Direct evidence of non-ideal MHD in the solar wind and switchbacks
Abstract
The low frequency solar wind and its switchbacks are sometimes characterized as ideal-MHD plasmas containing Alfvenic turbulence and, sometimes, as non-ideal plasmas whose turbulence cannot be Alfvenic. The reason for this ambiguity is that definitive measurements of electric fields in the plasma rest frame at fluid frequencies have not been made and such measurements rule out the possibility of one or the other of the two modes. The FIELDS electric field measurement on the Parker Solar Probe is capable of such measurements which are reported in this paper. At radial distances less than 40 solar radii on orbit 10, perpendicular and parallel electric fields in the plasma rest frame at frequencies of 0.01 to 0.1 Hz and over a broad frequency range are observed. The parallel electric fields survive in the presence of calibration errors because their amplitude, but not their existence, is affected by them. Errors in the perpendicular electric field or the solar wind velocity can produce large errors in the plasma rest frame perpendicular electric field because it is the difference of two large quantities, the electric field and the negative velocity-cross-magnetic-field. Evidence is presented that this does not happen, at least much of the time. Because both perpendicular and parallel electric fields in the plasma rest frame are observed at low frequencies, the solar wind and its switchbacks reside in a non ideal magnetohydrodynamic environment. Consequently, standard ideal MHD treatments, including ideal Alfven, slow, and fast wave formulations, cannot adequately describe the turbulent solar wind dynamics. Similar considerations may apply in other astrophysical plasmas.
Related
- Effects of Alfvénicity on the compressible energy cascade in magnetohydrodynamic solar-wind turbulence: Evidence from Parker Solar Probe, Solar Orbiter, and WIND observations
- Direct Four-Spacecraft Measurement of Reconnection Exhaust Thickness in the Solar Wind
- Effects of Alfvénicity on the Compressible Energy Cascade in Magnetohydrodynamic Solar Wind Turbulence: Evidence from Parker Solar Probe, Solar Orbiter, and WIND observations
- Direct Measurement of Polar Coronal Hole-like Solar Wind in Its Acceleration Phase
- Direct Measurement of Polar Coronal Hole-like Solar Wind in its Acceleration Phase
BibTeX
@misc{mozer2026direct,
title = {{Direct evidence of non-ideal MHD in the solar wind and switchbacks}},
author = {Forrest Mozer and Oleksiy Agapitov and Kyung-Eun Choi and Richard Sydora},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2605.14114},
eprint = {2605.14114},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2605.14114},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Direct evidence of non-ideal MHD in the solar wind and switchbacks
AU - Forrest Mozer
AU - Oleksiy Agapitov
AU - Kyung-Eun Choi
AU - Richard Sydora
PY - 2026
DA - 2026/11/02
PB - arXiv
DO - 10.48550/arxiv.2605.14114
UR - https://arxiv.org/abs/2605.14114
AB - The low frequency solar wind and its switchbacks are sometimes characterized as ideal-MHD plasmas containing Alfvenic turbulence and, sometimes, as non-ideal plasmas whose turbulence cannot be Alfvenic. The reason for this ambiguity is that definitive measurements of electric fields in the plasma rest frame at fluid frequencies have not been made and such measurements rule out the possibility of one or the other of the two modes. The FIELDS electric field measurement on the Parker Solar Probe is capable of such measurements which are reported in this paper. At radial distances less than 40 solar radii on orbit 10, perpendicular and parallel electric fields in the plasma rest frame at frequencies of 0.01 to 0.1 Hz and over a broad frequency range are observed. The parallel electric fields survive in the presence of calibration errors because their amplitude, but not their existence, is affected by them. Errors in the perpendicular electric field or the solar wind velocity can produce large errors in the plasma rest frame perpendicular electric field because it is the difference of two large quantities, the electric field and the negative velocity-cross-magnetic-field. Evidence is presented that this does not happen, at least much of the time. Because both perpendicular and parallel electric fields in the plasma rest frame are observed at low frequencies, the solar wind and its switchbacks reside in a non ideal magnetohydrodynamic environment. Consequently, standard ideal MHD treatments, including ideal Alfven, slow, and fast wave formulations, cannot adequately describe the turbulent solar wind dynamics. Similar considerations may apply in other astrophysical plasmas.
ER -