The History of the Long-lived South Tropical Oval That Interacted with the GRS in May 1997

R Hueso, A. Sanchez-Lavega (UPV), J. Lecacheux (Obs. Meudon), F. Colas (BDL), J.M. Gomez (GEA), I. Miyazaki (Japan), D. Parker (USA)

A unique, large-scale and long-lived oval, has been observed since 1983 in the South Tropical Zone of Jupiter, close to the latitude of the GRS (A. Sanchez-Lavega et al., B.A.A.S., Vol. 26, 1102. 1994). In mid-May 1997, the oval penetrated in the interior of the GRS, interacting with it. The main characteristics of this feature based on our photographic records (1983-1986) and CCD images (1987-1997) are the following: Latitude (graphic) = -21.5 degrees (extremes -20 to -23 deg.); Zonal velocity (relative to System III) = -4 m/s (extremes -2 to -7 m/s); Major axis (East-West = 9600 km; Minor axis (North-South) = 6000 km; Tangential velocity (along the Northern flank) = 95 m/s (anticyclonic vorticity); Lifetime about 14 years (first tentative observation in 1983, tracking confirmed since 1986); Color: most time was a "white" oval surrounded by a dark ring, but in 1993 the southern part was red very similar to the GRS. Its reflectivity at a wavelength of 890 nm (methane absorption band) and 2.12-2.3 microns (hydrogen-methane absorption blend) was higher than its surroundings but lower than the GRS and the temperate WOS. From the above data, we conclude that this feature resembled the GRS and WOS and it is another archetype of jovian vortices. Its origin was probably related to a period of intense activity in the Southern edge of the South Equatorial Belt. We present detailed measurements of its interaction with features of the South Equatorial Belt, and with the GRS in 1997.