On Stochastic Ion Heating in the Inner Heliosphere: Radial Trends and Parker Solar Probe Observations

ORAL

Abstract

Stochastic heating (SH) is a non-linear plasma heating mechanism, frequently proposed as a candidate to explain the strong heating of the solar wind ions perpendicular to the magnetic field. It is driven by the violation of magnetic moment invariance due to large-amplitude, low-frequency Alfvenic turbulent fluctuations. Using Helios and Parker Solar Probe (PSP) observations, we track the radial variation of SH throughout the inner heliosphere from 0.16 to 1 au. We find that SH is increasingly important as one observes plasma closer to the Sun, specifically that the stochastic heating rate varies as $Q_{SH} \sim r^{-2.5}$. In accordance with theoretical predictions, observations of flattop shaped proton velocity distributions are characteristic for periods where SH is predicted to be a dominant heating mechanism. We also find that $Q_{SH}$ does not significantly vary inside intermittent structures, such as switchbacks regularly measured by PSP.

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Authors

  • Mihailo Martinovic

    Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA.

  • Kristopher Klein

    University of Arizona, Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA.

  • Benjamin Chandran

    Department of Physics & Astronomy, University of New Hampshire, Durham, NH 03824, USA

  • Jia Huang

    Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI 48109, USA

  • Emily Lichko

    Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA.

  • Justin Kasper

    Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI 48109, USA

  • Michael Stevens

    Smithsonian Astrophysical Observatory, Cambridge, MA 02138 USA.

  • Sofiane Bourouaine

    Department of Aerospace, Physics and Space Sciences, Florida Institute of Technology, 150 W Univeristy Blvd, Melbourne, Fl, 32901, USA