bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of nitrogen and oxygen far ultraviolet auroral emissions
Authors: Meier R. R. , Conway R. R. , Feldman P. D. , Strickland D. J. , Gentieu E. P.
Published: February 2008

A far ultraviolet rocket observation of an auroral arc has been analyzed by using laboratory measured emission cross sections and self‐consistent models of the atmospheric composition and energetic electron flux. We find that the observed arc was produced by a precipitating electron flux of 5–8 erg cm−2 s−1 energy content and 1.75‐ to 2.5‐keV characteristic energy. The N2 Lyman‐Birge‐Hopfield spectral synthesis shows that the vibrational populations for the observed emissions are in agreement with laboratory electron impact spectra and the Franck‐Condon factors to υ″ = 0. This precludes any cascade process to the a¹Πg state, which significantly changes the relative populations. Altitude profiles of the various bands can be reproduced by theory. Dissociation of N2 can account for N I lines at 1134, 1200, and 1493 Å, and N II 1085 Å. Contrary to previous observations of auroras and the dayglow, there is no evidence of multiple scattering of 1200‐Å radiation by atomic nitrogen in the present observations. The atomic oxygen density required to explain the O I 1356, 1304, and 989‐Å emissions is 4×1010 cm−3 at 120 km, a factor of 3.5 lower than the Jacchia (1971) model.
Electric currents above Saint‐Santin: 1. Data
Authors: Mazaudier Christine
Published: February 2008

This paper provides a presentation of the method used at Saint‐Santin for calculating ionospheric currents. We have compared the horizontal integrated currents with ground magnetic data, and we observe the same abnormal circulation as found by Mayaud (1965–1979). This result raises the problem of the global Sq system pattern, which cannot be identified with our Saint‐Santin data alone.
Polar cusp ion drift studies through high‐resolution interferometry of O+ 7320‐Å emission
Authors: Smith R. W. , Sivjee G. G. , Stewart R. D. , McCormac F. G. , Deehr C. S.
Published: February 2008

High‐resolution Fabry‐Perot interferometric measurements of Doppler shift in the O+(²P°3/2 → ²D°5/2) emissions from daytime polar cusp auroras over Longyearbyen (Λ = 75°N), Svalbard, are presented to illustrate some temporal aspects of polar F region ion drifts. These measurements show some of the features expected of a pass under the throat region of a twin cell convection pattern. The dayside limits of the morning and evening convection cells can be discerned from the Doppler shift observations, but the expected strong poleward flow near local noon is not present. Ion convection velocities are found to vary from 100 to 800 ms−1. The interferogram contains profiles of the OH (8, 3) P1(2) rotational line at 7316.4 Å (completely resolved from the O+(²P°3/2 → ²D°5/2) 7320.2‐Å line), and the O+(²P°1/2 → ²D°5/2) 7319.4‐Å line which shows up on the short‐wavelength shoulder of O+(²P°3/2 → ²D°5/2) 7320.2‐Å line; all these lines appear in different orders. Most of the time the interferogram yields the 7320.2‐Å/7319.4‐Å intensity ratio value equal to the statistically weighted ratio of Å coefficients for the ²P1/2.3/2→ ²D5/2 transitions, though at times enhancement of the 7319.4‐Å line with respect to the 7320.2‐Å line is observed. The OH emission is generally weaker than the O+ 7320‐Å line, a result confirmed by simultaneous spectrophotometric observations which record maximum O+(²P) doublet intensities in the range of 20–230 R. Spectroscopic observations also confirm the absence of the N21P (5, 3) band or any other auroral emission in the cusp auroral spectra around 7320 Å, which may complicate interferometric studies of the ion line; the nearest OH rotational line is at 7316.4 Å. Additionally, the O+ 7320 Å doublet is at least an order of magnitude more intense than the OH 7316.4‐Å line in long‐rayed auroral forms occurring in the cusp region prior to and after local magnetic noon; during local magnetic noon the average energy of precipitating particles is much less than the energy of maximum ionization cross section for O. Temporal variations in the O+ 7320–7330‐Å emissions, observed with the spectrometer, indicate an effective lifetime of O+(²P) in the range 2.4±0.4 to 5±1 s; these time constants correspond to peak O+ emission heights above 200 km.
An experimental test of the ionosphere electron gas cooling rate by excitation of the fine structure of the ground state of atomic oxygen
Authors: Carlson Herbert C. , Mantas George P.
Published: February 2008

Excitation of the fine structure levels of the ground state of atomic oxygen, O (³P), is currently believed to be the dominant cooling mechanism for the electron gas of the bottomside ionosphere (roughly, below 250 km). Recent refinements in theoretical excitation cross section calculations have reduced its magnitude by about a factor of 3. This cooling rate, however, has never been measured. The work reported here presents the results of the first experiment designed to measure this cooling rate. The technique is to measure the time relaxation rate of the temperature of the lower F region electron gas, after it is artifically heated by radio waves from a ground‐based high‐power HF transmitter. The experimental measurements presented favor the cooling rate corresponding to the lowest of the currently available theoretical excitation cross sections. The measurements do not, however, exclude the possibility that even this rate might still be too high by a considerable factor.
Plasma and electric field boundaries at high and low altitudes on July 29, 1977
Authors: Fennell J. F. , Johnson R. G. , Young D. T. , Torbert R. B. , Moore T. E.
Published: February 2008

The IMS event of July 29, 1977, was the topic of a coordinated data analysis workshop in October 1979. During this workshop the hot plasma observations obtained by several spacecraft (GEOS 1, ATS 6, S3‐3, and AE‐C) both at high and low altitudes were compared. The high‐altitude data show that the magnetopause was compressed to between 6.6 and 7.0 RE near 1300 MLT. The plasma ion composition measured, at high altitudes outside the plasmasphere, by GEOS 1 was seen to be primarily O+. These heavy ions were also observed at low altitudes outside the plasmasphere. Both GEOS 1 and S3‐3 observations show that at times these ions were found well below the plasmapause inside the plasmasphere. Comparisons of the low‐altitude (S3‐3) plasma and DC electric field data show that the outer limits of the plasmasphere was not always corotating at the low L shells (L ≲ 3) on this disturbed day. The corotation boundary, the estimated plasmapause boundary, and the boundary of the inner edge of plasma sheet ions were usually found to be at the same position. The inner edge of the plasma sheet electrons near dawn and dusk, plus the polar cap boundaries, were determined from the low‐altitude data. The inner edge of plasma sheet electrons was observed at higher latitudes (L shells) than the plasmasphere boundary during disturbed times. This inner edge of the plasma sheet showed a strong dawn to dusk asymmetry. These inner edges of the plasma sheet ions and electrons were found to be in relatively good agreement with the predictions of the Rice University convection model (Wolf et al., this issue). The inner edge of the plasma sheet electrons was found to be in good agreement with inner edge of the >80‐keV ring current ion precipitation. The S3‐3 data showed that late on July 29 the auroral precipitation extended above Λ ∼ 85.7° on the nightside. At the same time the inner edge of the ring current and plasma sheet also moved to high latitudes (Λ ∼ 72°), reflecting an apparent inflation of the magnetosphere.
Electrostatic potential in the auroral ionosphere derived from Chatanika Radar observations
Authors: Foster J. C. , Banks P. M. , Doupnik J. R.
Published: February 2008

A technique is described for determining the latitudinal variation of the electrostatic potential associated with the ionospheric convection electric field. Using the north‐south electric field component derived from radar convection velocity experiments, the integral of E• dl is taken northward along the magnetic meridian, starting at low latitudes. The radar data consist of up to 40 independent measurements of plasma convection spanning 15° of invariant latitude centered on Chatanika, Alaska (65°Λ), with half‐hour temporal resolution. It has been found that (1) the electric field contributions to the potential at and below 60°Λ are small under most circumstances and (2) the latitudinal variation of the potential is smooth and regular, permiting the potentials to be contoured across local time. It is found from the experiments that the potential often varies uniformly over 10° latitude at dawn and dusk. Electric fields of 50 mV/m are common. It is also noted that the latitude of the greatest negative potential in the premidnight sector coincides with the Harang discontinuity in ionospheric currents. The potentials calculated from the measured plasma drifts exhibit a regular local time variation. Equipotential contours derived from the latitude‐local time potential field obtained with the long‐duration radar experiments, while not providing a snapshot of the instantaneous pattern, elucidate the large‐scale diurnal variation of the electrostatic potential at auroral latitudes. From such contours it is found that a two‐cell convection pattern with varying degrees of asymmetry is consistently present at auroral latitudes, that a cross‐polar cap potential drop of 70–120 kV is present in moderately disturbed conditions, and that substorms perturb the potential pattern at all local times.
Plasma, fluid instabilities in ionospheric holes
Authors: Bernhardt Paul A.
Published: February 2008

Instabilities can be both triggered and quenched by chemical releases which generate ionospheric holes. Vapors, such as H2O, H2, and CO2, rapidly react with the O+ ions in the upper atmosphere, producing polyatomic ions such as H2O+, H3O+, OH+ and O2+. These ions quickly combine with electrons, leaving neutral species. The enhanced F region neutralization initially tends to quench the fluid instabilities in the modified region. After the injected vapors dissipate, chemical quenching becomes unimportant. At late times, the sides of the ionospheric hole may become unstable to fluid instabilities. The wind‐driven gradient‐drift instability, the current‐convective instability, and the gravitational Rayleigh‐Taylor instability are three classes of instabilities which may produce irregularities in ionospheric holes. These instabilities are investigated by using local, linear perturbation analysis. The removal of preexisting plasma irregularities by reactive chemical releases is also investigated.
Experimental evidence on the dependence of 140‐megahertz radar auroral backscatter characteristics on ionospheric conductivity
Authors: Haldoupis C. , Nielsen E. , Goertz C. K.
Published: February 2008

From combined STARE and magnetometer observations during a moderately disturbed period, it is deduced that the conductivity rather than the electric field is the prime agent responsible for the long‐period variations of both the ground magnetic signatures and the backscatter cross section. At times, there is an almost linear dependence between backscatter amplitude and conductivity suggesting that, within the framework of a nonlinear saturation mechanism, it is the relative amplitude Δn/n of the plasma wave irregularities rather than the absolute amplitude Δn that must be limited. In addition to backscatter amplitude modulation, there is also a modulation observed in the E field direction which is interpreted as being due to secondary east‐west polarization electric fields controlled by conductivity modifications in the region.
Equivalent ionospheric current systems representing solar daily variations of the polar geomagnetic field
Authors: Matsushita S. , Xu Wen‐Yao
Published: February 2008

Equivalent ionospheric current systems of the solar daily geomagnetic variations in both high and mid‐low latitudes during a solar active period are estimated for three seasons and the yearly average, and are compared with those during a solar quiet period. Field‐aligned electric currents as well as the wind dynamo effects that produce the obtained electric current systems are examined. Since unreasonably large electric conductivity or wind speed is required to simulate the polar currents by the wind dynamo, it is concluded that field‐aligned currents play a basic role in producing the current systems at high latitudes.
Field‐aligned current and the auroral electrojets in the post‐noon quadrant
Authors: Rostoker Gordon , Mareschal Marianne
Published: February 2008

It is shown that in the post‐noon quadrant, the combination of field‐aligned Currents associated with the eastward auroral electrojet and polar cap currents produces a magnetic field perturbation pattern on the ground and at TRIAD altitude (800 km) in good agreement with observations. This model permits downward net field‐aligned current flow across the post‐noon sector auroral oval while at the same time replicating the observation of a sharp level shift in the east‐west component of the magnetic perturbation field at 800‐km altitude attributed, until now, to net upward field‐aligned current. These results reconcile the contentions of Hughes and Rostoker (1977, 1979) that there is net downward field‐aligned current across the post‐noon auroral oval and of Sugiura and Potemra (1976) that the net current flow in the post‐noon quadrant is upward.
Numerical calculations relevant to the initial expansion of the polar wind
Authors: Singh Nagendra , Schunk R. W.
Published: February 2008

The collisionless expansion of an H+‐O+ electron plasma into a vacuum was studied because of the relevance to the polar wind. A systematic parameter study was conducted by varying the ion composition, the initial ion‐electron temperature ratio, and the scale length of the density gradient at the plasma‐vacuum interface. The effect of gravity on O+ was also simulated. The character of the expansion is different depending on whether H+ is the major or minor ion. When H+ is the major ion, the density profile in the expansion region is always concave. On the other hand, when H+ is a minor ion, a distinct plateau forms in the H+ density, H+ drift velocity, and electrostatic potential profiles. The longer the density‐gradient scale length at the plasma‐vacuum interface, the longer it took for plateau formation. However, after plateau formation, the expansion proceeds nearly in an identical fashion regardless of the initial density‐gradient scale length. When O+ was fixed to simulate gravity, the lower end of the plateau region remained fixed at the location of the initial plasma‐vacuum interface, whereas when O+ was allowed to expand the H+ plateau region moved along with the moving O+ density front. For all cases, energetic H+ and O+ ions were observed in the expansion region. This suggests that the energization of ionospheric ions through the process of plasma expansion could be one of the mechanisms for creating the energetic ion population of ionospheric origin in the magnetosphere. Such a process would operate over the entire high‐latitude region, not just on auroral field lines. Since the largest density‐gradient scale length at the plasma‐vacuum interface that was considered is much less than typical ionospheric scale lengths, the numerical results cannot be directly applied to the polar wind. However, they illustrate the basic physical processes occuring in the polar wind expansion.
Equatorial plasma bubbles: Vertically elongated wedges from the bottomside F layer
Authors: Tsunoda R. T. , Livingston R. C. , McClure J. P. , Hanson W. B.
Published: February 2008

We address the question regarding the two‐dimensional shape of equatorial plasma bubbles in the plane transverse to the geomagnetic field. By comparing the east‐west spatial relationship of ion‐density depletions measured in‐situ by the Atmospheric Explorer E (AE‐E) satellite to backscatter plumes measured by the ALTAIR radar, we show that plasma bubbles are vertically elongated depletions that extend upward from the bottom side of the F layer, in the form of tilted wedges, rather than more isotropically shaped but isolated structures. The shape of plasma bubbles is inferred from (1) ion density depletions that exceeded 99% in the ‘neck’ regions of plumes and (2) the eastward drift velocities of the plumes. The expected electrodynamics of vertically elongated plasma bubbles are consistent with the observations of large eastward drift velocities of plumes that are comparable to F region plasma drift measurements made at Jicamarca and to F region neutral wind measurements made at Kwajalein. The results also reveal that the west wall of large‐scale altitude modulations of the bottomside F layer that produces the primary plumes and bubbles becomes structured, and evolves with the generation of secondary plumes and bubbles.
Charge exchange in the Io torus and exosphere
Authors: Johnson R. E. , Strobel D. F.
Published: February 2008

Cross sections for charge‐exchange reactions of potential importance in the Io torus and the interaction of torus plasma with Io's atmosphere are estimated with an accuracy of about a factor of 2. The size of the cross sections for a given collision velocity are shown to depend entirely on the spacing of the energy levels between the initial and final states of the reactions. Reaction rates for charge‐exchange cross sections, calculated at the corotation velocity in Io's reference frame, are compared to reaction rates for electron impact ionization and recombination at a number of radii from 5.1 RJ to 7.1 RJ for a model torus. Inside Io's orbit, charge‐exchange processes are the principal mechanism for ionization of neutrals (except Na and K) and the dominant source of ions accelerated to corotation, the primary mode of multiply charged ion recombination, and a major contributor to mass loss via fast neutrals. As a consequence, the ratios of ion concentrations are critically dependent on charge‐exchange rates and the neutral densities. Charge‐exchange reactions of torus ions with molecular species in Io's exosphere may yield a net supply of neutrals and plasma to the Io torus. Expressions are given to obtain the velocity dependence of the charge‐exchange cross sections and to calculate cross sections for reactions not considered here.
Role of Rayleigh‐Taylor instabilities on prompt striation evolution
Authors: Sperling J. L.
Published: February 2008

A Rayleigh‐Taylor instability driven by ion inertia is suggested to be a source of additional growth for prompt striations following the saturation of the seed, kinetic, loss cone instability. The destabilization of Rayleigh‐Taylor modes on the prompt striation scale size implies the simultaneous excitation of large scale size Rayleigh‐Taylor modes. The long‐term effect of prompt striations on large scale fluid turbulence and on the outer scale of the power spectral density may be minimal.
Global empirical model of the Venus thermosphere
Authors: Hedin A. E. , Niemann H. B. , Kasprzak W. T. , Seiff A.
Published: February 2008

Direct measurements of neutral CO2, O, CO, N2, He, and N densities from the Pioneer Venus Orbiter Neutral Mass Spectrometer are described in terms of a spherical harmonic representation (latitude and local time coordinates) of exospheric temperature and number densities at 150 km, using modified Bates temperature profiles. The exospheric temperatures are determined from the altitude variations of atomic oxygen. A global average temperature of 228°K is derived with a first harmonic variation of 57%. The altitude profiles are extended downward to 100 km by using empirical formulas to provide a transition through the turbopause region (simulating the effect of eddy diffusion and vertical flows) and matching entry probe density data. The model reflects the observed variations of temperature and density with the 10.7 cm radio flux index. For a given change in flux at the planet, the exospheric temperature on Venus changes by only 10% of the change seen in the terrestrial thermosphere.
Spiky ion acoustic waves in collisionless auroral plasma
Authors: Lotko W. , Kennel C. F.
Published: February 2008

A theory of spiky electric fields in ‘inverted V’ precipitation regions is formulated and compared with recent spacecraft observations of solitary waves and double layers. The theory predicts that the electric fields propagate along the magnetic field as perturbed ion acoustic solitons that intensify by exchanging momentum with reflected particles. The solitons have minimum scale lengths of about 100 m and maximum electric potential and field amplitudes of 1–10 V and 1–10 mV/m. They propagate at the local ion acoustic speed (Cs ∼ 10–100 km/s), Doppler‐shifted by the drift speed of upward flowing cold ions. Both rarefactive and compressive solitons, with negative and positive electric potentials, respectively, are possible. Upward propagating compressive modes intensify when the upward flow of ionospheric ions exceeds roughly 10 Cs. The rarefactive mode intensifies when the upward field‐aligned current at 1 RE exceeds 0.1–1 μA/m² or when the upward cold ion drift is supersonic. The kinematic and dynamic properties of rarefactive solitons are consistent with the recent observations, although further analysis, both theoretical and experimental, are required for an unambiguous interpretation. The evolution of localized ion acoustic modes into small amplitude double layers is also discussed.
The role of parametric decay instabilities in generating ionospheric irregularities
Authors: Kuo S. P. , Cheo B. R. , Lee M. C.
Published: February 2008

We show that purely growing instabilities driven by the saturation spectrum of parametric decay instabilities can produce a broad spectrum of ionospheric irregularities. The threshold field |Eth| of the instabilities decreases with the scale lengths λ of the ionospheric irregularities as |Eth| ∝ λ−2 in the small‐scale range (<15 m) but becomes an increasing function as |Eth| ∝ λ in the large‐scale range. The minimum threshold field (∼2 mV/m) occurs at λ ∼ 20 m. The growth rate γ of the instabilities maximizes at λ ∼ 6 m and decreases drastically as γ ∝ λ−2 with scale lengths larger than a few kilometers. The excitation of kilometer‐scale irregularities is strictly restricted by the instabilities themselves and by the spatial inhomogeneity of the medium. These results are drawn from the analyses of four‐wave interaction. Ion‐neutral collisions impose no net effect on the instabilities when the excited ionospheric irregularities have a field‐aligned nature.
Identification of radio emission from the Io flux tube
Authors: Riddle A. C.
Published: February 2008

Many theories and observations suggest that Jovian decametric radio emission is generated in flux tubes that pass close to Io's orbit. However, comparison of theory and observation is hindered by lack of knowledge as to which specific flux tube is responsible for a particular emission. In this note, emission from the instantaneous Io flux tube is identified. This makes possible a mapping of emissions onto the causative flux tubes for a significant range of Jovian longitudes (240°–360°).
Generation of conic ions by auroral electric fields
Authors: Yang W. H. , Kan J. R.
Published: February 2008

Perpendicular accelerations of ions by the auroral electric fields are examined systematically using the test particle approach to assess their contribution to the ion conies observed on high‐latitude field lines. The results show (1) that the existence of a nonzero parallel electric field component (E∥ ≠ 0) is a necessary condition for the static auroral electric fields to accelerate ions continuously across auroral field lines, (2) that the highly nonuniform two‐dimensional auroral arc electric fields (with latitudinal thickness Lx ≤ ρi; the ion gyroradius) can contribute to conic ions with energy up to a few keV; (3) that the moderately nonuniform two‐dimensional electric field of the inverted V scale (Lx ≫ ρi) can contribute to low energy conic ions less than a few tens electron volts, and (4) that the O+ ions can be accelerated across field lines more efficiently than the H+ ions, resulting in more energetic and more coniclike O+ ions than H+ ions.
An empirical electric field model derived from Chatanika radar data
Authors: Foster John C.
Published: February 2008

Plasma convection velocity observations obtained with the Chatanika, Alaska incoherent scatter radar have been used to prepare a quantitative empirical model of the convection electric field at auroral latitudes between 58°Λ and 75°Λ. Vector averaging of the individual days' data and smoothing across 2.5 hours of local time were used to reduce substorm perturbations. Tables of the vector electric field components at 300‐km altitude have been prepared for moderately disturbed (Kp = 3) summer conditions. Resolution of the model is 0.5° of invariant latitude and one half hour of magnetic local time. The model field is asymmetric with the afternoon convection cell dominant in magnitude and spatial extent and corresponds to conditions in which the cross polar cap potential is approximately 70 kV.
The problem of cooling the cold Io torus
Authors: Richardson John D. , Siscoe George L.
Published: February 2008

The transport of ions inward from Io's orbit is first modeled on the assumption that radial diffusion is the dominant transport mechanism and then modeled with a combination of diffusive and convective transport. Included in the model are thermal as well as number density transport, radiation, ionization and pickup of local neutrals, recombination, charge exchange, and Coulomb interactions. Pure diffusive transport is capable of accounting for the dramatic inward depletion of the torus only by invoking recombination or by postulating a massive increase in the production rate of torus ions sometime prior to Voyager encounter. It is shown that radical time dependence (it is necessary to increase the source strength by a factor of ≳20 before the arrival of Voyager) cannot account simultaneously for the density and temperature observations. Similarly, recombination is found to be much too slow to be the cause of the observed density decrease inside of Io. The model combining convection and diffusion can reasonably match the data, but only with a diffusion coefficient 100 times less than that derived from Pioneer observations. It is shown that the Pioneer derived diffusion rate combined with Voyager temperature and density measurements imply a large non‐radiative sink of energy in the inner torus.
Ions upstream of the Earth's bow shock: A theoretical comparison of alternative source populations
Authors: Schwartz Steven J. , Thomsen Michelle F. , Gosling John T.
Published: February 2008

A theoretical framework is developed for studying trajectories of ions reflected or leaked upstream from the earth's bow shock and subject solely to the Lorentz force in a steady interplanetary magnetic field B and the V×B electric field. We include the effects of a sharp shock potential rise. Expressions are derived for the guiding center motion and gyromotion in a frame (the Hoffman‐Teller frame) moving parallel to the shock surface with sufficient speed to transform the incident solar wind velocity into motion entirely along the interplanetary magnetic field; the appropriate equations are also provided to transform these motions back to the observer's frame. The utility of these expressions is illustrated by comparing the predicted upstream motions for four different source models for upstream ions: magnetic moment‐conserving reflection of solar wind ions, specular reflection of solar wind ions, magnetic moment‐conserving leakage of magnetosheath ions, and leakage of magnetosheath ions parallel to the shock normal. This comparison reveals that, for identical geometries, the reflection models produce higher epergies and/or gyromotion than do the leakage models. We further argue that in a single simple encounter with the shock, an ion should behave in an unmagnetized manner and hence should not conserve its magnetic moment. Conservation of magnetic moment, if it is to occur, would seem to require multiple encounters with the shock. We investigate the conditions under which such multiple encounters can occur and find that under most quasi‐parallel geometries neither leaked nor reflected ions should probably conserve their magnetic moments.
On the equation of state of solar wind ions derived from Helios measurements
Authors: Marsch E. , Mühlhäuser K. H. , Rosenbauer H. , Schwenn R.
Published: February 2008

Observations of solar wind ion velocity distributions made by the Helios spacecraft between 0.3 and 1 AU are used to study the radial evolution of the so‐called adiabatic invariants, for example, the ion magnetic moments. Significant differences between the parameters of protons and α particles have been found in dependence on the wind velocity. On the average, adiabaticity is observed to be violated. We interpret this violation of adiabatic invariance as evidence that protons are heated perpendicular to the field in fast streams and, with less statistical significance, that α particles are cooled more strongly than for adiabatic expansion parallel to the magnetic field. The contribution of the differential streaming energy to the total internal energy of the ions is briefly investigated. Also, average heliocentric radial profiles for the ion heat fluxes are presented, and the possible role of the ion heat flux in supplying thermal energy during the radial expansion of the wind is examined. Our findings suggest that wave‐particle interactions and (or) Coulomb collisions (or other yet unknown processes) have to be invoked in order to explain the thermal energy state of solar wind ions and their radial temperature profiles.
Concerning sources of 0(¹D) in aurora: Electron impact and dissociative recombination
Authors: Sharp W. E. , Ortland D. , Cageao R.
Published: February 2008

The electron impact and dissociative recombination source functions of 0(¹D) in aurora are examined. The data from nine AE‐D passes plus one rocket flight are examined at altitudes between 150 km and 335 km. It is found that in nightime aurora 90% of the total source function is unindentified below 200 km. Electron impact (including thermal electrons) and dissociative recombination are probably adequate source functions above 250 km.
Monte Carlo calculations of the O+ velocity distribution in the auroral ionosphere
Authors: Barakat A. R. , Schunk R. W. , St.‐Maurice J. P.
Published: February 2008

The O+ velocity distribution in the high latitude F region has been calculated by using a Monte Carlo technique. The calculations were restricted to the altitudes where O+ −O collisions dominate, i.e., between about 200–350 km. The Monte Carlo calculations confirm the earlier predictions, which were based on a simple relaxation collision model, that the O+ velocity distribution takes a toroidal shape for large convection electric fields. However, the toroidal features appear only for electric fields greater than about 80–100 mV/m when a more rigorous ion neutral collision model is used, whereas the relaxation collision model predicted toroidal features for electric fields greater than about 40 mV/m. Since a toroidal velocity distribution is unstable, ionospheric irregularities can be expected at altitudes between 200–350 km when the convection electric field exceeds 80–100 mV/m.
Mirror instability and the origin of morningside auroral structure
Authors: Chiu Y. T. , Schulz M. , Fennell J. F. , Kishi A. M.
Published: February 2008

Auroral optical imagery shows marked differences between auroral features of the evening and morning sectors: The separation between diffuse and discrete auroras in the evening sector is not distinct in the morning sector, which is dominated by auroral patches and multiple banded structures aligned along some direction. Plasma distribution function signatures also show marked differences: downward electron beams and inverted‐V signatures prefer the evening sector, while the electron spectra on the morning sector are similar to the diffuse aurora. We have constructed a theory of morningside auroras consistent with these features. The theory is based on modulation of the growth rates of electron cyclotron waves by the mirror instability, which is in turn driven by inward‐convected ions that have become anisotropic. This modulation produces alternating bands of enhanced and reduced electron precipitation which approximate the observed multiple auroral bands and patches of the morning sector.
Millstone Hill incoherent scatter observations of auroral convection over 60° < Λ < 75°: 3. Average patterns versus Kp
Authors: Oliver W. L. , Holt J. M. , Wand R. H. , Evans J. V.
Published: February 2008

The Millstone Hill radar, Westford, Massachusetts (Λ = 56°), has been upgraded for observations in support of the International Magnetospheric Study (IMS) by means of the addition of a 150‐ft. diameter fully steerable antenna. This antenna allows measurements of F‐region ion drifts, from which F‐region electric fields can be derived, using the existing UHF (68‐cm wavelength) radar. This paper describes analytical models of the mean electric field behavior in the auroral zone over the interval 60° < Λ < 75° as determined from our measurements made during the year 1978. There was a greater preponderance of summer data in our 1978 observations and also more periods in which the inferred interplanetary magnetic field was directed toward the sun. A separate model is obtained for each of the three Kp ranges (< 2−, 2o to 3−, > 3o). Each model incorporates a polynomial description of intensity with invariant latitude and a sinusoidal harmonic variation in local time with 102 degrees of freedom for each of the perpendicular electric field components. Coefficients of this model are provided for numerical computation by users. Tabulations of these fields and a computer program to calculate fields and potentials are available on request from the authors. The results are compared with models published by Heppner [1977]. Each of these average field models is consistent with a two‐cell convection pattern having antisunward plasma flow over the pole and return paths eastward and westward through the dawn and dusk meridians. The centers of the vortices are near the far limit of observation (Λ = 75°). The entire convection pattern appears to be rotated by as much as two hours toward earlier local times from the nominal noon‐midnight over‐the‐pole flow direction, though this conclusion is influenced strongly by our least reliable (highest latitude) data. The dusk cell is dominant in size and strength; however, both the pattern rotation and cell dissimilarity lessen as Kp increases. The Harang discontinuity, which was recognizable on individual days, is largely absent in the average patterns, presumably as a result of the variability in its position. Nevertheless, we do see a residual, low‐speed, late‐evening protrusion of the dusk cell extending toward lower latitudes with increasing local time, reaching as far as 0300 LT for low Kp but only to midnight for high Kp. For low Kp, we observe a region of very small average flow from dawn to noon, apparently disconnected from the overall convection pattern. The dawn cell encroaches into this region as Kp increases, but the 1000–1200 LT sector maintains its low‐speed character even for high Kp. The cross‐polar‐cap potential varies linearly with Kp as V = 10.06 + 14.44 Kp kV, but the smoothing in our observations may have caused this to be an underestimate. Penetration of auroral electric fields to mid‐latitudes is most likely to occur and to be strongest in the evening sector.
The morphology of a multi‐bubble system in the ionosphere
Authors: Chen J. , Satyanarayana P. , Ossakow S. L.
Published: February 2008

A multi‐bubble model is developed to study the morphology of a finite array of plasma density depletions (bubbles) in the context of equatorial F‐region irregularities during spread F. The Pedersen current conservation equation with quasi‐neutrality is solved analytically by using an electrostatic analogy. The solution is exact with no a priori assumption regarding the separation distance. A two‐bubble system with a piecewise constant density profile is first analyzed, and the technique is then applied to multi‐bubble systems to calculate the polarization electric field and the rise velocities. It is shown that the influence of the neighboring bubbles is relatively short ranged and that a small number of bubbles can adequately model the essential physics in a large array of bubbles. For moderately short separation distances, it is found that the E×B rise velocity is substantially reduced in comparison with the single‐bubble case and that the rise velocity is strongly sheared resulting in deformation of the contours. It is found that these results compare favorably with observational evidence. The implications of the new morphological results on the stability and dynamical behavior of the bubbles are discussed. The theory is also applied to multi‐plasma density enhancements such as one might encounter in plasma cloud striation fingers.
Energetic oxygen and sulfur ions in the Jovian magnetosphere and their contribution to the auroral excitation
Authors: Gehrels N. , Stone E. C.
Published: February 2008

Observations of 1 to 20 MeV/nuc oxygen, sodium, and sulfur ions in the Jovian magnetosphere are reported. Measurements made by the cosmic ray subsystem on Voyager 1 and 2 are used to calculate abundances and energy spectra in the region from 5 to 20 Jovian radii (RJ). The phase space density of the oxygen ions calculated from the spectra has a positive radial gradient between 6 and 17 RJ, indicating an inward diffusive flow. The upper limit for the diffusion coefficient D at 9 RJ is ∼10−5 s−1. This limit, combined with the analysis of Voyager plasma observations by Siscoe et al. (1981), implies an upper limit to the production rate of oxygen and sulfur ions from Io of ∼1028 ions/s. If D(9 RJ) is ∼4×10−6 s−1, then ∼2×1024 oxygen and sulfur ions with > 70 MeV/nuc‐G are lost per second as they diffuse inward from 12 to 8 RJ. Assuming these ions are scattered into the loss cone, they deliver ∼4×1012 W to the Jovian atmosphere. Extrapolations to lower magnetic moments suggest that the 1013–1014 W required to produce the observed ultraviolet auroral emissions could result from the precipitation of ∼1026 oxygen and sulfur ions/s with magnetic moments ≳10 to 30 MeV/nuc‐G (≳35 to 100 keV/nuc at 10 RJ). The ions with ≳70 MeV/nuc‐G deposit their energy between ∼67° and ∼72° magnetic latitude at an average depth of ∼1019 cm−2 of H2 (∼500‐km altitude), which is above the homopause. If the extrapolated spectrum extends down to ∼10 MeV/nuc‐G, then 10 times more energy (∼1013 W) is carried inward across 10 RJ by the energetic oxygen and sulfur ions than flows outward with the plasma, indicating the presence of an energy source in the middle or outer magnetosphere.
On the structure of the magnetic slow switch‐off shock
Authors: Swift D. W.
Published: February 2008

A particle code is used to simulate the evolution of a magnetic slow shock. The initial state is two uniform plasmas related by the Rankine‐Hugoniot jump conditions and separated by a transition layer a few ion gyroradii thick. The code follows the evolution of the system in time. Two principal features of the results are the upstream escape of the hot shocked plasma and a damped, left‐handed circularly polarized wave on the trailing edge of the shock. Analysis of the trailing wave train indicates that ion cyclotron interaction is important in heating the plasma. The upstream escape of particles results in a temporal broadening of the shock profile. The implications of the simulation results in magnetic merging processes in the neighborhood of an x type neutral point are described.
Observations and modeling of multi‐frequency VHF and GHz scintillations in the equatorial region
Authors: Franke S. J. , Liu C. H.
Published: February 2008

Amplitude scintillation spectra and statistics obtained simultaneously at VHF (257.55 MHz), L band (1541.5 MHz), and C band (3945.5 MHz) from the MARISAT communications satellite (15°W) are presented. The measurements were made at Ascension Island (7°58′S, 14°25′W, 30°S DIP) over a high elevation propagation path within a few degrees of the magnetic meridian plane. The multi‐frequency data and the unique propagation geometry enable us to study the structures of the equatorial ionospheric irregularities closely. Numerical simulation is used to model a specific event. Comparisons between the modeling results and the observations indicate that the data are consistent with the recently measured (in situ) two‐component power law irregularity spectrum with a shallow large‐scale regime and a steeper small‐scale regime, and a spectral break at about 1‐km scale size.
Ion‐Pedersen drift and parallel electric field effects on plasma jetting
Authors: Sperling J. L.
Published: February 2008

The combination of ion‐Pedersen currents and parallel electric fields are shown to affect significantly both the jetting of ionospheric plasma clouds transverse to the geomagnetic field and the Alfven waves generated by the moving plasma. Ion‐Pedersen currents and parallel electric fields invalidate the “frozen‐in” field approximation and cause Alfven waves to decay. They also imply an eigenvalue condition on the size of the plasma cloud transverse to the geomagnetic field and the direction of cloud motion. The attenuation of Alfven waves reduces the likelihood that the waves can cause an electromagnetic pulse on the ground and implies that the initial directed energy in the plasma jet is coupled, over great distances, to ions and electrons. It is suggested that two phenomena are more likely to occur at higher altitudes (e.g., > 500 km), where neutral and ambient densities become smaller. First, there is the substantial displacement of plasma clouds with an accompanying temporary change in the geomagnetic field. Second, the Alfven waves created in response to the motion of plasma clouds are less subject to attenuation and more likely to cause an electromagnetic pulse on the ground.
Lower thermospheric structure from Millstone Hill Incoherent Scatter Radar Measurements: 1. Daily mean temperature
Authors: Wand Ronald H.
Published: February 2008

Daytime temperature determinations from 151 days of incoherent scatter radar measurements at Millstone Hill (42.6°N) from 1970 to 1975 were analyzed to characterize the mean daily temperature in the lower thermosphere (105–125 km). An analytical model fitted to the measured temperatures contained terms to specify the dependencies of the mean daily temperature on day of year (annual and semiannual terms), solar cycle, solar rotation, and geomagnetic activity. The model representation, whose coefficients are tabulated, showed that seasonal, solar cycle, and geomagnetic effects were all of comparable magnitude and could each produce a variation of 5–10% in the mean temperature. The solar rotation effects were found to be small. The annual term and the smaller semiannual term combined to produce a summer or later summer temperature maximum. Geomagnetic activity effects were determined on the basis of a delayed Kp index, and a propagation delay of 3.7 hours was obtained from the model fit to the lower thermospheric temperature measurements. An increase in either mean solar flux or Kp produced an increase in the mean daily temperature, the magnitude of the increase generally being larger at the highest altitudes. Comparison of the model results with a model based on temperatures measured at Saint Santin (44°N) showed similar seasonal variations but a larger solar cycle dependence at Millstone Hill. The strong Kp dependence found at Millstone Hill is attributed to the relatively high geomagnetic latitude of this station.
A theoretical study of plasmaspheric hiss generation
Authors: Huang C. Y. , Goertz C. K. , Anderson R. R.
Published: February 2008

An investigation of the generation of plasmaspheric hiss by the whistler mode instability has been carried out. Using combined ray‐tracing and growth rate calculations, the path‐integrated growth rates of a large number of waves have been calculated using a distribution function of the form F ∝ E−n sinm α. In general, the waves damp out before being magnetospherically reflected, or soon after. This is true of all the waves traced, independent of the distribution functions used for the energetic (resonant) electrons. Thus the growth rates are generally low, since the waves undergo few equatorial transits. A comparison of these results with observed spectra indicates that while some spectral characteristics are in qualitative agreement, there is a major discrepancy in the intensity levels.
The shift of the auroral electron precipitation boundaries in the dawn‐dusk sector in association with geomagnetic activity and interplanetary magnetic field
Authors: Makita K. , Meng C.‐I. , Akasofu S.‐I.
Published: February 2008

On the basis of the auroral precipitating electron data along the dawn‐dusk meridian from a Defense Meteorological Satellite Program satellite (DMSP‐F2), we show that the electron precipitation region extends poleward, often to the geomagnetic latitudes ≳85° from the average oval location, during quiet periods (namely, during periods of a large positive Bz component). This result may be interpreted as an indication that only a small amount of geomagnetic flux interconnects with the northward IMF, resulting in a contracted “open” region (the polar cap). The control of the location of the poleward boundary by the north–south component of the IMF is also statistically examined. The rate of latitudinal movement is about 0.4° to 0.8° per 1 nT for positive IMF Bz values and about 0.7° to 1.1° per 1 nT for negative IMF Bz values. The shift of the equatorward boundary is not obvious, however, for positive IMF Bz values. As geomagnetic activity increases, both the poleward and equatorward boundaries shift toward lower latitudes. The equatorward shift of the poleward boundary is greater than that of the equatorward boundary, resulting in a thinner electron precipitation region during disturbed periods than during quiet periods.
Simulations of beam excited minor species gyroharmonics in the Porcupine Experiment
Authors: Roth I. , Carlson C. W. , Hudson M. K. , Lysak R. L.
Published: February 2008

The Porcupine sounding rocket experiment included a spinning daughter payload equipped with a xenon plasma gun that emitted an ion beam nearly transverse to the magnetic field. Wave instruments on the main payload detected electrostatic waves at hydrogen gyroharmonics and at the lower hybrid frequency within the beam. We have performed a series of computer simulations to investigate the behavior of a system including a xenon beam, modeled from the rocket experiment, and a background ionosphere plasma of oxygen plus a small concentration of hydrogen. In these one‐dimensional simulations, a spatially homogeneous xenon beam is injected perpendicular to the magnetic field and at various angles with respect to the wave propagation vectors. Waves are excited over a range of these angles with a maximum growth near 0°, when the xenon beam is in the wave propagation direction. Despite the small hydrogen concentration (∼1%), the wave spectral analysis shows narrow peaks near the hydrogen gyrofrequencies at low beam densities, which disappear at high beam densities when the spectrum is dominated by the lower hybrid peak. A similar transition in the spectrum was seen on the rocket flight due to beam spreading with increasing distance from the xenon gun. Theoretical interpretation is given in terms of a transition from a resonant instability at low beam densities to a nonresonant instability at high beam densities.