Helium-3 enhancements and unusual ion charge state composition in coronal mass ejections.

摘要

Using data from the MASS high-resolution solar wind spectrometer on the WIND spacecraft, six enhanced {dollar}sp3{dollar}He{dollar}sp{lcub}2+{rcub}/sp4{dollar}He{dollar}sp{lcub}2+{rcub}{dollar} periods were found from 1995 to 1998. The enhancements vary from a factor of five to almost a hundred times higher than average values previously reported. All enhanced {dollar}sp3{dollar}He{dollar}sp{lcub}2+{rcub}{dollar} periods were associated with the passage of CME-ejecta. The observed time periods were either within but towards the end of the CME-associated magnetic clouds or trailing the magnetic cloud by about 24 hours. Four of six events have enhanced overall densities ({dollar}>{dollar}30 cm{dollar}sp{lcub}-3{rcub}){dollar} as well as enhanced {dollar}sp3{dollar}He{dollar}sp{lcub}2+{rcub}{dollar} abundances. All enhanced {dollar}sp3{dollar}He{dollar}sp{lcub}2+{rcub}{dollar} periods have a mixture of low (cold) iron charge states along with high (hot) oxygen charge states. Two periods have singly charged helium present with {dollar}sp4{dollar}He{dollar}sp{lcub}+{rcub}/sp4{dollar}He{dollar}sp{lcub}2+{rcub}{dollar} ratios of 1.0 {dollar}pm{dollar} 0.5% and 12 {dollar}pm{dollar} 6%. In addition, during one of these two periods we observed C{dollar}sp{lcub}2+{rcub},{dollar} N{dollar}sp{lcub}2+{rcub},{dollar} and O{dollar}sp{lcub}2+{rcub}{dollar} for the first time in the solar wind.; The unusual charge state composition of these enhanced {dollar}sp3{dollar}He{dollar}sp{lcub}2+{rcub}{dollar} events suggest the plasma came from a relatively cold and dense solar region. In addition one of our enhanced {dollar}sp3{dollar}He{dollar}sp{lcub}2+{rcub}{dollar} events has optical observations from SoHO to suggest it came from the prominence core within a partial halo CME. We suggest that the enhanced {dollar}sp3{dollar}He{dollar}sp{lcub}2+{rcub}{dollar} plasma in all six of our events originated from the prominence core embedded within the CME as observed from spaceborne coronagraphs. Different fractionation theories that might explain the {dollar}sp3{dollar}He{dollar}sp{lcub}2+{rcub}{dollar} enhancement will be discussed.; In addition, ionic and elemental abundances were determined in twenty-one magnetic clouds. Four of these magnetic clouds were associated with the four {dollar}sp3{dollar}He{dollar}sp{lcub}2+{rcub}{dollar}-enhanced events. In general, charge states of carbon, nitrogen and oxygen indicate that the twenty-one magnetic clouds contain "hotter" plasma than that found in the typical slow speed solar wind. Elemental abundances of other minor ions indicate that the "FIP effect", in which the abundances of elements with low first ionization potentials is enhanced, was operating in magnetic clouds.