VARIABLE CARBON AND OXYGEN ABUNDANCES IN THE SOLAR-WIND AS OBSERVED IN EARTHS MAGNETOSHEATH BY AMPTE CCE

During periods of enhanced solar wind pressure, the dayside boundary of Earth's magnetosphere occasionally was compressed below the apogee of the AMPTE/CCE satellite at 8.8 R+. Then, while in the magnetosheath, the CHEM instrument on CCE sampled the charge state composition of the solar wind thermalized by the bow shock. These measurements are unique because CHEM was the first instrument to determine individually the charge, mass, and energy of the incident ions. We present a comprehensive list of the solar wind oxygen and carbon charge states and abundances measured in all magnetosheath periods during the lifetime of CCE, 1984-1988. Two different charge state ratios, C6+/C5+ and O7+/O6+, are used to infer the coronal source temperature of the solar wind flow responsible for the magnetosphere compression. In most cases, we can also identify the solar source feature (coronal hole, flare, or disappearing filament) of the flow. We find the carbon-to-oxygen abundance ratio C/O to be highly variable between different flow intervals. Specifically, there is a strong correlation between the inferred coronal source temperature and C/O: While the flows emanating from coronal holes have an average value consistent with the photospheric C/O value, the flows from flares or disappearing filaments have a higher average C/O value than the photosphere. Also, the range of C/O values in the latter flows is much greater than the range of coronal hole C/O values. This result is discussed in relation to the composition of other solar particle populations, and to its possible significance with respect to the FIP-dependent fractionation effect.