On the dynamical nature of Saturn’s North Polar hexagon
Year: 2017
Type: article
Abstract: An explanation of long-lived Saturn’s North Polar hexagonal circumpolar jetin terms of instability of the coupled system polar vortex - circumpolar jet isproposed in the framework of the rotating shallow water model, wherescarcely known vertical structure of the Saturn’s atmosphere is averaged out.The absence of a hexagonal structure at Saturn’s South Pole is explainedsimilarly. By using the latest state-of-the-art observed winds in Saturn’spolar regions a detailed linear stability analysis of the circumpolar jet isperformed (i) excluding (“jet-only” configuration), and (2) including(“jet+vortex” configuration) the north polar vortex in the system. A domainof parameters: latitude of the circumpolar jet and curvature of its azimuthalvelocity profile, where the most unstable mode of the system has azimuthalwavenumber 6, is identified. Fully nonlinear simulations are then performed,initialized either with the most unstable mode of small amplitude, or withthe random combination of unstable modes. It is shown that developingbarotropic instability of the “jet+vortex” system produces a long-livingstructure akin to the observed hexagon, which is not the case of the“jet-only” system, which was studied in this context in a number of papersin literature. The north polar vortex, thus, plays a decisive dynamical role.The influence of moist convection, which was recently suggested to be at theorigin of Saturn’s north polar vortex system in the literature, is investigatedin the framework of the model and does not alter the conclusions.
Source: Icarus
Language: English
Topic: Astro and Planetary Science
Subfield: Space and Planetary Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: green
Funder: Agence Nationale de la Recherche
OpenAlex ID: W2696489094