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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.

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At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

On the spectrum of the secondary auroral electrons

Results are presented from a statistical study of the spectral characteristics of the (power-law-portion) secondary electrons associated with inverted-V electron precipitation events (IVEs). A total of 106 IVEs observed at low altitudes (below 1000 km) by the DE 2 spacecraft are included in data base. Spectral parameters for the electrons between 20 eV and 100 eV are plotted against the different parameters pertaining to the locations of the IVEs and the primary beams to determine their empirical dependences. It is found that the differential spectrum of the secondary electrons can be modeled by a power law, J proportional to E exp -gamma, with an averaged gamma of 1.85. This spectral parameter is relatively insensitive to the variation of locations of the IVEs, but it depends on the primary beam parameters. These results are compared with predictions, and theories on the generation of the low-energy auroral power-law secondary electrons are assessed. The analysis shows that collisional processses are the dominant source of the secondary electrons.

Fung, S. F.↗
NASA NTRS1990

Structure of an energetic narrow discrete arc

Particle distributions, waves, dc electric fields, and magnetic fields were measured by two sounding rockets at altitudes of 950 and 430 km through an energetic (greater than 5 keV) narrow (about 10 km) stable discrete arc. Although the payloads' magnetic footprints were separated by only 50 km, differences in the arc's structure were observed including the spatial width, peak energy, and characteristic spectra. The energetic electron precipitation included both slowly varying isotropic fluxes that formed an inverted-V energy-time signature and rapidly varying field-aligned fluxes at or below the isotropic spectral peak. The isotropic precipitation had a flux discontinuity inside the arc indicating the arc was present on a boundary between two different magnetospheric plasmas. Dispersive and nondispersive bursts of field-aligned electrons were measured throughout the arc, appearing over broad energy ranges or as monoenergetic beams. Dispersive bursts gave variable source distances less than 8000 km. Plateauing of some of the most intense bursts suggests that waves stabilized these electrons. During the lower altitude arc crossing, the field-aligned component formed a separate inverted-V energy-time signature whose peak energy was half the isotropic peak energy.

Mcfadden, J. P.↗
NASA NTRS2000

Effect of Negative Ions on the Conductivity of the Titan Atmosphere

In an earlier paper, Borucki et al (1987) calculated the electrical conductivity and electrical charge on aerosols in Titan's atmosphere due to the ionization by galactic cosmic rays and electron precipitation from Saturn's magnetosphere. The lower atmosphere was predicted to be substantially more conducting than the atmospheres of Earth and Venus because of the high concentration of free electrons. The prediction of a high conductivity is based on the lack of electrophillic species which form negative ions with low mobility and which reduce the number of free electrons. At that time, no molecular species capable of forming negative ions in concentrations sufficient to perturb the atmospheric conductivity were identified. Recently, E. Bakes and her colleagues have been investigating the formation of nitrogenous macromolecules using quantum mechanical methods. Their calculations indicate that the molecules will be highly electrophillic and are likely to be present in the atmosphere at mixing ratios of order 10(exp -7). This mixing ratio is sufficiently large that a substantial reduction in the conductivity is expected at altitudes below 100 km. Revision of the atmospheric model to accommodate the presence of negative ions and to increase the fidelity of the modeling will be described.

Borucki, W. J.↗
NASA NTRS1987

The precipitation of energetic heavy ions into the upper atmosphere of Jupiter

Evidence for auroral particle precipitation at Jupiter was provided by the ultraviolet spectrometers onboard the Voyagers 1 and 2 spacecraft and by the International Ultraviolet Explorer (IUE). Magnetospheric measurements made by instruments onboard the Voyager spacecraft show that energetic sulfur and oxygen ions are precipitating into the upper atmosphere of Jupiter. A theoretical model has been constructed describing the interaction of precipitating oxygen with the Jovian atmosphere. The auroral energy is deposited in the atmosphere by means of ionization, excitation, and dissociation and heating of the atmospheric gas. Energetic ion and electron precipitation are shown to have similar effects on the atmosphere and ionosphere of Jupiter.

Horanyi, M.↗
NASA NTRS2023

Energetic Proton Acceleration By EMIC Waves in Io’s Footprint Tail

In this study, we present a survey of energetic proton observations associated with Io’s footprint tail (FPT) and compare their signatures with in situ measurements of the plasma waves and lower-energy electron environments. We find further supporting evidence that proton acceleration in Io’s FPT is likely a consequence of wave–particle interactions via electromagnetic ion cyclotron waves that are generated by precipitating electrons into Jupiter’s ionosphere. This idea was originally proposed by Clark et al. (2020) and Sulaiman et al. (2020) based on NASA’s Juno mission likely transiting Io’s Main Alfvén Wing (MAW) during its twelfth orbit (i.e., PJ12). Additionally, the analysis of > 50 keV protons presented here highlights important observational details about the Io–Jupiter interaction as follows: 1) proton acceleration in Io’s FPT is a persistent feature and the energy flux carried by the protons is highest at smaller Io-Alfvén tail distances; 2) energetic protons exhibit positive correlations with both plasma waves and <100 keV/Q electrons; 3) during a small number of Io FPT crossings, the protons display finer spatial/temporal structure reminiscent of the electron observations reported by Szalay et al. (2018); and 4) the proton pitch angle distributions are characterized by two types: conic distributions in or near Io’s MAW and isotropic elsewhere.

space physics↗
NASA NTRS1978

Observations of low-energy electrons from AE-C in the south polar cusp during the geomagnetic storm of September 21, 1977

The present paper deals with the characteristics of low-energy electrons measured onboard the Atmosphere Explorer C (AE-C) satellite above the south polar cusp during the intense geomagnetic storm of September 21, 1977. The low-energy electron fluxes measured with the Photoelectron Spectrometer experiment indicate that the dayside polar cusp was displaced down to 69-72 deg invariant latitude during the storm. A region of intense fluxes of precipitating electrons was observed in the region near 1700 MLT between 66 and 69 deg invariant latitude, which statistically coincides with that of ascending field-alignment currents in the disturbed afternoon auroral region.

Potemra, T. A.↗
NASA NTRS1993

The nightside ionosphere of Venus under varying levels of solar EUV flux

Solar activity varied widely over the 14 year lifetime of the Pioneer Venus Orbiter (PVO), and these variations directly affected the properties of the nightside ionosphere. At solar maximum, when solar EUV was largest, the Venus ionosphere was found to extend to highest altitudes and nightward ion transport was the main source of the nightside ionosphere. At solar minimum, nightward ion transport was reduced, and electron precipitation was thought to be the main source. In this study, we have attempted a separation of spatial variations from temporal variations by examining the altitude profiles of the magnetic field, and electron density and temperature for three different solar EUV flux ranges. In the upper ionosphere and near-planet magnetotail (h greater than 1800 km), the solar EUV flux effects are significant. The electron density decreases about an order of magnitude from high to low EUV flux, while the electron temperature at least doubles. The magnetic field also increases 2 - 3 nT. In the lower ionosphere (200 - 600 km), lower EUV fluxes are associated with slightly reduced density, and higher temperature. These results are in accord with recent entry phase observations, where the electron density measured above the ionospheric density peak is lower than that observed at solar maximum during the early Pioneer Venus mission.

Ho, C. M.↗
NASA NTRS1993

The Nightside Ionosphere of Venus Under Varying Levels of Solar EUV Flux

Solar activity varied widely over the 14 year lifetime of the Pioneer Venus Orbiter, and these variations directly affected the properties of the nightside ionosphere. At solar maximum, when solar EUV was largest, the Venus ionosphere was found to extend to highest altitudes and nightward ion transport was the main source of the nightside ionosphere. At solar minimum, nightward ion transport was reduced, and electron precipitation was thought to be the main source. In this study, we have attempted a separation of spatial variations from temporal variations by examining the altitude profiles of the magnetic field, and electron density and temperature for three different solar EUV flux ranges. In the upper ionosphere and near-planet magnetotail (h greater than 1800 km), the solar EUV effects are significant. The electron density decreases about an order of magnitude from high to low EUV flux, while the electron temperature at least doubles. The magnetic field also increases 2 - 3 nT. In the lower ionosphere (200 - 600 km), lower EUV fluxes are associated with slightly reduced density, and higher temperature. These results are in accord with recent entry phase observations, where the electron density measured above the ionospheric density peak is lower than that observed at solar maximum during the early Pioneer Venus mission.

Ho, C. M.↗
NASA NTRS2008

A Hot Microflare Observed with RHESSI and HINODE

RHESSI and Hinode observations of a GOES B-class flare are combined to investigate the origin of 15 MK plasma. The absence of any detectable hard X-ray emission coupled with weak blueshifted emission lines (indicating upward velocities averaging only 14 km/s) suggests that this was a result of direct heating in the corona, as opposed to nonthermal electron precipitation causing chromospheric evaporation. These findings are in agreement with a recent hydrodynamical simulation of microflare plasmas that found that higher temperatures can be attained when less energy is used to accelerate electrons out of the thermal distribution. In addition, unusual redshifts in the 2 MK Fe xv line (indicating downward velocities of approx.14 km/s) were observed cospatial with one of the flare ribbons during the event. Downflows of such high-temperature plasma are not predicted by any common flare model.

Milligan, Ryan O.↗
NASA NTRS1998

Characterizing the Nightside Auroral Gap Using Polar-UVI Images

Using images from the Ultraviolet Imager (UVI) aboard the Polar spacecraft, we identify an unusual morphological feature of the auroral oval marked by a drastic decrease of auroral luminosity near local midnight during the growth and/or recovery phases of some substorms. This feature has not been previously described in much detail. The nightside cap appears in roughly 10% of the substorms during our study period of January and February, 1997. Two nightside gap events are characterized in detail as case studies of this phenomenon. We show that the nightside gap typically spans 1.0-1.5 hours in local time between 2200 LT and 2400 MLT and extends across the entire north/south direction of the auroral oval. Within this well-defined region, the energy flux is only 20-30% of the adjacent auroral activity at levels generally < 1.5 erg/sq cm.s. These phenomena indicate that there exists a region in the plasma sheet which maps to the nightside gap sector that is depleted of electrons during these events. Another possibility is that within the gap region, which lacks discrete auroral structures, no significant field-aligned currents exist and there is an insufficient ionospheric potential to accelerate precipitating electrons.

Chua, D.↗
NASA NTRSDate not supplied

Dione: A Pathfinder Mission for Understanding the Iono-sphere-Thermosphere Responses to Magnetospheric Forcing

Dione is a NASA small satellite prototype for future constellations that in different configurations will provide global and localized measurements of Ionosphere-Thermosphere responses to Magnetospheric energy input in a variety of scales, enabling their better forecast and prediction. This is done with a comprehensive sensor package which includes four instruments: a miniaturized fluxgate magnetometer providing magnetic field measurements with two sensor heads, an ion sensor that measures vector plasma drifts and deduce the in-situ electric fields, an electrostatic analyzer that measures precipitating electrons and up-going secondary electrons, and a neutral mass spectrometer measuring total neutral density and composition. Dione is 3-axis stabilized in a circular low-earth (400-600 km), high-inclination orbit, traversing the auroral precipitation and high latitude currents in every orbit. This paper focuses on the mission-level architecture, but provides contextual information on the science objectives, instruments, and space-craft.

Jaime Esper↗
NASA NTRS1976

Optical emissions from the mid-day aurora

Intensities of various optical emissions from mid-day auroras and spectral profile of N2(+) ING bands measured aboard a jet aircraft are presented. The data are compared with simple calculations based on present knowledge of the types and energy distributions of particles precipitating in the mid-day auroral region and the available cross-sections for the excitation of various optical emissions in air. The analysis concerns the interaction of magnetosheath protons with the atmosphere, electron interaction with the atmosphere, resonant scattering of sunlight by N2(+) ions, and auroral emissions around 3886 A. It is shown that most of the OI red and green line emissions in the mid-day aurora are excited by the low-energy electrons precipitating in the cusp region, but only part of the N2 and N2(+) emissions can be so accounted, while precipitating protons excite the rest of N2 and N2(+) emission. The emission feature around 3886 A observed in mid-day aurora is most likely He 3888 A blended with N2(+) ING(1, 1) band.

Sivjee, G. G.↗
NASA NTRS1994

Correlative analysis of hard and soft x ray observations of solar flares

We have developed a promising new technique for jointly analyzing BATSE hard X-ray observations of solar flares with simultaneous soft X-ray observations. The technique is based upon a model in which electric currents and associated electric fields are responsible for the respective heating and particle acceleration that occur in solar flares. A useful by-product of this technique is the strength and evolution of the coronal electric field. The latter permits one to derive important flare parameters such as the current density, the number of current filaments composing the loop, and ultimately the hard X-ray spectrum produced by the runaway electrons. We are continuing to explore the technique by applying it to additional flares for which we have joint BATSE/Yohkoh observations. A central assumption of our analysis is the constant of proportionality alpha relating the hard X-ray flux above 50 keV and the rate of electron acceleration. For a thick-target model of hard X-ray production, it can be shown that cv is in fact related to the spectral index and low-energy cutoff of precipitating electrons. The next step in our analysis is to place observational constraints on the latter parameters using the joint BATSE/Yohkoh data.

Zarro, Dominic M.↗
NASA NTRS1981

The significance of VLF transmitters in the precipitation of inner belt electrons

The launch of the P78-1 low-altitude satellite containing a high-resolution electron spectrometer and the ISEE spacecraft with a plasma wave experiment have made it possible to perform simultaneous measurements of the waves, the plasma densities, and the precipitating electrons. It was found that nearly monochromatic waves in the range from 10 kHz to 25 kHz were frequently present in the near equatorial regions, their frequencies, narrow bandwidth, and geographic locations being consistent with various ground-based VLF transmitters as the sources. In the energy spectra of the precipitating electrons observed at low altitudes, narrow and at times multiple peaks often appear with central energies that decrease with increasing L shell. The narrow widths suggest that the interactions take place within a restricted range of latitudes which, based on other considerations, are likely equatorial.

Imhof, W. L.↗
NASA NTRS1974

Investigation of electron dynamics in the magnetosphere with electron beams injected from sounding rockets

This paper describes an empirical study of the basic mechanisms by which electrons precipitate from the geomagnetic field to produce 'auroral X rays' during periods of geomagnetic activity. The study was based on data obtained by the Echo satellites. Echo I, launched in 1970, injected 40 keV, 0.1 amp electron pulses at low latitude (L ? 2.6) and successfully measured the returning pulses from the conjugate region. Electric fields and multiple Coulomb scattering were studied. Echo II, launched in 1972 from high latitude (L ? 8) studied the interaction of the beams with background radiation and the detailed motion of the beams near the rocket. Evidence for a beam plasma instability was obtained. Echo III launched in April 1974, (L ? 5.5) detected a series of conjugate echoes during the presence of a strong convective field in the magnetosphere. It was shown that the electric field measurement in the ionosphere using the incoherent backscatter radar and detectors on the rocket was transferred to the equatorial plane as though field lines were equipotentials.

Winckler, J. R.↗
NASA NTRS2009

Storm/Quiet Ratio Comparisons Between TIMED/SABER NO (sup +)(v) Volume Emission Rates and Incoherent Scatter Radar Electron Densities at E-Region Altitudes

Broadband infrared limb emission at 4.3 microns is measured by the TIMED/SABER instrument. At night, these emission observations at E-region altitudes are used to derive the so called NO+(v) Volume Emission Rate (VER). NO+(v) VER can be derived by removing the background CO2(v3) 4.3 microns radiance contribution using SABER-based non-LTE radiation transfer models, and by performing a standard Abel inversion on the residual radiance. SABER observations show that NO+(v) VER is significantly enhanced during magnetic storms in accordance with increased ionization of the neutral atmosphere by auroral electron precipitation, followed by vibrational excitation of NO+ (i.e., NO+(v)) from fast exothermic ion-neutral reactions, and prompt infrared emission at 4.3 m. Due to charge neutrality, the NO+(v) VER enhancements are highly correlated with electron density enhancements, as observed for example by Incoherent Scatter Radar (ISR). In order to characterize the response of the storm-time E-region from both SABER and ISR measurements, a Storm/Quiet ratio (SQR) quantity is defined as a function of altitude. For SABER, the SQR is the ratio of the storm-to-quiet NO+(v) VER. SQR is the storm-to-quiet ratio of electron densities for ISR. In this work, we compare SABER and ISR SQR values between 100 to 120 km. Results indicate good agreement between these measurements. SQR values are intended to be used as a correction factor to be included in an empirical storm-time correction to the International Reference Ionosphere model at E-region altitudes.

Fernandez, J. R.↗
NASA NTRS1977

Variations in electron density in the middle latitude D-region above Urbana, Illinois

Electron density measurements made with the partial reflections technique above Urbana, Illinois (44 deg 10 min N, 88 deg 10 min W) were analyzed for day-to-day variations, seasonal variations, magnetic storm aftereffects, and stratosphere-ionosphere coupling effects. As well as showing a winter anomaly, the electron densities near 76 km were significantly lower in fall than in spring. Magnetic storm aftereffects of the type predicted by models of energetic electron precipitation at middle latitudes were observed. No strong correlations were found between stratospheric and D-region time series, or between the occurrence of stratospheric warmings and D-region changes. It is likely that most of the electron density variation was due to variations in the transport of minor neutral constituents. The spring-fall differences were also probably caused by differences in minor constituent concentrations rather than the effect of temperature changes on the recombination coefficient.

Wratt, D. S.↗