Sayanagi, Kunio M. and Blalock, John J. and Dyudina, Ulyana A. and Ewald, Shawn P. and Ingersoll, Andrew P. (2017) Cassini ISS Observation of Saturn’s North Polar Vortex and Comparison to the South Polar Vortex. Icarus, 285 . pp. 68-82. ISSN 0019-1035. http://resolver.caltech.edu/CaltechAUTHORS:20161216-141533007
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We present analyses of Saturn’s north pole using high-resolution images captured in late 2012 by the Cassini spacecraft’s Imaging Science Subsystem (ISS) camera. The images reveal the presence of an intense cyclonic vortex centered at the north pole. In the red and green visible continuum wavelengths, the north polar region exhibits a cyclonically spiraling cloud morphology extending from the pole to 85°N planetocentric latitude, with a 4700 km radius. Images captured in the methane bands, which sense upper tropospheric haze, show an approximately circular hole in the haze extending up to 1.5° latitude away from the pole. The spiraling morphology and the “eye”-like hole at the center are reminiscent of a terrestrial tropical cyclone. In the System III reference frame (rotation period of 10h39m22.4s, Seidelmann et al. 2007; Archinal et al. 2011), the eastward wind speed increases to about 140 m s^(−1) at 89°N planetocentric latitude. The vorticity is (6.5± 1.5)×10^(−4)s^(−1) at the pole, and decreases to (1.3± 1.2)×10^(−4)s^(−1) at 89°N. In addition, we present an analysis of Saturn’s south polar vortex using images captured in January 2007 to compare its cloud morphology to the north pole. The set of images captured in 2007 includes filters that have not been analyzed before. Images captured in the violet filter (400 nm) also reveal a bright polar cloud. The south polar morphology in 2007 was more smooth and lacked the small clouds apparent around the north pole in 2012. Saturn underwent equinox in August 2009. The 2007 observation captured the pre-equinox south pole, and the 2012 observation captured the post-equinox north pole. Thus, the observed differences between the poles are likely due to seasonal effects. If these differences indeed are caused by seasonal effects, continuing observations of the summer north pole by the Cassini mission should show a formation of a polar cloud that appears bright in short-wavelength filters.
|Additional Information:||© 2016 Elsevier Inc. Received date: 16 February 2016; Revised date: 1 December 2016; Accepted date: 5 December 2016; Available online: 13 December 2016. Our work was supported by the Cassini-Huygens mission, a cooperative project of NASA, ESA, ASI, managed by JPL, a division of the California Institute of Technology, under a contract with NASA. KMS acknowledges support from NASA Outer Planets Research Grant NNX12AR38G, NASA Planetary Atmospheres Program Grant NNX14AK07G, NASA Cassini Data Analysis Program Grant NNX15AD33G, and NSF Astronomy and Astrophysics Grant 1212216. API acknowledges support from NSF grant AST-1411952 and by the Cassini Project of NASA.|
|Subject Keywords:||Atmospheres, dynamics; Saturn, atmosphere; Jovian planets; Saturn|
|Official Citation:||Kunio M. Sayanagi, John J. Blalock, Ulyana A. Dyudina, Shawn P. Ewald, Andrew P. Ingersoll, Cassini ISS observation of Saturn’s north polar vortex and comparison to the south polar vortex, Icarus, Volume 285, 15 March 2017, Pages 68-82, ISSN 0019-1035, http://dx.doi.org/10.1016/j.icarus.2016.12.011. (http://www.sciencedirect.com/science/article/pii/S001910351630817X)|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||16 Dec 2016 23:01|
|Last Modified:||11 Jan 2017 23:48|
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