Comparison of the structure and dynamics of Jupiter's Great Red Spot between the Voyager 1 and 2 encounters

We have consistently navigated the highest resolution images available of Jupiter's Great Red Spot (GRS) from the Voyager ISS experiment. From them we have measured apparent displacements of cloud features around and within the Red Spot which can be interpreted as wind vectors. We have used the wind field information to determine the circulation characteristics of the collar and to map the relative vorticity and horizontal divergence of the central GRS region, Color ratios and ground-based data have been used to complement these observations. Derived quantities from the IRIS data set taken simultaneously with the Voyager images have been obtained in order to determine the thermal structure, infrared cloud opacity, NH3 abundance, and para H-2 fraction above the Great Red Spot, There is evidence of non-chaotic activity in the central region of the Red Spot. Small eddy structures consisting of coherent cloud features with apparently two-dimensional turbulent motions are present in this region along with larger classical cyclonic vortices, The surrounding anticyclonic collar circulates with higher velocities and appears to be detached from the core by an abrupt transition region, The central region appears to be elevated over the surrounding collar and exhibits evidence for upwelling and some outflow of material. Differences in the collar structure and velocity profiles between the Voyager encounters can be attributed to differences in the ingestion rate of westward-moving South Equatorial Belt vortices caused by a blocking South Tropical Zone Disturbance which, moving eastward, overtook and passed the Red Spot between the two encounters. This disturbance appears to temporarily increase in brightness during conjunctions with the Red Spot and has been tracked for 20 years. (C) 1996 Academic Press, Inc.