Saturn's Global Zonal Winds Explored by Cassini/VIMS 5‐μm Images

• Published in: Geophysical research letters 2018-07, Vol.45 (14), p.6823-6831
• Main Authors: Studwell, Aaron, Li, Liming, Jiang, Xun, Baines, Kevin H., Fry, Patrick M., Momary, Thomas W., Dyudina, Ulyana A.
• Format: Article
• Language: English
• Subjects: Atmospheric dynamics; Atmospheric models; Barotropic mode; Cassini mission; Cassini VIMS images; Clouds; Dynamics; General circulation; global profile of zonal winds; Infrared imagery; Infrared spectrometers; Latitude; Observational studies; Planets; Polar environments; Polar regions; Pressure; Saturn; Spacecraft; Stratosphere; temporal variation of zonal winds; Vertical shear; vertical shear of zonal winds; Vertical wind shear; Wavelengths; Wind; Wind measurement; Wind structure; Winds; Zonal winds
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2018GL078139

The Cassini Visual and Infrared Mapping Spectrometer (VIMS) 5‐μm images are used to derive Saturn's global zonal winds around the 2,000‐hPa level. The comparison of zonal winds between 2,000 and 300–500 hPa shows a general consistency of wind structure between the two pressure levels on a global scale. However at some latitudes, the magnitude of the zonal winds differs between these levels. The equatorial zonal winds are stronger downward, while the zonal winds in the middle and high latitudes are generally weaker downward. These new wind measurements also imply that barotropic and baroclinic instabilities probably exist through the relatively deep atmosphere at some latitudes. Finally, our analysis reveals that the VIMS winds in the two polar regions are basically constant with time except for a westerly jet centered at ~88°N, which decreased from 135 ± 7 m/s in 2008 to 91 ± 12 m/s in 2017. Plain Language Summary Images of giant planets at the visible wavelengths are widely used to track visible clouds and hence estimate the atmospheric winds at the pressure levels of the visible clouds. On the other hand, images at the infrared wavelengths (e.g., 5 μm), which are sensitive to the pressure levels below the visible clouds, can be used to measure the relatively deep winds. Here we use the infrared images recorded by the Cassini spacecraft to measure Saturn's zonal winds (i.e., atmospheric wind in the longitudinal direction) at the relatively deep pressure levels around 2,000 mbar. We provide the global profile of the zonal winds around 2,000 mbar for the first time. The comparison of the global profile of zonal winds between 2,000 mbar and 300–500 mbar reveals interesting characteristics of the vertical shear of zonal winds and the related stabilities on Saturn. In addition, the comparison of the 2,000‐mbar zonal winds among different years suggests important temporal characteristics of zonal winds in the polar region of Saturn. This observational study will not only provide key information about the large‐scale atmospheric dynamics but also help us develop the theories and models of the general circulation on the giant planets. Key Points The global profile of zonal winds around 2,000 mbar is generated for the first time; the new profile suggests vertical wind shear The vertical shear of zonal winds helps better understand the atmospheric dynamics (e.g., stability) Measurements of zonal winds in multiple years suggest the temporal variations of zonal winds