# Editorial: Kinetic plasma dynamics in the light of novel in situ heliospheric observations: synergistic view with theories and simulations

Parisa Mostafavi, Rungployphan Kieokaew, Trevor Bowen, Daniele Telloni

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Parisa Mostafavi, Rungployphan Kieokaew, Trevor Bowen, Daniele Telloni. Editorial: Kinetic plasma dynamics in the light of novel in situ heliospheric observations: synergistic view with theories and simulations. Frontiers in Astronomy and Space Sciences, 2024, 11, 10.3389/fspas.2024.1491455. hal-04919118

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OPEN ACCESS

EDITED AND REVIEWED BY
Scott William McIntosh,
National Center for Atmospheric Research
(UCAR), United States

*CORRESPONDENCE
Parisa Mostafavi,
✉ parisamostafavi@jhuapl.edu

RECEIVED 04 September 2024

ACCEPTED 17 September 2024

PUBLISHED 26 September 2024

CITATION

Mostafavi P, Kieokaew R, Bowen T and Telloni D (2024) Editorial: Kinetic plasma dynamics in the light of novel *in situ* heliospheric observations: synergistic view with theories and simulations.
*Front. Astron. Space Sci.* 11:1491455.
doi: 10.3389/fspas.2024.1491455

COPYRIGHT

© 2024 Mostafavi, Kieokaew, Bowen and Telloni. This is an open-access article distributed under the terms of the [Creative Commons Attribution License (CC BY)](https://creativecommons.org/licenses/by/4.0/). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

# Editorial: Kinetic plasma dynamics in the light of novel *in situ* heliospheric observations: synergistic view with theories and simulations

Parisa Mostafavi¹*, Rungployphan Kieokaew², Trevor Bowen³ and Daniele Telloni⁴

¹Johns Hopkins Applied Physics Laboratory, Laurel, MD, United States, ²Institut de Recherche en Astrophysique et Planétologie, CNRS, UPS, CNES, Toulouse, France, ³Space Sciences Laboratory, University of California, Berkeley, Berkeley, CA, United States, ⁴National Institute for Astrophysics, Astrophysical Observatory of Torino, Turin, Italy

KEYWORDS

heliosphere, space plasma, turbulence, solar wind, pickup ions, numerical simulation, space missions, collisions

## Editorial on the Research Topic

### Kinetic plasma dynamics in the light of novel *in situ* heliospheric observations: synergistic view with theories and simulations

The solar wind, a plasma stream emanating from the Sun, consists of various ion species, primarily protons (*H*⁺), alpha particles (*He*²⁺), and minor heavier ions such as *O*⁶⁺ and *Fe*¹²⁺. Despite the presence of dynamic ion populations, which show variable abundances that fluctuate within the background solar wind as well as in structures (e.g., coronal mass ejections, stream interaction regions, etc.), the physics of heating and acceleration of each ion population remains elusive (Robbins et al., 1970; Marsch et al., 1982; von Steiger et al., 1995; Marsch, 2010; Verscharen et al., 2019; Đurovcová et al., 2019; Mostafavi et al., 2022; Mostafavi et al., 2024). Moreover, energetic non-thermal pickup ions (PUIs), which predominantly originate from charge exchanges between interstellar neutral atoms and solar wind ions within the heliosphere (Semar, 1970), play a significant role in the transport of energy, momentum, and mass throughout the outer heliosphere (Burlaga et al., 1996; Zank, 2015; McComas et al., 2017; Zank et al., 1996), yet remain poorly understood.

Each plasma species often exhibits complex distribution functions that deviate from a simple Maxwellian profile, displaying non-Maxwellian features that are critical to understanding their kinetic behavior. These non-Maxwellian distributions are sources of free energy that can drive various kinetic instabilities and wave-particle interactions, processes essential to the heating and acceleration of solar wind ions. Understanding how the solar wind and energetic PUIs react, particularly in relation to turbulence, collisional processing, and large-scale heliospheric dynamics, is key to advancing our knowledge of solar wind behavior and its interactions across different regions of the heliosphere. Space missions such as Parker Solar Probe and Solar Orbiter (near the Sun), IBEX, WIND, and STEREO (at 1 AU), and New Horizons (currently in the outer heliosphere) have opened
new windows into these processes, offering unprecedented *in situ*
and remote measurements from the Sun's vicinity to the far reaches
of the heliosphere.

The primary aim of this Research Topic was to expand our
understanding of the science questions related to the heating and
acceleration of solar wind ions and energetic PUIs, particularly
through non-Maxwellian velocity distributions, wave-particle
interactions, and turbulence in both the inner and outer heliosphere.
This Research Topic hosts four significant contributions that
enhance our understanding of these effects in the solar wind.

Previous observations revealed that solar wind ions exhibit
distinct kinetic non-thermal features such as the differential
flows that suggest preferential acceleration of alpha particles
compared to protons (Ryan and Axford, 1975; Marsch et al.,
1982; Óurovcová et al., 2019; Mostafavi et al., 2022). Additionally,
Coulomb collisions during a transit time of a particle can be
crucial in reducing the ion non-thermal features (Kasper et al.,
2008; Mostafavi et al., 2022; Ran et al., 2024). In this Research Topic,
Johnson et al. introduce an application of collisional analysis to the
alpha-proton differential flow. By comparing *in situ* observations
from the Parker Solar Probe and the Wind spacecraft, they find
strong evidence that Coulomb collisions play significant roles
in shaping the differential flow through the inner heliosphere.
These results underscore the importance of considering collisional
processes in models of solar wind acceleration and heating.

While the role of Coulomb collisions in shaping ion dynamics
is crucial, understanding the mechanisms of energy dissipation
and turbulence in collisionless plasmas is equally important
(Bourouaine et al., 2013). Here, Guerrero Guio et al. advance this
understanding through a detailed investigation into the probability
distribution functions of magnetic field increments, employing
both single-spacecraft and multi-spacecraft approaches. Their study
reveals a transition from Gaussian to non-Gaussian distributions
at smaller scales, indicating the presence of intermittency within
the turbulent cascade. Moreover, they demonstrate that the multi-
point approach tends to underestimate intermittency due to its
focus on larger scales, highlighting the needs for high-resolution
measurements in capturing the true nature of heliospheric
turbulence. This finding is particularly relevant to the upcoming
Helioswarm mission (Klein et al., 2023).

In the outer heliosphere, beyond the ionization cavity which
is about 4 au from the Sun, PUIs become an important source of
turbulence (Zank et al., 1996; Isenberg et al., 2023; Adhikari et al.,
2023). In this Research Topic, Wang et al. explore the temporal
and latitudinal dependence of turbulence driven by PUIs in the
outer heliosphere. Utilizing a latitude-dependent solar wind speed
model and an advanced ionization rate model, this study provides a
comprehensive analysis of the temporal and spatial variation in the
strength of low-frequency turbulence driven by PUIs from 1998 to
2020. They highlight the significant variability in turbulence driving
rates with solar activity and latitude, emphasizing the need for
turbulence transport models to incorporate these dynamic factors
to accurately predict solar wind heating and cosmic ray modulation.

Finally, Odstrcil advances the field of predictive modeling
for space weather events, with a particular focus on multi-CME
interactions within the heliosphere. This paper enhances our
understanding of how multiple coronal mass ejections interact
as they propagate through the heliosphere, a complex process

that can lead to significant space weather impacts on Earth
and throughout the solar system. While this paper primarily
addresses space weather forecasting, its relevance to kinetic plasma
dynamics cannot be understated. The improved modeling tools
and interpretations presented are crucial for understanding how
large-scale heliospheric disturbances affect the solar wind's kinetic
properties, thereby linking space weather events to the broader
theme of solar wind dynamics.

Together, these papers illustrate the significant advancements in
the study of plasma dynamics within the heliosphere, from inner to
outer regions. They reflect a growing synergy between observational
data, theoretical models, and numerical simulations, offering a more
integrated understanding of the solar wind ions, turbulence, non-
thermal energetic PUIs, and space weather phenomena. As we
continue to explore the heliosphere with the current and future
missions and advanced models, the insights from these studies will
be instrumental in guiding future research and improving predictive
models of space physics.

Author contributions

PM: Writing–original draft, Writing–review and editing. RK:
Writing–review and editing. TB: Writing–review and editing. DT:
Writing–review and editing.

Funding

The author(s) declare financial support was received for
the research, authorship, and/or publication of this article.
PM acknowledges the partial support by NASA HGIO grant
80NSSC23K0419, NASA HTMS grant 80NSSC24K0724, and the
NSF SHINE award 2401162. We also acknowledge the support
by NASA SHIELD DRIVE Science Center. RK acknowledges the
support by the French Space Agency (CNES: Centre national
d'études spatiales). PM and RK acknowledge the support by the
International Space Science Institute (ISSI) in Bern, through ISSI
International Team project 563 (Ion Kinetic Instabilities in the
Solar Wind in Light of Parker Solar Probe and Solar Orbiter
Observations). TB acknowledges NASA grant No. 80NSSC24K0272.

Acknowledgments

We sincerely thank all the authors, reviewers and editors who
have participated in this Research Topic.

Conflict of interest

The authors declare that the research was conducted in the
absence of any commercial or financial relationships that could be
construed as a potential conflict of interest.

The author(s) declared that they were an editorial board member
of Frontiers, at the time of submission. This had no impact on the
peer review process and the final decision.
## Publisher's note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated

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