Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011jgra..11601315b&link_type=abstract
Journal of Geophysical Research, Volume 116, Issue A1, CiteID A01315
Astronomy and Astrophysics
Astrophysics
2
Solar Physics, Astrophysics, And Astronomy: Radio Emissions, Magnetospheric Physics: Substorms, Ionosphere: Plasma Waves And Instabilities (2772), Radio Science: Waves In Plasma (7867), Ionosphere: Wave Propagation (0689, 3285, 4275, 4455, 6934)
Scientific paper
Auroral medium frequency (MF) burst is an impulsive auroral radio emission observed at ground level between ˜1.3 and 4.5 MHz for a few minutes at substorm onsets. Despite multiple suggested theories, the exact generation mechanism for MF burst remains unknown. The foremost theory suggests that MF burst originates from Langmuir or upper hybrid waves excited over a range of altitudes in the bottomside or topside F region, which linearly mode convert to the electromagnetic LO mode, gaining access to ground level. Analysis of plasmas with two electron components implies the existence of additional normal modes, commonly referred to as the electron acoustic (EA) and electron cyclotron sound (ECS) modes, which have been suggested to potentially play a role in the generation of MF burst. Analytical calculations using Waves in Homogeneous, Anisotropic Multicomponent Plasmas, or WHAMP, and other dispersion-solving calculations are applied to applicable ionospheric normal modes (RX, LO, Langmuir or upper hybrid, EA, and ECS), compared to previous results, and applied to MF burst and the auroral plasma environment. Computation of resonant parallel energies suggests that, in the presence of an auroral electron distribution, instability of EA, ECS, LX, and Langmuir or upper hybrid modes is possible. The same analysis suggests that LO and RX modes are unlikely to be directly excited. Excitation of the EA or ECS mode in the frequency range applicable to MF burst is found to be more favorable for higher ionospheric plasma densities (fpe/fce > 2.36) and higher secondary electron temperatures (Th ≈ 100s of eV). Growth rate calculations suggest that growth of the EA or ECS mode is excitable by the auroral electron beam with higher growth rates for the ECS mode.
Bunch Nicholas L.
LaBelle James
Weatherwax Allan T.
Yoon Peter
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