PROPAGATION OF ELECTROMAGNETIC-WAVES PARALLEL TO THE MAGNETIC-FIELD IN THE NIGHTSIDE VENUS IONOSPHERE

A theoretical and numerical analysis of the propagation of electromagnetic waves in the nightside Venus ionosphere is presented. The special case of propagation parallel to the magnetic field is considered. The model assumes a source of electromagnetic radiation in the Venus atmosphere, such as produced by lightning, and specifically addresses wave propagation for realistic ionospheric parameters in the altitude range z = 130 - 160 km at the four frequencies detectable by the Pioneer Venus Orbiter Electric Field Detector (OEFD): 100 Hz, 730 Hz, 5.4 kHz, and 30 kHz. The results are summarized as follows. The f = 100 Hz and 730 Hz waves can propagate as whistler waves, provided f < f(ce), where f(ce) is the electron cyclotron frequency, and provided that the ionospheric electron density is sufficiently small that the waves are not strongly attenuated by collisional effects (i.e., Pedersen conductivity). The attenuation length scale lambda0 associated with the Pedersen conductivity is lambda0 approximately 2(c/omega(pe))[OMEGA(e)3/omega(v(en) + v(ei))2]1/2; for parameters typical of the nightside Venus ionosphere above 140 km, electron-ion collisions are more frequent than electron-neutral collisions and are therefore responsible for the attenuation of the waves. A parameterization of the wave intensities and Poynting flux as a function of magnetic field and peak electron density is presented. The waves are found to propagate most easily for high magnetic field and low electron density conditions (i.e., ionospheric holes); this result is consistent with observational data. The incident Poynting flux at the bottom of the ionosphere (z congruent-to 130 km) is estimated to be S congruent-to 0.1 W/m2 for the 100 Hz waves. The f = 5.4 kHz and 30 kHz cannot propagate through the nightside Venus ionosphere, as expected, because f(pe) > f > f(ce).