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

Our ability to observe extraterrestrial lightning is limited by our detection techniques, which rest mostly on our understanding of terrestrial lightning. However, gas discharge physics vastly depends on the environment. Here, we use the conventional breakdown threshold field, E-k, as a reference value for the initiation of atmospheric discharges. Its value depends on atmospheric composition, charge density, pressure, and temperature. Their effects are collectively approximated by scaling laws based on either atmospheric scale height, neutral density, or pressure. While these approximations have proven useful in numerical applications, they inherently limit the investigation of each specific parameter independently. To remove this limitation, we introduce a new model, which couples a Boltzmann solver with standard Global Reference Atmospheric Models (GRAM) and lets us perform systematic calculations of the breakdown at every altitude for realistic, altitude dependent gas mixtures. We develop Ek profiles from the ground to the ionosphere for Earth, Venus, and Mars and show that for all three planets, classic approximations based on atmospheric scale heights and neutral gas densities become inaccurate respectively above the tropopause and mesopause. We investigate specifically the role of atomic oxygen and atmospheric water. We conclude that hypothesized Martian discharge is favored by the planet's low atmospheric pressure. On Venus, discharges in the cloud layer require electrical conditions comparable to those in Earth thunderclouds but remain more likely than volcano lightning.