Long-Lived Vortices and Profile Changes in the 23.7°N High-Speed Jovian Jet

Abstract

This paper addresses the question of up to what extent there are changes in the jovian jets as seen at cloud level and how they relate to the cloud morphology changes. We focus on the particularly interesting region at 24°N where the most intense jovian jet as observed at visual wavelengths resides. The studied period goes from 1991 to 1998, and the analysis is based on CCD images obtained with ground-based telescopes, complemented with a set from the HST imagery archive in the spectral range from ∼300 to 890 nm. The morphology of the North Temperate Belt (NTB) was characterized by the presence of a series of long-lived spots with lifetimes >4 years that formed in the anticyclonic flank of the jet at planetographic latitude 23.3 N following the development of the 1990 large-scale disturbance that changed the albedo of this belt (Sanchez-Lavega et al. 1991). They are rapidly moving mid-scale ovals (zonal velocity 123.9 ms −1, mean size ∼6500 km east–west times 3200 km north–south) with weak anticyclonic vorticity. The detailed structure of the zonal wind velocity profile of the 23.7°N jet between 1994 and 1998 was also measured using both cloud tracking and a correlation technique based on zonal reflectivity profiles. The jet peak speed during the 1994–1998 period appeared to be about 50 ms −1 slower and its shape broader in latitude when compared to that measured with the Voyager's in 1979. It seems that the differences in the profile between 1979 and the 1990s are related to the observed different cloud morphology in the region.