Electromagnetic Signatures of Kinetic Alfvén Wave Turbulence at Ion Inertial Scales in Earth's High-β Magnetosheath
Abstract
We present a multi-diagnostic electromagnetic analysis of a dayside magnetosheath interval observed by the Magnetospheric Multiscale (MMS) mission on 2015 December 28 at high ion beta (βi = 14.4), using burst-mode measurements. We combine the scale-dependent electric-to-magnetic field ratio, the parallel electric field, the magnetic compressibility, the wave-normal angle and circular-polarization measure, and the ion--electron frozen-in residuals. The electric-to-magnetic field ratio rises with wavenumber with a log--log slope of +0.92, whereas the ideal advection contribution remains flat, supporting dispersive fluctuations. A wave-normal angle of 75∘ and a circular-polarization measure centred near zero support quasi-perpendicular propagation, while the compressibility and the ion temperature anisotropy do not support mirror-mode dominance. A continuous broken power-law fit gives fbreak = 0.48 ± 0.06 Hz, corresponding to k⊥ di = 0.85 ± 0.11 and k⊥ ρi = 3.23 ± 0.42. Because di and ρi are well separated at this βi, the break is more consistent with the ion inertial scale than with the ion gyroscale. Four-spacecraft phase differencing independently supports the Doppler conversion around the break. Above the break, the kinetic-range index is −2.86 ± 0.06 (stat) ± 0.18 (fit window), closer to the weakly damped dispersive limit than to the strongly damped limit, with a fluid-scale index of −1.81 ± 0.08 below it. The observations are consistent with quasi-perpendicular KAW-like turbulence, but do not uniquely identify the mode; the spectral index constrains the cascade rather than the dissipation mechanism.
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BibTeX
@misc{chettri2026electromagnetic,
title = {{Electromagnetic Signatures of Kinetic Alfvén Wave Turbulence at Ion Inertial Scales in Earth's High-$β$ Magnetosheath}},
author = {Mani K Chettri and Rupak Mukherjee and Hemam D. Singh},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2605.25199},
eprint = {2605.25199},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2605.25199},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - Electromagnetic Signatures of Kinetic Alfvén Wave Turbulence at Ion Inertial Scales in Earth's High-β Magnetosheath
AU - Mani K Chettri
AU - Rupak Mukherjee
AU - Hemam D. Singh
PY - 2026
DA - 2026/09/25
PB - arXiv
DO - 10.48550/arxiv.2605.25199
UR - https://arxiv.org/abs/2605.25199
AB - We present a multi-diagnostic electromagnetic analysis of a dayside magnetosheath interval observed by the Magnetospheric Multiscale (MMS) mission on 2015 December 28 at high ion beta (β_i = 14.4), using burst-mode measurements. We combine the scale-dependent electric-to-magnetic field ratio, the parallel electric field, the magnetic compressibility, the wave-normal angle and circular-polarization measure, and the ion--electron frozen-in residuals. The electric-to-magnetic field ratio rises with wavenumber with a log--log slope of +0.92, whereas the ideal advection contribution remains flat, supporting dispersive fluctuations. A wave-normal angle of 75^∘ and a circular-polarization measure centred near zero support quasi-perpendicular propagation, while the compressibility and the ion temperature anisotropy do not support mirror-mode dominance. A continuous broken power-law fit gives f_break = 0.48 ± 0.06 Hz, corresponding to k_⊥ d_i = 0.85 ± 0.11 and k_⊥ ρ_i = 3.23 ± 0.42. Because d_i and ρ_i are well separated at this β_i, the break is more consistent with the ion inertial scale than with the ion gyroscale. Four-spacecraft phase differencing independently supports the Doppler conversion around the break. Above the break, the kinetic-range index is −2.86 ± 0.06 (stat) ± 0.18 (fit window), closer to the weakly damped dispersive limit than to the strongly damped limit, with a fluid-scale index of −1.81 ± 0.08 below it. The observations are consistent with quasi-perpendicular KAW-like turbulence, but do not uniquely identify the mode; the spectral index constrains the cascade rather than the dissipation mechanism.
ER -