FURTHER EVIDENCE FOR LIGHTNING ON VENUS

Impulsive electrical signals at all frequencies recorded by the plasma wave instrument or Pioneer Venus are found to cluster around periapsis. The signals are strongest at 100 Hz and have a secondary peak at 5. 4 kHz. These characteristics are consistent with generation by lightning in the Venus atmosphere and the direct propagation of whistler mode signals below the electron gyro frequency and the partial transmission of electromagnetic waves in the presence of electron density inhomogeneities above the electron gyro frequency. The scattering by electron density inhomogeneities may also weaken any correlation with surface topographical features. Thus, the source of these signals may either be intercloud lightning at high altitudes or lightning in volcanic plumes near the ground, despite the large scatter in inferred source locations.