Generation of lightning in Jupiter's water cloud

Abstract

Lightning is a familiar feature of storms on the Earth, and has also been seen on Jupiter and inferred indirectly to occur on Venus and Neptune. On Jupiter, lightning may be important as a source of energy to drive chemical reactions in the atmosphere, perhaps determining the abundances of molecules such as CO, HCN and C2H2. Lightning may be generated in Jupiter's water clouds by a mechanism similar to that which operates in terrestrial thunderstorms. Here we investigate the development of lightning by modelling the thunderstorm separation of electrical charge on precipitating ice particles at varying depths in Jupiter's atmosphere. We find that lightning can indeed be generated in the jovian water clouds, and that--in agreement with estimates from the analysis of Voyager images--it is most likely to occur at the 3- or 4-bar pressure level. Our model also predicts that a condensed-water abundance in the range of at least 1-2 g m-3 is required for lightning to occur in jovian thunderstorms--a prediction that may be tested when the Galileo probe arrives at Jupiter on 7 December 1995.

Dynamical implications of Jupiter's tropospheric ammonia abundance

“…As evidenced by their visibility in the 889 nm methane band, the storm tops stand up to 50 km above the surrounding cloud deck. These thunderstorms are probably driven by condensation of water, as ammonia and H 2 S are too scarce to drive thunderstorm-strength updrafts or cause cloud electrification (Gierasch and Conrath, 1985;Gibbard et al, 1995;Yair et al, 1995). The lightning occurs at altitudes ∼ 80-120 km below the ammonia clouds, at pressures of 5-10 bars (Borucki and Williams, 1986;Little et al, 1999;Dyudina et al, 2002), consistent with the water-condensation pressure of ∼ 6 bars.…”

Charging of ice-vapor interfaces: applications to thunderstorms

“…About 20 fC per collision is transferred from one to the other, leading to powerful in-cloud electric fields and often lightning, thus maintaining Earth's electrical circuit. We present a simple analytic model that is consistent with these wide-ranging observations and which allows speculation that the same processes can lead to lightning on Jupiter (Gibbard et al 1995) and elsewhere in the solar system. Before step 1, "fixed protons" and "protons before move" produce net dipole moments that are neither up nor down in all three boxes as shown to the right (e.g., compare protons above and below a horizontal line in the middle of a box).…”

“…Such charging can cause ice crystals to orient (Vonnegut, 1965) and possibly levitate (Gibbard et al, 1995) in the electrical atmosphere of thunderclouds. Surface charging can modify many atmospheric processes such as collection of ions, aerosols, and droplets by ice (Martin et al 1980;Pruppacher and Klett, 1980 p. 619), and aggregation of snow crystals in clouds (Odencrantz and Buecher, 1967;Finnegan and Pitter, 1988) and in wind-blown snow (Schmidt, 1982).…”

Charge Generation and Separation Processes

“…A 2D axi-symmetric cloud model with detailed bin-microphysics was developed by Yair et al (1995aYair et al ( , 1995bYair et al ( , 1998 to study lightning generation in Jupiter. It was later complemented by the 1D model of Gibbard et al (1995). The deep H 2 O clouds in Jupiter's atmosphere were shown to be the most suitable candidate for lightning generation, based on non-inductive processes equivalent to those operating in terrestrial clouds.…”