Spatiotemporal Variability of Saturn's Zonal Winds Observed by Cassini

Abstract

The strong zonal winds on giant planets are among the most interesting phenomena in our solar system. Observations recorded by the Composite Infrared Spectrometer (CIRS), the Imaging Science Subsystem (ISS), and the Visual and Infrared Mapping Spectrometer (VIMS) on the Cassini spacecraft are utilized to investigate spatiotemporal variations in Saturn's zonal winds. A general thermal wind equation works for investigating the vertical structure of zonal winds at all latitudes, but it has integration gaps near the equator caused by the cylindrical integration path. Here, we develop an algorithm to address this limitation, which is validated by the observed zonal winds. The algorithm is combined with the CIRS-retrieved temperature and the ISS-measured winds to generate a complete picture of the vertical structure of Saturn's zonal winds for the upper troposphere (i.e., 50–500 mbar), which suggests that the equatorial zonal winds have complicated vertical structures. The zonal winds from 10°S to 10°N initially decrease with altitude and then increase. Additionally, the intense narrow equatorial jet between 3°S and 3°N widens with altitude. The zonal winds are further used to examine the atmospheric stability, which implies some unstable regions. Finally, the analysis of Cassini multi-instrument observations reveals different temporal behaviors of zonal winds in the vertical direction, which suggests that seasonally varying solar flux is one of the drivers of temporal variations in zonal winds.