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At least 433 records · Page 24
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NASA NTRS1980

Possible infrared aurorae on Jupiter

Infrared brightenings near the poles of Jupiter at 8 microns were observed in early 1980 by the NASA 3-m Infrared Telescope Facility at Mauna Kea and the Mayall 4-m telescope at the Kitt Peak National Observatory. It is suggested that these brightenings are related to the auroral zones which are determined by the magnetic mapping of the magnetotail onto the atmosphere, rather than by the Io flux tube. They were present in both hemispheres in January, present only in the north in February, and probably absent in the south in March. When visible, they were only seen in the hemisphere where the auroral zone was oriented toward the earth and absent otherwise.

Caldwell, J.↗
NASA NTRS1974

Aurora

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Anger, C.↗
NASA NTRS1981

The aurora - An electrical discharge phenomenon surrounding the earth

An attempt to model the processes underlying the appearance of auroral phenomena as a chain of events beginning with power production and resulting in auroral light emissions is presented. Power is produced by the interaction of the solar wind with the earth magnetosphere, creating a dynamo effect which is a function of the solar wind speed and the magnitude and orientation of the solar wind magnetic field. The dynamo power generates the convective motion of magnetospheric plasma, and subsequent magnetic-field aligned currents communicate the dynamo power to the polar ionosphere. The currents close as Pederson currents, and the associated Lorentz force accelerates the ionosphere in the direction of the convective motion. An electric potential structure develops at a few thousand km height, forcing current-carrying electrons to flow down the field lines to the ionosphere, where interactions with atmospheric constituents create auroral displays.

Akasofu, S.-I.↗
NASA NTRS1982

The ultraviolet spectrum of an aurora 530-1520 A

Ultraviolet spectra between 530 and 1520 A of an active auroral arc were obtained at 6.5-A instrumental resolution. Several new emission features are identified, including several bands of the N2 Birge-Hopfield (1, v-double-prime) progression and numerous N I multiplets, the latter being preponderant at low altitudes. The improved instrumental resolution over previous experiments in the wavelength region below 1200 A allows for a partial resolution of the complex structure between 900 and 1100 A reported in earlier work. The ratio of O I 1356 to N2 Lyman-Birge-Hopfield is smaller than in the dayglow at a similar altitude, and this is interpreted as evidence for a depletion of atomic oxygen in the auroral ionosphere relative to mid-latitude composition.

Feldman, P. D.↗
NASA NTRS1982

Polar views of the earth's aurora with Dynamics Explorer

Preliminary examination of the first global auroral images gained with the vacuum-ultraviolet imaging photometer on board DE 1 reveals a remarkable spatial configuration of auroral luminosities. Frequently the northern auroral oval is bifurcated by a sun-aligned arc extending from the midday auroral zone to the nighttime sector of the oval. Simultaneous plasma measurements with the low-altitude DE-2 spacecraft are used to show that the character of plasmas above the polar arc is similar to those found over the poleward zones of the auroral oval. The spatial distribution of auroral luminosities is suggestive of a two-cell structure of current systems and convection electric fields over the earth's polar cap and a similar division of the corresponding lobe in the magnetotail.

Frank, L. A.↗
NASA NTRS1983

The inner edge of the plasma sheet and the diffuse aurora

Three dimensional measurements from the ISEE-1 low energy electron spectrometer are used to map the location of the inner edge of the plasma sheet and study the anisotropies in the electron distribution function associated with this boundary. Lower energy plasma sheet electrons have inner edges closer to the Earth than higher energies with the separations at different energies being larger near dawn and after dusk than at midnight. Lowest energy inner edges are frequently located adjacent to the plasmapause in the dawn hemisphere but are often separated from it in the dusk hemisphere by a gap of at least several Re. The energy dispersion is minimal in the afternoon quadrant where the inner edge is near the magnetopause and frequently oscillating on a time scale of minutes. The location of the inner edge is probably determined primarily by the motion of electrons in the existing electric and magnetic fields rather than by strong diffusion as has sometimes been supposed.

Fairfield, D. H.↗
NASA NTRS1984

The inner edge of the plasma sheet and the diffuse aurora

Three dimensional measurements from the ISEE-1 low energy electron spectrometer are used to map the location of the inner edge of the plasma sheet and study the anisotropies in the electron distribution function associated with this boundary. Lower energy plasma sheet electrons have inner edges closer to the earth than higher energies with the separations at different energies being larger near dawn and after dusk than at midnight. Lowest energy inner edges are frequently located adjacent to the plasmapause in the dawn hemisphere but are often separated from it in the dusk hemisphere by a gap of at least several Re. The energy dispersion is minimal in the afternoon quadrant where the inner edge is near the magnetopause and frequently oscillating on a time scale of minutes. The location of the inner edge is probably determined primarily by the motion of electrons in the existing electric and magnetic fields rather than by strong diffusion as has sometimes been supposed. Previously announced in STAR as N83-32595

Fairfield, D. H.↗
NASA NTRS1984

Distribution of aurora and ionospheric currents observed simultaneously on a global scale

The instantaneous spatial distribution of auroral emissions is observed with auroral imaging photometers on board the spacecraft Dynamics Explorer 1 (DE 1) as ground-based meridian chains of magnetometers simultaneously detect the magnetic signatures of ionospheric and field-aligned currents flowing at northern polar latitudes. Ionospheric conductivities at nighttime auroral latitudes are estimated from the measured auroral luminosities and used with the measured polar magnetic variations to compute model distributions of ionospheric and field-aligned currents. Temporal resolution for the coordinated observations and model calculations is 12 minutes. Model ionospheric and field-aligned current distributions are overlayed on global auroral images to illustrate spatial relations on a global scale at the maximum epoch of an auroral substorm. Eccentric-dipole-latitude and magnetic-local-time coordinates are used. A model field-aligned current distribution is compared quantitatively with the distribution of field-aligned currents inferred from simultaneous observations by the DE-2 magnetometer.

Craven, J. D.↗
NASA NTRS1984

Lyman-Alpha Aurora

The existence of intense and variable H Ly a emission from Uranus is demonstrated utilizing the monochromatic imaging capabilities of the International Ultraviolet Explorer satellite. A series of 14 observations, using the IUE short wavelength spectrograph in low dispersion and covering the period from 3 March 1982 through 2 September 1983, shows the disk averaged Ly a brightness of Uranus to vary between 690 and 2230 Rayleighs. Model calculations indicates that 400 R of this emission can be attributed to resonant scattering of solar Ly a radiation. An upper limit of 100 R is obtained for the Raman scattering of solar Ly a by H2 (1280 A). This implies that 300 R is contributed to the planetary Ly a emission by Rayleigh scattering. In addition to being unexpectedly strong, the Uranian Ly a emission has been observed to vary by a factor of two in one 24 hr period and by about 50% in one 5 hr period.

Durrance, S. T.↗
NASA NTRS1985

Charging of DMSP/F6 spacecraft in aurora on 10 January 1983

Spacecraft charging has been widely observed in geosynchronous orbit on the ATS-5 and ATS-6 pair and on the SCATHA spacecraft. An adequate theory for explaining the observations exist. Neither the data or theory can be exported to low polar orbit and its drastically different environment. Evidence of charging on the DMSP F6 spacecraft is presented. A simple model is set up explaining the observations. Two independent instruments on the spacecraft showed charging to a moderate (44 volts) negative potential. The selection spectrometer showed a flux of 2 billion electrons per sq. cm. sec. ster. peaked at 9.5 keV. This was marginally sufficient to overcome the flux of cold ambient ions. Charging calculations are presented showing where simplications are justified and where serious uncertainties exist. More serious charging is predicted for the Shuttle in polar orbit.

Besse, A. L.↗
NASA NTRS1985

Cosmic rays 10Be biennal data and their relationship to aurorae and sunspots

The galactic cosmic ray (C.R.) variations which should give information on three dimensional aspects of the heliospheric magnetic fields and on the solar wind, which modulate their influx into the Solar System were studied. In order to decode the information from the C.R. series it is necessary to know the mechanisms through which the modulation is produced. It it clear that a balance of effects with sources at different heliospheric latitudes results in the modulated C.R. intensity. It is found that the modulation of 10Be in polar ice may be due to at least two main contributions: (1) negative and in phase with the Solar flare activity modulating the cosmic ray flux in Forbush-type decreases, and (2) positive in phase with the appearance of large wind streams situated at both polar coronal holes. It is found that the high heliolatitude activity is related to a stable periodicity of 11.1y whereas the low heliolatitude activity contributes to the wondering of the solar cycles.

Attolini, M. R.↗
NASA NTRS1984

Acceleration of barium ions near 8000 km above an aurora

A barium shaped charge, named Limerick, was released from a rocket launched from Poker Flat Research Range, Alaska, on March 30, 1982, at 1033 UT. The release took place in a small auroral breakup. The jet of ionized barium reached an altitude of 8100 km 14.5 min after release, indicating that there were no parallel electric fields below this altitude. At 8100 km the jet appeared to stop. Analysis shows that the barium at this altitude was effectively removed from the tip. It is concluded that the barium was actually accelerated upward, resulting in a large decrease in the line-of-sight density and hence the optical intensity. The parallel electric potential in the acceleration region must have been greater than 1 kV over an altitude interval of less than 200 km. The acceleration region, although presumably auroral in origin, did not seem to be related to individual auroral structures, but appeared to be a large-scale horizontal structure. The perpendicular electric field below, as deduced from the drift of the barium, was temporally and spatially very uniform and showed no variation related to individual auroral structures passing through.

Stenbaek-Nielsen, H. C.↗
NASA NTRS1986

Rocket observations of ultraviolet and optical emissions in the dayside aurora

Observations of the emissions extending from the UV to the near-IR region of the spectrum obtained at Cape Parry, Canada on December 7, 1981 are examined. The flight path of the rocket used to obtain the observations, launch conditions, and optical and UV instruments for measurement of the emission from the cleft precipitation region are described. Emission rates and altitude and zenith angles for emission features O I (989 A), O I (1304 A), O I (1356 A), O I (6300 A), O I (7774 A), O I (8446 A), H I (1216 A), and O II (834 A) are studied. The particle energy flux for the emission feature are estimated. The data suggested that there is an emission layer at 250-300 km.

Christensen, A. B.↗
NASA NTRS1987

Rocket observation of the N II 2143 A emission in an aurora

Using a rocket-mounted spectrometer with a multichannel detector, the existence of the N II 2143 A doublet in the auroral ultraviolet spectrum was confirmed. The measured intensity is in agreement with previous auroral observations and is consistent with a peak electron-impact cross section of 1-2 x 10 to the -18th sq cm. By comparing an altitude profile of the 2143 A emission to the N2(+) 3914 A emission, a deactivation rate for the N(+)(5S) state was obtained. The most likely quencher is N2, although the possibility of a reaction with O2 cannot be ruled out. For N2, the deduced value of the quenching coefficient equals 5.5 x 10 to the -10th cu cm/s.

Siskind, David E.↗
NASA NTRS1987

Superthermal electron processes in the upper atmosphere of Uranus: Aurora and electroglow

Strong ultraviolet emissions from the upper atmosphere of Uranus suggest that both auroral and electroglow phenomena are of significant aeronomical consequences in the structure of the upper atmosphere. Combined modeling and data analysis were performed to determine the effect of electroglow and auroral phenomena on the global heat and atomic hydrogen budgets in the Uranus upper atmosphere. The results indicate that the auroral and electroglow heat sources are not adequate to explain the high exospheric temperature observed at Uranus, but that the atomic hydrogen supplied by these processes is more than sufficient to explain the observations. The various superthermal electron distributions modeled have significantly different efficiencies for the various processes such as UV emission, heating, ionization, and atomic hydrogen production, and produce quite different H2 band spectra. However, additional information on the UV spectra and global parameters is needed before modeling can be used to distinguish between the possible mechanisms for electroglow.

Waite, J. H., Jr.↗
NASA NTRS1988

Mapping of auroral kilometric radiation sources to the aurora

Auroral kilometric radiation (AKR) and optical auroral emissions are observed simultaneously using plasma wave instrumentation and auroral imaging photometers carried on the DE 1 spacecraft. The DE 1 plasma wave instrument measures the relative phase of signals from orthogonal electric dipole antennas, and from these measurements, apparent source directions can be determined with a high degree of precision. Wave data are analyzed for several strong AKR events, and source directions are determined for several emission frequencies. By assuming that the AKR originates at cyclotron resonant altitudes, a candidate source field line is identified. When the selected source field line is traced down to auroral altitudes on the concurrent DE 1 auroral image, a striking correspondece between the AKR source field line and localized auroral features is produced. The magnetic mapping study provides strong evidence that AKR sources occur on field lines associated with discrete auroral arcs, and it provides confirmation that AKR is generated near the electron cyclotron frequency.

Huff, R. L.↗