In Situ Measurement of Curvature of Magnetic Field in Turbulent Space Plasmas: A Statistical Study

Abstract

Key Points:• We report a statistical study of magnetic-field curvature by MMS • The curvature field is observed to be distributed with distinct powerlaw tails • Magnitude of the curvature and magnetic field are found to be anti-correlated AbstractUsing in situ data, accumulated in the turbulent magnetosheath by the Magnetospheric Multi-Scale (MMS) Mission, we report the first measurements of magnetic field curvature and discuss its role in the turbulent space plasmas. Consistent with previous simulation results, the Probability Distribution Function (PDF) of the curvature is shown to have distinct power-law tails for both high and low value limits. We find that the magneticfield-line curvature is intermittently distributed in space. High curvature values reside near weak magnetic-field regions, while low curvature values are correlated with small magnitude of the force acting normal to the field lines. This novel statistical characterization of magnetic curvature in space plasma provides a starting point for assessing, in a turbulence context, the applicability and impact of particle energization processes, such as curvature drift, that rely on this fundamental quantity. Plain Language SummaryMagnetic fields are observed everywhere in the universe; ranging from the core region of some planets and most stars, to the solar wind, and other astrophysical systems.Most of these systems are in highly turbulent state. The magnetic field in these turbulent systems are twisted and stretched randomly in a complex manner. The quantity, curvature, measures how sharply the magnetic fields are "bent". Curvature is important for studying how charged particles are accelerated and how energy is dissipated in turbulent plasmas. These fast charged particles can be harmful for the spacecraft and onboard astronauts. Energy dissipation, on the other hand, directly controls the electromagnetic environment of Earth's magnetosphere and therefore, controlling the space weather.We investigate, in a statistical way, the magnetic-field curvature from in situ measurement by the National Aeronautics and Space Administration's Magnetospheric Multiscale spacecraft. We find that, using simple theoretical arguments along with the guidance of numerical simulations, we are able to closely predict the statistical behavior of magnetic field curvature in these turbulent systems.

Discontinuity analysis of the leading switchback transition regions

“…On average, the curvature of the reconnecting switchback current sheets is µ κ = −2.38 (±3.65) × 10 −9 [km −1 ]. This value is by several orders of magnitude smaller than curvatures often observed at or near reconnecting current sheets at 1 AU (Akhavan-Tafti et al 2019a;Bandyopadhyay et al 2020;Yang et al 2019;Norgren et al 2018). This may be an artifact of how κ is determined here (using single-spacecraft measurements).…”

“…The color shading shows the average magnetic field intensity inside the switchbacks' leading transition regions, |B| Transition . The figure indicates that (1) there is no clear (anti)correlation between magnetic curvature and |B| Transition (Bandyopadhyay et al 2020) in leading RD-type switchback transition regions (μ |B|,Transition = 43.2 (±16.9) [nT ]), and (2) the reconnecting leading switchback transition regions of Froment et al (2021) are characterized by small and positive relative jump in proton velocity 0 < |V| SPIKE − |V| QL < 0.5 V A,QL . Particlein-Cell (PIC) simulations by Swisdak et al (2003) suggest that diamagnetic drifts can suppress reconnection when the velocity of the convecting structure becomes comparable to the local Alfvén velocity.…”

Large-scale Structure and Turbulence Transport in the Inner Solar Wind: Comparison of Parker Solar Probe’s First Five Orbits with a Global 3D Reynolds-averaged MHD Model

“…Such realizations are clearly not unique, but they permit exploration of how properties of the underlying probability distribution can influence the quality of the comparison with the observations. Interplanetary magnetic fluctuations at 1 au have near-Gaussian probability distributions in the inertial range (e.g., Padhye et al 2001;Bandyopadhyay et al 2020b). However, observations of the near-Sun magnetic field by PSP (Bale et al 2019) indicate that fluctuations in the radial component do not have symmetric distributions; instead, these are biased toward reversals in the magnetic polarity and their probability distributions are characterized by a significant skewness (R. Chhiber 2022, in preparation).…”

Particle transport through localized interactions with sharp magnetic field bends in MHD turbulence

“…Quite remarkably, recent in situ measurements of the statistics of field line curvature in the magnetosheath confirm those findings, in particular at large curvature (Bandyopadhyay et al. 2020; Huang et al. 2020).…”