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Fractionation of the Solar Wind

Published online by Cambridge University Press:  30 March 2016

R. Von Steiger
R. Von Steiger*
Affiliation:
Physikalisches Institut, Sidlerstrasse 5, CH-3012 Bern, Switzerland

Extract

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The composition of the solar wind (SW) is not a true sample of the solar composition, but it is fractionated with respect to the solar photosphere. This fractionation follows the well-known first ionization potential (FIP) pattern: When plotting the SW abundances with respect to the solar abundances as a function of FIP, a step function is obtained (Fig. 1). The step at ∼ 10eV has a height of 3-5 in the slow SW, but this is reduced to 1.5-2 in the fast streams, which originate in the coronal holes. The data given in Fig. 1 are collected and discussed in von Steiger & Geiss (1994), including the “FIP exceptions”, Kr and Xe.

The process leading to the observed overabundance of the low-FIPs has been located to operate by atom-ion separation across magnetic field lines in the chromosphere (Geiss, 1982), because this is the only region of the solar atmosphere where a significant fraction of the gas is neutral. The fractionated abundances observed in the S W are thus important tracers for processes and conditions at this site.

References

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