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At least 109 records · Page 6

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NASA NTRS1985

The boundary layers as the primary transport regions of the earth's magnetotail

A comprehensive survey of ISEE and IMP LEPEDEA plasma measurements in the earth's magnetotail reveals that the magnetospheric boundary layer and the plasma sheet boundary layer are the primary transport regions there. These plasma measurements also reveal various components of the plasma sheet, including the central plasma sheet and plasma sheet boundary layer. A significant new result reported here is that of cold- and hot-plasma components that are spatially co-present within the central plasma sheet. Such plasma components cannot be explained merely by temporal variations in spectra involving the entire plasma sheet. Contributions to a low temperature component of the plasma sheet enter directly from the boundary layer located along the magnetotail flanks. Field-aligned flows predominate within the plasma sheet boundary layer which is almost always present and is located near the high- and low-latitude border of the plasma sheet. The plasma sheet boundary layer comprises highly anisotropic ion distributions, including counter-streaming ion beams, that evolve into the hot, isotropic component of the plasma sheet. Tailward acceleration regions generate these ion beams with plasma input from the magnetospheric boundary layer. Antisunward-flowing ion beams, at E/q less than 1 kV and of ionospheric composition, are frequently observed in the plasma sheet boundary layer and in tail lobes. These ion beams are likely accelerated at low altitude over the polar cap and especially along auroral field lines.

Eastman, T. E.↗

NASA NTRS1972

Energy distribution functions of kilovolt ions in a modified Penning discharge

The distribution function of ion energy parallel to the magnetic field of a Penning discharge was measured with a retarding potential energy analyzer. Simultaneous measurements of the ion energy distribution function perpendicular to the magnetic field were made with a charge-exchange neutral detector. The ion energy distribution functions are approximately Maxwellian, and their kinetic temperatures are equal within experimental error. This suggests that turbulent processes previously observed Maxwellianize the velocity distribution along a radius in velocity space, and result in an isotropic energy distribution. The kinetic temperatures are on the order of kilovolts, and the tails of the ion energy distribution functions are Maxwellian up to a factor of 7 e-folds in energy. When the distributions depart from Maxwellian, they are enhanced above the Maxwellian tail. Above densities of about 10 to the 10th power particles/cc, this enhancement appears to be the result of a second, higher temperature Maxwellian distribution. At these high particle energies, only the ions perpendicular to the magnetic field lines were investigated.

Roth, J. R.↗

NASA NTRS1987

Enhancements of energetic ions associated with travelling compression regions in the deep geomagnetic tail

This paper presents a representative example of an enhancement in energetic ion flux associated with the International Sun-Earth Explorer 3 (ISEE 3) spacecraft's encounter with a traveling compression region (TCR). Data from the energetic particle anisotropy spectrometer (EPAS) instrument on ISEE 3 are studied, along with magnetic field data from the vector helium magnetometer. It is concluded that the ion enhancements seen are spatial in nature, thus supporting the idea that TCRs are the lobe signatures of plasmoids moving along the magnetotail, away from earth.

Murphy, N.↗

NASA NTRS1986

CO(+) fluorescence in comets

Calculations of the fluorescent equilibrium of the CO(+) molecule to determine the Swings and Greenstein effects as a function of heliocentric radial velocity have been carried out. The previously ignored Baldet-Johnson (B-A) bands were included in addition to the comet tail (A-X) and first negative (B-X) bands, thus allowing a determination of the absolute intensities of all bands. As with certain other molecules such as OH and CN, the Swings effect on individual lines is large enough that integrated band fluxes in the comet tail system also exhibit the Swings effect. The flux variations for velocities in the range - 50 to + 350 km/s have been calculated and may be used to map the acceleration of CO(+) ions into the tail, even with low dispersion spectra.

Magnani, L.↗

NASA NTRS1995

Magnetic Merging Locations Deduced from: Slow-Mode Shock Orientation Determinations, Boundary Layer Wave Intensities and Energetic Ion Velocity Dispersion in the Distant Geomagnetic Tail

Several techniques will be used to determine the location of the magnetic reconnection in the distant geomagnetic tail using the ISEE-3. Techniques to be used are calculated wave-particle scattering time, plasmoid source location (if a plasmoid is found), analysis of the magnetic field geometry and slow-mode shock orientation, and examination of the magnetic field Bz components and plasma bulk speeds.

geomagnetic tail ISEE-3 magnetic fields↗

NASA NTRS2024

Ion Diffusive Transport Across the Separatrix Between the Low-Latitude Mantle and the Plasma Sheet By Kinetic Alfvén Waves: MMS Observation

To understand the entry of the cool low‐latitude mantle ions into the tail plasma sheet near the flanks under persistent interplanetary magnetic field B y , we evaluate the role of the cross‐field diffusive transport by kinetic Alfvén waves (KAWs) by investigating two events observed by multiscale (MMS) spacecraft. Around the separatrix between the open and closed field‐line regions, a two‐component mixing of hot plasma sheet ions of a few keV with cool mantle ions of a few hundred eV was observed, indicating transport across the separatrix. The waves observed between 0.01 and 10 Hz around the separatrix had characteristics consistent with those of KAWs. The consistency allowed us to estimate the wave vectors as a function of frequency by fitting KAW dispersion to the observations. Using the observed wave powers, plasma moments, and the estimated wave vectors, we computed the cross‐field diffusion rates associated with KAWs. The diffusion rates were found to be comparable to or larger than the Bohm diffusion rates during the intervals when the two‐component mixing was observed, indicating that the KAW diffusive transport can play a role in the entry of low‐latitude mantle ions into the plasma sheet.

Kinetic Alfvén waves↗

NASA NTRS1996

AMPTE/CCE and SCATHA simultaneous observations of magnetic signatures associated with a substorm onset

Magnetic field signatures associated with a substorm onset event are examined by making use of simultaneous observations from the Active Magnetosphere Particle Tracer Explorer (AMPTE)/Charge Composition Explorer (CCE) and Spacecraft Charging AT High Altitude (SCATHA). The observations of the two satellites are discussed in relation to their differences and the relative positions of the satellites. Despite the small separation between the satellites, AMPTE/CCE observed the start of irregular magnetic field fluctuations a few tens of seconds earlier than SCATHA, indicating that the CCE was within, or closer to, the onset region. It was found that the amplitude of the fluctuations was largest in the north-south component. The results indicate that the magnetic field fluctuations were excited locally and the coherence length was less than a multiple of Larmor radius of thermal protons. It is suggested that the tail current disruption is described as a system of chaotic filamentary electric currents which flow in various directions, but preferentially anti-parallel to the cross-tail current, and that ions play an important role in the triggering of the tail current disruption.

Ohtani, S.↗

NASA NTRS1972

Two early missions to the comets.

Early missions to the comets Grigg-Skjellerup in 1977 and Encke in 1980 are suggested as precursors to more ambitious missions to Encke rendezvous in 1984 and Halley intercept in 1986. The spacecraft structures, power systems, telemetry, configurations, and launch vehicles considered appropriate for these two missions are actual equipments ready for applications. The mission objectives would be exploration of the nature of the solar wind interaction with comets, the composition of the gaseous cometary atmosphere, and possibly the details of the trailing portion of a comet (ion and dust tails).

Farquhar, R. W.↗

NASA NTRS1981

Ground-based cometary spectroscopy

The observational problems presented by bright comets near perihelion are discussed. High and low resolution spectra (3100-800A) of the bright comets Kohoutek, Kobayashi-Berger-Milon, West and d'Arrest are presented. Digital reduction of calibrated photographic spectra to relative intensity versus wavelength, can provide useful information. The reduction of comet spectra to absolute intensities involves, however, large uncertainties and should be interpreted cautiously. Data on recent comets lead to the following results: tentative identification of a new ion in the tail of comets, namely, NH(+); spectroscopic resolution of the fragmented nucleus of comet West; and an accurate monochromatic intensity profile of the Co+ emission (4020A) in comet West.

Wyckoff, S.↗

NASA NTRS1984

STS atmospheric luminosities

During the STS-8 space shuttle mission special photographic and TV operations were carried out to record the properties of the spacecraft induced luminosities. One of these luminous phenomena is the quiescent vehicle glow which was photographed during the STS-8 mission with an image intensified photographic camera, with and without an objective grating. During the latter part of the mission the altitude of the shuttle was relatively low (120 n.m. = 222 km) and unprecedentedly high intensity of the glow was observed. The crew reported that the glow was easily visible to the naked eye. The proper orientation of the shuttle with respect to the velocity vector and the objective grating permitted the exposure of good objective spectrum of the glow in the visible region. From the results it is clear that the spectrum appears to be a continuum as observed by the image intensifier objective grating camera. Qualitative examination of the data shows that there is very tail little glow ion the wavelength range of 4300 to about 5000 angstroms. Above 5000 angstroms the glow becomes stronger towards the red and then it falls off towards higher wavelength and of the spectrum presumably because of the responsivity of the device.

Mende, S. B.↗

NASA NTRS1986

International Ultraviolet Explorer (IUE) observation of Halley's Comet

The main objectives of the IUE Halley's Comet program are: study of the physical and chemical properties of a comet clearly different from those observed previously with IUE; study of the long-term evolution of the gas and dust coma and the ion and dust tails, by combining IUE data with UV and in-situ observations obtained by other spacecraft; and assessment of the gas and dust environment of Halley in terms of its possible impact on the trajectories of the flyby spacecraft. Another program investigates the CS scale length, and the rotational profile of CS in order to test and calibrate dynamic-flow models of comets. These observations will begin in August 1985 when the heliocentric distance of the comet is 2.8 AU and its total visual magnitude + 13. They will continue into the ninth IUE observing period, through mid-1986.

Kondo, Y.↗

NASA NTRS1986

Optical spectrophotometry of Comet P/Giacobini-Zinner and emission profiles of H2O+

Two-dimensional CCD spectrograms were obtained of Comet P/Giacobini-Zinner (1984e) on five occasions between July and October 1985. Spatial emission profiles of H2O+ were extracted at 6198 angstroms (the strongest ionic line in the visible spectrum). This emission line traces the extent of the ion, or plasma, tail. The spectrographic slit was placed approximately along the trajectory of the ICE spacecraft on September 11, 1985; the resulting H2O+ profile has a full-width-half-maximum of about 5700 km, about three times that of the plasma density profile measured by ICE, and has a full-width-zero-intensity of about 30,000 km, very similar to the ICE values. H2O production rates for the comet are derived and compared with those of Comet P/Halley (1982i).

Strauss, M. A.↗

NASA NTRS1986

Solar wind-plasma interaction: The AMPTE solar wind plasma releases

In situ measurements during AMPTE solar wind ion releases are described. The creation of a diamagnetic cavity, compression and draping of magnetic field lines, recoil of the entire artificial comet, and ion beam and tail formation are discussed. The wave measurements were used to determine the time variation of the plasma density from the measurement of the electron plasma frequency and to determine the state of cloud expansion and cavity formation. Features found include absence of strong turbulence and anomalous diffusion in the cavity boundary, and the appearance of very intense shock-like emission in front of the plasma clouds. The first effect suggests partially unknowm processes leading to magnetic field penetration into the region of the clouds. The direct observation of the interaction processes between the fast streaming solar wind plasma and the expanding cloud plasma of the Li and artificial comet releases may have relevance to astrophysical situations as, for instance, encountered in solar flares, interstellar clouds, or during accretion of matter onto compact objects.

Source record↗

NASA NTRS1986

Is CO2 responsible for the outbursts of comet Halley?

Spectroscopic data from the IUE are reported which show a strong correlation between a visible outburst from the near-nuclear region of comet Halley on 18.8 March 1986 and the sudden appearance of a large column abundance of CO2(+) ions in the tail. These data suggest that CO2 may play a significant role in the outburst process. This outburst may have been the source of the detached clumps of CO(+) emission recorded by ground-based observers on 19 and 20 March, 1986.

Feldman, P. D.↗

NASA NTRS1987

On the generation of broadband electrostatic noise

Linear theory analysis and particle simulation studies were carried out to understand the mechanisms generating broadband electrostatic noise (BEN) and the effects of BEN on particles as well as the nonlinear saturation level in the geomagnetic tail region. Streaming ion beams as well as warm ions and electrons are used to model the plasma-sheet particle population. When the beam ion temperature is comparable to the temperature of the warm plasma-sheet particles, electrostatic ion cyclotron instabilities become unstable, giving rise to low-frequency noise at omega less than about n(Omega i), where Omega i is the ion gyrofrequency.

Ashour-Abdalla, M.↗

NASA NTRS1992

Planet-B: A Japanese Mars aeronomy observer

An introduction is given to a Japanese Mars mission (Planet-B) which is being planned at the Institute of Space and Aeronautical Science (ISAS), Japan. Planet-B aims to study the upper atmosphere of Mars and its interaction with the solar wind. The launch of Planet-B is planned for 1996 on a new launcher, M-L, which is being developed at ISAS. In addition to the interaction with the solar wind, the structure of the Martian upper atmosphere is thought to be controlled by the meteorological condition in the lower atmosphere. The orbit of Planet-B was chosen so that it will pass two important regions, the region where the solar wind interacts with the Martian upper atmosphere and the tail region where ion acceleration is taking place. Considering the drag due to the Martian atmosphere, the periapsis altitude of 150 km and apoapsis of 10 Martian radii are planned. The orbit plane will be nearly parallel to the ecliptic plane. The altitude of the spacecraft will be spin stabilized and its spin axis will be controlled to the point of the earth. The dry weight of the spacecraft will be about 250 kg, including the scientific payload which consists of a magnetometer, plasma instruments, HF sounder, UV imaging spectrometer, and lower atmosphere monitor.

Tsuruda, K.↗

NASA NTRS1993

Observations of the plasma flow in Comet P/Swift-Tuttle

We present direct ground based observations of the plasma flow sunward and tailward of the nucleus of Comet P/Swift-Tuttle. The observations are long-slit high resolution spectra of the H2O(+) emission centered at 6199 A with a velocity resolution of about 7 km/s FWHM and a spatial resolution of about 10 exp 4 km at the comet. Emission is visible from just inside the predicted position of the cometopause on the sunward side of the nucleus out to 5 x 10 exp 5 km on the tailward side. The deceleration of the solar plasma on the sunward side is clearly observed as is the acceleration of cometary ions into the tail. These observations show the effectiveness of ground based methods for the systematic study of cometary plasmas and point to the need for a better theoretical understanding of their acceleration mechanisms.

Brown, Michael E.↗

NASA NTRS1995

Preferential heating of light ions during an ionospheric Ar(+) injection experiment

The Argon Release for Controlled Studies (ARCS) 4 sounding rocket was launched northward into high altitude from Poker Flat Research Range on February 23, 1990. The vehicle crossed geomagnetic field lines containing discrete auroral activity. An instrumented subpayload released 100-eV and 200-eV Ar(+) ion beams sequentially, in a direction largely perpendicular to both the local geomagnetic field and the subpayload spin axis. The instrumented main payload was separated along field lines from the beam emitting subpayload by a distance which increased at a steady rate of approximately 2.4 m/s. Three dimensional mass spectrometric ion observations of ambient H(+) and O(+) ions, obtained on board the main payload, are presented. Main payload electric field observations in the frequency range 0-16 kHz, are also presented. These observations are presented to demonstrate the operation of transverse ion acceleration, which was differential with respect to ion mass, primarily during 100-eV beam operations. The preferential transverse acceleration of ambient H(+) ions, as compared with ambient O(+) ions, during the second, third, fourth, and fifth 100-eV beam operations, is attributed to a resonance among the injected Ar(+) ions, beam-generated lower hybrid waves, and H(+) ions in the tail of the ambient thermal distribution. This work provides experimental support of processes predicted by previously published theory and simulations.

Pollock, C. J.↗