MODEL INTERPRETATION OF JOVIAN LIGHTNING ACTIVITY AND THE GALILEO PROBE RESULTS

An axisymmetric numerical cloud model with detailed microphysics is us ed to evaluate the development of water clouds under various Jovian co nditions. 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 en try probe trajectory. The results show that for midlatitude conditions , with reasonable assumptions, the water clouds in the deep Jovian tro posphere have an electrical dipole structure, with a large positive ch arge center located at the 3 bar pressure level and a lower negative c harge center at the 4.5 bar level. This structure :is modified as the cloud matures and the breakdown electric field is exceeded and lightni ng occurs. Our model predicts that the weak convection, which occurs a t the stable equatorial region, is capable of producing water clouds w ith 10 m s(-1) updrafts and water and ice content of 5 g kg(-1). Charg e separation and lightning generation in these clouds is less intensiv e and lightning frequency is lower than at midlatitudes. For a law oxy gen abundance of 0.2 times solar, we show that ice clouds form at temp eratures where charge separation is weak, and no lightning can occur. The results suggest a very low probability that there was lightning ac tivity near the path of the descending probe.