Zhu, X;
He, J;
Verscharen, D;
Zhao, J;
(2019)
Composition of wave modes in magnetosheath turbulence from sub-ion to sub-electron scales.
The Astrophysical Journal
, 878
(48)
10.3847/1538-4357/ab1be7.
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Abstract
The nature of plasma turbulence remains unclear at kinetic scales, especially sub17 electron scales. We simultaneously investigate spectra of magnetic and electric fields from proton scales (~1 Hz) down to sub-electron scales (~1 kHz) using MMS measurements in the magnetosheath turbulence. We find that magnetic field spectra exhibit identical behavior between ion and electron scales, while bifurcate at about 30 Hz (around electron inertial scale) and then aggregate around 1 kHz (around electron gyrofrequency). Kinetic Alfvén waves (KAWs) are identified in the range from 1 Hz to 30 Hz: (1) the power spectral indices of PSD(B) and PSD(E) are about -3 and -1; (2) parallel magnetic and electric fluctuations are present but subdominant. Magnetic 25 field spectra obtained from postnoon region events show a clear spectral enhancement, which is identified as quasi-parallel whistler waves (WWs). Electric field spectra present a wide bulge around 800Hz, which is also seen as island-like patterns in the time-period wavelet spectra. The electric field spectral enhancement is dominated by field-parallel fluctuations and is, therefore, diagnosed as ion acoustic waves (IAWs). We also perform a quantitative analysis of the multiple mode types using polarization predictions from two-fluid theory. We obtain the energy partition of electromagnetic fields for different wave modes and successfully reproduce the observed PSDs of B⊥, B∥, E⊥, and E∥. Our findings suggest that the magnetosheath turbulence consists of a mixture of multiple wave modes (KAW, WW, and IAW) in the range from sub-ion scales to sub-electron scales.
| Type: | Article |
|---|---|
| Title: | Composition of wave modes in magnetosheath turbulence from sub-ion to sub-electron scales |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.3847/1538-4357/ab1be7 |
| Publisher version: | https://doi.org/10.3847/1538-4357/ab1be7 |
| Language: | English |
| Additional information: | This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions. |
| Keywords: | turbulence; waves |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10072853 |
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