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Hybrid Simulations of Magnetodisc Transport Driven by the Rayleigh‐Taylor Instability.

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Title: Hybrid Simulations of Magnetodisc Transport Driven by the Rayleigh‐Taylor Instability.
Authors: Stauffer, B. H.1, Delamere, P. A.1 padelamere@alaska.edu, Ma, X.2, Neupane, B. R.1, Burkholder, B. L.1
Source: Journal of Geophysical Research. Space Physics. Jul2019, Vol. 124 Issue 7, p5107-5120. 14p.
Subject Terms: Plasma transport processes, Rayleigh-Taylor instability, Magnetosphere, Magnetic fields, Magnetic reconnection
Abstract: Plasma transport in the rapidly rotating giant magnetospheres is thought to involve a centrifugally driven flux tube interchange instability, similar to the Rayleigh‐Taylor (RT) instability. In three dimensions, the convective flow patterns associated with the RT instability can produce strong guide field reconnection, allowing plasma mass to move radially outward while conserving magnetic flux (Ma et al., 2016, https://doi.org/10.1002/2015JA022122). We present a set of hybrid (kinetic ion/fluid electron) plasma simulations of the RT instability using high plasma beta conditions appropriate for the inner and middle magnetosphere at Jupiter and Saturn. A density gradient, combined with a centrifugal force, provide appropriate RT onset conditions. Pressure balance requires only a temperature gradient as the magnetic pressure is constant. Pressure balance is achieved with a temperature gradient in a fixed magnetic field. The three‐dimensional simulation domain represents a local volume of the magnetodisc resonant cavity. Simulated RT growth rates compare favorably with linear theory, where the fundamental mode of the resonant cavity determines the largest (stabilizing) parallel wavelength. We suggest that the perpendicular scale of RT structures is determined by the fundamental mode, which limits growth due to magnetic tension. Finally, we investigated strong guide field magnetic reconnection and diffusive processes as plausible mechanisms to facilitate kinetic‐scale radial transport. Key Points: Hybrid simulations of the Rayleigh‐Taylor instability show magnetic field fluctuations similar to those observed at SaturnThe Rayleigh‐Taylor fingers include diffusive transport, patchy reconnection sites, and kinetic‐scale structures due to an inverse cascadeThe perpendicular scale of the Rayleigh‐Taylor fingers are limited by the parallel wavelengths in the magnetodisc resonant cavity [ABSTRACT FROM AUTHOR]
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Abstract:Plasma transport in the rapidly rotating giant magnetospheres is thought to involve a centrifugally driven flux tube interchange instability, similar to the Rayleigh‐Taylor (RT) instability. In three dimensions, the convective flow patterns associated with the RT instability can produce strong guide field reconnection, allowing plasma mass to move radially outward while conserving magnetic flux (Ma et al., 2016, https://doi.org/10.1002/2015JA022122). We present a set of hybrid (kinetic ion/fluid electron) plasma simulations of the RT instability using high plasma beta conditions appropriate for the inner and middle magnetosphere at Jupiter and Saturn. A density gradient, combined with a centrifugal force, provide appropriate RT onset conditions. Pressure balance requires only a temperature gradient as the magnetic pressure is constant. Pressure balance is achieved with a temperature gradient in a fixed magnetic field. The three‐dimensional simulation domain represents a local volume of the magnetodisc resonant cavity. Simulated RT growth rates compare favorably with linear theory, where the fundamental mode of the resonant cavity determines the largest (stabilizing) parallel wavelength. We suggest that the perpendicular scale of RT structures is determined by the fundamental mode, which limits growth due to magnetic tension. Finally, we investigated strong guide field magnetic reconnection and diffusive processes as plausible mechanisms to facilitate kinetic‐scale radial transport. Key Points: Hybrid simulations of the Rayleigh‐Taylor instability show magnetic field fluctuations similar to those observed at SaturnThe Rayleigh‐Taylor fingers include diffusive transport, patchy reconnection sites, and kinetic‐scale structures due to an inverse cascadeThe perpendicular scale of the Rayleigh‐Taylor fingers are limited by the parallel wavelengths in the magnetodisc resonant cavity [ABSTRACT FROM AUTHOR]
ISSN:21699380
DOI:10.1029/2018JA026420