Woodham, LD;
Wicks, RT;
Verscharen, D;
Owen, CJ;
(2018)
The Role of Proton Cyclotron Resonance as a Dissipation Mechanism in Solar Wind Turbulence: A Statistical Study at Ion-kinetic Scales.
The Astrophysical Journal
, 856
(1)
, Article 49. 10.3847/1538-4357/aab03d.
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Abstract
We use magnetic field and ion moment data from the MFI and SWE instruments on board the Wind spacecraft to study the nature of solar wind turbulence at ion-kinetic scales. We analyze the spectral properties of magnetic field fluctuations between 0.1 and 5.4 Hz during 2012 using an automated routine, computing high-resolution 92 s power and magnetic helicity spectra. To ensure the spectral features are physical, we make the first in-flight measurement of the MFI "noise-floor" using tail-lobe crossings of the Earth's magnetosphere during early 2004. We utilize Taylor's hypothesis to Doppler-shift into the spacecraft frequency frame, finding that the spectral break observed at these frequencies is best associated with the proton cyclotron resonance scale, 1/k_c, rather than the proton inertial length, d_i , or proton gyroscale, ρ_i . This agreement is strongest when we consider periods where {\beta }_{i,\perp }\sim 1, and is consistent with a spectral break at d_i for {\beta }_{i,\perp }\ll 1 and at ρ_i for {\beta }_{i,\perp }\gg 1. We also find that the coherent magnetic helicity signature observed at these frequencies is bounded at low frequencies by 1/k_c , and its absolute value reaches a maximum at ρ_i . These results hold in both slow and fast wind streams, but with a better correlation in the more Alfvénic fast wind where the helicity signature is strongest. We conclude that these findings are consistent with proton cyclotron resonance as an important mechanism for dissipation of turbulent energy in the solar wind, occurring at least half the time in our selected interval. However, we do not rule out additional mechanisms.
| Type: | Article |
|---|---|
| Title: | The Role of Proton Cyclotron Resonance as a Dissipation Mechanism in Solar Wind Turbulence: A Statistical Study at Ion-kinetic Scales |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.3847/1538-4357/aab03d |
| Publisher version: | https://doi.org/10.3847/1538-4357/aab03d |
| Language: | English |
| Additional information: | © 2018. The American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence (https://creativecommons.org/licenses/by/3.0/). |
| Keywords: | plasmas, solar wind, Sun: heliosphere, 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 UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics > Advanced Instrumentation Systems |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10046317 |
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