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1. The Solar Orbiter magnetometer

   https://doi.org/10.1051/0004-6361/201937257  

   Horbury, T. S. ; O’Brien, H. ; Carrasco Blazquez, I. ; Bendyk, M. ; Brown, P. ; Hudson, R. ; Evans, V. ; Oddy, T. M. ; Carr, C. M. ; Beek, T. J. ; et al ( October 2020 , Astronomy & Astrophysics)

   null (Ed.)

   The magnetometer instrument on the Solar Orbiter mission is designed to measure the magnetic field local to the spacecraft continuously for the entire mission duration. The need to characterise not only the background magnetic field but also its variations on scales from far above to well below the proton gyroscale result in challenging requirements on stability, precision, and noise, as well as magnetic and operational limitations on both the spacecraft and other instruments. The challenging vibration and thermal environment has led to significant development of the mechanical sensor design. The overall instrument design, performance, data products, and operational strategy are described. 

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2. Ion Kinetics of Plasma Flows: Earth's Magnetosheath versus Solar Wind

   https://doi.org/10.3847/1538-4357/ac96e4  

   Artemyev, A. V. ; Shi, C. ; Lin, Y. ; Nishimura, Y. ; Gonzalez, C. ; Verniero, J. ; Wang, X. ; Velli, M. ; Tenerani, A. ; Sioulas, N. ( November 2022 , The Astrophysical Journal)

   Revealing the formation, dynamics, and contribution to plasma heating of magnetic field fluctuations in the solar wind is an important task for heliospheric physics and for a general plasma turbulence theory. Spacecraft observations in the solar wind are limited to spatially localized measurements, so that the evolution of fluctuation properties with solar wind propagation is mostly studied via statistical analyses of data sets collected by different spacecraft at various radial distances from the Sun. In this study we investigate the evolution of turbulence in the Earth’s magnetosheath, a plasma system sharing many properties with the solar wind. The near-Earth space environment is being explored by multiple spacecraft missions, which may allow us to trace the evolution of magnetosheath fluctuations with simultaneous measurements at different distances from their origin, the Earth’s bow shock. We compare ARTEMIS and Magnetospheric Multiscale (MMS) Mission measurements in the Earth magnetosheath and Parker Solar Probe measurements of the solar wind at different radial distances. The comparison is supported by three numerical simulations of the magnetosheath magnetic and plasma fluctuations: global hybrid simulation resolving ion kinetic and including effects of Earth’s dipole field and realistic bow shock, hybrid and Hall-MHD simulations in expanding boxes that mimic the magnetosheath volume expansion with the radial distance from the dayside bow shock. The comparison shows that the magnetosheath can be considered as a miniaturized version of the solar wind system with much stronger plasma thermal anisotropy and an almost equal amount of forward and backward propagating Alfvén waves. Thus, many processes, such as turbulence development and kinetic instability contributions to plasma heating, occurring on slow timescales and over large distances in the solar wind, occur more rapidly in the magnetosheath and can be investigated in detail by multiple near-Earth spacecraft.

    

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3. On the Local Structure of Stochastic Parker Spirals in the Solar Wind

   https://doi.org/10.3847/1538-4357/aca279  

   Bian, N. H. ; Li, Gang ( December 2022 , The Astrophysical Journal)

   Abstract We present a Langevin model describing the local structure of the interplanetary magnetic field lines. It is established on the basis of the analysis of the Lagrangian properties of strong Alfvénic turbulence, which provides a new perspective on the critical balance condition. The model is consistent with the k ∥ − 2 spectrum of magnetic fluctuations derived from in situ measurements. We show that the magnetic field line diffusivity at the spacecraft position can be inferred from the wavelet analysis of one-point measurements of the fluctuating magnetic fields in the solar wind independently of the three-dimensional nature of the anisotropy. 

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4. Linear Mode Decomposition in Magnetohydrodynamics Revisited

   https://doi.org/10.3847/1538-4365/acdf5d  

   Zank, G. P. ; Zhao, L. -L. ; Adhikari, L. ; Nakanotani, M. ; Pitňa, A. ; Telloni, D. ; Che, H. ( August 2023 , The Astrophysical Journal Supplement Series)

   Small-amplitude fluctuations in the magnetized solar wind are measured typically by a single spacecraft. In the magnetohydrodynamics (MHD) description, fluctuations are typically expressed in terms of the fundamental modes admitted by the system. An important question is how to resolve an observed set of fluctuations, typically plasma moments such as the density, velocity, pressure, and magnetic field fluctuations, into their constituent fundamental MHD modal components. Despite its importance in understanding the basic elements of waves and turbulence in the solar wind, this problem has not yet been fully resolved. Here, we introduce a new method that identifies between wave modes and advected structures such as magnetic islands or entropy modes and computes the phase information associated with the eligible MHD modes. The mode-decomposition method developed here identifies the admissible modes in an MHD plasma from a set of plasma and magnetic field fluctuations measured by a single spacecraft at a specific frequency and an inferred wavenumberk_m. We present data from three typical intervals measured by the Wind and Solar Orbiter spacecraft at ∼1 au and show how the new method identifies both propagating (wave) and nonpropagating (structures) modes, including entropy and magnetic island modes. This allows us to identify and characterize the separate MHD modes in an observed plasma parcel and to derive wavenumber spectra of entropic density, fast and slow magnetosonic, Alfvénic, and magnetic island fluctuations for the first time. These results help identify the fundamental building blocks of turbulence in the magnetized solar wind.

    

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5. Cross‐Comparison of Observations With the Predictions of Global Hybrid Simulations for Multiple IMF Discontinuities Impacting the Bow Shock and Magnetosheath

   https://doi.org/10.1029/2023JA032328  

   Lee, S H ; Sibeck, D G ; Wang, X ; Lin, Y ; Angelopoulos, V ; Giles, B L ; Torbert, R B ; Russell, C T ; Wei, H ; Burch, J L ( April 2024 , Journal of Geophysical Research: Space Physics)

   We use the three‐dimensional (3‐D) global hybrid code ANGIE3D to simulate the interaction of four solar wind tangential discontinuities (TDs) observed by ARTEMIS P1 from 0740 UT to 0800 UT on 28 December 2019 with the bow shock, magnetosheath, and magnetosphere. We demonstrate how the four discontinuities produce foreshock transients, a magnetosheath cavity‐like structure, and a brief magnetopause crossing observed by THEMIS and MMS spacecraft from 0800 UT to 0830 UT. THEMIS D observed entries into foreshock transients exhibiting low density, low magnetic field strength, and high temperature cores bounded by compressional regions with high densities and high magnetic field strengths. The MMS spacecraft observed cavities with strongly depressed magnetic field strengths and highly deflected velocity in the magnetosheath downstream from the foreshock. Dawnside THEMIS A magnetosheath observations indicate a brief magnetosphere entry exhibiting enhanced magnetic field strength, low density, and decreased and deflected velocity (sunward flow). The solar wind inputs into the 3‐D hybrid simulations resemble those seen by ARTEMIS. We simulate the interaction of four oblique TDs with properties similar to those in the observation. We place virtual spacecraft at the locations where observations were made. The hybrid simulations predict similar characteristics of the foreshock transients, a magnetosheath cavity, and a magnetopause crossing with characteristics similar to those observed by the multi‐spacecraft observations. The detailed and successful comparison of the interaction involving multiple TDs will be presented.

    

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