Jupiter's main auroral emission; local time and temporal variability

Details Jupiter's main auroral emission; local time and temporal variability Jupiter's main auroral emission; local time and temporal variability

Sep 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008epsc.conf..719g&link_type=abstract

European Planetary Science Congress 2008, Proceedings of the conference held 21-25 September, 2008 in Münster, Germany. Online a

Physics

Scientific paper

Jupiter's main auroral oval is associated with the ionosphere-magnetosphere coupling current system which is related to the breakdown of corotation in the middle magnetosphere. Its auroral footpath is usually represented as a smooth line closing around the pole. However, this simplistic view is misleading in many regards. We have constructed a new reference contour in the northern hemisphere (Figure 1), based on more than 1000 HST/UV images, which does not look like an oval and does not close around the pole. We use this reference contour to quantify the effects of temporal and local time variability of the magnetospheric plasma characteristics on the location of the main auroral emission. Beyond the orbit of Ganymede (15RJ), two key ingredients are expected to have a measurable influence on the instantaneous shape of the main emission contour: the azimuthal current flowing in the current sheet [1,2] and the corotation breakdown distance. The former affects the radial extent of the magnetic field lines, and the latter determines the radial location of the field aligned currents transmitting momentum from the planet to the lagging plasma. So far, models used to magnetically map the auroral main emission between the ionosphere and the equatorial plane assumed that these two parameters are constant and axisymmetric. However, in situ observations, mainly by Galileo, have revealed large local time asymmetries and temporal variations in the plasma flows and distribution. These variations have an impact on the azimuthal current and the distance at which the plasma angular velocity becomes significantly smaller than planetary rotation. We use a new magnetic field model [3], inherited from VIP4 and including a magnetic anomaly in the northern hemisphere, to simulate the effects of these asymmetries on the location of the main auroral emission, and interpret the large scattering of the corresponding HST data point. References [1] Grodent, D. et al. (2008) JGR, 113, A01206, doi:10.1029/2007JA012601. [2] Radioti, A. et al. (2008) JGR, 113, A01215, doi:10.1029/2007JA012610. [3] Grodent, D. et al. (2008) JGR, in revision, doi:10.1029/2008JA013185.

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