Jupiter: New Estimates of Mean Zonal Flow at the Cloud Level

Previous estimates of the mean zonal flow on Jupiter from Voyager images by Ingersoll et al. (1981, J. Geophys. Res. 86, 8733-8743) and by Limaye et al. (1982, J. Atmos. Sci. 39, 1413-1432) showed good agreement in the locations of the easterly and westerly jets but differed somewhat in magnitude. Recent measurements of the high-speed jet located near 24 deg N (planetographic) latitude by Maxworthy (1984, Planet. Space Scl. 32, 1053-1058) from high spatial and temporal resolution Voyager images indicate that both Ingersoll et al., and Limaye et al. underestimated the magnitude of the jet by more than 30-40 m s -I. In an attempt to examine the differences in the magnitude of the Jovian jets determined from Voyager 1 and 2 images, a new approach to determine the zonal mean east-west component of motion was investigated. The new technique, based on a simple, digital pattern matching approach and applied on pairs of mapped images (cylindrical mosaics) yields a profile of the mean zonal component that reproduces the exact locations of the easterly and westerly jets between ± 60 deg latitude. Not only do the jet magnitudes but also the wings of the jets agree remarkably well from mosaic pair to pair. Further, the latitudinal resolution is five (mid-latitudes) to eight times (equatorial) greater than previous results. Results have been obtained for all of the Voyager 1 and 2 cylindrical mosaics. The correlation coefficient between Voyager 1 and Voyager 2 average mean zonal flow between ± 60 deg latitude determined from violet filter mosaics is 0.9978. A slight latitude offset (averaging + 0.15 deg) possibly due to navigation errors, is detectable in the Voyager 1 data. Independent cloud motion measurements in two high resolution image pairs (orange and violet) acquired from Voyager 1 cameras agree well with the average mean zonal flow for the fastest Jovian jet at 23.8 deg N latitude. Comparison with Maxworthy's results suggests longitudinal variations in cloud motions approaching about 20 m s -I as well as some possible sampling problems. In particular, the jet magnitude is about 163 ± 9 (RMS) m s -1, which compares well with 182 ± 10 m s -I reported by Maxworthy. There is excellent agreement in the location of the peak magnitude as well as its shape.