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Analytical assessment of Kelvin-Helmholtz instability growth at Ganymede's upstream magnetopause
  • Nawapat Kaweeyanun,
  • Adam Masters,
  • Xianzhe Jia
Nawapat Kaweeyanun
Imperial College London

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Adam Masters
Imperial College London
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Xianzhe Jia
University of Michigan-Ann Arbor
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Ganymede is the only Solar System moon that generates a permanent magnetic field. Dynamics inside Ganymede’s magnetosphere is likely driven by energy-transfer interactions on its upstream magnetopause. Previously in Kaweeyanun et al. (2020), we created a steady-state analytical model of Ganymede’s magnetopause and predicted global-scale magnetic reconnection to occur frequently throughout the surface. Using the same model, this paper provides the first assessment of Kelvin-Helmholtz (K-H) instability growth on the magnetopause in isolation from reconnection effects. The linear K-H instability growth rate is calculated at Ganymede’s equatorial magnetopause flank points under the magnetohydrodynamic with finite Larmor radius effect (MHD-FLR) theory, which accounts for inter-flank growth rate asymmetry due to large gyroradii of Jovian plasma ions. The calculation gives growth rates between γ ≈ 0.01-48 /s with notable enhancement at the equatorial flank point closer to Jupiter. Then, the ideal MHD K-H instability onset condition is evaluated across the entire Ganymedean magnetopause. We find the conditions along both magnetopause flanks to be K-H favorable at all latitudes with growth rates similar to those at respective equatorial flank points. Using Mercury’s magnetopause case as a comparison, we determined that nonlinear K-H vortices are viable at Ganymede based on the calculated growth rates, but the vortex growth will likely be suppressed once global reconnection is taken into account.
Aug 2021Published in Journal of Geophysical Research: Space Physics volume 126 issue 8. 10.1029/2021JA029338