Obliquely propagating electromagnetic drift ion cyclotron instability

Abstract

[1] Identification of wave characteristics during current disruption events in the near-Earth geomagnetic tail region is important for understanding the substorm onset mechanism. The present paper discusses a linear stability analysis in the ion cyclotron frequency range of a plasma possessing the temperature anisotropy and cross-field flow. It is found that the ion cyclotron drift waves propagating in quasi-perpendicular direction with respect to the ambient magnetic field are characterized by low frequencies (w ] 0.5W i ), while quasi-parallel waves have frequencies close to the ion cyclotron frequency (w ∼ W i ). This finding is consistent with the observation by THEMIS spacecraft of a current disruption event in which similar high-and low-frequency band structures are present. The interpretation of the low-frequency mode as the quasi-perpendicular mode is consistent with a recent data analysis. The present paper shows that the high-frequency quasi-parallel mode can simultaneously be excited with the low-frequency quasi-perpendicular mode.

Magnetic Field Dipolarization and Its Associated Ion Flux Variations in the Dawnside Deep Inner Magnetosphere: Arase Observations

“…It was proposed by Lui et al (), Yoon et al (), and Mok et al () that the magnetic fluctuations during dipolarization are excited by the drift‐driven electromagnetic ion cyclotron (EMIC) instability, in which free energy is supplied from the cross‐field drift motion of magnetized ions. The dispersion relation predicts that they have dominant wave power in the parallel and radial components, and a characteristic frequency near f G (O + ).…”

“…In the present study, we analyzed the Arase/MGF and MEP-i data for the two events of dipolarization found at (r eq , MLT eq )~(5.3 R E , 5.5 hr) and (5.1 R E , 5.7 hr) around 15:00 UT on 27 March 2017. It was found that (1) It was proposed by Lui et al (2008), Yoon et al (2009), and Mok et al (2010) that the magnetic fluctuations during dipolarization are excited by the drift-driven electromagnetic ion cyclotron (EMIC) instability, in which free energy is supplied from the cross-field drift motion of magnetized ions. The dispersion relation predicts that they have dominant wave power in the parallel and radial components, and a characteristic frequency near f G (O + ).…”

Magnetic fluctuations embedded in dipolarization inside geosynchronous orbit and their associated selective acceleration of O+ ions

“…Free energy to excite this type of EMIC waves is supplied from the cross‐field drift motion of magnetized ions instead of temperature anisotropy. The linear theory of the drift‐driven EMIC instability is introduced by Lui et al [] and Mok et al []. They found that the instability includes two types of waves: a wave propagating in the quasi‐perpendicular direction with respect to the magnetic field with low frequency ( X ≪ 0.5) and a wave propagating in the quasi‐parallel direction with X ∼1.…”

“…We use the perturbed fluid equation documented by Yoon and Lui [] and derive the dispersion relation of the drift‐driven EMIC instability, following the work by Mok et al [], in which the ambient magnetic field is along the z axis, the cross‐field drift velocity lies along the y axis, and the wave vector is confined in the y ‐ z plane. Figure gives the dispersion relation for isotropic plasma with the cross‐field ion drift velocity of 0.05 V A , where V A is the Alfven velocity.…”

Van Allen Probes observations of magnetic field dipolarization and its associated O+ flux variations in the inner magnetosphere at L < 6.6

“…The fluctuating electric field in the inner magnetosphere during substorms has been observed by many satellites, for example, ISEE-1 [Maynard et al, 1982], CRRES [Maynard et al, 1996], and Cluster [Ohtani et al, 2007]. The generation mechanism of the fluctuating magnetic and electric fields during dipolarization is considered to be the drift-driven electromagnetic ioncyclotron instability [e.g., Lui et al, 2008;Yoon et al, 2009;Mok et al, 2010;Huang et al, 2012;Nosé et al, 2014]. Numerical simulation studies reported that such electromagnetic fluctuations are very effective for particle acceleration [Artemyev et al, 2009;Zelenyi et al, 2011].…”