SEARCH · Engineering Papers

Results for “Ionosphere”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 757 records · Page 42

All sources NASA NTRS DOE OSTI

NASA NTRS1980

Changes in the terrestrial atmosphere-ionosphere-magnetosphere system due to ion propulsion for solar power satellite placement

In order to construct solar power satellites using earth-based materials, sections of a satellite must be lifted from low earth to geosynchronous orbit. The most plausible method of accomplishing this task is by means of ion propulsion based on the relatively abundant terrestrial atmospheric component, Ar. The proposed propulsion system will release a dense beam of about 5 keV Ar(+). The total amount of Ar(+) injected in transporting the components for each solar power satellite is comparable to the total ion content of the ionosphere-plasmasphere system while the total energy injected is larger than that of this system. Preliminary estimates are given of the effects massive Ar(+) injections have on the ionosphere-plasmasphere system with specific emphasis on potential communications disruptions. The effects stem from direct Ar(+) precipitation into the atmosphere and from Ar(+) beam induced precipitation of MeV radiation belt protons.

Curtis, S. A.↗

NASA NTRS1980

The dynamic behavior of the Venus ionosphere in response to solar wind interactions

The dynamics of the Venus ionosphere relates to the variations in the solar wind and the ionosheath magnetic fields as demonstrated by the electron density and temperature measurements of the Pioneer Venus orbiter electron probe. The mean ionopause height increases from 330 km at the subsolar point to 700 km at the dusk terminator, and to 1000 km at the dawn terminator; the dayside ionopause expands and contracts with solar wind pressure variations. Extreme spatial irregularities in the shape of holes, horizontally stratified layers, and detached plasma clouds are observed in the nightside ionosphere. The ion pickup on the dayside is described in terms of solar wind discontinuities inducing a wavelike pattern at the ionopause which is penetrated by the ionosheath plasma and magnetic fields which remove the plasma in the form of detached plasma clouds.

Brace, L. H.↗

NASA NTRS1980

Model calculations of the dayside ionosphere of Venus - Energetics

A model of the energy balance of the dayside ionosphere of Venus is presented. Calculations of the dayside electron and ion temperature profiles are carried out and compared with data from experiments on the Pioneer Venus orbiter. The coupled heat conduction equations for electrons and ions are solved for several values of the solar zenith angle. It is shown that thermal conductivities are inhibited by the presence of a horizontal magnetic field. A realistic model of the magnetic field that includes fluctuations is employed in deriving an appropriate expression for the thermal conductivity. The contributions of photoelectrons, ion chemistry, Joule heating, and solar wind heating to the energy balance of the ionosphere are considered.

Cravens, T. E.↗

NASA NTRS1980

Empirical models of the electron temperature and density in the Venus ionosphere

The electron temperature and density of the Venus ionosphere is characterized using data from the Pioneer Venus orbiter electron temperature probe experiment for the full range of solar zenith angles and local times. Values for the electron density are nearly uniform across the day side with a sharp decrease in the vicinity of the terminator. The model shows a substantial night side ionosphere which can be accounted for by a combination of several transport processes, and by local production by precipitating particles. The electron temperature model demonstrates the high temperatures seen on both the day side and night side. It is found that the night side is much more variable than the day side, and that there is no obvious north-south asymmetry in either the temperature or the density.

Theis, R. F.↗

NASA NTRS1980

Transport of ionospheric O/+/ ions across the Venus terminator and implications

Data from the Pioneer Venus orbiter retarding potential analyzer demonstrate that the velocity of ionospheric O(+) ions in the vicinity of the terminator is directed antisunward and radially inward toward the planet in the range of 1-8 km/s. The velocity tends to increase with altitude, and may increase to still larger values just below the ionopause. The Alfven Mach number of the flow is generally greater than 1, indicating that the flow is controlled more by inertial forces than by magnetic forces. The ion Mach number is also greater than one. The flux of O(+) ions across the terminator planetwise is estimated to be equal to the integrated recombination rate of O2(+) on the night side within a factor of 2. Ion transport contributes substantially, and possibly predominantly, to the maintenance of the night side ionosphere.

Knudsen, W. C.↗

NASA NTRS1981

Negative ions in the ionospheres of planetary bodies without atmospheres

It is noted that negative ions may be formed in the ionospheres of Mercury, the moon, and Jupiter's satellites with densities of a few percent of the ionospheric electron density. Negative ions result from three mechanisms at the planetary surface: charge inversion during energetic proton scattering, with simultaneous secondary negative ion emission, and micrometeorite impacts. The density and distribution of negative ions around planetary bodies depends primarily on the negative ion lifetimes determined through photodetachment by solar radiation.

Wekhof, A.↗

NASA NTRS1981

Dynamic variations observed in thermal and superthermal ion distributions in the dayside ionosphere of Venus

In-situ measurements of the ion composition and concentration of the ionosphere of Venus are obtained with the Bennett RF ion mass spectrometer (OIMS) on the Pioneer Venus Orbiter (PVO). Dayside ion profiles exhibit considerable variability in the height of the ionopause as well as the scale heights of the ion constituents, which reflect the compression and expansion of the ionosphere in response to solar wind variations. Near the dayside upper boundary of the thermal O+ distribution, super-thermal ions are detected by the OIMS, presenting a complication for identifying the ion signature of the ionopause. Correlated with the presence of the superthermal ions, the ac electric field detector (OEFD) detects regions of intensified signals, with peak response in the 100 Hz frequency channel. It is expected that further analysis of the superthermal ion-electric field signatures will contribute to a clearer understanding of the physical processes underlying the formation of the ionopause.

Taylor, H. A., Jr.↗

NASA NTRS1981

Magnetic flux ropes in the Venus ionosphere - In situ observations of force-free structures

Force-free magnetic structures with cylindrical geometry appear under a variety of conditions in nature. Filamentary helical magnetic structures are observed to be associated with prominences and flares in the solar atmosphere, and can arise in superconductors and laboratory plasmas. Another example of cylindrcal quasi-force-free configurations appears to exist in the Venus ionosphere. Magnetic flux ropes with diameters of approximately 20-30 km have been observed by the Pioneer Venus Orbiter to be a nearly ubiquitous feature of the dayside Venus ionosphere. Models of flux ropes suggest that many of these structures tend to be quasi-force-free, while others are correlated with pressure variations in the ambient thermal plasma.

Elphic, R. C.↗

NASA NTRS1981

An electrodynamic model of electric currents and magnetic fields in the dayside ionosphere of Venus

The electric current configuration induced in the ionosphere of Venus by the interaction of the solar wind has been calculated in previous papers (Cloutier and Daniell, 1973; Daniell and Cloutier, 1977; Cloutier and Daniell, 1979) for average steady-state solar wind conditions and interplanetary magnetic field. This model is generalized to include the effects of (1) plasma depletion and magnetic field enhancement near the ionopause, (2) velocity-shear-induced MHD instabilities of the Kelvin-Helmholtz type within the ionosphere, and (3) variations in solar wind parameters and interplanetary magnetic field. It is shown that the magnetic field configuration resulting from the model varies in response to changes in solar wind and interplanetary field conditions, and that these variations produce magnetic field profiles in excellent agreement with those seen by the Pioneer-Venus Orbiter. The formation of flux-ropes by the Kelving-Helmholtz instability is shown to be a natural consequence of the model, with the spatial distribution and size of the flux-ropes determined by the magnetic Reynolds number.

Cloutier, P. A.↗

NASA NTRS1981

Global ionospheric electric field measurements in April 1978

This paper presents an introduction to a global campaign of simultaneous quasi-static electric field measurements from radars, balloons, and satellites at various places within the earth's environment for April 8-14, 1978. The 7-day time period encompassed both extended magnetically quiet times as well as two magnetic storms. These storms were related to SSCs that followed solar flares, one of which included a day-long solar proton event. The wide variety of instrumentation and associated operating modes involved in this campaign is described. Sample conjunctions between satellites and ionospheric measurements are shown that demonstrate that field line mapping is valid under certain circumstances. Some of the largest ionospheric electric fields ever reported with greater than 100-km scale size occurred on April 11, and these events are discussed in detail.

Holzworth, R.↗

NASA NTRS1981

Saturn ionosphere - Theoretical interpretation

Voyager 1 high latitude and Pioneer 11 equatorial ionospheric structure indicate a solar EUV-controlled ionosphere with a possible molecular ion in the topside. Vibrationally excited H2 in the high latitudes may be an important loss mechanism. Dynamical effects are expected to be important for determining the peak density and its location.

Atreya, S. K.↗

NASA NTRS1981

Speed-dependent collision effects on radar back-scattering from the ionosphere

A computer code to accurately compute the fluctuation spectrum for linearly speed dependent collision frequencies was developed. The effect of ignoring the speed dependence on the estimates of ionospheric parameters was determined. It is shown that disagreements between the rocket and the incoherent scatter estimates could be partially resolved if the correct speed dependence of the i-n collision frequency is not ignored. This problem is also relevant to the study of ionospheric irregularities in the auroral E-region and their effects on the radio communication with satellites.

Theimer, O.↗

NASA NTRS1980

Microwave heating of the lower ionosphere

Changes in the properties of the lower ionosphere due to ohmic heating of the plasma by the solar power satellite (SPS) microwave power beam are considered. The development of a predictive model of the underdense interaction of an electromagnetic beam and the lower ionosphere is described. The extent to which the Platteville and Arecibo experiments simulate SPS conditions is considered.

Meltz, G.↗

NASA NTRS1981

On the maintenance of the Venus nightside ionosphere - Electron precipitation and plasma transport

The relative contributions of electron precipitation and transport of dayside plasma to the maintenance of the Venus nightside ionosphere during the long Venusian night are investigated based on simultaneous Pioneer Venus Orbiter Retarding Potential Analyzer measurements of suprathermal electron fluxes and plasma densities. In about 20 orbits, the nightside integral electron flux of electrons with energies between 5 and 45 eV is observed to be relatively constant in time and altitude, while plasma density is observed to vary by a factor of 10 or more with no correlation with the electron flux. Ionization rates and ion density height profiles are computed for O(+) and O2(+) as a function of magnetic dip angle based on a typical electron spectrum, or a downward flux of O(+) ions. Comparison of the computed profiles with the measured median O(+) and O2(+) density profiles reveals that the measured profiles can only be reproduced by a downward flux of O(+) equal to about 10 to the 8th/sq cm per sec; suprathermal electron energy distributions produce O2(+) and O(+) levels only about half and one tenth those usually observed, respectively. It is thus concluded that transport of O(+) ions from the dayside Venus ionosphere is responsible for approximately 75% of the typical nightside ionization, with variations in O(+) transport mechanism responsible for most of the observed nightside density variations. The remaining ionization is attributed to suprathermal electrons, which contribute principally to the O2(+) peak.

Spenner, K.↗

NASA NTRS1981

Ionospheric remote sensing of medium-scale gravity waves and tornadic storms

Gravity waves associated with severe storms are investigated on the basis of ionospheric sounding using a ground-based Doppler system. Reverse-group ray tracing computations are used to determine the origin of over 20 gravity waves detected within 800 km of Huntsville, Alabama in association with a group of tornadoes, isolated tornadoes in the presence of a squall line, and isolated tornadoes in the absence of a squall line. Gravity waves associated with tornadoes are found either to be generated by thunderstorms with enhanced convection embedded in a squall line, or in an isolated cloud with enhanced convection. The computed wave sources are observed in all cases to be located near the points where the tornadoes touched down more than an hour after wave excitation. Results show that gravity waves play an important role in troposphere-ionosphere coupling during times of intense convection associated with tornadic storm activity.

Hung, R. J.↗

NASA NTRS1981

The ionospheric peak on the Venus dayside

The behavior of the ionospheric peak on the dayside of Venus is described and interpreted by combining radio occultation measurements with theoretical calculations. The theoretical models are shown to be able to reproduce the measured electron densities very accurately when careful consideration is given to such parameters as the level of solar activity, the electron temperature, and the neutral density. What is more, the models are able to provide a check on the accuracy of neutral atmospheric models in the vicinity of 140 km. Chemical equilibrium is assumed for the calculation of ion and electron densities. A table giving Pioneer Venus radio occultation measurements of the Venus dayside ionosphere is included.

Cravens, T. E.↗

NASA NTRS1981

Energization of ionospheric ions by electrostatic hydrogen cyclotron waves

Interactions between ionospheric ions and electrostatic hydrogen cyclotron waves are studied numerically in an investigation of a possible mechanism for the energization of the low-energy ionospheric ions flowing along geomagnetic field lines to high altitudes. Ion equations of motion are solved numerically for a given number of O(+), He(+) and He(2+) ions initially in a Maxwellian distribution. All the ions considered are found capable of undergoing stochastic acceleration by a coherent electrostatic hydrogen cyclotron wave with parameters typical of the auroral plasma above 1 earth radius. The fraction of the initial ion population undergoing heating depends strongly on the mass, charge and initial temperature of the ion species, with O(+) ions only heated when their initial temperature is approximately greater than the hydrogen temperature and the lighter ions able to be heated even when cold, due to cyclotron resonant stochastic heating.

Singh, N.↗

NASA NTRS1981

Evidence for the acceleration of ionospheric O/+/ in the magnetosheath of Venus

Plasma spectra from 12 orbits of the Pioneer-Venus Orbiter are reported which suggest the presence of ionospheric material in the magnetosheath plasma near and sunward of the terminator plane. Each spectrum shows a high E/q peak, consistent with O(+) moving at a speed lower than or comparable to that of the ambient magnetosheath plasma. It is pointed out that even though the data set is limited, the most intense heavy-ion fluxes clearly occur at altitudes less than a few thousand km. With the identification of the energetic component at O(+), the data reveal a trend for the speed of O(+) near the planet to be lower than the local magnetosheath speed, whereas the two speeds are comparable at altitudes above a few thousand km. These data, in combination with related observations that indicate O(+) moving at ambient speed in the distant wake, suggest that ionospheric material is swept up by the magnetosheath, accelerated to ambient speed within a few thousand km, and carried back through the wake region.

Mihalov, J. D.↗