Saturn's south polar vortex compared to other large vortices in the Solar System

Observations made by the Imaging Science Subsystem (ISS), Visible and infrared Mapping Spectrometer (VIMS) and the long-wavelength Composite infrared Spectrometer (CIRS) aboard the Cassini spacecraft reveal that the large, long-lived cyclonic vortex at Saturn's south pole has a 4200-km-diameter cloud-free nearly circular region. This region has a 4 K warm core extending from the troposphere into the stratosphere, concentric cloud walls extending 20-70 km above the internal Clouds, and numerous external clouds whose anticyclonic vorticity suggests a convective origin. The rotation speeds of the vortex reach 150 +/- 20 ms(-1). The Saturn polar vortex has features in common with terrestrial hurricanes and with the Venus polar vortex. Neptune and other giant planets may also have strong polar vortices. (C) 2009 Elsevier Inc. All rights reserved.