A Strong Instability in the Ion Cyclotron Frequency Range of the Upward Sheared Flow of the Oxygen Ions in Aurora
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A Strong Instability in the Ion Cyclotron Frequency Range of the Upward Sheared Flow of the Oxygen Ions in Aurora V. V. Mikhailenko
∗
BK21 FOUR Information Technology, Pusan National University, Busan 46241, Korea
V. S. Mikhailenko Plasma Research Center, Pusan National University, Busan 46241, Korea
Hae June Lee
†
Department of Electrical Engineering, Pusan National University, Busan 46241, Korea (Received 14 September 2020; revised 29 October 2020; accepted 30 October 2020) The dispersion relation of a new electrostatic ion cyclotron (IC) instability of a plasma with a sheared current of the oxygen ions along the magnetic field is investigated analytically and solved by numerical analysis. The considered case corresponds to the upward sheared flow of the oxygen ions in the aurora where the velocity shearing rate of ion current may be larger than the cyclotron frequency of O+ ion. In such a plasma, we found a new instability in the IC frequency range which develops in the sheared flow and can have a growth rate larger than O+ cyclotron frequency. This instability develops jointly with the known IC instability for the uniform current with a growth rate much less than O+ cyclotron frequency. Keywords: Ionospheric plasma, Flow velocity shear, Ion cyclotron instability DOI: 10.3938/jkps.77.936
The aurora is arguably the most spectacular manifestation of the dynamical complexity of processes in the ionosphere-magnetosphere plasma. The field-aligned currents in the aurora are recognized as a reservoir of the free energy that can be released by the development of numerous current-driven instabilities, which can power plasma turbulence. It is well understood that the scattering of the ions and electrons by the plasma turbulence induces turbulent resistivity. Heating and acceleration of electrons and ions in the collisionless ionosphere plasma determine the evolution process of the turbulence in the aurora. Therefore, the investigation of these currentdriven instabilities and their nonlinear evolution is one of the fundamental tasks for the development of the contemporary aurora physics. It was established experimentally in detail [1–5] that the electric fields parallel to and across the background magnetic field exist in the upward current region of the aurora to upward flowing ions (UFI) and a down-going inverted-V profile electrons. The UFI consists mainly of O+ and H+ ions [2, 3], in which the flux of keV O+ ions exceeds that of H+ and has been recognized [2] as a major source of O+ ions in the magnetospheric plasma ∗ E-mail: † E-mail:
[email protected] [email protected]
pISSN:0374-4884/eISSN:1976-8524
as opposed to the solar wind. It was established by Kindel and Kennel [6] that the current-driven electrostatic ion-cyclotron (IC) instability [7] driven by the current along the magnetic field has the lowest threshold in the ionospheric plasma environment and should drive the IC waves in the auroral zone. The numerous observational data by satellites and rockets detected the development of the hydrogen and o
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