Atmospheric Dynamics near a Jovian 5-Micron Hotspot from Galileo Imaging

A. R. Vasavada, A. P. Ingersoll (Caltech), Galileo SSI Team

In December 1996 the Solid State Imaging (SSI) system aboard the Galileo orbiter acquired images of a jovian 5-micron hotspot similar to the Galileo probe entry site. The Galileo probe found its entry site to be depleted of volatiles. Ground-based and previous spacecraft observations reveal that hotspots are long-lived holes in the equatorial clouds, often associated with bright, presumably convective plumes. These results are consistent with the hypothesis that hotspots are regions of down-welling air depleted in volatiles by convection and condensation at other regions.

The Galileo orbiter images provide the meteorological context for the probe results. SSI obtained mosaics of a hotspot region at one and ten hour time intervals and at visible and near-infrared wavelengths. The best spatial resolution was 30 km/pixel. The images reveal the hotspot to be a well-defined hole in the tropospheric clouds, but more importantly show the first evidence for convergence over these regions. There is organized motion of clouds towards the hotspot from the south and little motion away from the hotspot in any direction. Small, high clouds east of the hotspot change appearance dramatically over one hour, possibly the result of rapid moist convection in these areas.