Linear Stability in the Inner Heliosphere: Helios Reëvaluated
arXiv:1912.00250 · doi:10.3847/1538-4357/ab5802
Abstract
Wave-particle instabilities driven by departures from local thermodynamic equilibrium have been conjectured to play a role in governing solar wind dynamics. We calculate the statistical variation of linear stability over a large subset of Helios I and II fast solar wind observations using a numerical evaluation of the Nyquist stability criterion, accounting for multiple sources of free energy associated with protons and helium including temperature anisotropies and relative drifts. We find that 88\% of the surveyed intervals are linearly unstable. The median growth rate of the unstable modes is within an order of magnitude of the turbulent transfer rate, fast enough to potentially impact the turbulent scale-to-scale energy transfer. This rate does not significantly change with radial distance, though the nature of the unstable modes, and which ion components are responsible for driving the instabilities, does vary. The effect of ion-ion collisions on stability is found to be significant; collisionally young wind is much more unstable than collsionally old wind, with very different kinds of instabilities present in the two kinds of wind.
10 Pages, 6 Figures, Accepted in ApJ
References in corpus (4)
- Predicted Impacts of Proton Temperature Anisotropy on Solar Wind Turbulence
- Diagnosing collisionless energy transfer using field-particle correlations: gyrokinetic turbulence
- A zone of preferential ion heating extends tens of solar radii from Sun
- Strong Preferential Ion Heating is Limited to within the Solar Alfven Surface
Cited by in corpus (4)
- Parker Solar Probe observations of proton beams simultaneous with ion-scale waves
- Inferred Linear Stability of Parker Solar Probe Observations using One- and Two-Component Proton Distributions
- The Electromagnetic Signature of Outward Propagating Ion-Scale Waves
- Electromagnetic Proton Beam Instabilities in the Inner Heliosphere: Energy Transfer Rate, Radial Distribution, and Effective Excitation