Inferred Linear Stability of Parker Solar Probe Observations Using One- And Two-component Proton Distributions

K. G. Klein, J. L. Verniero, B. Alterman, S. Bale, A. Case, J. C. Kasper, K. Korreck, D. Larson, E. Lichko, R. Livi, M. McManus, M. Martinović, A. Rahmati, M. Stevens, P. Whittlesey

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


The hot and diffuse nature of the Sun's extended atmosphere allows it to persist in non-equilibrium states for long enough that wave-particle instabilities can arise and modify the evolution of the expanding solar wind. Determining which instabilities arise, and how significant a role they play in governing the dynamics of the solar wind, has been a decades-long process involving in situ observations at a variety of radial distances. With new measurements from the Parker Solar Probe (PSP), we can study what wave modes are driven near the Sun, and calculate what instabilities are predicted for different models of the underlying particle populations. We model two hours-long intervals of PSP/SPAN-i measurements of the proton phase-space density during the PSP's fourth perihelion with the Sun using two commonly used descriptions for the underlying velocity distribution. The linear stability and growth rates associated with the two models are calculated and compared. We find that both selected intervals are susceptible to resonant instabilities, though the growth rates and kinds of modes driven unstable vary depending on whether the protons are modeled using one or two components. In some cases, the predicted growth rates are large enough to compete with other dynamic processes, such as the nonlinear turbulent transfer of energy, in contrast with relatively slower instabilities at larger radial distances from the Sun.

Original languageEnglish (US)
Article number7
JournalAstrophysical Journal
Issue number1
StatePublished - Mar 1 2021

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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