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Saturn's north polar vortex structure extracted from cloud images by the optical flow method

Tianshu, Liu and Sayanagi, Kunio M. and Brueshaber, Shawn R. and Blalock, John J. and Ingersoll, Andrew P. and Dyudina, Ulyana A. and Ewald, Shawn P. (2019) Saturn's north polar vortex structure extracted from cloud images by the optical flow method. Journal of Geophysical Research. Planets, 124 (11). pp. 3041-3062. ISSN 2169-9097. doi:10.1029/2019JE005974.

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The paper presents velocity fields with ~3‐km spatial resolution of Saturn's north polar vortex (NPV) retrieved using the optical flow method from a sequence of polar‐projected cloud images captured by the Imaging Science Subsystem camera on board NASA's Cassini spacecraft. The fields of the velocity magnitude, velocity variation, relative vorticity, divergence, and second invariant are determined to characterize the flow structures of the inner core of the NPV. The mean zonal and mean meridional velocity profiles of the NPV are compared with previous measurements. We also describe the relevant details of application of the optical flow method to planetary cloud‐tracking wind measurements. The mean zonal velocity profile is consistent with the previous measurements using correlation image velocimetry methods. The small but significant meridional velocity corresponds to outwardly spiraling streams observed in the region near the north pole (NP). The concentrated vorticity and second invariant within 1° planetographic latitude of the NP indicate strong rotational motion of the fluid. An analysis is presented to explore a possible physical origin of the observed spiraling node at the NP.

Item Type:Article
Related URLs:
URLURL TypeDescription QCLRelated ItemData
Tianshu, Liu0000-0001-6297-1660
Sayanagi, Kunio M.0000-0001-8729-0992
Blalock, John J.0000-0002-7460-1074
Ingersoll, Andrew P.0000-0002-2035-9198
Ewald, Shawn P.0000-0002-1567-9154
Additional Information:© 2019 American Geophysical Union. Received 25 MAR 2019; Accepted 25 SEP 2019; Accepted article online 15 OCT 2019; Published online 26 NOV 2019. K.M.S. was supported by NASA Cassini Data Analysis Program Grant NNX15AD33G. S.R.B. was supported by NASA NESSF Grant NNX16AP44H. The data used to generate the figures in this paper are available in “Saturn_NPV_Velocity_Data” at Harvard Dataverse. The link is
Group:Astronomy Department
Funding AgencyGrant Number
NASA Earth and Space Science FellowshipNNX16AP44H
Subject Keywords:Saturn; north polar vortex; flow structure; optical flow; cloud tracking; velocity
Issue or Number:11
Record Number:CaltechAUTHORS:20191015-133656221
Persistent URL:
Official Citation:Liu, T., Sayanagi, K. M., Brueshaber, S. R., Blalock, J. J., Ingersoll, A. P., Dyudina, U. A., & Ewald, S. P. (2019). Saturn's north polar vortex structure extracted from cloud images by the optical flow method. Journal of Geophysical Research: Planets, 124, 3041–3062.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:99276
Deposited By: Tony Diaz
Deposited On:15 Oct 2019 22:31
Last Modified:16 Nov 2021 17:45

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