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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Physics of auroral arc formation; Proceedings of the Chapman Conference on Formation of Auroral Arcs, Fairbanks, AK, July 21-25, 1980

The results of satellite, balloon-borne, and ground-based observations of auroral phenomena are discussed in terms of the morphology of auroral arcs and the behavior and characteristics of auroral electrons and ions. Further attention is given to auroral electric fields and field aligned currents, and to the development of models of auroral potential structures and energization of auroral particles. A simulation of space plasma phenomena is presented, along with numerical simulations of auroral potential structures and related phenomena, including the V-potential double layers and auroral arc deformations, and a simulation of auroral arcs. Plasma waves observed on auroral field lines and in laboratory conditions are reported, and theoretical studies of waves and turbulence in auroral plasmas are described.

Akasofu, S.-I.↗
NASA NTRS1983

Auroral hiss, Z mode radiation, and auroral kilometric radiation in the polar magnetosphere - DE 1 observations

The polar-orbiting DE 1 spacecraft has provided the first measurements of high-latitude auroral phenomena. Three types of plasma-wave emissions were observed: auroral hiss, Z-mode radiation, and auroral kilometric radiation. Whistler mode auroral hiss emissions were observed on virtually every pass over the auroral zone. The shape of the auroral hiss frequency-time spectrum is explained by a whistler mode propagation effect if the radiation is emitted from a spatially localized source below the spacecraft. Broadband Z emissions have been observed in the low-density region over the auroral zone and polar cap. The auroral hiss may be distinguished from the Z-mode radiation by the sharp upper cutoff of the whistler mode at the local electron plasma frequency. Auroral kilometric radiation usually occurs at frequencies above electron gyrofrequency, indicating that this radiation is propagating in the free-space R-X mode.

Gurnett, D. A.↗
DOE OSTI2021

Key Elements of Auroral Substorm Development and their Relationship to Recent Observations of Detached Sub-Auroral Phenomena Including STEVE-like Emissions

Since Akasofu introduced the concept of the substorm in 1964, numerous refinements have been added to the phenomenological model of how auroral substorms develop. Here, we review several of the most important of these including; polar cap patches, intensifications of the Polar Activated Band (PAB) at the poleward edge of the bulge, the development of new arcs poleward, the generation of auroral streamers, the evolution of streamers into auroral torches and omega bands, the association of streamers with particle injection and BBF activity in the tail, and wedgelet-like magnetic perturbations on the ground. We also review the concept of “contact breakups” which are breakups that appear to be triggered by the arrival of streamer-like forms in the equatorward regions of the oval. Finally, we remind the community that the addition of detached sub-auroral emissions was made to the phenomenological picture of substorm develop in the late 1960s along with the concept of auroral streamers. Newer observations of detached sub-auroral (STEVE-like emissions) from the Viking/UVI and POLAR/VIS imagers are presented which confirm that they are east-west aligned bands of emission that separate away from the equatorward edge of the auroral oval in response to intensifications of the poleward edge of the bulge and subsequent streamer production. We propose a new model for the formation of detached sub-auroral (STEVE-like) emissions in which a non-linear growth of a SAPS-driven instability (e.g. like the shear-flow/ballooning instability) at the plasmapause results in the disruption of the boundary separating hot plasma sheet particle from the cold plasmaspheric plasma. It is proposed that the resulting intermixing of plasma populations leads to both the observed STEVE-like emissions and also provides a source of cold plasma on open drift paths that can feed the long-lived drainage plumes that have recently been discovered.

58 GEOSCIENCES↗
NASA NTRS1977

Auroral kilometric radiation as an indicator of auroral magnetic disturbances

Satellite low-frequency radio measurements have shown that auroral kilometric radiation, an intense radio emission from the earth's auroral regions, is closely associated with auroral and magnetic disturbances. In this paper a detailed investigation of this relationship is presented, using the auroral electrojet (AE) index as an indicator of auroral magnetic disturbances and radio measurements from the Imp 6 spacecraft. This study indicates that the mean power flux of the 178-kHz radiation tends to be proportional to the 1.2 power of (AE) for AE more than 100 gamma and, with less certainty, to the square of (AE) for AE less than 100 gamma. The correlation coefficient between log AE and the logarithm of the power flux is 0.514. Occasionally, a kilometric radiation event is detected which is not detected by the ground magnetometer stations, even though an auroral substorm is in progress. This study shows that the remote detection of kilometric radio emissions from the earth can be used as a reasonably reliable indicator of auroral substorm activity.

Voots, G. R.↗
NASA NTRS1989

Modeled F region response to auroral dynamics based upon Dynamics Explorer auroral observations

Auroral images from the Dynamics Explorer 1 (DE 1) scanning auroral imager have been combined with in situ auroral precipitation data from the DE 2 low-altitude plasma instrument, to form a time-dependent global auroral energy flux model. This model has both good time (12 min) and spatial (100 km) resolution compared to that currently available for global-scale ionospheric and thermospheric modeling. The development and comparison of this model with others are discussed. Data from an aurorally active period, November 25, 1981, are presented and used as a case study for this model. Using a global ionospheric model, the effect of the DE auroral model is contrasted with that of a conventional empirical auroral energy flux model. Major differences in the modeled F region ionosphere are predicted from this comparative study.

Sojka, J. J.↗
NASA NTRS2000

Energy Characteristics of Auroral Electron Precipitation: A Comparison of Substorms and Pressure Pulse Related Auroral Activity

The Polar Ultraviolet Imager (UVI) observes auroral responses to incident solar wind pressure pulses and interplanetary shocks such as those associated with coronal mass ejections. The arrival of a CME pressure pulse at the front of the magnetosphere results in highly disturbed geomagnetic conditions and a substantial increase in both dayside and nightside auroral precipitation. Our observations show a simultaneous brightening over broad areas of the dayside and nightside aurora in response to a pressure pulse, indicating that more magnetospheric regions participate as sources for auroral precipitation than during isolated substorms. We estimate the average energies of incident auroral electrons using Polar UVI images and compare the precipitation energies during pressure pulse associated events to those during isolated auroral substorms. Electron precipitation during substorms has average energies greater than 10 keV and is structured both in local time and magnetic latitude. For auroral intensifications following the arrival of a pressure pulse or interplanetary shock, electron precipitation is less spatially structured and has greater ux of lower energy electrons (Eave _ 7 keV) than during isolated substorm, onsets. The average energies of the precipitating electrons inferred from UVI are consistent with those measured in-situ by the FAST spacecraft. These observations quantify the differences between global and local auroral precipitation processes and will provide a valuable experimental check for models of sudden storm commencements and magnetospheric response to perturbations in the solar wind.

Chua, D.↗
NASA NTRS2005

Correlation Between Low Frequency Auroral Kilometric Radiation (AKR) and Auroral Structures

Auroral Kilometric Radiation (AKR) is a radio wave emission that has long been associated with auroral activity. AKR is normally observed in the frequency range from -60 - 600 kHz. Low frequency AKR (or LF-AKR) events are characterized as a rapid extension of AKR related emissions to 30 kHz or lower in frequency for typically much less than 10 minutes. LF-AKR emissions predominantly occur within a frequency range of 20 kHz - 30 kHz, but there are LF-AKR related emissions that reach to a frequency of 5 kHz. This study correlates all instances of LF-AKR events during the first four years of observations from the IMAGE spacecraft's Radio Plasma Imager (WI) instrument with auroral observations from the wideband imaging camera (WIC) onboard IMAGE. The correlation between LF-AKR occurrence and WIC auroral observations shows that in the 295 confirmed cases of LF-AKR emissions, bifurcation of the aurora is seen in 74% of the cases. The bifurcation is seen in the dusk and midnight sectors of the auroral oval, where AKR is believed to be generated. The polarization of these LF-AKR emissions has yet to be identified. Although LF-AKR may not be the only phenomena correlated with bifurcated auroral structures, bifurcation will occur in most instances when LF-AKR is observed. The LF-AKR emissions may be an indicator of specific auroral processes sometimes occurring during storm-time conditions in which field-aligned density cavities extend a distance of perhaps 5-6 RE tailward from the Earth for a period of 10 minutes or less.

Paxamickas, Katherine A.↗
NASA NTRS1991

Harmonic H(+) gyrofrequency structures in auroral hiss observed by high-altitude auroral sounding rockets

Two recent sounding rocket experiments have yielded VLF wave data with spectral structures ordered by the hydrogen gyrofrequency. The spectral structures occur near and above the lower hybrid frequency in association with auroral hiss. These structures are observed within and near regions of auroral electron precipitation and transverse ion acceleration. They are accompanied by auroral hiss but are anticorrelated with spectral peaks at the lower hybrid frequency. They are typically found above 500 km altitude, have no measurable magnetic component, and are at least occasionally short wavelength. Because the spectral structures appear to be electrostatic, are ordered by the hydrogen gyrofrequency, and are short wavelength, the structures are interpreted as modes which connect the lower hybrid mode with the hydrogen Bernstein modes. A study of the plasma wave mode structure in the vicinity of the lower hybrid frequency is presented to substantiate this interpretation. These results imply that these waves are a common feature of the auroral zone ionsphere above 500 km altitude and exist any time that auroral hiss exists. The absence of previous satellite observations of this phenomenon can be explained by Doppler broadening.

Kintner, P. M.↗
NASA NTRS1999

Polar/Tide Observations of Field Aligned O(+) Flows at 5000 km Altitude over the Auroral Regions in Comparison to UVI Auroral Images

Measurements of thermal O(+) ion parameters from the Thermal Ion Dynamics Experiment (TIDE) on POLAR obtained near 5000 km altitude are compared with auroral images from the Ultra Violet Imager (UVI), for southern perigee passes. Ion parameters, including parallel velocity, density, and flux are combined with simultaneous auroral images to investigate relationships between their properties and the structure and brightness of the auroral forms. Results indicate field aligned upflowing O(+) ions over bright auroral regions and downward flows over dark regions. These and other relationships will be presented for several POLAR passes when both ion measurements and auroral images are observed under favorable conditions for comparison.

Stevenson, Benjamin Adam↗
NASA NTRS1998

The Nightside Auroral Gap: Implications for Magnetosphere-Ionosphere Coupling in the Midnight Auroral Zone

We present observations of a new synoptic scale feature of the nightside aurora identified by the Polar Ultraviolet Imager (UVI) in which a well defined segment of the pre-midnight auroral oval exhibits significantly reduced auroral luminosity in the atomic oxygen and Lyman-Birge-Hopfield (LBH) emission bands in comparison to adjacent auroral activity. This gap in the nightside aurora is typically observed in the 2200-2400 MLT sector and spans 1.0-1.5 hours in local time (710-1100 km). The energy flux ($\rm erg$ $\rm cm'{-2}$ $\rm s'{-1}$) is shown to be lower by as much as a factor of four in the nightside gap region in comparison to the adjacent auroral activity. The appearance of the nightside gap does not depend on substorm phase. However, substorm intensifications are often observed on either side of the nightside gap which remains relatively inactive. Moreover, auroral breakups sometimes develop within the nightside gap, indicating that this feature may have dynamical implications for substorm onset location.

Chua, D. H.↗
DOE OSTI2020

Solving the auroral-arc-generator question by using an electron beam to unambiguously connect critical magnetospheric measurements to auroral images

Here, an active mapping mission is described that unambiguously connects measurements in the Earth's magnetosphere to visible aurora in the atmosphere. The core of the mission is an electron-beam source operated on a spacecraft in the equatorial magnetosphere, with the electron beam traveling along the Earth's magnetic-field lines to the atmosphere, depositing its energy to create an optical beam-spot in the atmosphere at the footpoint of the spacecraft's magnetic-field line. This optical spot can be imaged by ground-based cameras, putting the location of the spacecraft's magnetic footpoint into the context of the optical aurora. Scientific instruments carried on the spacecraft make critical measurements of the properties of the magnetosphere at the locations where the magnetosphere powers the aurora, allowing the determination of the plasma-physics mechanisms by which the magnetosphere drives the aurora, in particular answering the outstanding question of how the magnetosphere drives low-latitude auroral arcs. Long-standing questions in magnetosphere-ionosphere coupling that have not been answered because we could not unambiguously connect locations in the magnetosphere with their image in the ionosphere will finally be addressed. In this paper the properties of a “standard” growth-phase auroral arc are collected, theories of the magnetospheric generation of auroral arcs are reviewed, and critical magnetospheric measurements to discern the mechanisms that drive auroral arcs are determined. Further, the plasma physics of the experiment is investigated, including spacecraft-charging mitigation, beam stability, beam scattering, and electron orbit theory. Tradeoffs (keV versus MeV) concerning the energy of the electron beam are enumerated.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1980

Generation of auroral kilometric radiation and the structure of auroral acceleration region

Generation of auroral kilometric radiation (AKR) in the auroral acceleration region is studied. It is shown that auroral kilometric radiation can be generated by backscattered electrons trapped in the acceleration region via a cyclotron maser process. The parallel electric field in the acceleration region is required to be distributed over 1-2 earth radii. The observed AKR frequency spectrum can be used to estimate the altitude range of the auroral acceleration region. The altitudes of the lower and upper boundaries of the acceleration region determined from the AKR data are respectively approximately 2000 and 9000 km.

Lee, L. C.↗
NASA NTRS1987

Auroral precipitation caused by auroral kilometric radiation

If the auroral kilometric radiation (AKR) were generated by loss cone lasing on closed field lines, as has been proposed, then it should cause substantial auroral precipitation by the pitch angle scattering of energetic electrons into the loss cone. A rough estimate for this precipitation, based upon the observed AKR amplitudes, would imply a flux of at least 2 x 10 to the 8th el/sq cm sec over the projected ionospheric footprint of an individual laser and, if most of the AKR radio lasers occupied the same electron drift an L shell, an arc of 8 km width with a minimum average flux of roughly 10 to the 9th el/sq cm sec. It is believed that this will account for auroral arcs and other aspects of auroral electron precipitation.

Calvert, W.↗
NASA NTRS1995

The double oval UV auroral distribution. 1: Implications for the mapping of auroral arcs

During the later stages of the auroral substorm the luminosity distribution frequently resembles a double oval, one oval lying poleward of the normal or main UV auroral oval. We interpret the double oval morphology as being due to the plasma sheet boundary layer becoming active in the later stages of the substorm process. If the disturbance engulfs the nightside low-latitude boundary layers, then the double oval configuration extends into the dayside ionospheric region. The main UV oval is associated with the inner portion of the central plasma sheet and can rapidly change its auroral character from being diffuse to discrete. This transition is associated with the substorm process and is fundamental to understanding the near-Earth character of substorm onset. On the other hand, the poleward arc system in the nightside ionosphere occurs adjacent to or near the open-closed field line boundary. This system activates at the end of the optical expansion phase and is a part of the recovery phase configuration in substorms where it occurs. These two source regions for nightside discrete auroral arcs are important in resolving the controversy concerning the mapping of arcs to the magnetosphere. The dayside extension of this double oval configuration is also investigated and shows particle signatures which differ considerably from those on the nightside giving clues to the magnetospheric source regions of the aurora in the two local time sectors. Near-Earth substorm onsets are shown to be coupled to processes occurring much further tailward and indicate the importance of understanding the temporal development of features within the double oval. Using 'variance images,' a new technqiue for the investigation of these dynamics is outlined.

Elphinstone, R. D.↗
NASA NTRS1989

A comparison of ionospheric conductances and auroral luminosities observed simultaneously with the Chatanika radar and the DE 1 auroral imagers

Auroral luminosities at vacuum ultraviolet (VUV) wavelengths are combined with simultaneous and coincident ionospheric electron density measurements made by the Chatanika radar to relate ionospheric conductances to optical emissions. The auroral luminosities are obtained along the magnetic meridian through Chatanika with the auroral imaging photometers on the Dynamics Explorer 1 satellite as the radar scans in the magnetic meridian to measure electron density and conductivity as a function of altitude and latitude. The observations are used to determine an empirical relationship between the luminosities measured at VUV wavelengths and the Hall and Pedersen conductances.

Robinson, R. M.↗
NASA NTRS1989

The response of thermospheric nitric oxide to an auroral storm. II - Auroral latitudes

NOAA 6 and 7 particle measurements are used, in conjunction with a statistical model of the auroral particle precipitation, to study the response of auroral NO to the auroral storm of September 19, 1984. The results of a time-dependent photochemical calculation show that particle precipitation can more effectively produce NO than can Joule heating, in contrast to nonauroral latitudes where heating is important. Both the model and the NO data show NO increases as a result of the storm; however, the absolute magnitude of the NO in the model, as well as the amplitude of the increase, significantly exceeded what was observed. Two possible explanations for the this discrepancy are proposed.

Siskind, D. E.↗
NASA NTRS1998

Auroral Kilometric Radiation and the Auroral Electrojet Index for the January 1997 Magnetic Cloud Event

Auroral kilometric radiation (AKR) observations by Polar and Geotail are compared with the auroral electro jet index for the January 1997 magnetic cloud event. These two-spacecraft measurements are complementary in covering the AKR emission cones throughout the event and,together,reasonably represent the auroral electrojet AE index. We point out, however, limitations of both the AKR index and the AE index in providing truly global measurements of substorm activity.

Kurth, W. S.↗
NASA NTRS2011

Current Closure in the Auroral Ionosphere: Results from the Auroral Current and Electrodynamics Structure Rocket Mission

The Auroral Current and Electrodynamics Structure (ACES) mission consisted of two sounding rockets launched nearly simultaneously from Poker Flat Research Range, AK on January 29, 2009 into a dynamic multiple-arc aurora. The ACES rocket mission was designed to observe electrodynamic and plasma parameters above and within the current closure region of the auroral ionosphere. Two well instrumented payloads were flown along very similar magnetic field footprints, at different altitudes, with small temporal separation between both payloads. The higher altitude payload (apogee 360 km), obtained in-situ measurements of electrodynamic and plasma parameters above the current closure region to determine the input signature. The low altitude payload (apogee 130 km), made similar observations within the current closure region. Results are presented comparing observations of the electric fields, magnetic components, and the differential electron energy flux at magnetic footpoints common to both payloads. In situ data is compared to the ground based all-sky imager data, which presents the evolution of the auroral event as the payloads traversed through magnetically similar regions. Current measurements derived from the magnetometers on the high altitude payload observed upward and downward field-aligned currents. The effect of collisions with the neutral atmosphere is investigated to determine it is a significant mechanism to explain discrepancies in the low energy electron flux. The high altitude payload also observed time-dispersed arrivals in the electron flux and perturbations in the electric and magnetic field components, which are indicative of Alfven waves.

Kaeppler, S. R.↗