On the possible excitation of electromagnetic ion cyclotron waves in solar ejecta

Details On the possible excitation of electromagnetic ion cyclotron waves in solar ejecta On the possible excitation of electromagnetic ion cyclotron waves in solar ejecta

Apr 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998jgr...103.6543f&link_type=abstract

Journal of Geophysical Research, vol. 103, p. 6543

Physics

7

Coronal Mass Ejection, Ion Cyclotron Radiation, Magnetohydrodynamic Stability, Electromagnetic Radiation, Proton Density (Concentration), Helium Ions, Kinetic Equations, Solar Protons, Plasma Layers

Scientific paper

We study the possibility of exciting electromagnetic ion cyclotron waves (EICWs) in solar ejecta by a kinetic instability driven by ion temperature anisotropies. Our approach is to vary key parameters about assumed baseline values. Since T(p, parallel) is greater than T(p, perpendicular) in most solar ejecta, the polarization of the unstable waves is right-handed. If the average proton beta is low, the activity is negligible for moderate temperature ratios T(p, parallel)/T(p, perpendicular). Increasing beta(p) increases both the frequency range and the instability growth rate. Increasing the temperature anisotropy brings about qualitatively similar effects as increasing beta(p), with comparable growth rates. Increasing the relative alpha-to-proton density ratio eta has two effects: the active frequency range is shifted toward lower frequencies and the growth rate increases. Between eta = 0 and eta = 0.15, the maximum growth rate increases by a factor of about 20, highlighting the importance of the alphas for generating this instability. A case that may represent some magnetic clouds with exceptional parameters, beta(p) = 0.2, T(p, parallel)/T(p, perpendicular) = 10, and eta = 0.08-0.15, is considered. The maximum growth rate is found to be twice the reference CME case, while the active frequency range is three times wider. We conclude that EICWs should be present in some ejecta and possibly also in some magnetic clouds.

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