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Shelley, E. G.

Publications and source records attributed to Shelley, E. G..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Observations of plasma dynamics in the coma of P/Halley by the Giotto Ion Mass Spectrometer

Observations in the coma of P/Halley by the Giotto Ion Mass Spectrometer (IMS) are reported. The High Energy Range Spectrometer (HERS) of the IMS obtained measurements of protons and alpha particles from the far upstream region to the near ionopause region and of ions from mass 12 to 32 at distances of about 250,000 to 40,000 km from the nucleus. Plasma parameters from the High Intensity Spectrometer (HIS) of the IMS obtained between 150,000 to 5000 km from the nucleus are also discussed. The distribution functions of water group ions (water group will be used to refer to ions of 16 to 18 m/q, where m is in AMU and q is in unit charges) are observed to be spherically symmetric in velocity space, indicating strong pitch angle scattering. The discontinuity known as the magnetic pile-up boundary (MPB) is apparent only in proton, alpha, and magnetometer data, indicating that it is a tangential discontinuity of solar wind origin. HERS observations show no significant change in the properties of the heavy ions across the MPB. A comparison of the observations to an MHD model is made. The plasma flow directions at all distances greater than 30,000 km from the nucleus are in agreement with MHD calculations. However, despite the agreement in flow direction, within 200,000 km of the nucleus the magnitude of the velocity is lower than predicted by the MHD model and the density is much larger (a factor of 4). Within 30,000 km of the nucleus there are large theoretical differences between the MHD model flow calculations for the plane containing the magnetic field and for the plane perpendicular to the magnetic field. The observations agreed much better with the pattern calculated for the plane perpendicular to the magnetic field. The data obtained by the High Energy Range Spectrometer (HERS) of the IMS that are published herein were provided to the International Halley Watch archive.

Goldstein, B. E.↗
NASA NTRS1991

Interpretation of the ion mass spectra in the mass range 25-35 obtained in the inner coma of Halley's comet by the HIS-sensor of the Giotto IMS Experiment

The IMS-HIS double-focussing mass spectrometer that flew on the Giotto spacecraft covered the mass per charge range from 12 to 56 (AMU/e). By comparing flight data, calibration data, and results of model calculations of the ion population in the inner coma, the absolute mass scale is established, and ions in the mass range 25 to 35 are identified. Ions resulting from protonation of molecules with high proton affinity are relatively abundant, enabling us to estimate relative source strengths for H2CO, CH3OH, HCN, and H2S, providing for the first time a positive in situ measurement of methanol. Also, upper limits for NO and some hydrocarbons are derived.

Geiss, J.↗
NASA NTRS1991

Ion reflection and transmission during reconnection at the earth's subsolar magnetopause

Composition measurements in an accelerated flow event at the earth's dayside magnetopause show evidence for reflection and transmission of magnetospheric and magnetosheath ion species. Furthermore, a single velocity transformation approximately tangent to the magnetopause surface orders the individual transmitted and reflected ion distributions on both sides of the magnetopause into field-aligned flow at V(A), the local Alfven speed. These observations provide strong evidence for a kinetic description of magnetic reconnection at the magnetopause.

Fuselier, S. A.↗
NASA NTRS1991

On the origins of energetic ions in the earth's dayside magnetosheath

Energetic ion events in the earth's dayside subsolar magnetosheath (0900 - 1300 Local Time) are surveyed using data from the AMPTE/CCE Hot Plasma Composition Experiment. Ion species carrying the signature of their origin O(+) and energetic He(2+) are used to distinguish between magnetospheric and solar wind origins for the energetic ion events. The results of this survey indicate that the majority of energetic (10-17 keV/e) H(+) and He(2+) ions observed in the dayside magnetosheath are accelerated from the solar wind population. The energetic He(2+) to H(+) density ratio in the magnetosheath is consistent with that predicted from first-order Fermi acceleration of solar wind ions in the turbulent regions upstream and downstream from the earth's quasi-parallel bow shock. The simultaneous occurrence of both energetic He(2+) and magnetospheric O(+) indicates that, on occasion, both Fermi acceleration of solar wind ions and leakage of magnetospheric ions occurs in the dayside magnetosheath.

Fuselier, S. A.↗
NASA NTRS1990

Ion composition measurements within magnetospheric flux transfer events

Magnetic field signatures from the AMPTE/CCE spacecraft are used to identify two magnetospheric FTEs (flux transfer events). Electron distributions measured in the plane of the magnetopause inside these FTEs complement previously reported electron measurements. Ion composition measurements in the energy range 0 to 20 keV/e within an FTE are reported. It is found that the ion distributions, the ion composition, and the flow velocities are unique to the FTE and unlike either the adjacent magnetosphere, the nearby boundary layer, or the nearby magnetosheath. The H(+), He(+), and He(2+) distribution functions in the FTEs have reversed temperature anisotropies and the relative He(2+) abundance is depressed with respect to either the magnetosheath or the low latitude boundary layer.

Klumpar, D. M.↗
NASA NTRS1989

Direct injection of ionospheric O(+) into the dayside low latitude boundary layer

Observations from the AMPTE/Charge Composition Explorer (AMPTE/CCE) indicate the presence of two distinct O(+) populations in the dayside subsolar low latitude boundary layer during some periods of northward Interplanetary Magnetic Field (IMF). The first population is O(+) convected into the boundary layer from the outer magnetosphere and has been reported previously. It is suggested here that the new, second, O(+) population is injected into the dayside boundary layer directly from the high latitude ionosphere. This second population can have a significant density and distinct characteristics such as field-aligned flow relative to boundary layer H(+) that modify both the plasma composition and dynamics in the low latitude boundary layer.

Fuselier, S. A.↗
NASA NTRS1988

AMPTE/CCE observations of shell-like He(2+) and O(6+) distributions in the magnetosheath

Simultaneous observations of solar wind He(2+) and O(6+) shell-like distributions in the magnetosheath were obtained by the AMPTE CCE on November 1, 1984. It is found that the present distributions are centered on the downstream H(+) bulk velocity and have radii proportional to the mass/charge ratio. The results support an electrostatic cross-shock potential model.

Fuselier, S. A.↗
NASA NTRS1988

Transverse ion energization and low-frequency plasma waves in the mid-altitude auroral zone - A case study

Evidence of transverse ion energization at altitudes of several earth radii in the auroral zone was reexamined using several hundred hours of high-sensitivity and high-resolution plasma data obtained by the Dynamics Explorer 1 satellite. The data on particle environment encountered at midaltitudes in the auroral zone disclosed rapid variations in the values of total density, thermal structure, and composition of the plasma in the interval measured; the modes of low-frequency plasma waves also varied rapidly. It was not possible to unambiguously identify in these data particle and wave signature of local transverse ion energization; however, many intervals were found where local transverse ion heating was consistent with the observations.

Peterson, W. K.↗
NASA NTRS1988

Counter-streaming electrons at the geomagnetic equator near 9 earth radii

AMPTE/CEE observations are used to study short-lived, highly anisotropic electron distributions in the region of the equatorial magnetosphere bewtween 6.6 earth radii and the CCE apogee at 8.8 earth radii. Intense bursts of highly collimated counterstreaming electrons were observed at keV energies with durations of a few tens of seconds to a few minutes near the geomagnetic equator on L-shells that intersect the high-latitude ionosphere in the region normally associated with the auroral zone. It is found that the counterstreaming electrons at energies below the peak energy are accompanied by simultaneous deep depressions of the locally mirroring fluxes. It is suggested that these equatorial electrons may result from the release of auroral electrons trapped beneath the auroral accelerating potentials at lower altitudes along the same magnetic flux tubes.

Klumpar, D. M.↗
NASA NTRS1988

Cometary H2(+) and solar wind He(2+) dynamics across the Halley cometopause

Two Mass/Charge (M/Q) of about 2 distributions were observed by the Giotto Ion Mass Spectrometer/High Energy Range Spectrometer (IMS/HERS) during the encounter with comet Halley. The first, present throughout the encounter, is identified as solar wind He(2+). The second, detectable only within about 600,000 km of the nucleus, is identified as H2(+) (produced primarily by dissociation and ionization of cometary H2O). When these two distributions are separated, distinct differences in their dynamics are apparent, particularly in the density and velocity profiles near the 'cometopause'.

Fuselier, S. A.↗
NASA NTRS1988

Quantitative parametrization of energetic ionospheric ion outflow

Upflowing ionospheric ion (UFI) data from the DE 1 energetic ion composition spectrometer, acquired from near the maximum to the minimum of solar cycle 21, were used to determine the UFI outflow rate as a function of geomagnetic and solar activity conditions. Its solar and magnetic dependences were parameterized empiricaly. It was found that the ion outflow rate increases exponentially with Kp by a factor of 20 for O(+) and 4 for H(+) from Kp = 0 to 6.

Yau, A. W.↗
NASA NTRS1987

Counterstreaming ion events in the magnetosphere

This paper presents general characteristics of more than 60 counterstreaming ion (CSI) events observed by the ISEE 1 satellite. Often, both oxygen and hydrogen ions at a number of energy levels were observed among the CSIs, but some events showed only one of these ions at one or more energy levels involved. In a number of cases, either only H(+) or O(+) ions at just one energy level were seen counterstreaming, and in a few cases, the CSIs were observed to involve ions of one energy traveling parallel to the magnetic field and ions of another energy traveling simultaneously in the antiparallel direction. Moreover, some of the CSI events correlated well with electric wave activity. It is suggested that, in some CSI events, wave-particle interaction may be involved.

Horita, R. E.↗
NASA NTRS1987

The foreshock region upstream from the Comet Halley bow shock

A few hours prior to the crossing of the Comet Halley bow shock, the Giotto spacecraft intermittently encountered an electron foreshock region. The electron foreshock is characterized by magnetic connection to the cometary bow shock and increased field aligned electron heat flux directed away from the bow shock. A similar region was intermittently encountered by the ICE spacecraft prior to its crossing of the Giacobini-Zinner bow wave. During periods of magnetic connection with the Halley bow shock, enhanced magnetic field fluctuations were observed. These enhancements are interpreted as indirect evidence of an ion foreshock in the electron foreshock. No clearly identifiable backstreaming protons are observed during these periods of magnetic connection, however, because it may be difficult to separate a backstreaming population from the cometary pick-up proton population already present in the upstream region.

Fuselier, S. A.↗
NASA NTRS1987

The role of ring current O(+) in the formation of stable auroral red arcs

Observations of thermal and energetic ion populations by the Dynamics Explorer 1 satellite in the magnetospheric energy source region as well as nearly simultaneous Langmuir probe measurements of enhanced electron temperatures by Dynamics Explorer 2 within the stable auroral red (SAR) arc at F region heights are used to examine the role of heavy ions in the formation of SAR arcs. It is found that sufficient energy is transferred to the electron gas at high altitudes via Coulomb collisions between the observed ring current ions and thermal electrons to support the enhanced F region electron temperatures measured on these field lines. The latitudinal variation in the electron heating rates calculated using observed ion populations is consistent with the observed variation in electron temperature across the SAR arc. In all cases, ring current O(+) is the major source of energy for the SAR arcs.

Kozyra, J. U.↗
NASA NTRS1987

Solar cycle variation of some mass dependent characteristics of upflowing beams of terrestrial ions

Examination of the S3-3 and DE ion composition data spread over a solar cycle indicates that some characteristics of energetic upflowing terrestrial ion beams above the auroral zone show dependence on solar cycle. At solar maximum the different ion beam mass components have comparable mean energies, and O(+) dominates the beam composition. The ion energies are consistent with having been acquired from the potential drop below the satellite inferred from the electron loss cone distributions. At solar minimum the beam composition is dominated by H(+), but the O(+) has a higher mean energy and is hotter than the H(+) component. Also, the O(+) has more energy than it could itself have acquired from the potential drop. These observations are qualitatively consistent with the ion beams having acquired their energies from a parallel electric field and being partially thermalized through the two-stream instability between the two ion species, with this effect being modulated by the beam composition.

Collin, H. L.↗
NASA NTRS1987

Experimental tests of a toroidal electrostatic analyzer

A toroidal electrostatic analyzer of a design suitable for space plasma instrumentation has been constructed and tested. Experimental results are compared with second-order ion optical theory and are in good agreement. Verifying the ion optics of the toroid was simplified by use of a position-sensing microchannel-plate detector mounted on a positioning system with three translational degrees of freedom located at the toroid exit. The toroidal analyzer described here is the first optical element in a fully toroidal mass spectrograph intended for analysis of kilovolt magnetospheric plasmas.

Young, D. T.↗
NASA NTRS1986

Ion temperature and flow profiles in Comet Halley's close environment

The Giotto high intensity spectrometer identified the contact surface 4800 km from the comet nucleus. This boundary is clearly seen by a drastic drop in the temperatures of different ion species from 2000 K outside to values as low as 300 K inside. Inside the contact surface outflow speed = > 1 km/sec, in contrast to a value around 0 right outside. These numbers might be affected by a potential charge-up of the spacecraft. Outside the contact surface, the ion temperature rises gradually with increasing distance. Between 9000 and 10,000 km distance the ion density increases by a factor of 4. At 27,000 km distance there is again a rather abrupt jump to significantly higher temperatures, higher outflow speeds, and lower densities.

Schwenn, R.↗