Strong jet and a new thermal wave in Saturn's equatorial stratosphere

Abstract

The strong jet, with a speed between 500 and 600 m/s, is inferred in the equatorial region of Saturn by combining the nadir and limb observations of Composite Infrared Spectrometer (CIRS) aboard the Cassini spacecraft. A similar jet was discovered on Jupiter (F. M. Flasar et al., 2004a). These discoveries raise the possibility that intense jets are common in the equatorial stratospheres of giant planets. An equatorial wave with wavenumber ~9 is revealed in the stratosphere of Saturn by the CIRS high spatial-resolution thermal maps. Our discussion based on the phase velocity suggests that the equatorial wave is probably a Rossby-gravity wave. The discovery of an equatorial wave in the stratosphere suggests that Saturn's equatorial oscillations (T. Fouchet et al., 2008; G. S. Orton et al., 2008) may be driven by vertically propagating waves, the same mechanism that drives the quasi-biennial oscillation (QBO) on Earth.

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