Scaling of conventional breakdown threshold: Impact for predictions of lightning and TLEs on Earth, Venus, and Mars

Voyager 1 observations of Jupiter confirmed the existence of extraterrestrial lightning but its presence on our closest neighbors, Mars and Venus remains controversial. In particular, the current detection effort rests on the physics of terrestrial lightning, which may be very different in other planetary atmospheres. The meteorological processes able to trigger lightning discharges in extraterrestrial atmospheres remain ill-defined, as do the expected characteristics of such discharges. In this work, we use the conventional breakdown threshold field, Ek, as a reference value for the initiation of atmospheric discharges. Its exact value depends on atmospheric composition, charge density, pressure, and temperature, but approximate altitude profiles can be obtained by means of scaling laws. We develop Ek profiles from ground to the ionosphere for Earth, Venus, and Mars to include the possibility of upper atmospheric discharges and TLEs. We establish that classic approximations, which use atmospheric scale heights and neutral gas density respectively become inaccurate above the tropopause and mesopause of all three planets. We also compare the results with reported or hypothesized electrical activity in the peer-reviewed literature and investigate the role of atomic oxygen in the drop of the electric field threshold. We conclude that hypothesized Martian discharges would be favored by the planet's low atmospheric pressure while electrical discharges in the Venusian cloud deck would require similar charging than in Earth's thunderstorms and that Venusian volcano lightning is less likely due to significantly more stringent initiation conditions.