SEARCH · Search NASA

Results for “aurora”

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 253 records · Page 14

All sources NASA NTRS DOE OSTI

NASA NTRS1980

Limit on rotational energy available to excite Jovian aurora

There is a fundamental relationship between the power that is extracted from Jupiter's rotation to drive magnetospheric processes and the rate at which mass is injected into the Io plasma torus. Half of this power is consumed by bulk motion of the plasma and the other half represents an upper limit on the energy from rotation available for dissipation and in particular to excite the Jovian aurora. Since the rotation of the planet is the only plausible source of energy, the power inferred from the observed auroral intensities requires a plasma injection rate of 2.6 x 10 to the 29th AMU/sec or greater. This in turn leads to a residence time of a torus particle of 48 days or less. These results raise doubts about the applicability of equilibrium thermodynamics to the determination of plasma parameters in the Io torus.

Eviatar, A.↗

NASA NTRS1981

Wave-particle interactions at the magnetopause - Contributions to the dayside aurora

The observations on ISEE 1 and ISEE 2 correlate the presence of intense electromagnetic and electrostatic emissions with enhanced fluxes of 1-6 keV electrons at the earth's magnetopause. The measured proton to electron ratio in the 1-10 keV energy range indicates the presence of substantial fluxes of electrons at energies below 1 keV. The 1.3-1.7 keV proton flux was essentially unchanged as the spacecraft moved from the magnetosheath into the wave-particle layer at and inside the magnetopause. The consequences of the magnetopause wave-particle interactions reported are consistent with the known features of the dayside aurora.

Tsurutani, B. T.↗

NASA NTRS1981

Morphology of Saturn's aurora

Aurorally-excited emissions of atomic and molecular hydrogen come from a narrow circumpolar band near 80 deg north and south latitude on Saturn. The aurorae, which lie near the edge of the polar cap region, are continuously excited in both the north and south. If the strong variations observed in the auroral intensity are temporal, rather than longitudinal, they may be related to the periodic structure in the Saturn kilometric radiation.

Sandel, B. R.↗

NASA NTRS1982

The spectrum of the Jovian Aurora 1150-1700 A

A series of observations of the northern hemisphere of Jupiter was made in January 1981 using the International Ultraviolet Explorer short-wavelength spectrograph. Exposures of 15 minutes each were made at regular intervals of about 45 minutes around the time when Jupiter's north magnetic pole was tilted toward the earth. The auroral emissions of H Lyman-alpha, and the H2 Lyman- and Werner-bands are seen to emanate from a localized region near the north pole. Their intensity increases and decreases in a periodic way as the planet rotates with the maximum occurring at lambda sub III approximately equal to 185 deg. Using the three observations nearest the observed maximum, a composite spectrum of the aurora is obtained with about 8 A resolution and high signal-to-noise ratio, and many of the H2 Lyman- and Werner-bands in this spectral region (1150-1700 A) are identified. This spectrum is compared with a laboratory H2 spectrum and with photoabsorption cross sections for CH4 and C2H6. An upper limit to the slant column density of these hydrocarbons above the auroral emissions is found to be approximately 2 x 10 to the 17th/sq cm.

Durrance, S. T.↗

NASA NTRS1982

Spectroscopy of the O I 989- and 7990-A multiplets in the dayglow and aurora

Several examples are presented to illustrate the behavior of the 989- to 7990-A complex. For the most part, these are chosen to correspond to particular observations of the airglow and aurora. In particular, the 989-A dayglow is computed for comparison with the data of Gentieu et al. (1979). In addition, line ratios are provided for comparison with the high-resolution data reported by Christensen et al. (1982). Several examples of auroral phenomena, including expected emissions from the dayside cleft region, are adduced, and the implications of high-resolution observations of line ratios and selective absorption by N2 are addressed. Finally, the utility of 989- to 7990-A multiplets as diagnostics of the atmospheric O I abundance is studied.

Meier, R. R.↗

NASA NTRS1983

Periodicities in the occurrence of aurora as indicators of solar variability

A compilation of records of the aurora observed in China from the Time of the Legends (2000 - 3000 B.C.) to the mid-18th century has been used to infer the frequencies and strengths of solar activity prior to modern times. A merging of this analysis with auroral and solar activity patterns during the last 200 years provides basically continuous information about solar activity during the last 2000 years. The results show periodicities in solar activity that contain average components with a long period (approx. 412 years), three middle periods (approx. 38 years, approx. 77 years, and approx. 130 years), and the well known short period (approx. 11 years).

Nian-Zu, D.↗

NASA NTRS1983

Aurora on Uranus - A Faraday disc dynamo mechanism

A mechanism is proposed whereby the solar wind flowing past the magnetosphere of Uranus causes a Faraday disk dynamo topology to be established and power to be extracted from the kinetic energy of rotation of Uranus. An immediate consequence of this dynamo is the generation of Birkeland currents that flow in and out of the sunlit polar cap with the accompanying production of polar aurora. The power extracted from planetary rotation is calculated as a function of planetary dipole magnetic moment and the ionospheric conductivity of Uranus. For plausible values of ionospheric conductivity, the observed auroral power requires a magnetic moment corresponding to a surface equatorial field of the order of 4 Gauss, slightly larger than the value 1.8 Gauss given by the empirical 'magnetic Bodes law'.

Hill, T. W.↗

NASA NTRS1983

The 300- to 900-A spectrum of a nightside aurora

Attention is given to the results of a satellite observation of a nightside aurora. The observations had been made with the aid of an instrument which was designed specifically to detect and to measure accurately the intensity of features in a wavelength range from 300 to 900 A. The considered data were acquired by an EUV spectrometer on the USAF STP 78-1 satellite launched on February 24, 1979. A bright, discrete auroral arc was selected for study, taking into account the intense O II, 834 A emission line as the most distinctive auroral diagnostic feature in the wavelength region from 300 to 900 A. There is found to be an excellent correspondence between most of the auroral features and the brightest O II laboratory discharge emission lines.

Paresce, F.↗

NASA NTRS1984

The plasma wave environment of an auroral arc - Electrostatic ion cyclotron waves in the diffuse aurora

Electric field plasma wave observations were made with a sounding rocket payload in and near a quiet auroral arc. This payload was launched on March 9, 1978 from Poker Flat, Alaska. The payload trajectory was close to the magnetic meridian and passed over a 40 kR auroral arc. The present investigation is concerned with ac electric field observations in the ELF and lower VLF covering a frequency range from 2.5 Hz to 8 kHz. Attention is given to aspects of instrumentation, the general situation, a data analysis, and the obtained results. Waves were observed at low altitude in a region of downward parallel current and diffuse aurora. These waves had properties consistent with those expected for hydrogen and oxygen electrostatic ion cyclotron (EIC) waves.

Bering, E. A.↗

NASA NTRS1984

Origin of the plasma in a cross-polar cap auroral feature (theta aurora)

Ion composition data obtained from a particularly well observed cross-polar cap auroral feature (theta aurora) are presented. Two components of the hot plasma are identified, one from the ionosphere below and the second from the distant plasma sheet. These observations provide strong support for the conclusion that the cross-polar cap auroral feature occurs on field lines closing through the distant plasma sheet or plasma sheet boundary layer. Taken together with the previously published observations, these new results establish substantial constraints on models for the overall polar cap topology. However, they do not unambiguously favor either of the two principal topologies discussed in the literature.

Peterson, W. K.↗

NASA NTRS1985

Cosmic ray secular variations in terrestrial records and aurorae

The rediscovery that the Sun and the solar wind can undergo important changes on historical time scales has brought into question the stability of the cyclic behavior of past time series of solar and solar-terrestrial origin. It was found by Vector Fourier analysis that the solar 11 year cycle is present in the series of 10Be, delta 180, in ice cores and of thermoluminescence (TL) in sea sediments during the last Millennia with a frequency modulation, related to the Sun behavior, as tested by comparison with the Sunspot number R sub z series. It was shown that the cyclogram of the series of yearly Aurorae from 1721 to 1979 linear-regression-corrected-for-R sub z is straight for the periodicity zeta=11,1y, which indicates that such periodicity is constant in time corresponding to the only line present in the 11y band. The maxima of this component appear at the same time together with the high speed solar wind streams taking place in coronal holes situated in high heliolatitudes. It is evidenced that the 11 year cycle has undergone frequency oscillations on a time scale of two centuries, although it is very difficult to determine the periodicities with high accuracy.

Attolini, M. R.↗

NASA NTRS1984

Comparison of the Jovian north and south pole aurorae using the IUE observatory

New results on the spatial and temporal variability of the auroral emissions from Jupiter have been obtained from three IUE observations of the south pole made during the period July 1983 to March 1984. The current observations, together with previous IUE studies of the north pole aurora, provide convincing evidence for persistent longitudinal asymmetries in the Jovian auroral emissions. The strongest emissions appear to originate from regions centered near lambda-III of about 0 deg at the south pole and lambda-III of about 185 deg at the north pole. Differences in surface magnetic field strength seem inadequate to explain the extent to which particles precipitating along field lines into a given longitude sector in one hemisphere are inhibited from precipitating along the same field lines into the opposite hemisphere. Thus, the IUE auroral results present a challenge to existing models of auroral production.

Skinner, T. E.↗

NASA NTRS1985

A simple model for polar cap convection patterns and generation of theta auroras

An addition of the uniform interplanetary magnetic field and the earth's dipole magnetic field is used to evaluate electric field convection patterns over the polar caps that result from solar wind flow across open geomagnetic field lines. The model also accounts for field-aligned patterns within, and auroral arcs across, the polar cap. The qualitative predictions derived from the model express the electric field magnitudes, aurora intensity, sunward and antisunward flow, and the dusk-side reversal of the convection field in terms of the x and y components of the interplanetary magnetic field.

Lyons, L. R.↗

NASA NTRS1985

Idealized model of polar cap currents, fields, and auroras

During periods of northward Bz, the electric field applied to the magnetosphere is generally opposite to that occurring during southward Bz and complicated patterns of convection result, showing some features reversed in comparison with the southward Bz case. A study is conducted of a simple generalization of early work on idealized convection models, which allows for coexistence of sunward convection over the central polar cap and antisunward convection elsewhere in the cap. The present model, valid for By approximately 0, has a four-cell convection pattern and is based on the combination of ionospheric current conservation with a relation between parallel auroral currents and parallel potential drops. Global magnetospheric issues involving, e.g., reconnection are not considered. The central result of this paper is an expression giving the parallel potential drop for polar cap auroras (with By approximately 0) in terms of the polar cap convection field profile.

Cornwall, J. M.↗

NASA NTRS1985

Images of the earth's aurora and geocorona from the Dynamics Explorer mission

Several series of auroral and geocoronal images from th Dynamics Explorer Mission are presented and analyzed. It is found that the motion of the transpolar arc of a theta aurora is correlated with the y-component of the IMF; the arc motion is in the general direction of the y-component. In addition, a sequence of global images of a small auroral substorm shows the initial development of intense luminosities in a relatively small spatial region or 'bright spot' in the premidnight sector of the auroral oval and a subsequent appearance of an expanding area of lesser intensities at low latitudes and contiguous to the midnight boundary of the bright spot. Finally, a series of images of the geocorona in scattered solar Ly-alpha emissions is used to obtain a best-fit spherical model of atomic hydrogen densities in the earth's exosphere; a Chamberlain model provides an adequate fit to radial distances of 4.5 earth-radii, beyond which an exponential fit is used. The geocoronal tail is detected as an asymmetric increase in scattered Ly-alpha intensities in the antisolar direction.

Frank, L. A.↗

NASA NTRS1986

Jovian VLF chorus and Io torus aurora

A test particle model of the cyclotron resonance interaction of waves and trapped radiation belt particles is used to estimate the energetic electron fluxes precipitated by Jovian VLF chorus waves observed on the Voyager 1 and 2 spacecraft near the Io torus. The precipitation fluxes induced by 1-s-long chorus wave packets at L = 7.6 and 8.6 are estimated to be bursts of 5s duration with a peak of 0.3-3 and 0.7-7 ergs/sq cm s that consist of electrons of 5-100 keV energy and that arrives at the ionosphere 15 s after the generation of the chorus wave at the equatorial plane. The effects in the Jovian ionosphere of the chorus-induced precipitation are estimated using existing ionospheric models. A possible experiment for measuring Jovian chorus-induced aurora is proposed and discussed.

Inan, U. S.↗

NASA NTRS1986

Production of flickering aurora and field-aligned electron flux by electromagnetic ion cyclotron waves

Recent observations have suggested that flickering aurora is produced by a modulation of the field-aligned component of the electron flux within an auroral arc. It is proposed that a portion of the field-aligned electrons are of ionospheric origin and that these electrons are accelerated and their flux modulated by electromagnetic ion cyclotron waves that occur below the main acceleration region on auroral arc field lines. A model of the electromagnetic ion cyclotron wave shows that the parallel phase velocity of the wave increase as the wave propagates toward the ionosphere. A test particle calculation shows that ionospheric electrons trapped or reflected by the wave are accelerated to energies of several keV and that their flux is modulated at the wave frequency. The relative amplitudes of the model wave electric fields are consistent with the observations of small-scale low-frequency ionospheric and magnetospheric electric fields near auroral arcs of approximately 10 mV/m and 100 mV/m, respectively. The large-amplitude ion cyclotron waves also produce a ponderomotive force and a self-consistent ambipolar electric field. Energy considerations show that the downward energy flux in the electromagnetic ion cyclotron wave can be several percent of the total downward auroral electron energy flux.

Temerin, M.↗

NASA NTRS1986

The role of energetic O(+) precipitation in a mid-latitude aurora

It is shown that fluxes of precipitating energetic O(+) that have been observed by satellites in the topside ionosphere can explain the magnitude of the N2+(1 N) (first negative) 3914-angstroms and N2(2 P) (second positive) 3371-angstroms emission rate observed during a mid-latitude aurora over Logan, Utah (41 degrees N, 111 degrees W), on 21-22 September 1982. Heavy particle precipitation has previously been invoked to explain the anomalously high populations in the upper vibrational levels of the N2+(1 N) system that are evident in the observed emissions. An improved model is used to investigate the impact of precipitating heavy ions on the atmosphere. The nocturnal thermospheric heating rate and ionization rate during one of these events can be equivalent to the daytime EUV heating and ionization rates. The observed spectrum can be explained by energetic O(+) precipitation to within the uncertainties of the inputs to the model.

Ishimoto, M.↗