Lightning on Venus: Orbiter Detection of Whistler Signals

Recently Taylor et al. (1979a) presented preliminary evidence for lightning on Venus, based on Pioneer Venus orbiter detection of whistler mode signals as the spacecraft first traversed the nightside ionosphere near periapsis. The initial periapsis eclipse season for the orbiter has now been completed, and the plasma wave instrument (OEFD) obtained low -altitude nightside data for about 100 orbits. We present here an analysis of the impulsive whistler mode signals measured during these orbits, and we discuss the connection with atmospheric lightning. It is shown that the signals are detected in the 100 -Hz channel when the local magnetic field is sufficiently strong and steady and when the field is oriented to point down below the ionosphere. These facts strongly support the previous lightning interpretation.