ON THE POSSIBLE EXCITATION OF ELECTROMAGNETIC ION-CYCLOTRON WAVES IN SOLAR EJECTA

We study the possibility of exciting electromagnetic ion cyclotron wav es (EICWs) in solar ejecta (CMEs) by a kinetic instability driven by i on temperature anisotropies. Our approach is to vary key parameters ab out assumed baseline values. Since T-p,T-parallel to > T-p,T-perpendic ular to in most solar ejecta, the polarization of the unstable waves i s right-handed. If the average proton beta is low (beta(p) less than o r equal to 0.3), the activity is negligible for moderate temperature r atios, T-p,T-parallel to/T-p,T-perpendicular to. Increasing beta(p) in creases both the frequency range and the instability growth rate. Incr easing the temperature anisotropy brings about qualitatively similar e ffects as increasing beta(p), with comparable growth rates. Increasing the relative alpha-to-proton density ratio eta has two effects: the a ctive frequency range is shifted toward lower frequencies and the grow th rate increases. Between eta = 0 and eta = 0.15, the maximum growth rate increases by a factor of similar to 20, highlighting the importan ce of the alphas for generating this instability. A case that may repr esent some magnetic clouds with exceptional parameters, beta(p) = 0.2, T-p,T-parallel to/T-p,T-perpendicular to = 10, and eta = 0.08 - 0.15, is considered. The maximum growth rate is found to be twice the refer ence CME case, while the active frequency range is 3 times wider. We c onclude that EICWs should be present in some ejecta and possibly also in those magnetic clouds with relatively weak magnetic field, high He+ content, and large T-p,T-parallel to/T-p,T-perpendicular to ratios, and whose beta(p) is high, for example, through interaction with a suc ceeding fast stream. We also suggest that substantial changes with res pect to normal conditions should occur in the power spectrum of EICWs in the terrestrial plasma depletion layer when a CME, or a magnetic cl oud, with negative anisotropy passes Earth.