A. B. Galvin

Comet Giacobini-Zinner - In situ observations of energetic heavy ions

Conclusive evidence is presented for the existence of energetic (∼535,0000 to 150,000 electron volts), heavy (>-12 atomic mass units), singly charged cometary ions within ∼1.5 x 106 kilometers of comet Giacobini-Zinner. The observations were made with the University of Maryland/Max-Planck-Institut ultralow-energy charge analyzer on, the International Cometary Explorer spacecraft. The most direct evidence for establishing the mass of these ions was obtained from an analysis of the energy signals in one of the solid-state detectors; it is significant at the three-sigma level. Maximum fluxes were recorded ∼1 hour before and ∼1 hour after closest approach to the cometary nucleus. Transformation of the particle angular distributions observed at ∼50,000 kilometers radial distance from the comet during the inbound pass into a rest frame in which the distributions are nearly isotropic requires a transformation velocity that is consistent with the local solar wind velocity if one assumes that these particles are primarily singly ionized with a mass of 18 � 6 atomic mass units. The existence of a frame of reference in which these water-group ions were isotropic implies that they underwent strong pitch angle scattering after their ionization. Particle energies in the rest frame extend to substantially higher values than would be expected if these ions were locally ionized and then picked up by the solar wind, implying that the ions were accelerated or heated. The derived ion density, ∼0.1 per cubic centimeter, is consistent with a crude model for the production and transport of pickup ions.

The solar wind and suprathermal ion composition investigation on the wind spacecraft

The Solar Wind and Suprathermal Ion Composition Experiment (SMS) on WIND is designed to determine uniquely the elemental, isotopic, and ionic-charge composition of the solar wind, the temperatures and mean speeds of all major solar-wind ions, from H through Fe, at solar wind speeds ranging from 175 kms−1 (protons) to 1280 kms−1 (Fe+8), and the composition, charge states as well as the 3-dimensional distribution functions of suprathermal ions, including interstellar pick-up He+, of energies up to 230 keV/e. The experiment consists of three instruments with a common Data Processing Unit. Each of the three instruments uses electrostatic analysis followed by a time-of-flight and, as required, an energy measurement. The observations made by SMS will make valuable contributions to the ISTP objectives by providing information regarding the composition and energy distribution of matter entering the magnetosphere. In addition SMS results will have an impact on many areas of solar and heliospheric physics, in particular providing important and unique information on: (i) conditions and processes in the region of the corona where the solar wind is accelerated; (ii) the location of the source regions of the solar wind in the corona; (iii) coronal heating processes; (iv) the extent and causes of variations in the composition of the solar atmosphere; (v) plasma processes in the solar wind; (vi) the acceleration of particles in the solar wind; and (vii) the physics of the pick-up process of interstellar He as well as lunar particles in the solar wind, and the isotopic composition of interstellar helium.

SOLAR WIND IRON AND OXYGEN CHARGE STATES AND RELATIVE ABUNDANCES MEASURED BY SWICS ON ULYSSES

We present the results of a survey of iron and oxygen charge state distributions as detected by the Solar Wind Ion Composition Spectrometer (SWICS) on the Ulysses spacecraft. The results are categorized in terms of the ionization temperature determined every ~ 13 minute instrument cycle from the O+7 to O+6 ratio. Our preliminary Fe/O abundance ratio is 0.12 averaged over this 3 month survey. The Fe charge state distributions accumulated during times of high oxygen ionization temperatures are clearly non-isothermal.

Concurrent observations of solar wind oxygen by Geotail in the magnetosphere and wind in interplanetary space

We present an initial report on the first direct, concurrent measurements of solar wind oxygen (O) charge state variations inside and outside Earths magnetosphere. On 10-11 Jan 1997 a magnetic cloud, with a spatial scale of at least ∼100 RE engulfed the magnetosphere. At ∼1200 UT on 10 Jan 1997, the Wind/SWICS ion charge-state spectrometer, at ∼90 RE upstream of Earth, detected an increase in the solar wind O charge state ratio Γo = (O+7 + O+8) / O+6 at ∼0.5-30 keV/e which persisted until ∼2400 UT on 10 Jan 1997. After ∼1110 UT on 10 Jan 1997, Geotail was in and near the mid-afternoon to dusk magnetosphere. The ∼9.4-210 keV/e Γo value from the Geotail/STICS spectrometer showed a longer-term, gradual increase over ∼8–10 hr. Then, after ∼0600 UT on 11 Jan 1997, Wind observed a Γo decrease at a high speed solar wind stream onset. About 6 hr later Γo decreased promptly at Geotail during a plasma sheet substorm injection. Both instances are long durations compared to nominal 3-hr substorm time-scales.

SILICON AND OXYGEN CHARGE STATE DISTRIBUTIONS AND RELATIVE ABUNDANCES IN THE SOLAR WIND MEASURED BY SWICS ON ULYSSES

ABSTRACT We report an initial survey of solar wind silicon and oxygen using data obtained with the Ulysses Solar Wind Ion Composition Spectrometer (SWICS). In this study, the O +7 /O +6 ratio is used to group silicon counts accumulated over a two month period. Results on Si charge state distributions, relative Si/O abundances, and associated proton kinetic temperature and speed distributions are presented.

Solar Wind Charge States Measured by Ulysses/SWICS in the South Polar Hole

The Ulysses mission now has an extensive data base covering several passes of the south polar coronal hole as the spacecraft proceeds to higher latitudes. Using composition measurements from the SWICS experiment on the Ulysses spacecraft, we have obtained charge state distributions, and hence inferred coronal ionization temperatures, for several solar wind species. In particular, we present an overview of Oxygen ionization temperature measurements, based on the O7+/O6+ ratio, for the period January 1993 until April 1994 (∼23°S to ∼61°S heliographic latitude), and detailed Oxygen, Silicon and Iron charge state distributions of the south polar hole during a two month period of nearly continuous hole coverage, Dec 1993–Jan 1994 (∼45°S to 52°S heliographic latitude).

IONS WITH LOW CHARGES IN THE SOLAR WIND AS MEASURED BY SWICS ON BOARD ULYSSES

We present new data on rare ions in the solar wind. Using the Ulysses-SWICS instrument with its very low background we have searched for low-charge ions during a 6-d period of low-speed solar wind and established sensitive upper limits for many species. In the solar wind, we found He(1+)/He(2+) of less than 5 x 10 exp -4. This result and the charge state distributions of heavier elements indicate that all components of the investigated ion population went through a regular coronal expansion and experienced the typical electron temperatures of 1 to 2 million Kelvin. We argue that the virtual absence of low-charge ions demonstrates a very low level of nonsolar contamination in the source region of the solar wind sample we studied. Since this sample showed the FlP effect typical for low-speed solar wind, i.e., an enhancement in the abundances of elements with low first ionization potential, we conclude that this enhancement was caused by an ion-atom separation mechanism operating near the solar surface and not by foreign material in the corona.

MAGNESIUM, CARBON, AND OXYGEN ABUNDANCES IN DIFFERENT SOLAR WIND FLOW TYPES, AS MEASURED BY SWICS ON ULYSSES

ABSTRACT The SWICS instrument on the Ulysses spacecraft has now gathered an almost continuous database of in-ecliptic solar wind composition data for many months. In this paper, we concentrate on the elements Mg, C, and O. We report relative abundances C/O and Mg/O and correlate their variations with different solar wind conditions and flow types, as inferred from the coronal freezingin temperature. We find average abundance ratios of C/O = 0.62 and Mg/O = 0.13 over a period of almost 3 months. The daily Mg/O averages during this period are clearly correlated with the coronal temperature, while the same correlation is weaker for the C/O daily averages. This finding is briefly discussed in relation to the FIP fractionation effect.

Comparison of lunar and terrestrial ion measurements obtained by the WIND and GEOTAIL spacecraft outside and inside the Earth's magnetosphere

Abstract The WIND spacecraft, launched on November 1, 1994, undergoes prior to its halo orbit insertion several lunar swing-by maneuvers. The GEOTAIL spacecraft, skimming around the dayside magnetopause (Dec. 1994), passes also several times behind the moon. The HEP-LD spectrometer onboard of GEOTAIL and the Solar Wind and Suprathermal Ion Composition (SMS) Experiment onboard of the WIND spacecraft are well positioned for observing ions in the mass range between II and Fe in the direct vicinity of the moon. We report first observations of lunar pickup-ions in the magnetotail at a distance of ≈ 80 R e .

Search for lunar pickup ions

Abstract During lunar flybys in December 1994 and January 1996 pickup ions, generated by solar photons, solar wind and micrometeoroid impacts, were detected by the SMS experiment on the WIND-S/C in the energy range E = 6.5 - 226 KeV/e. Near the moon the ions have not yet reached their full pickup energy, but they can be identified by the directional properties of the additional flux increases in sectors 4–8, the high mass and the charge state (singly charged ions) in contrast to solar wind ions which are multiply charged. Lunar pickup ions in the mass range 12–42 amu/e could be identified but no singly charged iron ions were found. The pickup ions give a qualitative picture of the lunar surface composition. The results obtained earlier by Hilchenbach et al. (1991) near the Earth with a similar experiment on board the AMPTE satellite could generally be confirmed.