Model interpretation of Jovian lightning activity and the Galileo Probe results

An axisymmetric numerical cloud model with detailed microphysics is used to evaluate the development of water clouds under various Jovian conditions. A formulation of the noninductive ice-ice charge separation mechanism is used to calculate the electrical structure of the clouds and to identify the charged regions at the altitudes of the Galileo entry probe trajectory. The results show that for midlatitude conditions, with reasonable assumptions, the water clouds in the deep Jovian troposphere have an electrical dipole structure, with a large positive charge center located at the 3 bar pressure level and a lower negative charge center at the 4.5 bar level. This structure is modified as the cloud matures and the breakdown electric field is exceeded and lightning occurs. Our model predicts that the weak convection, which occurs at the stable equatorial region, is capable of producing water clouds with 10 m s^-1 updrafts and water and ice content of 5 g kg^-1. Charge separation and lightning generation in these clouds is less intensive and lightning frequency is lower than at midlatitudes. For a low oxygen abundance of 0.2 times solar, we show that ice clouds fonn at temperatures where charge separation is weak, and no lightning can occur. The results suggest a very low probability that there was lightning activity near the path of the descending probe.