphere is thought to be magnetically closed).
Large‐scale Birkeland currents in the dayside polar region during strongly northward IMF: A new Birkeland current system
Authors: Iijima T. , Potemra T. A. , Zanetti L. J. , Bythrow P. F.
Published: February 2008

Stable, well‐defined patterns of transverse magnetic disturbances have been observed in the polar regions that persist during periods of strongly positive Bz (≥ 5 nT) and that increase in amplitude as Bz increases. This has been determined from an examination of magnetic field data acquired during 146 orbits of MAGSAT over the south polar regions during November 1979 to January 1980 and supplemented by four consecutive orbits of TRIAD over the north polar region in July 1977. The characteristics of these polar disturbances include the following: (1) they occur at latitudes poleward of the Region 1 Birkeland current system at daytime magnetic local times (0600 MLT through noon to 1800 MLT); (2) the spatial distribution along the dawn‐dusk direction resembles the “W”‐shaped distribution of electric fields observed in the polar cap during periods of positive Bz (Burke et al. [1979]); (3) these patterns show remarkable stability, showing little change from orbit to orbit, up to seven orbits of MAGSAT (equivalent to a period of 10 hours); and (4) the magnitude of the peak disturbance, ΔB, correlates with a “complementary” magnetospheric transmission function of the form: ϵ* = (By² + Bz²)½ cos θ/2, where θ is the angle between the positive z axis and the interplanetary magnetic field (IMF). If the magnetic disturbances are interpreted in terms of Birkeland currents, they flow downward on the duskside and flow away on the morningside (identical to the cusp current flow reported by Iijima and Potemra [1976b]). During periods of negative By the region of morningside (upward flowing) currents is much larger than the eveningside (downward flowing) current region in the southern hemisphere. The density of the currents in the smaller spatial region is larger than the density of the currents in the larger region. This pattern systematically reverses during periods of positive By. We interpret these observations as evidence for a large‐scale, stable Birkeland current system in the polar region that is associated with merging on field lines in the geomagnetic tail. This current system intensifies and is more stable as Bz becomes more northward (reminiscent of the behavior of the Region 1 current system with increasing southward values of Bz). The new stable polar cap current system described here is referred to as the “NBZ” Birkeland current system for “northward Bz” and is important because of its relationship to a variety of other northward By phenomena such as polar cap auroral arcs (“theta aurora”) and multicell convective flow patterns. The existence of these stable NBZ currents and the correlation of their amplitudes with the IMF substantiate the fact that energy continues to flow to the earth's polar regions during periods of strongly northward IMF.
Theory of plasma waves in the auroral E region
Authors: Fejer Bela G. , Providakes Jason , Farley Donald T.
Published: February 2008

We have extended the linear fluid theory of electrojet plasma waves to the region where ion magnetization effects are important. Our general dispersion relation includes the effect of cross‐field and field‐aligned drifts, ion inertia, electron density gradients, and recombination. In the absence of density gradients and recombinational damping, the oscillation frequency at marginal instability is changed by the ion magnetization effects from the ion acoustic frequency, ω = kCs, to the modified ion cyclotron frequency ω² = Ωi² + k²Cs². These upper E region waves can be driven by field‐aligned and/or cross‐field drifts and have the smallest threshold drift velocities at heights where electron‐ion and/or anomalous electron collision frequencies are important. In the upper E region the most unstable wavelengths correspond to k⊥Ri ∼ 1, where Ri is the ion Larmor radius. Electron density gradients can increase or decrease considerably the threshold drift velocity for large‐scale (a few tens of meters and larger) waves. Recombinational damping increases the threshold drift velocity for marginal instability of two‐stream ion cyclotron waves and imposes a threshold drift velocity for the excitation of large‐scale gradient drift waves propagating nearly perpendicular to the magnetic field. The effect of recombination is surprisingly important, even for wavelengths as short as 10–20 m, for altitudes at which νi ∼ Ωi. At these altitudes and above, the effect of even a very small k∥ becomes increasingly important. The theory puts a number of earlier theoretical results together in one framework and provides new results and insights that may explain some puzzling observations such as those of Moorcroft (1979), who sometimes failed to see echoes with the 398‐MHz Homer radar when the electric field measured with the Chatanika radar far exceeded the normal instability threshold.
Thermal fluctuations from an artificial ion beam injection into the ionosphere
Authors: Hudson M. K. , Roth I.
Published: February 2008

Simulations of argon beam experiments flown on two sounding rocket flights (ARCS 1, 2) reveal two bands of electrostatic wave emissions, one at high frequencies around the upper hybrid mode, the other at low frequencies around the lower hybrid mode. The latter is significantly enhanced by the argon beam in the simulations, and the enhancement was clearly observed on ARCS 2. This enhancement at phase velocities greater than the beam velocity is suggested to be due to an increase in the thermal fluctuation level of the plasma when the argon beam is present. Inclusion of electron dynamics and oblique angles of wave propagation with respect to B allows investigation of electron heating. Electron tail heating is observed parallel to B for
, while background ions are heated perpendicular to B.
Global compressional oscillations of the terrestrial magnetosphere: The evidence and a model
Authors: Kivelson Margaret Galland , Etcheto Jacqueline , Trotignon Jean Gabriel
Published: February 2008

Compressional oscillations of nearly constant frequency (period ≲ 8 min) were observed from L ≃ 5 to L ≃ 10 near local noon over an interval of almost 3 hours during a dayside radial pass of the ISEE 1 spacecraft on August 12, 1982. The density fluctuations, measured by the electron density experiment, were in phase with the compressional magnetic oscillations measured by the magnetometer. We relate the observations to an analytical model of a global compressional wave reflected at the gradient of the magnetic field and plasma density near the plasmapause and standing in the outer magnetosphere. Qualitative arguments based on the model lead one to expect that conditions in the outer magnetosphere are not normally compatible with the standing wave solution, that when such a solution can be found, only the lowest eigenfrequencies will be present, and that some variation in period with local time may occur.
Observation of a coronal transient from 1.2 to 6 solar radii
Authors: Illing R. M. E. , Hundhausen A. J.
Published: February 2008

We describe in detail the eruptive prominence associated coronal mass ejection of August 5, 1980, as seen in both the Solar Maximum Mission (SMM) coronagraph polarimeter and the Mauna Loa Observatory (MLO) K coronameter and prominence monitor. This event gives us the first detailed look at the propagation of a “depletion” transient into the outer corona. The event begins in the MLO K coronameter as a rising depletion of material, but appears later in the SMM coronagraph as an ordinary coronal mass ejection with a three‐part structure: a bright core within a dark lunette surrounded by a bright featureless “loop.” A joint time‐height plot of the major structures of the eruption seen by both instruments suggests that we can associate the three‐part structure in the outer corona with features in the low corona (prominence, prominence cavity, outer bright front). We argue from its observed mass that the leading loop in the SMM field of view is probably material that was in the background corona before the event. We suggest that this material has been displaced and set into motion by the rising “cavity.” One “leg” of the transient as seen by the SMM instrument is strongly bowed away from the bright core or prominence; this is in contrast to the straight, radial legs seen after Skylab mass ejections.
Radar and photometric measurements of an intense type A red aurora
Authors: Robinson R. M. , Mende S. B. , Vondrak R. R. , Kozyra J. U. , Nagy A. F.
Published: February 2008

On the evening of March 5, 1981, an intense, type A red aurora appeared over southern Alaska. Radar and photometric measurements were made of the aurora from the Chatanika radar site. The line of sight intensity of the 630.0‐nm emissions exceeded 150 kR and was accompanied by enhanced emissions at 486.1 and 427.8 nm. The Chatanika radar measured electron densities of 106 cm−3 and electron temperatures of 6000 K at an altitude of 400 km and an invariant latitude of 59° in association with the aurora. Comparison of optical and radar measurements indicated that the 630.0‐nm emissions were produced to a large degree by thermal excitation of O(¹D) in the region of high electron temperatures and densities. Model calculations indicate that the observed density and temperature enhancements and the related optical emissions were the results of a relatively short duration (5–10 min) pulse of precipitating, low‐energy (∼30 eV) electrons. Whereas conventional stable auroral red arcs are associated with a gradual decrease in ring current energy density during the recovery phase of a magnetic storm, the type A red aurora may be produced by impulsive ring current energy loss during the main phase.
Comparison of polar cap potential drops estimated from solar wind and ground magnetometer data: CDAW 6
Authors: Reiff P. H. , Spiro R. W. , Wolf R. A. , Kamide Y. , King J. H.
Published: February 2008

This paper compares two indirect methods of determining the maximum electrostatic potential difference across the high‐latitude ionosphere. One method estimates the cross‐polar‐cap potential difference from solar wind parameters using a theoretical formula with empirically determined coefficients, while the other method is based on the inversion of ground magnetograms from a global network of magnetometers. These techniques are each applied to the two intervals chosen for study during the Coordinated Data Analysis Workshop (CDAW) 6. During the first interval (March 22, 1979) the potential drop predicted from solar wind parameters is in encouraging agreement with that inferred from the ground magnetograms, while for the second interval (March 31–April 1, 1979) the theoretically predicted potential drop was substantially larger than that calculated from the magnetogram inversion technique. The disagreement is likely due, in part, to uncertainties in the ionospheric conductivity model upon which the magnetogram inversion technique depends. For the March 22 interval, the conductivity model agrees reasonably well with in situ particle flux data; a similar comparison has not been made for the second interval. In addition, the March 31 interval was characterized by small‐scale variations in the solar wind, which may affect the validity of the predicted value of the cross‐polar‐cap potential drop. The difference in the nature of the substorms within the two intervals may also be significant.
Charged particle behavior in low‐frequency geomagnetic pulsations: 4. Compressional waves
Authors: Kivelson Margaret G. , Southwood David J.
Published: February 2008

In this fourth paper of a series concerning charged particle behavior in ultralow frequency waves in the terrestrial magnetosphere, we examine the particle flux response expected in waves with a strong compressional magnetic component. Two effects, which we label betatron and mirror, dominate the behavior expected for nonresonant particles with the mirror effect expected in most circumstances. Resonant behavior is a strong function of signal symmetry, much as discussed in earlier papers. We conclude by examining recently published observations of particle flux oscillations associated with compressional signals.
Solar wind flow about the outer planets: Gas dynamic modeling of the Jupiter and Saturn bow shocks
Authors: Slavin J. A. , Smith E. J. , Spreiter J. R. , Stahara S. S.
Published: February 2008

Pioneer 10 and 11 and Voyager 1 and 2 observations are used to study global aspects of the solar wind interaction with Jupiter and Saturn. Solar wind measurements before and after the encounters are used to determine average upstream flow parameters at 5 and 9 AU. Bow shock and magnetopause position are found to vary as the fourth root of dynamic pressure at Jupiter and the sixth root at Saturn. The average distances to the nose of the magnetopause based upon the Pioneer and Voyager boundary crossings for Jupiter and Saturn are 68 RJ and 19 RS, respectively, after correction for varying solar wind pressure. In shape, the Jovian bow shock and magnetopause surfaces are similar to their terrestrial counterparts, but the width of the magnetosheath is 45% less than predicted by axisymmetric gas dynamic theory. This result is interpreted as evidence for strong polar flattening of the Jovian magnetosphere. The Saturnian magnetopause and bow shock boundaries are significantly more flared than at the earth with a subsolar magnetosheath that is 20% thinner than predicted by gas dynamic theory. On the basis of these results it is suggested that Saturn is intermediate between the earth and Jupiter in terms of polar flattening, with the unusual flaring of the Saturn magnetopause being due to the low ratio of static to dynamic pressure in the distant heliosphere.
Simulations of heavy ion heating by electromagnetic ion cyclotron waves driven by proton temperature anisotropies
Authors: Tanaka Motohiko
Published: February 2008

Heating of heavy ions by the electromagnetic ion cyclotron (EMIC) waves, which are driven by proton temperature anisotropies, is studied by means of hybrid particle simulations. Initially, relaxation of the temperature anisotropies in the proton distribution and isotropic heating of the heavy ions are observed (phase I), followed by substantial perpendicular heating of the heavy ions (phase II). The heavy ions are distinctly gyrophase modulated by the EMIC waves. The isotropic heating in phase I is due to magnetic trapping by the excited proton cyclotron waves. The perpendicular heating in phase II is attributed to cyclotron resonance with the EMIC waves, which becomes possible by means of the preceding heating in phase I. Saturation of the EMIC instability is instead attributed to magnetic trapping of the majority ions: protons. When the proton anisotropy is very large, (T⊥/T∥)p0 ≫ 1, frequency shift (decrease) of the proton cyclotron waves to less than ½Ωp is observed. Even if (T⊥/T∥)p0 ∼ 1, the EMIC waves are excited, and cold helium ions are well heated and gyrophase modulated. The present mechanism is not only relevant to He+ heating in the dayside equator of the magnetosphere, but it also predicts hot He2+ ions behind the earth's bow shock.
Fluctuations of precipitated electron intensity in flickering auroral arcs
Authors: Spiger R. J. , Anderson H. R.
Published: February 2008

This paper reports on electron spectra associated with two aurorae observed by ground‐based television. One auroral arc was observed to flicker, large variations in the precipitated electron energy occurring on a time scale of 114 ms. The major variations occur at the higher energies of the 0.5–20 keV range covered by the detectors. Changes in the particle flux occur primarily in the pitch angle range 0° to 60°. Analysis of the video data shows a larger variation in intensity along the lower border of the arc in keeping with the results of the electron spectra. The second arc was not observed to flicker, and the associated electron spectra and video data show no large variations in precipitated electron energy or video intensity modulation. While pitch angle distributions tend to be field‐aligned in the first arc, the distributions in the second arc are nearly isotropic or peaked from 60° to 90° in the downward hemisphere.
Solar and interplanetary ions at 2–4 MeV/nucleon during solar cycle 21: Systematic variations of H/He and He/CNO ratios and intensities
Authors: Shields Joseph C. , Armstrong Thomas P. , Eckes Steven P. , Briggs Patrick R.
Published: February 2008

Observations of protons, alpha particles, and medium group nuclei (C,N,O) have been made with particle counters aboard the IMP 7 and 8 (Explorer 47 and 50) spacecraft for the time period from October 1972 to the present. Since this interval includes nearly the complete solar cycle 21, and the data coverage is high, it is now possible to characterize the entirety of solar and interplanetary particles in the vicinity of the earth. Extensive and detailed catalogs of identified solar flare events have been prepared for two periods of time, classified as Solar Minimum (day 300 of 1974 through day 200 of 1977) and Solar Active (day 1 of 1978 through day 365 of 1981). Histograms of daily averaged particle fluxes have been prepared for three types of subintervals of the Solar Minimum and Active periods. These subintervals were for flare particle‐dominated times, quiet times, and the residual (nonflare, nonquiet). Comparison of these histograms yields a variety of salient differences between the compositions and intensities of particles in these subintervals. During Solar Minimum, for example, each type of subinterval displays distinctly different compositions both in the median and in the distribution, with flare times showing by far the greatest variability of proton/alpha and alpha/medium ratios. During Solar Active time there does not appear to be a compositionally distinct signature of flare times as compared to nonflare, nonquiet times. We discuss and characterize these results and other quantitative measures of solar and interplanetary charged particle fluxes in solar cycle 21.