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Excitation of plasma sheet instabilities by ionospheric O + ions
Author(s) -
Lakhina G. S.
Publication year - 1995
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/95gl03427
Subject(s) - physics , substorm , instability , magnetic field , atomic physics , excitation , plasma , ion , ionosphere , amplitude , plasma sheet , wavelength , excited state , geophysics , magnetosphere , optics , quantum mechanics , mechanics
It is shown that the presence of ionospheric O + ions in the inner central plasma sheet (ICPS) during growth phase of the substorms can excite nonresonant low‐frequency, long wavelength RH mode instability under certain conditions. For the ICPS parameters during enhanced convection events, the excited modes have real frequencies of (0.1–5.0) mHz, and the typical maximum growth rates of ∼ (0.1–4.0) mHz with corresponding wavelengths of ∼ (1–30) R E ( R E being the Earth's radius). The excited low‐frequency modes are expected to saturate to the maximum level of δ B ²/ B 0 ² ≈ (2.5 × 10 −3 −0.25), where δ B and δ B 0 are the fluctuating magnetic field associated with the unstable modes, and the equilibrium magnetic field respectively. The large amplitude magnetic field fluctuations due to the nonresonant low‐frequency instability driven by O + ions could twist the ICPS magnetic field into flux ropes, and also produce localised minima, in the magnetotail magnetic field near the neutral axis, which can be the potential sites for the excitation of the tearing modes leading to substorm onset.