Kelvin-Helmholtz Waves at Saturn's Magnetopause

Details Kelvin-Helmholtz Waves at Saturn's Magnetopause Kelvin-Helmholtz Waves at Saturn's Magnetopause

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsm23c1635w&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #SM23C-1635

Physics

[2724] Magnetospheric Physics / Magnetopause And Boundary Layers, [2752] Magnetospheric Physics / Mhd Waves And Instabilities, [5737] Planetary Sciences: Fluid Planets / Magnetospheres

Scientific paper

We have used a global magnetohydrodynamic simulation of the interaction between the solar wind and Saturn’s magnetosphere and Cassini magnetic field observations to investigate vorticity at Saturn’s magnetopause. We find that large vortices form for northward interplanetary magnetic field in a region near the morning magnetopause when the velocity shear is sufficiently large. The changes in the plasma and magnetic field parameters across the boundary are consistent with the Kelvin-Helmholtz (KH) instability. Waves are found on both the magnetosheath and magnetosphere side of the magnetopause boundary layer and the fastest growing mode occurs when kd~1 where k is wave number and d is the boundary layer thickness as expected from KH theory. The waves decrease when the IMF turns southward. For southward IMF a decrease in the mass density near the boundary causes the boundary to become stable to KH waves. The waves have periods of 1 to 4 hours with the higher frequency waves occurring for higher solar wind velocities. The waves were found for two plasma source rates at Enceladus (2X1029 AMU/s and 5X1028 AMU/s) but they had smaller amplitude and duration for the lower source rate. The vortices cause magnetic field oscillations on virtual spacecraft placed in the dayside magnetosphere. Cassini magnetic field oscillations [Daugherty et al., CASSINI MAG CALIBRATED SUMMARY AVERAGED, C-E/SWS/J/S-MAG-4-SUMM-AVERAGED-V1.0, NASA Planetary Data System, 2007] show similar oscillations both within the magnetosphere and at the magnetopause [Masters et al., Surface waves on Saturn’s dawn flank magnetopause driven by the Kelvin-Helmholtz instability, Planet. Space Sci., doi:10.1016/j.pss.2009.02.010, 2009]. We will compare the simulatied magnetic field oscillations with these observations.

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