Discrete cloud activity in Saturn’s equator during 1995, 1996 and 1997

Abstract

A regular extensive CCD imaging of Saturn allowed us to analyze the discrete cloud activity in the Equatorial Zone from 1995 to 1997. The large-scale storm observed in 1994 at +10° ( Sanchez-Lavega et al., 1994, 1996) was rediscovered in 1995, reaching a lifetime >1 year. Its slow motion characterized by a zonal velocity difference of −150 ms −1 relative to background flow is confirmed. Our red and near infrared observations showed a strong increase of white cloud activity in the southern Equatorial Zone (latitude −13.5°) during 1996, declining later on during 1997. Cloud tracking of two prominent plumes and other features allowed us to measure zonal wind velocities and to compare them to the Voyager zonal flow velocity profile. We note that in general the 1995–1997 features have velocities lower than those measured with the Voyagers. Altitude differences in the clouds and hence different zonal velocities, or real changes in the zonal jet as a consequence of Saturn’s insolation cycle and ring-shadowing, can be the reason for such differences.