Abstract
Abstract. We model the open magnetic field region in Saturn's southern polar ionosphere during two compression regions observed by the Cassini spacecraft upstream of Saturn in January 2004, and compare these with the auroral ovals observed simultaneously in ultraviolet images obtained by the Hubble Space Telescope. The modelling employs the paraboloid model of Saturn's magnetospheric magnetic field, whose parameters are varied according to the observed values of both the solar wind dynamic pressure and the interplanetary magnetic field (IMF) vector. It is shown that the open field area responds strongly to the IMF vector for both expanded and compressed magnetic models, corresponding to low and high dynamic pressure, respectively. It is also shown that the computed open field region agrees with the poleward boundary of the auroras as well as or better than those derived previously from a model in which only the variation of the IMF vector was taken into account. The results again support the hypothesis that the auroral oval at Saturn is associated with the open-closed field line boundary and hence with the solar wind interaction.
Highlights
This study used a fixed magnetospheric magnetic field model based on the “Pioneer-11” model developed by Belenkaya et al (2006b), with the behaviour of the open field region being studied by varying the direction and strength of the “penetrating” interplanetary magnetic field (IMF) vector based on observations made by Cassini
In the present paper we further develop this study by considering the influence of the prevailing IMF, and the effect of the varying solar wind dynamic pressure observed by Cassini, which modulates the size of the magnetosphere and the other parameters that describe the model
In this paper we model the open field region in these two cases, taking into account the observed IMF vector, and the observed solar wind dynamic pressure which modulates the size of the magnetosphere
Summary
Observations of the polar ultraviolet (UV) auroras at Saturn by the Hubble Space Telescope (HST) show that they generally form a ring around each pole, ∼1◦–3◦ wide in latitude, located between ∼10◦–20◦ co-latitude (Gerard et al, 1995, 2004; Cowley et al, 2004a; Badman et al, 2006). Cowley and Bunce (2003) and Cowley et al (2004a) suggested, on the basis of theoretical discussion, that the magnetospheric. Observations of the polar ultraviolet (UV) auroras at Saturn by the Hubble Space Telescope (HST) show that they generally form a ring around each pole, ∼1◦–3◦ wide in latitude, located between ∼10◦–20◦ co-latitude (Gerard et al, 1995, 2004; Cowley et al, 2004a; Badman et al, 2006). Cowley and Bunce (2003) and Cowley et al (2004a) suggested, on the basis of theoretical discussion, that the magnetospheric. Belenkaya et al.: Dependence of the open-closed field line boundary a b c d e f g h i j k l m
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