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See detailThe Magnetodiscs and Aurorae of Giant Planets
Szego, Karoly; Achilleos, Nicholas; Arridge, Chris et al

Book published by Springer Science & Business Media B.V. - Previously published in Space Science Reviews, Volume 187, Issues 1-4, 2015 (2016)

This volume contains the reports discussed during the Workshop “Giant Planet Magne- todiscs and Aurorae” held 26–30 November 2012, at the International Space Science Insti- tute, organised together with ... [more ▼]

This volume contains the reports discussed during the Workshop “Giant Planet Magne- todiscs and Aurorae” held 26–30 November 2012, at the International Space Science Insti- tute, organised together with the Europlanet project, supported by FP7 (Grant No. 228319). Magnetodiscs are large current sheets surrounding Jupiter and Saturn (also Uranus and Neptune) that are filled with plasma principally originating in the natural satellites of these worlds. They are also solar system analogues for astrophysical discs. Magnetodiscs are spe- cial features of the fast rotating giant planets, a special feature of rotationally driven magne- tospheres. Their structure is modified by variability in their plasma sources and by the solar wind. Auroral signatures in the optical and radio wavebands allow a diagnostic of these dynamical processes and enable the visualisation of these large plasma and field structures.The objective of this workshop was to address outstanding issues in the structure and dynamics of magnetodiscs using a comparative approach (see details under topics). More specifically, we aimed to review current understanding of magnetodiscs and auroral re- sponses to magnetodisc dynamics; characterise and understand radial plasma transport in magnetodiscs; determine how magnetic reconnection works in magnetodiscs, and describe the effects on plasma transport; describe the associated auroral responses to internal and ex- ternal magnetospheric processes; characterise how the solar wind influences magnetodiscs and the auroral responses to solar wind-driven dynamics; characterise the spectral and spa- tial properties of auroral emissions produced by magnetodisc dynamics; answer the ques- tion of whether there are significant differences between solar wind- and internally-driven dynamics; and determine the sources of local-time asymmetries in magnetodiscs. This volume is a unique synthesis of all aspects of the giant magnetospheres and their aurorae; it provides an interdisciplinary approach to understanding the coupled system from the solar wind to the atmosphere; it combines the latest observations with current theory and models; and it also contains sufficient breadth for students of magnetospheric and space physics to use as a reference for future research. [less ▲]

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See detailMagnetosphere-ionosphere mapping at Jupiter: Quantifying the effects of using different internal field models
Vogt, Marissa F.; Bunce, Emma J.; Kivelson, Margaret G. et al

Conference (2015, June)

The lack of global field models accurate beyond the inner magnetosphere (< 30 RJ) makes it difficult to relate Jupiter’s polar auroral features to magnetospheric source regions. Vogt et al. [2011] map ... [more ▼]

The lack of global field models accurate beyond the inner magnetosphere (< 30 RJ) makes it difficult to relate Jupiter’s polar auroral features to magnetospheric source regions. Vogt et al. [2011] map Jupiter’s equatorial magnetosphere to the ionosphere using a flux equivalence calculation that requires equal flux at the equatorial and ionospheric ends of flux tubes. This approach is more accurate than tracing field lines in a global field model, but only if it is based on an accurate model of Jupiter’s internal field. At present there are three widely used internal field models – VIP4, the Grodent anomaly model (GAM), and VIPAL. We will present results of a recently published study that quantifies how the choice of an internal field model affects the mapping of various auroral features using the Vogt et al. [2011] flux equivalence calculation. We find that different internal field models can shift the ionospheric mapping of points in the equatorial plane by several degrees and shift the magnetospheric mapping to the equator by ~30 Jovian radii radially and by less than one hour in local time. These shifts are consistent with differences in how well each model maps the Ganymede footprint, underscoring the need for more accurate Jovian internal field models. Understanding these differences is important for the continued analysis of HST images and in planning for Juno’s arrival at Jupiter in 2016. We will discuss differences in the size and location of the open/closed field line boundary and the mapping of specific auroral features, like polar dawn spots. We will also present some new analysis of the mapping of Jupiter’s main auroral oval and relate this to temporal variability observed in Jupiter’s magnetodisk. [less ▲]

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See detailOn the origin of the 2-3 minutes quasi-periodicity in the Jovian magnetosphere
Bonfond, Bertrand ULg; Vogt, Marissa F.; Gérard, Jean-Claude ULg et al

Poster (2011, October 05)

Several kinds of periodicities have been observed at Jupiter since the first probes fly-by. However, pre- vious investigations mainly focused on the longer timescales, such as the 40 minutes (QP40) or the ... [more ▼]

Several kinds of periodicities have been observed at Jupiter since the first probes fly-by. However, pre- vious investigations mainly focused on the longer timescales, such as the 40 minutes (QP40) or the 2- 3 days quasi-periodicity. Here we describe the recent finding of the 2-3 minutes quasi-periodic occurrence of UV flares in the active region of the polar aurora. These observations are then compared to other measurements of such quasi-periodic behaviors in electron and magnetic field data and their probably common origin is discussed. [less ▲]

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See detailImproved mapping of Jupiter’s auroral features to magnetospheric sources
Vogt, Marissa. F.; Kivelson, Margaret. G.; Khurana, Krishan. K. et al

in Journal of Geophysical Research. Space Physics (2011), 116

The magnetospheric mapping of Jupiter's polar auroral emissions is highly uncertain because global Jovian field models are known to be inaccurate beyond ∼30 RJ. Furthermore, the boundary between open and ... [more ▼]

The magnetospheric mapping of Jupiter's polar auroral emissions is highly uncertain because global Jovian field models are known to be inaccurate beyond ∼30 RJ. Furthermore, the boundary between open and closed flux in the ionosphere is not well defined because, unlike the Earth, the main auroral oval emissions at Jupiter are likely associated with the breakdown of plasma corotation and not the open/closed flux boundary in the polar cap. We have mapped contours of constant radial distance from the magnetic equator to the ionosphere in order to understand how auroral features relate to magnetospheric sources. Instead of following model field lines, we map equatorial regions to the ionosphere by requiring that the magnetic flux in some specified region at the equator equals the magnetic flux in the area to which it maps in the ionosphere. Equating the fluxes in this way allows us to link a given position in the magnetosphere to a position in the ionosphere. We find that the polar auroral active region maps to field lines beyond the dayside magnetopause that can be interpreted as Jupiter's polar cusp; the swirl region maps to lobe field lines on the night side and can be interpreted as Jupiter's polar cap; the dark region spans both open and closed field lines and must be explained by multiple processes. Additionally, we conclude that the flux through most of the area inside the main oval matches the magnetic flux contained in the magnetotail lobes and is probably open to the solar wind. [less ▲]

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See detailRelating Jupiter's auroral features to magnetospheric sources
Vogt, Marissa F.; Kivelson, Margaret G.; Khurana, Krishan K. et al

Poster (2010, December)

In order to understand the physical processes that produce the various auroral features we must first understand how the auroral emissions are linked to magnetospheric sources. However, magnetic mapping ... [more ▼]

In order to understand the physical processes that produce the various auroral features we must first understand how the auroral emissions are linked to magnetospheric sources. However, magnetic mapping of Jupiter’s polar auroral emissions to equatorial regions in which source currents are plausibly generated is highly uncertain because the available field models are inaccurate beyond ~30 Jovian radii. We have related auroral features to their magnetospheric sources through a flux equivalence calculation, where we require that the magnetic flux in some specified region at the equator equals the magnetic flux in the area to which it links in the ionosphere. This approach is preferred to tracing model field lines for mapping the auroral polar regions, because the latter method is inaccurate at large distances. Here we present our results, highlighting new mappings for the southern hemisphere, and will compare our mapping to auroral observations from both hemispheres. In particular we relate equatorial regions in which reconnection events have been identified with the locations of polar dawn spots and other possible auroral signatures of tail reconnection. We find that the mapping reproduces several other key auroral features. The polar auroral active region maps to just outside the dayside magnetopause, a region that we identify as the Jovian polar cusp. The polar auroral swirl region maps to open tail field lines and is interpreted as the Jovian polar cap. These interpretations are consistent with some earlier predictions based on auroral observations. We identify the boundary between open and closed flux in the ionosphere, which previously was not well defined. We show that the magnetic flux through the regions interpreted as the polar caps in both hemispheres closely matches the estimated flux through the tail lobe, consistent with the suggestion that this area maps to open field lines. [less ▲]

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