Abstract
Abstract A statistical analysis of 15,210 electron velocity distribution function (VDF) fits, observed within ±2 hr of 52 interplanetary (IP) shocks by the Wind spacecraft near 1 au, is presented. This is the second in a three-part series on electron VDFs near IP shocks. The electron velocity moment statistics for the dense, low-energy core, tenuous, hot halo, and field-aligned beam/strahl are a statistically significant list of values illustrated with both histograms and tabular lists for reference and baselines in future work. Given the large statistics in this investigation, the beam/strahl fit results in the upstream are now the most comprehensive attempt to parameterize the beam/strahl electron velocity moments in the ambient solar wind. The median density, temperature, beta, and temperature anisotropy values for the core(halo)[beam/strahl] components, with subscripts ec(eh)[eb], of all fit results, respectively, are , , , and . This work will also serve as a 1 au baseline and reference for missions like Parker Solar Probe and Solar Orbiter.
Highlights
Background and MotivationThe solar wind is a nonequilibrium, collisionless, ionized, kinetic gas that propagates away from the Sun at supersonic speeds (e.g., Kasper et al 2006; Wilson et al 2018, and references therein)
We include appendices that provide additional details for the reader on the parameter definitions (Appendix A), numerical velocity moment integration methodology (Appendix B), extra statistical tables and histograms (Appendix C) that show one-variable statistics separated by different selection criteria defined in Section 2, and a literature review of previous electron velocity distribution function (VDF) studies in the near-Earth solar wind (Appendix D) for reference and direct comparison with the results presented
Data from tables show one-variable statistics of parameters from the electron VDF fit results, found within ±2 hr of 52 IP shocks found in the Wind shock database from the Harvard Smithsonian Center for Astrophysics15 between 1995 February 26 and 2000 February 20
Summary
The solar wind is a nonequilibrium, collisionless (or weakly collisional), ionized, kinetic gas that propagates away from the Sun at supersonic speeds (e.g., Kasper et al 2006; Wilson et al 2018, and references therein). There is a dearth of statistical results for suprathermal electron velocity moments in the solar wind (for comparison to previous work and this work, see Appendix D for lists of electron parameters in tabular form), especially studies that separate the electron distribution into at least the three dominant components (e.g., Štverák et al 2009): the cold, dense core with energies Eec 15 eV; the hot, tenuous halo with Eeh 20 eV; and the antisunward, field-aligned beam called the strahl with Eeb ∼ few × 10 eV. We include appendices that provide additional details for the reader on the parameter definitions (Appendix A), numerical velocity moment integration methodology (Appendix B), extra statistical tables and histograms (Appendix C) that show one-variable statistics separated by different selection criteria defined, and a literature review of previous electron VDF studies in the near-Earth solar wind (Appendix D) for reference and direct comparison with the results presented We include appendices that provide additional details for the reader on the parameter definitions (Appendix A), numerical velocity moment integration methodology (Appendix B), extra statistical tables and histograms (Appendix C) that show one-variable statistics separated by different selection criteria defined in Section 2, and a literature review of previous electron VDF studies in the near-Earth solar wind (Appendix D) for reference and direct comparison with the results presented
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