A strong vortex in Saturn's South Pole

Abstract

Saturn's southern pole was observed at high resolution by the Cassini Imaging Science Subsystem (ISS) during the spacecraft insertion orbit in July 2004. Cloud tracking of individual features on images taken at a wavelength of 938 nm reveal the existence of a strong polar vortex enclosed by a jet with maximum speed of 160 ± 10 m s −1 relative to System III rotation frame, and peak at 87 °S planetographic latitude. Radiative transfer models of the reflected light, based on the Cassini images complemented by Hubble Space Telescope images from March 2004, indicate that the aerosol particles in the vortex are structured vertically in three detached layers. We find two hazes and one dense cloud distributed in altitude between ∼ 500 mbar (top of the dense cloud) and few mbar (top of the stratospheric haze), spanning a vertical altitude range of ∼ 200 km . The vortex area coincides with a thermal hot spot recently reported, indicating that winds decrease with altitude above polar clouds.