ANALYSIS OF VOYAGER 2 IMAGES OF JOVIAN LIGHTNING

Voyager 2 images have been examined and found to contain bright spots due to lightning activity that is confined to two narrow latitude bands centered at 49° N and 13.5° N latitude and to a single region near 60° N latitude. No lightning activity is observed in the southern hemisphere even though a large area was observed with the same sensitivity as that used for northern hemisphere observations. The brightest band of lightning activity occurs at 49° N, but no unusual cloud features can be associated with this activity. This result is consistent with the depth of the lightning activity being 80 km below the ammonia clouds and thus not producing readily observed disturbances in the visible clouds. The secondary band of lightning activity that appears at 13.5° N is restricted in longitude to the "disturbed" zone. One of the two storms found in this tropical band is very close to the location of a bright cloud feature that extends some 3.5° in latitude. If it is assumed that the deflection of this feature is caused by the westerly flow of an air parcel over a hill in the potential temperature surface located at the 5- to 10-bar level, then the air parcel moving over the hill would be forced to rise sufficiently high that the free convection level would be reached. This situation could be the cause of the lightning activity in this region. The energy dissipation rate by lightning activity in the Voyager 2 images is 3200 W/km2 when attenuation by clouds is considered. The energy dissipation rate is approximately 50% greater than that found in the Voyager 1 images. The ratio of the energy dissipated by Jovian lightning to the thermal flux available to drive convection motions is found to be three decades larger than the terrestrial ratio. This value is similar to the ratio for the two planets found by Ingersoll (1990) for the conversion of thermal energy flux to mechanical energy. © 1992.