Open AccessInterpreting observations of MF/HF radio emissions: Unstable wave modes and possibilities to passively diagnose ionospheric densities
Author(s) -
Weatherwax A. T.,
Yoon Peter H.,
LaBelle J.
Publication year - 2002
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2001ja000315
Subject(s) - ionosphere , physics , cyclotron , computational physics , electron , instability , electron density , lower hybrid oscillation , harmonics , plasma , radio wave , f region , electron precipitation , geophysics , satellite , atmospheric sciences , magnetosphere , astronomy , mechanics , nuclear physics , quantum mechanics , voltage
Recent satellite observations by the Wind spacecraft, as well as earlier observations by the ISIS 1 and 2 satellites, of MF/HF radio emissions have been attributed to upper hybrid/ Z mode waves generated in the topside ionosphere at two and three times the local electron gyrofrequency f ce . We calculate the growth rates of such emissions for various wave modes as a function of altitude in the topside ionosphere and for a variety of electron density profiles, employing a modified loss‐cone/horseshoe electron distribution function as the free energy source. These calculations represent the first application of this instability model to the topside ionosphere, in parallel to earlier efforts involving wave excitation in the bottomside of the F region. In addition to the Z mode, which is known to be unstable at points where the upper hybrid frequency matches cyclotron harmonics, the X mode can be directly generated near the first harmonic of the electron cyclotron frequency for certain density profiles. We further put forth how these emissions might be used as a remote diagnostic of ionospheric plasma properties.