Plasma in Saturn's nightside magnetosphere and the implications for global circulation

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We present a bulk ion flow map from the nightside equatorial region of Saturn's magnetosphere derived from the Cassini CAPS ion mass spectrometer data. The map clearly demonstrates the dominance of corotation flow over radial flow and suggests that the flux tubes sampled are still closed and attached to the planet up to distances of 50 R{sub s}. The plasma characteristics in the near-midnight region are described and indicate a transition between the region of the magnetosphere containing plasma on closed drift paths and that containing flux tubes which may not complete a full rotation around the planet. Data from ... continued below

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Mcandrews, Hazel J; Wilson, R J; Henderson, M G; Tokar, R L; Jackman, C M; Khurana, K K et al. January 1, 2009.

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We present a bulk ion flow map from the nightside equatorial region of Saturn's magnetosphere derived from the Cassini CAPS ion mass spectrometer data. The map clearly demonstrates the dominance of corotation flow over radial flow and suggests that the flux tubes sampled are still closed and attached to the planet up to distances of 50 R{sub s}. The plasma characteristics in the near-midnight region are described and indicate a transition between the region of the magnetosphere containing plasma on closed drift paths and that containing flux tubes which may not complete a full rotation around the planet. Data from the electron spectrometer reveal two plasma states of high and low density. These are attributed either to the sampling of mass-loaded and depleted flux tubes, respectively, or to the latitudinal structure of the plasma sheet Depleted, returning flux tubes are not, in general, directly observed in the ions, although the electron observations suggest that such a process must take place in order to produce the low density population. Flux tube content is conserved below a limIt defined by the mass-loading and magnetic field strength and indicates that the flux tubes sampled may survive their passage through the tail. The conditions for mass release are evaluated using measured densities, angular velocities and magnetic field strength, The results suggest that for the relatively dense ion populations detectable by IMS, the condition for flux-tube breakage has not yet been exceeded, However, the low-density regimes observed in the electron data suggest that loaded flux tubes at greater distances do exceed the threshold for mass loss and subsequently return to the inner magnetosphere significantly depleted of plasma.

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  • Journal Name: Planetary and Space Science

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  • Report No.: LA-UR-09-00674
  • Report No.: LA-UR-09-674
  • Grant Number: AC52-06NA25396
  • DOI: 10.1016/j.pss.2009.03.003 | External Link
  • Office of Scientific & Technical Information Report Number: 956376
  • Archival Resource Key: ark:/67531/metadc932854

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  • January 1, 2009

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  • Nov. 13, 2016, 7:26 p.m.

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  • Dec. 12, 2016, 6:50 p.m.

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Mcandrews, Hazel J; Wilson, R J; Henderson, M G; Tokar, R L; Jackman, C M; Khurana, K K et al. Plasma in Saturn's nightside magnetosphere and the implications for global circulation, article, January 1, 2009; [New Mexico]. (digital.library.unt.edu/ark:/67531/metadc932854/: accessed August 17, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.