Lightning generation in a jovian thundercloud: Results from an axisymmetric numerical cloud model

An axisymmetric cloud model with detailed microphysics was used to calculate the electrical development of a jovian water cloud. The charge separation mechanism was based on the noninductive interaction between ice crystals and graupel particles in the presence of supercooled liquid droplets. The results show that for plausible concentrations of cloud condensation and freezing nuclei in the atmosphere, the electric field in a jovian thundercloud builds rapidly and exceeds its breakdown value. Low concentrations of cloud condensation nuclei produced shallow clouds and did not separate enough charge to produce critical fields. We simulated the lightning discharge by assuming that a flash occurred wherever the electric field, which resulted from the obtained space charge configuration, exceeded the local breakdown value. A lightning flash was assumed to neutralize a 20-Km channel within the cloud. The calculated flash rate suggests that the 192-sec exposure time of Voyager 1 camera, may have captured several superimposed lightning flashes. The energy calculated for such a simulated lightning discharge was of the order of 10¹²-10¹³ J, which translates to 10⁹-10¹⁰ J in the optical energy range, in agreement with Voyager’s observations of Jupiter’s lightning.