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Linear Stability in the Inner Heliosphere: Helios Re\"evaluated
Solar and Stellar Astrophysics · Submitted 30 Nov 2019
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim We find that 88\% of the surveyed intervals are linearly unstable.
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The abstract, sentence by sentence
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.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Wave-particle instabilities driven by departures from local thermodynamic equilibrium have been conjectured to play a role in governing solar wind dynamics. | background 1.00 | 0.04 | 0.03 | speculative 0.91 |
| s1 | 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. | method 0.85 | 0.97 | 0.05 | asserted 0.98 |
| s2 | We find that 88\% of the surveyed intervals are linearly unstable. | result 1.00 | 0.97 | 0.55 | asserted 1.00 |
| s3 | 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. | result 0.72 | 0.95 | 0.20 | asserted 0.65 |
| s4 | 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. | result 1.00 | 0.93 | 0.14 | asserted 1.00 |
| s5 | 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. | result 1.00 | 0.95 | 0.12 | asserted 1.00 |
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The paper
Original 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.
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2 arXiv papers cite this in 2 sentences
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Cites as background 1 paper
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Departures of particle velocity distributions from local thermodynamic equilibrium in the weakly collisional solar wind are frequently observed (see [ref] and [ref] for a review of such measurements) and are associated with wave-particle instabilities, a class of interactions that act to move particle distributions towards equilibrium while simultaneously emitting a variety of plasma waves.
The multi-scale nature of the solar wind · Introduction · 0.93
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