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NASA NTRS1985

Absolute electron density measurements in the equatorial ionosphere

Accurate measurement of the electron density profile and its variations is crucial to further progress in understanding the physics of the disturbed equatorial ionosphere. To accomplish this, a plasma frequency probe was included in the payload complement of two rockets flown during the Condor rocket campaign conducted from Peru in March 1983. This paper presents density profiles of the disturbed equatorial ionosphere from a night-time flight in which spread-F conditions were present and from a day-time flight during strong electrojet conditions. Results from both flights are in excellent agreement with simultaneous radar data in that the regions of highly disturbed plasma coincide with the radar signatures. The spread-F rocket penetrated a topside depletion during both the upleg and downleg. The electrojet measurements showed a profile peaking at 1.3 x 10 to the 5th per cu cm at 106 km, with large scale fluctuations having amplitudes of roughly 10 percent seen only in the upward gradient in electron density. This is in agreement with plasma instability theory. It is further shown that simultaneous measurements by fixed-bias Langmuir probes, when normalized at a single point to the altitude profile of electron density, are inadequate to correctly parameterize the observed enhancements and depletions.

Baker, K. D.↗

NASA NTRS1986

Observations of the artificially injected Porcupine xenon ion beam in the ionosphere

Results are given of ion beam injection experiments performed in the auroral ionosphere in connection with the German Sounding Rocket Project Porcupine. A heavy (xenon) ion beam was injected into the collisionless ionospheric plasma approximately perpendicular to the ambient magnetic field at altitudes from 190 km to about 450 km. The beam propagates nearly undistorted across the plasma because it is essentially depolarized; at the same time the beam is not current neutralized. This unexpected behavior poses the interconnected problems of how the beam manages to become charge neutralized, how current closure is maintained, and what is the mechanism of depolarization.

Haeusler, B.↗

NASA NTRS1986

Is Jupiter's ionosphere a significant plasma source for its magnetosphere?

A semikinetic model was used to study the steady state, collisionless, polar wind outflow from the Jovian polar caps. H(+)-escape fluxes and energies were calculated for a range of conditions, including several values of the ambient electron temperature, different hot electron populations, and both with and without the effects of the centrifugal force. The calculations indicate that if hot electron populations exist over the Jovian polar caps, as they do on earth, polar wind escape fluxes of the order of 10 to the 8th per sq cm s are possible. When integrated over the polar cap area, escape fluxes of this order of magnitude imply an ionospheric source strength of 2 x 10 to the 28th ions/s, which is comparable to the present estimate of the total magnetospheric plasma source population. Therefore, the ionosphere may play an important role in populating the Jovian magnetosphere, specifically the hidden, low energy, light ion component of the population.

Nagy, A. F.↗

NASA NTRS1985

Evidence of solar wind energy deposition into the ionosphere of Mars

Suprathermal electron fluxes measured in the ionosphere of Mars by the retarding potential analyzer (RPA) on Viking lander 1 are presented and compared with the photoelectron flux that is produced by the absorption of the solar EUV. The calculation of the equilibrium photoelectron population on Mars is based on the multistream electron transport theory and a model neutral atmosphere and ionosphere that was actually observed by Viking lander 1. From the theoretical equilibrium photoelectron population, the expected RPA volt-ampere characteristic curves are computed and compared with those recorded by the instrument. The theoretical and the observed RPA currents below about 170 km are in agreement, confirming that the solar EUV is the main source of suprathermal electrons at these altitudes. Above about 170 km an additional source of suprathermal electrons is required to explain the observations.

Mantas, G. P.↗

NASA NTRS1985

Theory of the current-driven ion cyclotron instability in the bottomside ionosphere

A comprehensive treatment of the theory of electrostatic ion cyclotron instability in the collisional bottomside ionosphere is given. The linear dispersion relations for the ion cyclotron instability (electron and ion collisions) are derived. Analytical solutions to the dispersion relation are obtained in three limits: collisionless; weakly collisional; and collisional. In addition, the linear dispersion relation is solved numerically, using parameters typical of the high-latitude bottomside ionosphere. It is pointed out that the linear growth rates in the bottomside collisional regime can be of the same order as the corresponding topside collisionless growth rates. A nonlinear saturation mechanism for the electrostatic ion cyclotron instability is proposed on the basis of Dupree's (1966) resonance broadening theory.

Satyanarayana, P.↗

NASA NTRS1986

Ar(+) in the terrestrial ionosphere

The Ar(+) densities in the terrestrial ionosphere are computed for both low and high solar activity models. The reaction N2(+)(v greater than 0) + Ar yields N2 + Ar(+) is found to be a significant source of Ar(+) nearly equal to photoionization and electron impact ionization in the high solar activity model. Peak densities of Ar(+) of 11 per cu cm near 190 km and 22 per cu cm near 220 km are predicted for the low and high solar activity models. It is suggested that a simultaneous measurement of Ar(+) and Ar densities would provide a test for the presence of vibrationally excited N2(+) in the terrestrial ionosphere.

Fox, J. L.↗

NASA NTRS1985

Global energy regulation in the solar wind-magnetosphere-ionosphere system

Some basic concepts which are essential in the understanding of global energy regulation in the solar wind-magnetosphere-ionosphere system are introduced. The importance of line-tying concept is particularly emphasized in connection with the solar wind energy, energy release in the magnetosphere and energy dissipation in the ionosphere.

Sato, T.↗

NASA NTRS1986

A theoretical study of the production and decay of localized electron density enhancements in the polar ionosphere

Uniform convection patterns were introduced into a high latitude time-dependent F region model (HLTD) to study if soft auroral particle precipitation is a necessary precondition to blob formation in the ionosphere. Attention was limited to the conditions leading to the formation of parent blobs (dimensions of at least 10 km) due to plasma instabilities. Consideration was given to the effects of discrete auroral structures and to different O(+) precipitation ionization rate profiles during solar maximum conditions in the thermosphere. Blobs were assumed to be produced on the dayside due to ionization caused by sun-aligned arcs. The simulations indicated that parent blobs would form whenever plasma flux tubes in the ionosphere were exposed to soft particle precipitation lasting more than 10 min. The blobs cease to exist when convected to a region with a high particle production rate where the background particle density exceeds that of the blobs. Conditions wherein either hard or soft particle production can produce blobs are outlined.

Sojka, J. J.↗

NASA NTRS1986

Observations of ionospheric magnetospheric coupling - DE and Chatanika coincidences

Observations from several experiments on board the Dynamics Explorer 1 and 2 (DE 1 and 2) spacecraft and ground-based radar measurements from the Chatanika radar are combined in order to examine the details of ionospheric/magnetospheric coupling in the local evening sector. DE 1 and DE 2 were in coplanar polar orbits that provided measurements almost simultaneously in time and magnetically coincident with the Chatanika radar from L = 3 to L = 17. The coupling processes are inferred from the density, temperature, composition, and angular distributions of the low-energy plasma observed from the E region of the ionosphere to magnetospheric altitudes of 2.5 earth radii. Plasma characteristics of the plasmasphere, main trough, auroral zone, and polar cap can be studied in this data set. The observations imply that as L increases, the dominant coupling mechanism between the ionosphere and magnetosphere in the measured energy range changes from equilibrium diffusion to perpendicular acceleration and finally to parallel acceleration.

Green, J. L.↗

NASA NTRS1986

Ionospheric convection signatures observed by DE 2 during northward interplanetary magnetic field

Observations of the ionospheric convection signature at high latitudes are examined during periods of prolonged northward interplanetary magnetic field (IMF). The data from Dynamics Explorer 2 show that a four-cell convection pattern can frequently be observed in a region that is displaced to the sunward side of the dawn-dusk meridian regardless of season. In the eclipsed ionosphere, extremely structured or turbulent flow exists with no identifiable connection to a more coherent pattern that may simultaneously exist in the dayside region. The two highest-latitude convection cells that form part of the coherent dayside pattern show a dependence on the y component of the IMF. This dependence is such that a clockwise circulating cell displaced toward dawn dominates the high-latitude region when B(Y) is positive. Anti-clockwise circulation displaced toward dusk dominates the highest latitudes when B(Y) is negative. Examination of the simultaneously observed energetic particle environment suggests that both open and closed field lines may be associated with the high-latitude convection cells. On occasions these entire cells can exist on open field lines. The existence of closed field lines in regions of sunward flow is also apparent in the data.

Heelis, R. A.↗

NASA NTRS1986

A study of large, medium and small scale structures in the topside ionosphere

Alouette and ISIS data were studied for large, medium, and small scale structures in the ionosphere. Correlation was also sought with measurements by other satellites, such as the Atmosphere Explorer C and E and the Dynamic Explorer 2 satellites, of both neutrals and ionization, and with measurements by ground facilities, such as the incoherent scatter radars. Large scale coherent wavelike structures were found from ISIS 2 electron density contours from above the F peak to nearly the satellite altitude. Such structures were also found to correlate with the observation by AE-C below the F peak during a conjunction of the two satellites. Vertical wavefronts found in the upper F region suggest the dominance of diffusion along field lines as well. Also discovered were multiple, evenly spaced field-aligned ducts in the F region that, at low latitudes, extended to the other hemisphere and were in the form of field-aligned sheets in the east-west direction. Low latitude heating events were discovered that could serve as sources for waves in the ionosphere.

Gross, Stanley H.↗

NASA NTRS1986

Magnetosphere-ionosphere interactions: Near Earth manifestations of the plasma universe

As the universe consists almost entirely of plasma, the understanding of astrophysical phenomena must depend critically on the understanding of how matter behaves in the plasma state. In situ observations in the near Earth cosmical plasma offer an excellent opportunity of gaining such understanding. The near Earth cosmical plasma not only covers vast ranges of density and temperature, but is the site of a rich variety of complex plasma physical processes which are activated as a results of the interactions between the magnetosphere and the ionosphere. The geomagnetic field connects the ionosphere, tied by friction to the Earth, and the magnetosphere, dynamically coupled to the solar wind. This causes an exchange of energy an momentum between the two regions. The exchange is executed by magnetic-field-aligned electric currents, the so-called Birkeland currents. Both directly and indirectly (through instabilities and particle acceleration) these also lead to an exchange of plasma, which is selective and therefore causes chemical separation. Another essential aspect of the coupling is the role of electric fields, especially magnetic field aligned (parallel) electric fields, which have important consequences both for the dynamics of the coupling and, especially, for energization of charged particles.

Faelthammar, Carl-Gunne↗

NASA NTRS1986

Median density altitude profiles of the major ions in the central nightside Venus ionosphere

Altitude profiles of median values for total ion density, constituent ion densities, and the molecular ion group of the central nightside Venus ionosphere are presently derived from the Pioneer Venus retarding potential analyzer's measurements during the first five seasonal passages of the spacecraft through the nightside hemisphere. The altitude profiles for total ion density, constituent ions and the molecular ion group are compared with previously predicted profiles derived from numerical models in which the ionization source was O(+) ions transported from the dayside ionosphere and electron impact-produced ionization. The electron impact-produced profiles for O(+) is 2 orders of magnitude smaller than that observed.

Knudsen, William C.↗

NASA NTRS1987

Spectral studies of the sources of ionospheric electric fields

Spectral analyses (applying the Fourier analysis methods) were performed on three incoherent scatter radar data sets (obtained at Jicamarca, Peru; Chatanika, Alaska; and Arecibo, Puerto Rico) with the aim of investigating the origin of ionospheric electric fields in the frequency range of 0.01-2 cycles/h. In quiet times, atmospheric gravity waves appeared to be the most likely source of the ionospheric electric field. This hypothesis was tested by a direct simultaneous comparison of measurements of gravity waves in the mesosphere and of electric fields in the thermosphere during very quiet conditions. The results indicated that a gravity wave source is a plausible candidate for the electric field fluctuations.

Earle, G. D.↗

NASA NTRS1986

The vibrational distribution of O2(+) in the dayside ionosphere

The vibrational distributions of O2(+) in the X2Pi(g), A2Pi(u), a4Pi(u), and b4Sigma(-)g states in the dayside terrestrial ionosphere are calculated for both low and high solar activity models. The distributions are found to be significantly different from the O2(+) vibrational distributions found by Fox (1985) for the Venusian ionosphere. The sources and sinks of vibrational excitation and the implications for the chemistry, dayglow, and hot oxygen coronas are discussed. Finally, intensities of the first negative and second negative band systems of O2(+) are presented.

Fox, J. L.↗

NASA NTRS1986

Heating of upflowing ionospheric ions on auroral field lines

The upflow of ionospheric ions along auroral field lines is investigated on the basis of nearly simultaneous particle measurements obtained with DE-1 at 9000-15,000 km and DE-2 at 400-800 km during four auroral conjunction events in 1981. The data are presented in extensive graphs and maps and characterized in detail. The distributions of the upflowing ions are shown to be consistent with acceleration of a Maxwellian by a parallel electric field, but from the energy levels involved (hundreds of eV) it is inferred that an ionospheric source is being heated within or above the acceleration region, possibly by an ion two-stream instability.

Reiff, P. H.↗

NASA NTRS1987

Initial results from the operation of two argon ion generators in the auroral ionosphere

Two argon ion generators have been lofted by sounding rockets in order to investigate ion beam dynamics and beam effects on the ionosphere, and auroral electrodynamics during rocket passage over auroral arcs. The ion generators were on a subpayload that was separated from the main payload early in the flight. The main payload conducted the diagnostic measurements during ion beam operations. Evidence of heating of the ionosphere around the subpayload during each ion beam emission is noted.

Erlandson, R. E.↗

NASA NTRS1987

Electrodynamics and plasma processes in the ionosphere

The paper examines the advances achieved between 1983 and 1986 on understanding ionospheric electrodynamics and associated plasma processes, including an assessment of the roles of the E- and F-region neutral winds in providing the large-scale electric field in the ionosphere, as well as of the influence of electric fields of magnetospheric origin on the motion and distribution of plasma. Studies of the factors affecting the creation and evolution of plasma structure with many different scale sizes are discussed. Consideration is also given to the ground-based and in situ techniques used in these studies.

Heelis, R. A.↗