The nonlinear coupling of electromagnetic ion cyclotron and lower hybrid waves in the ring current region: the magnetic storm 1-7May 1998

Abstract

Abstract. The excitation of lower hybrid waves (LHWs) is a widely discussed mechanism of interaction between plasma species in space, and is one of the unresolved questions of magnetospheric multi-ion plasmas. In this paper we present the morphology, dynamics, and level of LHW activity generated by electromagnetic ion cyclotron (EMIC) waves during the 2-7 May 1998 storm period on the global scale. The LHWs were calculated based on a newly developed selfconsistent model (Khazanov et. al., 2002) that couples the system of two kinetic equations: one equation describes the ring current (RC) ion dynamic, and another equation describes the evolution of EMIC waves. It is found that the LHWs are excited by helium ions due to their mass dependent drift in the electric field of EMIC waves. The level of LHW activity is calculated assuming that the induced scattering process is the main saturation mechanism for these waves. The calculated LHWs electric fields are consistent with the observational data.

Strong pitch-angle diffusion of ring current ions in geomagnetic storm-associated conditions

“…It is also a storm that has been previously studied by this group (Khazanov et al, 2002(Khazanov et al, , 2003a, where the influence of self-consistently calculated ion cyclotron waves were examined (particularly the effects in the late recovery phase) as well as nonlinear coupling of EMIC and lower hybrid waves (Khazanov et al, 2004a). In this paper, as we point out above, the analysis focuses on answering the following question: Do EMIC waves cause strong pitch-angle diffusion of RC ions?…”

Reply to comment by R. M. Thorne and R. B. Horne on Khazanov et al. [2002] and Khazanov et al. [2006]

“…The nonlinear interaction of large amplitude EMIC waves, for example, the modulational instability that results in generation of solitons and is described by the derivative nonlinear Schrodinger equation [ Gamayunov and Khazanov , 1995, and references therein], leads to phase correlation, and in such a system the wave‐ion interaction is quite different in comparison with a quasi‐linear approach. Another possible mechanism of nonlinear EMIC wave saturation is due to lower hybrid wave generation with subsequent nonlinear scattering and Landau damping on thermal plasma [e.g., Gamayunov et al , 1992; Khazanov et al , 1997, 2004a]. In order to describe the latter nonlinear process, a full kinetic particle‐in‐cell (PIC) code should be used (for initial results, see Singh and Khazanov [2004] and Singh et al [2007]), and the hybrid model suggested for use by TH2007 is not an appropriate tool for modeling that process because the hybrid model treats electrons as a massless fluid.…”

Lower hybrid frequency range waves generated by ion polarization drift due to electromagnetic ion cyclotron waves: Analysis of an event observed by the Van Allen Probe B

“…The assumption of potentiality of the LHFR waves and smallness of their growth rate compared to their frequency, used by Khazanov et al . [, , , ], is removed in this modeling.…”

“…Such ions may have a larger polarization drift velocity in the pumping wave packet. Excitation of LHWs by the polarization ion drift in multicomponent plasmas was studied by Khazanov et al [1997aKhazanov et al [ , 1997bKhazanov et al [ , 2004. They applied these results to the ring current dynamics and considered the impact of LHWs generated by ion cyclotron waves on plasma energization, particle acceleration, and ion cyclotron wave saturation.…”

“…The time dynamics of these growth rates, their frequency distribution, and the frequency dependence of the ratio of the LHFR wave power spectral density (PSD) parallel and perpendicular to the ambient magnetic field to the total PSD were found and compared with the observations. The assumption of potentiality of the LHFR waves and smallness of their growth rate compared to their frequency, used by Khazanov et al [1996Khazanov et al [ , 1997aKhazanov et al [ , 1997bKhazanov et al [ , 2004, is removed in this modeling.…”