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All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

New Data on the Topside Electron Density Distribution

The existing uncertainties about the electron density profiles in the topside ionosphere, i.e., in the height region from hmF2 to approx. 2000 km, require the search for new data sources. The ISIS and Alouette topside sounder satellites from the sixties to the eighties recorded millions of ionograms and most were not analyzed in terms of electron density profiles. In recent years an effort started to digitize the analog recordings to prepare the ionograms for computerized analysis. As of November 2001 about 350,000 ionograms have been digitized from the original 7-track analog tapes. These data are available in binary and CDF format from the anonymous ftp site of the National Space Science Data Center. A search site and browse capabilities on CDAWeb assist the scientific usage of these data. All information and access links can be found at http://nssdc.gsfc.nasa.gov/space/isis/isis-status.html. This paper describes the ISIS data restoration effort and shows how the digital ionograms are automatically processed into electron density profiles from satellite orbit altitude (1400 km for ISIS-2) down to the F peak. Because of the large volume of data an automated processing algorithm is imperative. The automatic topside ionogram scaler with true height algorithm TOPIST software developed for this task is successfully scaling approx.70 % of the ionograms. An 'editing process' is available to manually scale the more difficult ionograms. The automated processing of the digitized ISIS ionograms is now underway, producing a much-needed database of topside electron density profiles for ionospheric modeling covering more than one solar cycle. The ISIS data restoration efforts are supported through NASA's Applied Systems and Information Research Program.

Huang, Xue-Qin↗
NASA NTRS1987

Parabolic heavy ion flow in the polar magnetosphere

Recent observations by the Dynamics Explorer 1 satellite over the dayside polar cap magnetosphere have indicated downward flows of heavy ions such as O(+), O(2+), N(+), and N(2+) with flow velocities of the order 1 km/s (Lockwood et al., 1985). These downward flows were interpreted as the result of 'parabolic' flow of these heavy ionospheric ions from a source region associated with the polar cleft topside ionosphere. Here, a two-dimensional kinetic model is utilized to elicit features of the transport of very low energy O(+) ions from the cleft ionosphere. Bulk parameter (density, flux, thermal energies, etc.) distributions in the noon-midnight meridian plane illustrate the effects of varying convection electric fields and source energies. The results illustrate that, particularly under conditions of weak convection electric fields and weak ion heating in the cleft region, much of the intermediate altitude polar cap magnetosphere may be populated by downward flowing heavy ions. It is further shown how two-dimensional transport effects may alter the characteristic vertical profiles of densities and fluxes from ordinary profiles computed in one-dimensional steady-state models.

Horwitz, J. L.↗
NASA NTRS1989

Time-dependent modeling of field-aligned current-generated ion transients in the polar wind

The time evolution of field-aligned current-generated transient features in the high-latitude ionosphere is investigated. Ionospheric return currents generate significant downward heavy ion flows in the topside ionosphere with peak values well exceeding 10 to the 8th sq cm/s. When the return current ceases, the polar ionosphere rapidly returns to its previous equilibrium state. During the recovery phase of the return current event, an upward propagating heavy ion transient is formed, which is mainly characterized by a relatively short O(+) upwelling event. On the other hand, the H(+) escape flux remains relatively constant (within 10-20 percent) during field-aligned current events. It is also found that upward currents generate a transient heavy ion outflow, which exceeds the ambient H(+) escape flux by a factor of 3 to 5, depending on the duration and strength of the field-aligned current event.

Gombosi, T. I.↗
NASA NTRS1988

Time-dependent polar wind modeling

In the presence of a strong magnetic field (such as the geomagnetic field) the plasma tends to flow along the magnetic-field lines; therefore, in most ionospheric flow calculations the use of the gyrotropic approximation is justified. Here, it is shown that the gyrotropic 20-moment approximation is equivalent to the gyrotropic 16-moment approximation. Consideration is then given to return-current-generated polar wind transients. Ionospheric return currents generate significant downward heavy ion flows in the topside ionosphere with peak values well exceeding 10 to the 8th/sq cm sec. When the return current ceases, the polar ionosphere rapidly returns to its previous equilibrium state. During the recovery phase of the return-current event, an upward-propagating heavy-ion transient is formed, which is mainly characterized by a relatively short O(+) upwelling event. The H(+) escape flux remains a relatively constant (within 10-20 percent) during field-aligned-current events.

Gombosi, T. I.↗
NASA NTRS1974

Stimulation of the Harris instability in the ionosphere

Observations made with a sweep frequency rf sounder on the satellite ISIS 1 in the topside ionosphere are reported, and the interpretation of diffuse signals at the lower harmonics of the electron cyclotron frequency is discussed. These signals are attributed to the stimulation of Harris instabilities of longitudinal plasma waves at multiples of the cyclotron frequency in a single electron distribution. The Harris instability is excited most readily when the frequency is near the midpoint between the harmonics of the cyclotron frequency. The cause of these instabilities is the large electron velocity anisotropy which results from collisionless cyclotron damping of the energy from the high power sounder pulse.

Benson, R. F.↗
NASA NTRS1990

International Reference Ionosphere: Plasma densities - Status 1988

An account is given of the changes proposed in 1988 for the International Reference Ionosphere electron density profile, as well as the status of their implementation. The fully analytical profile function under development for the entire ionosphere can be achieved with a linear combination of several LAY functions. Although four LAY functions are required to describe the density features of the middle ionosphere, three LAY functions suffice to reproduce electron densities in both the topside ionosphere and lower ionosphere. Attention is given to the way in which the LAY parameters are computationally derivable from characteristic profile points.

Rawer, K.↗
NASA NTRS1990

A mathematical model of the structure and evolution of small scale discrete auroral arcs

A three dimensional fluid model which includes the dispersive effect of electron inertia is used to study the nonlinear macroscopic plasma dynamics of small scale discrete auroral arcs within the auroral acceleration zone and ionosphere. The motion of the Alfven wave source relative to the magnetospheric and ionospheric plasma forms an oblique Alfven wave which is reflected from the topside ionosphere by the negative density gradient. The superposition of the incident and reflected wave can be described by a steady state analytical solution of the model equations with the appropriate boundary conditions. This two dimensional discrete auroral arc equilibrium provides a simple explanation of auroral acceleration associated with the parallel electric field. Three dimensional fully nonlinear numerical simulations indicate that the equilibrium arc configuration evolves three dimensionally through collisionless tearing and reconnection of the current layer. The interaction of the perturbed flow and the transverse magnetic field produces complex transverse structure that may be the origin of the folds and curls observed to be associated with small scale discrete arcs.

Seyler, C. E.↗
NASA NTRS1981

The atmosphere and ionosphere of Jupiter

The thermal structure of the upper atmosphere of Jupiter, the composition of the atmosphere and the strength of mechanical mixing, and sources and sinks of ionization in the Jupiter ionosphere are described from Voyager UV spectrometer, radio, IR, and imaging data. A topside ionospheric temperature of 1300 K was observed, along with an energy equilibrium between the plasma and neutral gas in the upper atmosphere. A composite thermal structure is provided, noting a close similarity to earth conditions at upper levels, and enhanced thermal behavior has been detected between the times of solar minimum and maximum activity. Ammonia photochemistry is examined, and measured concentrations of H2, CH4, C2H6, and C2H2 as a function of height are outlined. Eddy diffusion coefficient calculations are carried out, yielding a highest Ly-alpha intensity of 100 million sq cm/sec. The increased exospheric temperature between 1973 and 1980 is stressed to have no known satisfactory explanation.

Atreya, S. K.↗
NASA NTRS1996

Plasma Waves in the Magnetosheath of Venus

Research supported by this grant is divided into three basic topics of investigation. These are: (1) Plasma waves in the Venus magnetosheath, (2) Plasma waves in the Venus foreshock and solar wind, (3) plasma waves in the Venus nightside ionosphere and ionotail. The main issues addressed in the first area - Plasma waves in the Venus magnetosheath - dealt with the wave modes observed in the magnetosheath and upper ionosphere, and whether these waves are a significant source of heating for the topside ionosphere. The source of the waves was also investigated. In the second area - Plasma waves in the Venus foreshock and solar wind, we carried out some research on waves observed upstream of the planetary bow shock known as the foreshock. The foreshock and bow shock modify the ambient magnetic field and plasma, and need to be understood if we are to understand the magnetosheath. Although most of the research was directed to wave observations on the dayside of the planet, in the last of the three basic areas studied, we also analyzed data from the nightside. The plasma waves observed by the Pioneer Venus Orbiter on the nightside continue to be of considerable interest since they have been cited as evidence for lightning on Venus.

Strangeway, Robert J.↗
NASA NTRS1989

Solar wind interaction with the ionosphere of Venus inferred from radio scintillation measurements

The observation of S-band (2.3 GHz) radio scintillations in the ionosphere of Venus by the Pioneer Venus Orbiter is reported. In situ plasma measurements and propagation calculations show that the scintillations are caused by electron density irregularities in the topside ionosphere of Venus below the ionopause. It is suggested that these topside plasma irregularities are associated with the penetration of large-scale magnetic fields in the ionosphere. It is found that the disturbed plasma and the scintillations are a manifestation of high-dynamic solar wind interaction with the ionosphere.

Woo, Richard↗
NASA NTRS1984

Direct evidence for two-stage (bimodal) acceleration of ionospheric ions

Energetic ion composition spectrometer data gathered on hybrid conical ion distributions by the Dynamics Explorer 1 in the topside ionosphere are reported. The observed ion distributions were field-aligned and upward flowing, with energies up to 5 keV. Increases in ion energy were accompanied by a departure from field-alignment and a cone patterned upward flow, with the apex in the auroral field lines and the cone angle widening upward as the energy increased. Both transverse and parallel accelerations were imparted to the ions, with the transverse heating occurring in a 5000 km extent region centered at 18,000 km altitude. A bi-Maxwellian distribution, a temperature of 1.2 keV and a 260 eV parallel temperature were found at the top of the region.

Klumpar, D. M.↗
NASA NTRS1991

The plasma environment, charge state, and currents of Saturn's C and D rings

The charge state and associated currents of Saturn's C an D rings are studied by modeling the flow of ionospheric plasma from the mid- to low-latitude ionosphere to the vicinity of the rings. It is found that the plasma density near the C and D rings, at a given radial location, will experience a one to two order of magnitude diurnal variation. The surface charge density (SCD) of these rings can show significant radial and azimuthal variations due mainly to variation in the plasma density. The SCD also depends on structural features of the rings such as thickness and the nature of the particle size distribution. The associated azimuthal currents carried by these rings also show large diurnal variations resulting in field-aligned currents which close in the ionosphere. The resulting ionospheric electric field will probably not produce a significant amount of plasma convection in the topside ionosphere and inner plasmasphere.

Wilson, G. R.↗
NASA NTRS2006

Topside sounders as mobile ionospheric heaters

There is evidence that satellite-borne RF sounders can act as mobile ionospheric heaters in addition to performing topside sounding. The main objective of topside sounding is to use sounder-generated electromagnetic (em) waves to obtain ionospheric topside vertical electron-density (N(sub e) profiles. These profiles are obtained from mathematical inversions of the frequency vs. delay-time ionospheric reflection traces. In addition to these em reflection traces, a number of narrowband intense signals are observed starting at zero delay times after the transmitted pulses. Some of these signals, termed plasma resonances, appear at characteristic frequencies of the ambient medium such as at the electron cyclotron frequency f(sub ce), the harmonics nf(sub ce), the electron plasma frequency f(sub pe) and the upper-hybrid frequency f(sub uh), where (f(sub uh))(exp 2) = (f(sub ce))(exp 2) + (f(sub pe))(exp 2) . These signals have been attributed to the oblique echoes of sounder-generated electrostatic (es) waves. These resonances provide accurate in situ f(sub pe) and f(sub ce) values which, in turn, lead to accurate N(sub e) and [B] values where B is the ambient magnetic field. Resonances are also observed between the nf(sub ce) harmonics both above and below f(sub uh). The former, known as the Qn plasma resonances, are mainly attributed to the matching of the wave group velocity of sounder-generated (Bernstein-mode) es waves to the satellite velocity. The frequency spectrum of these waves in the magnetosphere can be used to detect non-Maxwellian electron velocity-distributions. In addition, these resonances also exhibit components that appear to be the result of plasma emissions stimulated by the sounder pulses. The plasma resonances observed between the nf(sub ce) harmonics and below f(sub uh), known as the Dn plasma resonances, are entirely attributed to such sounder-stimulated plasma emissions. There are other sounder-stimulated plasma phenomena that also fall into this category, e.g., ion affects on electron-resonant phenomena, proton-cyclotron echoes and N(sub e) field-aligned irregularities (FAI). Some of these phenomena are more pronounced when f(sub pe)/f(sub ce) approx. = n where n is an integer significantly greater than one. The observations suggest that the sounder-stimulated plasma phenomena are stimulated, or enhanced, on a time scale much less than one second. The purpose of this presentation is to review the above topics with particular emphasis on the sounder-stimulated plasma phenomena.

Benson, R. F.↗
NASA NTRS1990

Model of Jovian F region ionosphere (Jovian ionosphere model in offset dipole approximation)

The geomagnetic control of the Earth's atmosphere is well understood. In the F-region and the topside ionosphere, non-electrical forces transport plasma along the magnetic field lines only. In consequence, the worldwide distribution of ionization is strongly dependent on the dip angle. For example, the equatorial anomaly is roughly symmetrical about the dipole equator rather than the geographic. The same appears to be the case in the Jovian ionosphere (Mahajan, 1981). The influence of the magnetic field of Jupiter on its ionization pattern is one of several outstanding topics which need to be studied. Tan (1986) investigated the formation of the equatorial anomaly in the Jovian ionosphere under a centered dipole model. Tan (1988) further studied the effect of the tilt of the Jovian dipole. The results were in broad agreement with those of a diffusive equilibrium model (Tan and Wu, 1981). An off-centered dipole model is constructed and its effects on the ionization pattern are investigated.

Tan, A.↗
NASA NTRS1986

Transport of accelerated low-energy ions in the polar magnetosphere

Recent satellite observations of low-energy (0-50 eV) ionospheric ions in the polar cap magnetosphere suggest that these ions are injected at the dayside cleft topside ionosphere. Using a two-dimensional kinetic model, several consequences of this ion flow from a narrow cleft source have been simulated and observed. These include: (1) the Kp/convection-dependent filling of the polar magnetosphere with ionospheric heavy ions, in which these ions are 'blown' further into the polar cap magnetosphere from the cleft during high Kp/convection; (2) the mass- and energy-dependent dispersion of these ions, as in a kind of 'geomagnetic spectrometer'; (3) the creation of 'supersonic' ion outflows as a natural velocity-filter effect of this geomagnetic spectrometer; and (4) the 'parabolic flow' of gravitationally bound heavy ions from the cleft ionosphere resulting in downward flow into the polar cap.

Horwitz, J. L.↗
NASA NTRS2021

Electron Energy Interplay in the Geomagnetic Trap Below the Auroral Acceleration Region

This publication addresses the collisional superthermal electron dynamics below the auroral acceleration region (AAR). This region is the portion of an auroral field line with a field-aligned electric field that leads to the formation of precipitating monoenergetic keV electron fluxes that produce the discrete auroral displays observable from the ground. It is assumed that these precipitating electron fluxes are monoenergetic and accelerated through a potential drop, V, such that these electrons are peaked at an energy E0 = eV, where e is the electron charge. Monoenergetic electrons precipitating into the upper atmosphere degrade to lower energies via many different collisional processes and produce the secondary electron population with energies of 10–100s eV which escapes back to magnetospheric altitudes and becomes geomagnetically trapped between the AAR and the upper ionosphere. The secondary electrons in this geomagnetic trap transfer energy via elastic Coulomb collisions to the thermal electrons. That energy is then returned to the topside ionosphere as heat flux carried by the electron thermal conduction which is essential to maintaining the topside electron temperature.

George V Khazanov↗
NASA NTRS1994

Dynamics of three-dimensional plasma clouds with coupling to the background ionosphere

A three-dimensional, time-dependent model with a two-grid system was developed to study the expansion of a plasma cloud in the F region and topside ionosphere. The model maintains an adequate resolution for the released cloud motion and its interaction with the immediate environment, and it includes the effect due to the coupling with the distant part of the ionosphere (i.e., E region). Simulations were performed using realistic background ionospheric density profiles in both the E and F regions. The results show that the cloud coupling to the underlying E region affects the perpendicular cloud motion the most. The distant coupling acts to reduce the perturbation potential and perpendicular velocity and delays or eliminates the striations. These simulation results are consistent with simple analytical approximations. The simulation results also show that the distant coupling has a very small effect on 'localized' phenomena, such as the cloud expansion along the B RIGHT ARROW field and the electrostatic snowplow. The cloud-induced electric potential is attenuated in the lower E region. The electrons flow along the B RIGHT ARROW field, carrying the current to the E region and back to the cloud. The current closure is demonstrated in three dimensions for the first time for such a problem. The perpendicular current flowing through the plasma cloud is closed by the field-aligned electron current and the background perpendicular (mainly Pedersen) current in both the E and F regions. The 'image cloud' formation in t he E region is also clearly demonstrated. The variation of the density change in the 'image cloud' along the B RIGHT ARROW field and the features of the image cloud are shown.

Ma, T.-Z.↗
NASA NTRS1981

Kinetic response of ionospheric ions to onset of auroral electric fields

Examination of the exact analytic solution of a kinetic model of collisional interaction of ionospheric fions with atmospheric neutrals in the Bhatnagar-Gross-Krook approximation, shows that the onset of intense auroral electric fields in the topside ionosphere can produce the following kinetic effects: (1) heat the bulk ionospheric ions to approximately 2 eV, thus driving them up to higher altitudes where they can be subjected to collisionless plasma processes; (2) produce a nonMaxwellian superthermal tail in the distribution function; and (3) cause the ion distribution function to be anisotropic with respect to the magnetic field with the perpendicular average thermal energy exceeding the parallel thermal energy.

Chiu, Y. T.↗