The Importance of Venus Lightning Investigations

Lightning in planetary atmospheres arises due to the separation of electric charges in convective cloud systems. We expect that Venus should have strong thermally driven winds at its location of 0.72 AU from the Sun. Observations of the cloud tops and the vertical motions of the atmosphere by the VEGA balloons confirm this expectation. We have made extensive surveys for lightning on Venus with spacecraft in the Venusian ionosphere. However, as yet we do not have a complete mapping of the occurrence of lightning because at the low frequencies at which measurements have been made it is difficult for the waves generated to penetrate the ionosphere. We expect the lightning to be intense as it generates nitric oxide and nitric oxide as is abundant on Venus as on Earth. We have surveyed almost all the Venus Express 128 Hz magnetometer data recorded to date. These data reveal that lightning is extensive on Venus but still do not reveal its true occurrence rate or altitude of generation. This requires observations from multipoint monitors at frequencies that penetrate into the ionosphere and will allow us to determine the energy released by lightning in the Venusian atmosphere. Finally, it is essential for us to study similar planetary processes in different settings in order to fully understand the process itself. Lightning is an important terrestrial process. Venus gives us the opportunity to understand the process more deeply. In this presentation we review the present state of knowledge of Venus lightning.