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- Title
Solar Wind Current Sheets: MVA Inaccuracy and Recommended Single‐Spacecraft Methodology.
- Authors
Wang, R.; Vasko, I. Y.; Phan, T. D.; Mozer, F. S.
- Abstract
We present the analysis of 1,831 current sheets (CS) observed aboard four Cluster spacecraft in a pristine solar wind. Four‐spacecraft estimates of the CS normal and propagation velocity are compared with different single‐spacecraft estimates. The Minimum Variance Analysis (MVA) of the magnetic field is shown to be highly inaccurate in estimating the normal. The MVA normal often differs by more than 60° from the normal obtained by multi‐spacecraft timing method, likely due to ambient turbulent fluctuations. In contrast, the cross‐product of magnetic fields at the CS boundaries delivers the normal with an uncertainty of less than 15° at the confidence level of 90%. The CSs are essentially frozen into plasma flow, since their propagation velocity is consistent with local ion flow velocity within 20% at the confidence level of 90%. The single‐spacecraft methodology based on the cross‐product method and frozen‐in assumption delivers the CS thickness and current density amplitude within 20% of their actual values at the confidence level of 90%. The CSs are kinetic‐scale structures with half‐thickness λ from a few tenths to tens of local proton inertial length λp and scale‐dependent shear angle and current density amplitude, Δθ∝λ/λp0.5 ${\Delta }\theta \propto {\left(\lambda /{\lambda }_{p}\right)}^{0.5}$ and J0∝λ/λp−0.5 ${J}_{0}\propto {\left(\lambda /{\lambda }_{p}\right)}^{-0.5}$. The classification of the CSs in terms of tangential and rotational discontinuities remains a challenge, because even the four‐spacecraft normal has too large uncertainties to reveal the actual normal magnetic field component. The presented results will be valuable for the analysis of solar wind CSs, when only single‐spacecraft measurements are available. Plain Language Summary: Current sheets (CS) are sharp magnetic field rotations that could play a role in solar wind heating. These locally planar one‐dimensional structures are highly likely produced by turbulence cascade, though some may originate in solar corona. Most of the studies of solar wind CSs were carried out using single‐spacecraft measurements, the CS normal was typically computed using Minimum Variance Analysis (MVA), and the other CS properties were estimated using that normal. In this study we present multi‐spacecraft analysis of 1,831 CSs observed aboard four Cluster spacecraft and determine the CS normal using four‐spacecraft observations. We demonstrate that MVA is highly inaccurate in estimating the CS normal, while the cross‐product of magnetic fields at the CS boundaries delivers accurate estimates of the normal. We show that the single‐spacecraft methodology based on the cross‐product normal and the assumption that solar wind CSs are frozen into local plasma flow provides accurate estimates of the CS thickness and current density. This single‐spacecraft methodology assumes zero normal component of the magnetic field and does not allow classifying CSs in terms of tangential and rotational discontinuities, but we show that because of methodology uncertainties four‐spacecraft observations do not allow carrying out such a classification either. Key Points: Four‐spacecraft observations are used to estimate the normal and propagation velocity for more than 1,800 current sheets at 1 AUMVA is highly inaccurate in estimating the current sheet normal, while the cross‐product method delivers accurate estimatesSingle‐spacecraft methodology based on the cross‐product normal and frozen‐in assumption is accurate in estimating current sheet properties
- Subjects
CURRENT sheets; SOLAR corona; MAGNETIC fields; PLASMA flow; SOLAR wind; SOLAR heating; SOLAR cycle; PLASMA turbulence
- Publication
Journal of Geophysical Research. Space Physics, 2024, Vol 129, Issue 2, p1
- ISSN
2169-9380
- Publication type
Article
- DOI
10.1029/2023JA032215