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NASA NTRS1976

The response of the ionosphere to the injection of chemically reactive vapors

As a gas released in the ionosphere expands, it is rapidly cooled. When the vapor becomes sufficiently tenuous, it is reheated by collisions with the ambient atmosphere and its flow is then governed by diffusive expansion. As the injected gas becomes well mixed with the plasma, a hole is created by chemical processes. In the case of diatomic hydrogen release, depression of the electron concentrations is governed by the charge exchange reaction between oxygen ions and hydrogen, producing positive hydroxyl ions. Hydroxyl ions rapidly react with the electron gas to produce excited oxygen and hydrogen atoms. Enhanced airglow emissions result from the transition of the excited atoms to lower energy states. The electron temperature in the depleted region rises sharply causing a thermal expansion of the plasma and a further reduction in the local plasma concentration.

Bernhardt, P. A.↗

NASA NTRS1976

Ionization effects due to solar flare on terrestrial ionosphere

Sudden frequency deviation ionospheric disturbances related to the flares of May 18 and 19, 1973 were observed from the NASA/MSFC high frequency Doppler sounder array system in Huntsville, Alabama. The results are compared with those observed at Table Mountain near Boulder, Colorado and at the University of Hawaii.

Wu, S. T.↗

NASA NTRS1975

Propagation of acoustic modes in the transitional ionosphere

Continuum theory is unsatisfactory for describing wave propagation in the transitional ionosphere, since the mean free path is of the same order as the characteristic length (i.e., Knudsen number in this region is of the order of unity). Therefore a transition model in which isotropic electrons behave as a fluid while the ions are governed by the kinetic equation modified by ion-electron collision effects is proposed to study acoustic wave propagation in the upper atmosphere in the altitude region from 500 to 2000 km. The results show that the dissipation of acoustic waves by electrons is through the viscous and thermal conduction effects, and the dissipation of acoustic waves by ions is through Landau damping. Comparisons of the characteristics of acoustic mode propagation and wave dissipation mechanisms in the collision-dominated, transitional from collisional to collisionless, and collisionless media are also discussed.

Hung, R. J.↗

NASA NTRS1975

Coherence properties of wideband satellite signals caused by ionospheric scintillation

Radio scintillation on satellite signals caused by small-scale irregularities in F-region ionospheric electron density can be an important limitation on earth-satellite communication and navigation systems. Scintillation imposes distortion in both amplitude and phase on wideband signals. In the present work, the shallow-modulated phase screen theory is developed in terms of coherence bandwidth including a model based on a turbulent-like power-law description of the irregularities. The model results usually show a greater coherence bandwidth in the signal phase than in the signal amplitude. Therefore, systems that require phase coherence over a large bandwidth should be less affected than those requiring amplitude coherence.

Rufenach, C. L.↗

NASA NTRS1976

Analysis of the backscatter spectrum in an ionospheric modification experiment

The purpose of this study is to compare predictions of the backscatter spectrum, including effects of ionospheric inhomogeneity, with experimental observations of incoherent backscatter from an artificially heated region. Our calculations show that the strongest backscatter echo received is not from the reflection level but from a region some distance below (about 900-1100 m for an experiment carried out at Arecibo). By taking the standing wave pattern of the pump properly into account the present theory explains certain asymmetrical features of the upshifted and downshifted plasma lines in the backscatter spectrum.

Kim, H.↗

NASA NTRS1976

Ionospheric composition in SAR-arcs

Theoretical ion and electron density profiles in the SAR-arc region are calculated using a model of the ionosphere based on the coupled continuity, momentum, and energy equations for O(+), NO(+), and O2(+). It is found that an increase in the reaction O(+) + N2 yields NO(+) + N, which results from enhanced N2 vibrational excitation due to the high electron temperatures found in SAR arcs, can cause a reduction in F-region electron densities by up to a factor of two. The increase in the O(+) + N2 reaction rate is shown to result in a marked change in the ion composition in SAR arcs, with NO(+) being an important ion up to altitudes of about 350 km at night. Since observed electron-density depressions in SAR arcs generally vary between factors of two and seven, it is concluded that the increase in the O(+) + N2 reaction rate cannot account for these depressions by itself.

Raitt, W. J.↗

NASA NTRS1976

The partially aligned gradient instability in the ionosphere

Ionization irregularities which are almost but not exactly aligned along the magnetic field may grow much more rapidly than purely aligned irregularities in the presence of a background gradient of ionization and current flow. The stability of these irregularities is considered, taking into account the finite thickness of the gradient and shear in the ion motion. It is shown in particular that the normal E region of the ionosphere is usually stable, whereas sporadic E is often unstable, and this may limit the compression of metallic ions to form such layers. The F region may sometimes be unstable. Temperate zone conditions are considered throughout.

Whitehead, J. D.↗

NASA NTRS1976

Satellite measurements of ion composition and temperatures in the topside ionosphere during medium solar activity

Information on both ion density and temperature is obtained from analysis of Retarding Potential Analyzer data from the OGO-4 and Explorer-31 satellites. Results obtained from data in the altitude range of 700-2000 km during medium solar activity are presented. An attempt is made to describe the major altitude variations of ion densities and temperatures at middle and low latitudes. The transition heights, where the heavier and lighter ions are equal, are found to be about 1600 and 1300 km at middle and low latitudes, respectively, for daytime and 700 km at night for middle latitudes. Based on the observed data and using diffusive equilibrium as a first-order approximation, topside ionospheric composition models are given for medium solar activity.

Goel, M. K.↗

NASA NTRS1976

Recombination of NO/+/ in the ionosphere

Simultaneous nighttime measurements of ion and neutral concentrations and temperatures made by the Atmosphere Explorer-C satellite were used to determine the recombination rate coefficient of NO(+) as a function of electron temperature. The results agree in shape and absolute magnitude to within one standard deviation with those of Walls and Dunn (1974), indicating that NO(+) ions in the ionosphere may be in the ground vibrational state.

Torr, D. G.↗

NASA NTRS1976

A model study of diurnal behavior of the ionosphere and the protonosphere coupling

A new method to study dynamic behavior of the ionosphere-protonosphere coupling within the plasmasphere is developed and used to calculate ion distributions above 500 km using observed electron densities at 500 km. The method is based on the relation between the total magnetic flux tube content of H(+) above some reference height (e.g., 3000 km) and the H(+) flux at that height, which is uniquely determined by the coupled momentum and continuity equations for the quasi-steady state. The O(+) profile is perturbed from diffusive equilibrium only by ion drag with H(+). The time dependency is taken into account by applying self-consistent boundary conditions which are obtained from the solution of the time-dependent equation for the tube content of H(+). Calculations are carried out for two models. The first model deals with the ion dynamics in a tube of force which rotates with the earth. In the second model, effects of the cross-L plasma drifts are considered. Both models produce diurnal variations of H(+) and O(+) densities near 1000 km similar to observational results.

Marubashi, K.↗

NASA NTRS1976

The penetration of soft electrons into the ionosphere

Calculations are presented of energy spectra and angular and spatial distributions of electron fluxes in the ionosphere resulting from precipitation of monoenergetic (E = 25, 50, and 100 eV) electrons. The incident electrons are assumed to be isotropic over the downward direction. It is found that the resulting steady-state electron fluxes above ca. 300 km are highly anisotropic and that the pitch-angle distribution is energy dependent. About 15% of the incident electrons are backscattered elastically to the protonosphere. A much larger number of electrons escapes after they have deposited part of their energy in the atmosphere. The mean energy of the escaping electrons is about half that of the incident electrons. About 50% of the incident energy is absorbed in the atmosphere, the remainder being returned to the protonosphere. The rate of energy absorption is a maximum at heights between 300 and 400 km. Most of the energy is absorbed in ionization and excitation of atomic oxygen; an appreciable amount is absorbed as heat by the ambient electron gas. Altitude profiles are presented for the rates of ionization, excitation, and electron heating caused by soft-electron precipitation.

Mantas, G. P.↗

NASA NTRS1976

Ionospheric disturbances and gravity waves

The response of ionization to a gravity wave moving through the ionosphere is studied. Hydrodynamic equations are used, and local thermodynamic equilibrium is imposed for simplicity. The treatment involves a perturbation analysis, and the background medium is assumed to be time stationary, horizontally stratified, and known. It is shown that ionization may be locally resonant at each level for certain frequencies and directions, for which condition neutral and ionized particles are considered closely or critically coupled. The phase direction for this critical coupling is always downward in the absence of a magnetic field. A magnetic field results in two resonant directions for the same frequency, and these directions are mostly downward. Observed TID's associated with gravity waves may be indicative of such resonances. It is also noted that strong coupling may occur to neutral acoustic waves at high altitudes. Previous investigations restrict their use of momentum equations to the diffusion equation. The analysis also shows that such restrictions result in the neglect of terms arising from momentum transport due to any background ambipolar diffusion velocity and wave motion. These terms are mostly relevant at higher altitudes.

Eun, H.↗

NASA NTRS1976

The lower ionosphere of Titan

Ionization of the atmosphere of Titan by galactic cosmic rays is a very significant process throughout the altitude range from 100 to 400 km. An approximate form of the Boltzmann equation for cosmic-ray transport has been used to obtain local ionization rates. Models of both ion and neutral chemistry have been employed to compute electron and ion density profiles for three different values of the H2/CH4 abundance ratio. The peak electron density is of the order of 1000 per cu cm. The most abundant positive ions are C2/H9(+) and C3H9(+), while the predicted densities of the negative ions H(-) and CH3(-) are very small (less than one ten-thousandth that of the positive ions). It is suggested that inclusion of the ion chemistry is important in the computation of the H and CH3 density profiles in the lower ionosphere.

Capone, L. A.↗

NASA NTRS1976

Venus' night side ionosphere - Its origin and maintenance

A substantial nightside ionosphere has been observed on Venus by both Mariner 5 and Mariner 10. Major dayside ionic species such as O2(+) and other molecular ions have chemical lifetimes much shorter than the 244.3-day rotation period of the planet. Rapid transport of ions from the dayside to the nightside to the extent required seems most unlikely. Consequently, possibilities are investigated for local production of ions on the nightside itself. Constraints imposed by chemical lifetimes require atomic ions with low ionization potentials. It is suggested that metallic ions of meteoric origin are the positive charge carriers, and the plausibility of this mechanism is demonstrated. Other possibilities are examined and shown to be less likely. Meteor ablation on Venus, the aeronomy of metallic species, and the role of negative ions near the electron peaks of the atmosphere are discussed.

Butler, D. M.↗

NASA NTRS1976

Evolution of the ionosphere

Studies were made of the electron density profiles at various stages of atmospheric evolution, with the assumption that the atmospheric composition has changed due to the gradual increase of oxygen while the nitrogen level has remained constant. The result of model calculations indicates that when the oxygen content is less than about 1% of the present earth's atmosphere level, the major ions in the F2 region will change from O(+) to N(+). The maximum number density of N(+) ions reaches approximately 10 million per cu cm because of the absence of a rapid loss mechanism for N(+). The height of the N(+) ion density peak is much lower than the height of the F2 layer peak of the current ionosphere.

Shimizu, M.↗

NASA NTRS1976

Observations of large parallel electric fields in the auroral ionosphere

Rocket borne measurements employing a double probe technique were used to gather evidence for the existence of electric fields in the auroral ionosphere having components parallel to the magnetic field direction. An analysis of possible experimental errors leads to the conclusion that no known uncertainties can account for the roughly 10 mV/m parallel electric fields that are observed.

Mozer, F. S.↗

NASA NTRS1976

Description and catalog of ionospheric F-region data, Jicamarca Radar Observatory, November 1966 - April 1969

Equatorial ionospheric F-region data reduced from the Jicamarca Radar Observatory (JRO) incoherent scatter observations for particular periods is described. It lists in catalog form the times of the observations made during those periods. These F-region data include the electron concentration and the electron and ion temperatures. The data were inferred from the incoherent scatter observations of JRO.

Clark, W. L.↗

NASA NTRS1976

Analysis of satellite data on energetic particles of ionospheric origin

The principal result of this program has been the completion of a detailed statistical study of the properties of precipitating O(+) and H(+) ions during two principal magnetic storms. The results of the analysis of selected data of ion mass spectrometer experiment on satellites are given with emphasis on the morphology of the O(+) ions of ionospheric origin with energies in the 0.7 les than or equal to E less than or equal to 12 keV range that were discovered with this experiment.

Sharp, R. D.↗