Whistler-mode Propagation in the Collisional Ionosphere of Venus

Waves identified as whistler-mode waves have been observed in the nightside ionosphere of Venus by the Pioneer Venus Orbiter. These waves are propagating in a collisional, weakly magnetized ionosphere, and it has been argued that as such they should be damped through collisions, and the wave should not retain the characteristics of the whistler-mode because of non-linear modifications to the dispersion relation. We show that non-linearities do not modify the wave dispersion since the non-linear force causes a longitudinal current, and the associated charge separation electric field acts to balance the non-linear force. The quasi-longitudinal approximation is therefore appropriate for whistler-mode waves in the nightside ionosphere of Venus. Further, we find that while the waves will heat the bottomside ionosphere, little effect is found at altitudes where in situ observations were made by the Pioneer Venus Orbiter.