The Ionization State of the Solar Wind.
Abstract
The solar wind ionization state is "frozen" within a few solar radii of the photosphere, and measurements of the ions at 1 a.u. can therefore potentially yield information about conditions at the base of the coronal expansion. If ions are assumed to flow at a steady, common bulk speed in a plasma with a Maxwellian electron distribution, the interplanetary ionization state is characteristic of the electron temperature in the coronal "freezing-in" region. In this thesis, we examine the effect of relaxing one or more of these assumptions. The effects of intrinsic time variations (e.g. as in a coronal transient) in a uniform ion flow can be best understood through a Lagrangian approach of following individual fluid parcels; for example, in coronal outflow undergoing a strong shock, only fluid parcels shocked at or below the ambient freezing-in radius have their ionization state modified by the shock, and time-dependent ionization effects for the transition between two steady flows are thus likely to be limited to a narrow range of gas parcels which are shocked in the low corona and pass a fixed interplanetary observer in a few tens-of-minutes. We also find that differential flow of the ions in the freezing-in region can exert a strong influence on the relative abundance of various ionization stages in the solar wind, and so independent knowledge of ion flow speeds at the base will be needed if coronal temperatures are to be accurately inferred from solar wind ionization state measurements. Finally, because ionization occurs through collisions with electrons with energies above the ionization threshold, the ionization rate can be greatly increased in a non-Maxwellian electron distribution function with an enhanced high-energy tail. The ionization balances of some species are more sensitive to this high-energy tail than others, and so observations of the interplanetary ionization state of several species could be potentially exploited to constrain possible values of both the "core" and "tail" electron temperatures at the base of the solar wind.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1982
- Bibcode:
- 1982PhDT.........2O
- Keywords:
-
- Physics: Astronomy and Astrophysics;
- Electron Distribution;
- Interplanetary Gas;
- Ionization;
- Photosphere;
- Solar Corona;
- Solar Wind;
- Electron Energy;
- Hypotheses;
- Maxwell-Boltzmann Density Function;
- Solar Physics