Generation of ELF and VLF radiation by ionospheric electrojet modulation using high frequency heating waves

Summary form only given. Extra and very low frequency (ELF/VLF) wave generation by modulated polar electrojet currents is studied analytically and numerically. Through Ohmic heating by the amplitude modulated HF heating wave, the conductivity and thus the current of the electrojet are modulated accordingly to set up the ionospheric antenna current. The generation efficiency and signal quality of the ionospheric virtual antenna depend on the wave modulation scheme. Thus, four amplitude-modulation schemes are examined and compared. The nonlinear evolutions of the generated ELF/VLF waves enhanced by a stimulated thermal instability are studied numerically. Their spectra are also evaluated. The field intensity of the emission at the fundamental modulation frequency is found to increase with the modulation frequency in consistence with Tromso observations. The efficiency enhancement by the stimulated thermal instability is hampered by inelastic collisions of electrons with neutral particles (mainly due to vibration excitation of N/sub 2/) which cause this instability to saturate at low levels. However, electron´s inelastic collision loss rate drops rapidly to a low value in the energy regime from 3.5 to 6 eV. As the heating power exceeds a threshold level, significant electron heating enhanced by the instability is shown, which indeed causes a steep drop in the electron inelastic collision loss rate.