Dynamics and Interaction between a Large-Scale Vortex and the Great Red Spot in Jupiter

Abstract

A unique large-scale vortex, the White Tropical Oval (WTrO), was first observed in the South Tropical Zone of Jupiter, at the latitude of the Great Red Spot (GRS) in 1983. Its origin is probably related to a period of intense formation of eddies in the Southern edge of the South Equatorial Belt at latitude −20°. The WTrO survived many changes in the cloud structure of the South Equatorial Belt. However, in mid-May 1997, the WTrO was entrained by the GRS peripheral flow. Because of its large size, the WTrO did not circulate around the GRS's collar, as other smaller eddies do, but instead, after travelling one-quarter of the GRS ellipse it was expelled and finally destroyed when it became advected by the GRS's surrounding zonal flow. The GRS responded to this interaction by exhibiting small latitude and longitude displacements (≈3°). The main properties of the WTrO based on our prolonged imaging program (14 years) were the following: Average latitude (graphic) = −21.5° (extremes −20.5° to −23.5°); zonal velocity (relative to System III) = −4 m/s (extremes −2 to −7 m/s); major axis (east–west) = 8100 km; minor axis (north–south) = 5100 km. Its average zonal velocity showed a significant departure relative to the ambient flow velocity of −35 ms−1. The tangential velocity along the southern flank of the vortex was 8 to 40 ms−1, giving an area − averaged anticyclonic vorticity = 1.35 × 10−5s−1. This value is close to that of the ambient flow indicating that the WTrO was a weak vortex. Most of the time the WTrO showed a “white” oval form surrounded by a darker ring, although during some months in 1993 the southern part turned redder, with a color similar to that of the GRS. The relative spectral reflectivity from 230 nm to 2.3 μm suggests that the WTrO had a cloud structure similar to other well-known jovian anticyclones.