Using 3D Multi-Fluid Simulations to Investigate the Periodicity of the Auroral Brightness at Ganymede and its Dependence on Precipitating Particle Temperatures

Details Using 3D Multi-Fluid Simulations to Investigate the Periodicity of the Auroral Brightness at Ganymede and its Dependence on Precipitating Particle Temperatures Using 3D Multi-Fluid Simulations to Investigate the Periodicity of the Auroral Brightness at Ganymede and its Dependence on Precipitating Particle Temperatures

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm21b2010p&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #SM21B-2010

Physics

Plasma Physics

[0310] Atmospheric Composition And Structure / Airglow And Aurora, [2704] Magnetospheric Physics / Auroral Phenomena, [6222] Planetary Sciences: Solar System Objects / Ganymede, [7800] Space Plasma Physics

Scientific paper

The electrodynamic interaction of Ganymede's mini-magnetosphere with Jupiter's co-rotating magnetospheric plasma has been shown to give rise to strong current systems closing through the moon and its ionosphere as well as through its magnetopause and magnetotail current sheet. This interaction is strongly evidenced by the presence of aurorae at Ganymede and Ganymede's bright auroral footprint in Jupiter's ionosphere. This footprint is located equatorward of the main auroral emissions, at the magnetic longitude of the field line threading Ganymede. The brightness of Ganymede's auroral footprint at Jupiter along with its latitudinal position have been shown to depend on the position of Ganymede relative to the Jovian plasma sheet and on the variations of the current flowing in the Jovian current sheet. Previous studies based on ultraviolet images obtained with the Hubble Space Telescope (HST) have demonstrated that the size of the auroral footprint was not limited to that of the moon alone. Rather, it mapped to a region corresponding to Ganymede's magnetosphere (Grodent et al., 2009). It was recently shown that Ganymede's auroral footprint brightness is characterized by three timescales of variations: a long 5-hour periodic variation, a non-systematic 10-40-minute variation, and a short 100-second quasi-periodic variation (Grodent et al., 2009). As for Ganymede's aurora, observations with the HST revealed longitudinally non-uniform oxygen emissions, with the brightest emissions confined to the geomagnetic latitudes defining the boundaries of the polar caps (Feldman et al., 2000). The goal of the present study is to examine the relationship between the longest and the shortest timescale periodicities of Ganymede's auroral footprint brightness and local processes occurring at Ganymede, using a 3D multi-fluid model. The model allows characterization of the interaction between Ganymede's magnetosphere and the local Jovian plasma environment by tracking the energies and fluxes of charged particles precipitating into Ganymede's atmosphere. This information can be used to understand the dynamics of Ganymede's magnetosphere in response to varying upstream Jovian magnetospheric conditions and to the fluttering of the plasma sheet over Ganymede. This also provides insight into the variability in brightness and morphology of Ganymede's aurora, which can be used to examine any correlation with the variability of Ganymede's auroral footprint on Jupiter's ionosphere. The model agrees well with the HST observations of Ganymede's aurora, suggests the presence of short- and long-period variabilities in the auroral brightness at Ganymede, and supports the hypothesis of a correlation between the variability of Ganymede's auroral footprint brightness and that of the aurora at Ganymede. It also investigates the range of plausible auroral electron acceleration mechanisms by accounting for the precipitating electron temperatures in the calculation of the auroral brightness under various initial conditions for neutral gas, plasma density, and magnetic field orientation.

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