The Time-Dependent Nature of Winds, Reflectivity and Weather Systems on Jupiter

Using Voyager, Hubble Space Telescope, ground-based and Galileo spacecraft data, an analysis of the stability of Jupiter's zonal winds, temporal changes in cloud morphology and brightness, and behavior of long-lived cloud features was performed. In most cases, the entire planet was studied, although the focus of much of the work has been an area from 10°-25° N planetographic latitude, or the North Tropical Zone (NTrZ) and the belts adjacent to it. Although Jupiter's zonal winds are very constant over time, we found the 24° wind jet does change, possibly in a very short timespan of 10 months. This particular velocity change was not due to the lower spatial resolution of the observations or to variation in cloud height. The short timescale implies either a very shallow event or requires an instability to grow under the visible cloud deck for a much longer time, with the sudden change occurring only at the cloud tops. The change in velocity was accompanied by a large change in cloud albedo and morphology and historical records indicate such changes could appear every 10 to 12 years. The NTrZ does not often have long-lived weather features, but small ovals do appear from time to time. In the context of understanding how weather features react in the wind field, features at other latitudes on the planet were studied. These features do not move freely in the wind field, but have their own rotation and translation and if large enough, can force the local winds to be diverted. The three White Ovals at 33° S latitude have been observed since their formation in 1939. Their complex behavior includes variable drift rates, shrinkage of the individual ovals and oscillations in latitude. By 1996, these ovals had piled into a long train, which ended in 1998 with the merger of the two largest features. The way storms interact with the winds and each other is an important factor in atmospheric modeling, as it can depend on the presence of water below the visible ammonia clouds, a quantity which we cannot directly measure. Using the EPIC model, it was found that while the rough behavior of the Ovals could be matched without the presence of water, the detailed behavior could not.