The altitude distribution of impulsive signals in the night ionosphere of Venus

Abstract

A new examination of burst like signals in the night ionosphere of Venus has been undertaken to determine the rate of occurrence of such signals. On average at all frequencies the bursts occur most often at lowest altitudes. The rates of occurrence of bursts at 0.73, 5.4 and 30 kHz fall off rapidly with altitude. At 350 km these bursts occur about an order of magnitude less often than at 150 km. At 100‐Hz the rate of falloff with altitude is less rapid. The occurrence rate decreases from about 50% at 150 km to between 20 and 40% at 500 km and then decreases more slowly above 500 km. This decrease suggests a wave source at lowest altitudes but high altitude sources also appear to be present. The rate of occurrence is quite variable both from season to season and from the inbound to the outbound portion of the orbit. This variability is consistent with either temporally or spatially varying source regions for these impulsive signals. Lightning in the Venus atmosphere could produce emissions consistent with the properties of those signals observed at lowest altitudes.