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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

DMSP Spacecraft Charging in Auroral Environments

The Defense Meteorological Satellite Program (DMSP) spacecraft are a series of low-earth orbit (LEO) satellites whose mission is to observe the space environment using the precipitating energetic particle spectrometer (SSJ/4-5). DMSP satellites fly in a geosynchronous orbit at approx.840 km altitude which passes through Earth s ionosphere. The ionosphere is a region of partially ionized gas (plasma) formed by the photoionization of neutral atoms and molecules in the upper atmosphere of Earth. For satellites in LEO, such as DMSP, the plasma density is usually high and the main contributors to the currents to the spacecraft are the precipitating auroral electrons and ions from the magnetosphere as well as the cold plasma that constitutes the ionosphere. It is important to understand how the ionosphere and auroral electrons can accumulate surface charges on satellites because spacecraft charging has been the cause of a number of significant anomalies for on-board instrumentation on high altitude spacecraft. These range from limiting the sensitivity of measurements to instrument malfunction depending on the magnitude of the potential difference over the spacecraft surface. Interactive Data Language (IDL) software was developed to process SSJ/4-5 electron and ion data and to create a spectrogram of the particles number and energy fluxes. The purpose of this study is to identify DMSP spacecraft charging events and to present a preliminary statistical analysis. Nomenclature

Colson, Andrew↗
NASA NTRS1974

Incoherent scatter measurements of E region conductivities and currents in the auroral zone

Data taken by incoherent scatter radar have been used to investigate ionospheric conductivities and electrical currents. During quiet days, the conductivities appear to vary in a way consistent with ionization arising from solar EUV radiation. In the evening hours, enhancements in the northward electric field are found to precede small increases in the conductivities. Strong enhancements of the Hall conductivity relative to the Pedersen conductivity occur during negative bays when the electric field is in a southwestward direction. The ionospheric currents calculated in the geomagnetic east-west direction are in good agreement with the H component measured by a nearby magnetometer; this result indicates that the current causing the ground level magnetic fluctuations is a broad horizontal sheet current. The north-south ionospheric current, however, consistently disagrees with the observed D component in a manner that cannot easily be explained unless currents parallel to the earth's magnetic field are present.

Brekke, A.↗
NASA NTRS1972

Atmospheric waves and the ionosphere.

A review of evidence supporting the existence of atmospheric waves is presented, and a simple, theoretical approach for describing them is shown. Suggestions for gravity wave sources include equatorial and auroral electrojet, auroral and polar substorm heating, atmospheric jet streams, and large oceanic tides. There are reviewed previous studies dealing with the interaction between ionization and atmospheric waves believed to exist at ionospheric heights. These waves include acoustic waves, evanescent waves, and internal atmospheric gravity waves. It is explained that mode analysis, often employed when an increased number of layers is used for a more complete profile, is inapplicable for waves very close to a source.

Beer, T.↗
NASA NTRS1986

Dissociative excitation of the N(+)(5S) state by electron impact on N2 - Excitation function and quenching

Metastable N(+)(5S) ions were produced in the laboratory by dissociative excitation of N2 with energetic electrons. The resulting radiative decay of the N(+)(5S) state was observed with sufficient resolution to completely resolve the doublet from the nearby N2 molecular radiation. The excitation function was measured from threshold to 500 eV. The cross section peaks at a high electron energy and also exhibits a high threshold energy both of which are typical of dissociative excitation-ionization processes. This finding complicates the explanation of electron impact on N2 as the mechanism for the source of the 2145 A 'auroral mystery feature' by further increasing the required peak cross section. It is suggested that the apparent N(+)(5S) quenching in auroras may be an artifact due to the softening of the electron energy spectrum in the auroral E region.

Erdman, P. W.↗
NASA NTRS1981

Spectroscopic diagnostics of the formation of auroral arcs

The theory and mechanisms for spectroscopic observations of auroral arcs are examined. The emission rate ratios of various spectroscopic features are used to determine the average energy of the auroral particles, noting that only proton bombardment of the atmosphere can produce the observed emissions of atomic hydrogen, Balmer alpha, and Balmer beta. The atomic hydrogen particles can cause excitation, stripping, or ionization. Differences in subsequent electron observations due to the relative energy levels of the bombardment are described, and the use of the First Negative bands of molecular N ions and the ground configuration transition in singly atomic O for optical emission studies is outlined. The mean energy of the bombarding electron flux can be obtained and may be equalled under certain conditions by the proton flux. Finally, the characteristics of an ideal spectrometer for exploring auroral emissions are introduced.

Rees, M. H.↗
NASA NTRS1981

Venus nightside ionospheric holes - The signatures of parallel electric field acceleration regions

Attention is given to the existence of 'holes', that is, regions of density depletion in the nightside Venus ionosphere associated with regions of radial magnetic fields. The properties of the electrons within the core of these holes are thought to suggest an acceleration process along the magnetic field lines, a process also suggested by the Venera 9 and 10 observations of energetic ions in the Venus tail. On the basis of the observational information, these Venusian plasma depletions are attributed to the presence of parallel electric fields similar to those observed in the terrestrial auroral ionosphere. The resulting electric field accelerates electrons down the field lines, heating the depleted thermal electron population within the hole and producing ionization below the hole. At the same time, ionospheric ions are accelerated outward toward the plasmasheet.

Grebowsky, J. M.↗
NASA NTRS2005

A Comparative View of X-rays from the Solar System

With the advent of sophisticated X-ray observatories, viz., Chandra and XMM-Newton, the field of planetary X-ray astronomy is advancing at a faster pace. Several new solar system objects are now know to shine in X-rays at energies generally below 2 keV. Jupiter, Saturn, and Earth, all three magnetized planets, have been observed by Chandra and XMM-Newton. At Jupiter, both auroral and non-auroral disk X-ray emissions have been observed. The first soft X-ray observation of Earth's aurora by Chandra shows that it is highly variable. X-rays have been detected from Saturn's disk, but no convincing evidence of X-ray aurora has been seen. Several comets have been observed in X-rays by Chandra and XMM-Newton. Cometary X-rays are produced due to change exchange of solar wind ions with cold cometary neutrals. Soft X-rays have also been observed from Venus, Mars, Moon, Io, Europa, Io plasma torus, and heliosphere. The non-auroral X-ray emissions from Jupiter, Saturn, and Earth, and those from sunlit disk of Mars, Venus, and Moon are produced due to scattering of solar X-rays. The spectral characteristics of X-ray emission from comets, heliosphere, darkside of Moon, and Martian halo are quite similar, but they appear to be quite different from those of Jovian auroral X-rays. The X- ray aurora on Earth is generated by electron bremsstrahlung and on Jupiter by precipitation of highly-ionized energetic heavy ions. In this paper we will present a comparative overview of X-ray emission from different solar system objects and make an attempt to synthesize a coherent picture.

Bhardwaj, Anil↗
NASA NTRS1990

Bremsstrahlung X-rays from Jovian auroral electrons

The spectrum of X-rays from the planet Jupiter is calculated according to an auroral electron beam model. The electrons are assumed to be accelerated by a field-aligned potential drop and penetrate into the atmosphere as a Maxwellian beam of primaries which are scattered, degraded in energy, and merged with a population of ionization secondaries having a power law energy distribution. The soft X-rays observed by the Einstein Observatory satellite are due to bremsstrahlung from the secondary electrons in the H2 atmosphere. The X-ray intensity is best reconciled with a beam of primaries having a characteristic energy 30-100 keV and penetrating the homopause with an auroral energy flux typically of 10-20 ergs/sq cm s but no greater than 50 ergs/sq cm s.

Barbosa, D. D.↗
NASA NTRS1987

E and F region study of the evening sector auroral oval - A Chatanika/Dynamics Explorer 2/NOAA 6 comparison

Simultaneous data from the Chatanika radar and the DE 2 and NOAA 6 satellites are used to study the typical behavior of the winter evening-sector auroral plasma during moderate and steady magnetic activity. The equatorward edge of the auroral E layer, of the region 2 field-aligned currents, and of the region of intense convection are colocated. The auroral E layer extends several degrees south of the equatorward edge of the keV electron precipitation from the CPS. Although the main trough and ionization channel are embedded in a region of intense electric field where the plasma flows sunward at high speed, the flux tubes associated with these two features have different time histories. The midlatitude trough is located south of the region of electron precipitation, above a proton aurora. The ionization channel marks the poleward edge of the main trough and is colocated with the equatorward boundary of the electron precipitation from the central plasma sheet.

Senior, C.↗
NASA NTRS1977

Operation Aurorozone: An experiment in sun/weather

Operation Aurorozone was a highly coordinated sequence of 33 rocket flights launched from Poker Flat, Alaska, in September 1976. The effects of aurorally produced X-rays on stratospheric neutral and electrical parameters was studied. The sun/weather coupling between upper and lower regions of the atmosphere is thought to be related to these middle atmospheric parameters. The results show a consistent depletion of ozone above 1 mb during three independent auroral events, with magnitudes in excess of those expected from the measured energy radiation sources. Simultaneously, enhanced conductivity changes were observed to occur in accord with the measured ionizing radiations.

Goldberg, R. A.↗
NASA NTRS2017

Major Pathways to Electron Distribution Function Formation in Regions of Diffuse Aurora

This paper discusses the major pathways of electron distribution function formation in the region of diffuse aurora. The diffuse aurora accounts for about of 75% of the auroral energy precipitating into the upper atmosphere, and its origin has been the subject of much discussion. We show that an earthward stream of precipitating electrons initially injected from the Earth's plasma sheet via wave-particle interactions degrades in the atmosphere toward lower energies and produces secondary electrons via impact ionization of the neutral atmosphere. These electrons of magnetospheric origin are then reflected back into the magnetosphere along closed dipolar magnetic field lines, leading to a series of reflections and consequent magnetospheric interactions that greatly augment the initially precipitating flux at the upper ionospheric boundary (700-800 km). To date this, systematic magnetosphere-ionosphere coupling element has not been included in auroral research models, and, as we demonstrate in this article, has a dramatic effect (200-300%) on the formation of the precipitating fluxes that result in the diffuse aurora. It is shown that wave-particle interaction processes that drive precipitating fluxes in the region of diffuse aurora from the magnetospheric altitudes are only the first step in the formation of electron precipitation at ionospheric altitudes, and they cannot be separated from the atmospheric collisional machine that redistributes and transfers their energy inside the magnetosphere-ionosphere-atmosphere coupling system.

magnetospheric↗
NASA NTRS2012

Astrobiological Journeys to and from the South Polar Sea of Enceladus - Bidirectional Interactions with the Saturn Magnetosphere

The spectacularly cryovolcanic moon Enceladus is a major source of plasma for the Saturn magnetosphere via ionization of the ejected molecular species and ice grains. Field-aligned plasma flows from the Enceladus environment visibly impact the moon's magnetic footpoint in Saturn's polar auroral region, while water group and other ions from the moon emissions diffuse radially throughout the magnetosphere and may be the dominant source of oxygen for Titan's oxygen-poor upper atmosphere. But the moon-magnetosphere interaction is bidirectional in the sense that the moon surface is globally exposed to constant irradiation by the returning magnetospheric ions and by energetic electrons from the field-aligned and radially diffusing populations. The returning ion source operates both on global scales of the magnetosphere and locally for highly reactive species produced in the ejecta plume. All of these sources likely combine to produce a highly oxidized global surface layer. Since plasma electrons and ions are cooled by interaction with neutral gas and E-ring ice grains from Enceladus, the moon emissions have a governing effect on the seed populations of energetic particles that irradiate the surface. The proposed subsurface polar sea and transient crustal overturn in the south polar region could bring the polar surface oxidants into contact with hydrocarbons and ammonia to make oxidation product gases contributing to the cryovolcanic jets, a process first proposed by Cooper et al. (Plan. Sp. Sci., 2009). As has been previously suggested for Europa, the 'oxidants could contribute to enhanced astrobiological potential of Enceladus, perhaps even higher than for Europa where organic hydrocarbons have not yet been directly detected. Unlike Europa, Enceladus shows no sign of an oxygen-dominated exosphere that could otherwise be indicative of extreme surface and interior oxidation inhibiting the detectable survival and evolution of complex organics.

Cooper, John F.↗
NASA NTRS1989

The ionosphere of Neptune

Limited knowledge of ionospheric processes of the outer planets and practically no information on the upper atmosphere of Neptune result in a range of possible ionospheres for Neptune. Various cases are investigated in order to establish a theoretical framework of the ionospheric structure against which the radio occultation measurements can be evaluated. The peak electron densities could range from 1000/cu cm to 10 to the 6th/cu cm depending on ion loss processes and particle ionization processes. The scale height could also range from 300 km to 2000 km depending on the exospheric temperature. Although various assumptions must be made, it is predicted that an auroral ionosphere with large electron densities and a large scale height will be observed by the ingress radio occultation measurement, and that a compressed ionosphere with small electron densities will be seen during the egress measurement.

Shinagawa, H.↗
NASA NTRS1976

A snapshot of the polar ionosphere

This paper presents a picture of the north polar F layer and topside ionosphere obtained primarily from three satellites (Alouette 2, ISIS 1, ISIS 2) that passed over the region within a time interval of about 50 min on a magnetically quiet day. The horizontal distribution of electron densities at the peak of the F layer is found to be similar to synoptic results from the IGY. Energetic-particle and ionospheric-plasma data are also presented, and the F-layer data are discussed in terms of these measurements as well as in terms of electric-field and neutral N2 density measurements made by other satellites on other occasions. The major feature observed is a tongue of F-region ionization extending from the dayside across the polar cap, which is accounted for by antisunward drift due to magnetospheric convection. In the F layer and topside ionosphere, the main effect of auroral precipitation appears to be heating and expansion of the topside. A region of low F-layer density appears on the morning side of the polar cap, which may be due to convection and possibly also to enhanced N2 densities.

Whitteker, J. H.↗
NASA NTRS1972

Low energy electron precipitation and the ionospheric F-region in and north of the auroral zone.

Use of low-elevation sounding rocket (Polar 1) in the exploration of the F region morphology in and north of the auroral zone over northern Norway. The rocket which moved over a horizontal distance of some 400 km inside the F region, monitored low-energy electron precipitation and various upper-atmosphere excitation and ionization processes. The latitudinal variations of the less than 1 keV energy electron fluxes showed excellent agreement with corresponding variations in the F-region electron density and the O I (6300 A) emission below the rocket, indicating that the low-energy electrons are the main sources for these phenomena at these high latitudes. An N2(+) (4278 A) arc was located near the decrease in the 40-keV electron fluxes. This arc was produced by a nearly monoenergetic influx of some 3-keV electrons. The expected luminosity profile derived from this energy spectrum differs significantly from the observed one, and possible explanations for the discrepancy are discussed.

Evans, D. S.↗
NASA NTRS1981

Energetic particle precipitation at middle and low latitudes

The results from rocket observations of the nighttime electron density profile in the upper E region (120 to 200 km) over Wallops Island, Virginia are discussed. The observations demonstrated the importance of atmospheric tides in the formation of the intermediate layer near 150 km. These observations also show that, except perhaps on geomagnetically quiet nights, energetic particles are the dominant ionization source in the layer. Using rocket, satellite, and ground-based observations it is possible to study the global morphology of particle precipitation. It is found that, just as there are northern and southern auroral zones, there are also mid-latitude, low-latitude, and equatorial zones of precipitation. The evidence for these zones and the properties of the precipitating particles are summarized.

Smith, L. G.↗
NASA NTRS1981

Remote sensing of high-latitude ionization profiles by ground-based and spaceborne instrumentation

Ionospheric specification and modeling are now largely based on data provided by active remote sensing with radiowave techniques (ionosondes, incoherent-scatter radars, and satellite beacons). More recently, passive remote sensing techniques have been developed that can be used to monitor quantitatively the spatial distribution of high-latitude E-region ionization. These passive methods depend on the measurement, or inference, of the energy distribution of precipitating kilovolt electrons, the principal source of the nighttime E-region at high latitudes. To validate these techniques, coordinated measurements of the auroral ionosphere have been made with the Chatanika incoherent-scatter radar and a variety of ground-based and spaceborne sensors

Vondrak, R. R.↗