Abstract
Abstract. A wide variety of interactions take place between the magnetized solar wind plasma outflow from the Sun and celestial bodies within the solar system. Magnetized planets form magnetospheres in the solar wind, with the planetary field creating an obstacle in the flow. The reconnection efficiency of the solar-wind-magnetized planet interaction depends on the conditions in the magnetized plasma flow passing the planet. When the reconnection efficiency is very low, the interplanetary magnetic field (IMF) does not penetrate the magnetosphere, a condition that has been widely discussed in the recent literature for the case of Saturn. In the present paper, we study this issue for Saturn using Cassini magnetometer data, images of Saturn's ultraviolet aurora obtained by the HST, and the paraboloid model of Saturn's magnetospheric magnetic field. Two models are considered: first, an open model in which the IMF penetrates the magnetosphere, and second, a partially closed model in which field lines from the ionosphere go to the distant tail and interact with the solar wind at its end. We conclude that the open model is preferable, which is more obvious for southward IMF. For northward IMF, the model calculations do not allow us to reach definite conclusions. However, analysis of the observations available in the literature provides evidence in favor of the open model in this case too. The difference in magnetospheric structure for these two IMF orientations is due to the fact that the reconnection topology and location depend on the relative orientation of the IMF vector and the planetary dipole magnetic moment. When these vectors are parallel, two-dimensional reconnection occurs at the low-latitude neutral line. When they are antiparallel, three-dimensional reconnection takes place in the cusp regions. Different magnetospheric topologies determine different mapping of the open-closed boundary in the ionosphere, which can be considered as a proxy for the poleward edge of the auroral oval.
Highlights
The nature of the interaction of the solar wind with planetary magnetospheres in interplanetary space is a key question in heliospheric physics
Grodent et al (2003), Pallier and Prangé (2001), and Vogt et al (2011) suggested that the so-called auroral “swirl” region coincides with the region of open ionospheric flux, which observations show to occupy approximately one-third of the area inside Jupiter’s main oval. This interpretation was supported by the calculations of Belenkaya et al (2006a) using the paraboloid model of Jupiter’s magnetospheric magnetic field with an interplanetary magnetic field (IMF) value ∼ 0.5 nT, which is characteristic of Jupiter’s solar wind environment
For southward IMF, this study provides some evidence that the open magnetospheric model gives a better explanation for the observed dawn–dusk asymmetry of the area bounded by the auroral oval than the partially closed model
Summary
The nature of the interaction of the solar wind with planetary magnetospheres in interplanetary space is a key question in heliospheric physics. Grodent et al (2003), Pallier and Prangé (2001), and Vogt et al (2011) suggested that the so-called auroral “swirl” region coincides with the region of open ionospheric flux, which observations show to occupy approximately one-third of the area inside Jupiter’s main oval This interpretation was supported by the calculations of Belenkaya et al (2006a) using the paraboloid model of Jupiter’s magnetospheric magnetic field (see Alexeev and Belenkaya, 2005, and references therein) with an interplanetary magnetic field (IMF) value ∼ 0.5 nT, which is characteristic of Jupiter’s solar wind environment. In this paper we consider two modes of solar wind–magnetosphere interaction at Saturn, namely with zero and with nonzero permeability of the magnetopause to the IMF
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