Relative helium abundance and plasma properties in the solar wind

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1969

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Abstract

Data obtained on the Vela 3A and 3B satellites between July 196$ and July 196? have been used to study the relative abundance and plasma properties of helium in the solar wind. The long term average of the helium to hydrogen density ratio was 0.037. Of the 10,31H spectra used from this period, 90% gave helium-hydrogen ratios between 0.01 and 0.08. Comparisons with "solar surface" relative helium abundance measurements were made. The long term average of 0.037 is less.than the most recent determination of the "surface" ratio, i.e. 0.063. The helium-hydrogen ratios observed were greater than Q.O63 only 10% of the time. Mechanisms which allow regions of higher helium abundance in the solar chromosphere and corona are discussed. Large variations of the helium-hydrogen ratio were observed even when averages over solar rotations were computed. A possible solar cycle dependence in the solar wind helium abundance is suggested. Sudden large increases in the solar wind helium-hydrogen ratio are shown to correlate well with Forbush decreases and sudden commencement geomagnetic storms. Theories relating these increases to part of the solar chromosphere blown out into the solar wind during flares are discussed. The helium and hydrogen bulk velocities were found to be virtually equal at all times; and, a discussion of the phenomena of "frozen in flux" to explain this equality is given. It was found that the solar wind ion species are rarely in thermodynamic equilibrium. The helium temperature was, on the average, four times the hydrogen temperature, indicating that the two ion species have equal random velocities. Suggestions are presented for future extension of this and related research.

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