A Majority of Solar Wind Intervals Support Ion-Driven Instabilities
| Autor: | Klein, K. G., Alterman, B. A., Stevens, M. L., Vech, D., Kasper, J. C. |
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| Rok vydání: | 2018 |
| Předmět: | |
| Druh dokumentu: | Working Paper |
| DOI: | 10.1103/PhysRevLett.120.205102 |
| Popis: | We perform a statistical assessment of solar wind stability at 1 AU against ion sources of free energy using Nyquist's instability criterion. In contrast to typically employed threshold models which consider a single free-energy source, this method includes the effects of proton and He$^{2+}$ temperature anisotropy with respect to the background magnetic field as well as relative drifts between the proton core, proton beam, and He$^{2+}$ components on stability. Of 309 randomly selected spectra from the Wind spacecraft, $53.7\%$ are unstable when the ion components are modeled as drifting bi-Maxwellians; only $4.5\%$ of the spectra are unstable to long-wavelength instabilities. A majority of the instabilities occur for spectra where a proton beam is resolved. Nearly all observed instabilities have growth rates $\gamma$ slower than instrumental and ion-kinetic-scale timescales. Unstable spectra are associated with relatively-large He$^{2+}$ drift speeds and/or a departure of the core proton temperature from isotropy; other parametric dependencies of unstable spectra are also identified. Comment: 6 pages, 3 figures, 2 tables, accepted in Physical Review Letters; fixed typos in version 2 |
| Databáze: | arXiv |
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