Magnetospheric mapping of the dayside UV auroral oval at Saturn using simultaneous HST images, Cassini IMF data, and a global magnetic field model

Abstract

Abstract.We determine the field-aligned mapping of Saturn's auroras into the magnetosphere by combining UV images of the southern dayside oval obtained by the Hubble Space Telescope (HST) with a global model of the magnetospheric magnetic field. The model is tailored to simulate prevailing conditions in the interplanetary medium, corresponding to high solar wind dynamic pressure and variable interplanetary magnetic field (IMF) strength and direction determined from suitably lagged field data observed just upstream of Saturn's dayside bow shock by the Cassini spacecraft. Two out of four images obtained in February 2008 when such simultaneous data are available are examined in detail, exemplifying conditions for northward and southward IMF. The model field structure in the outer magnetosphere and tail is found to be very different in these cases. Nevertheless, the dayside UV oval is found to have a consistent location relative to the field structure in each case. The poleward boundary of the oval is located close to the open-closed field boundary and thus maps to the vicinity of the magnetopause, consistent with previous results. The equatorward boundary of the oval then maps typically near the outer boundary of the equatorial ring current appropriate to the compressed conditions prevailing. Similar results are also found for related images from the January 2004 HST data set. These new results thus show that the mapped dayside UV oval typically spans the outer magnetosphere between the outer part of the ring current and the magnetopause. It does not encompass the region of primary corotation flow breakdown within the inner Enceladus torus.

Open and partially closed models of the solar wind interaction with outer planet magnetospheres: the case of Saturn

“…9, in which for all cases from Table 1 The paraboloid model has been used for different magnetized planets and has given results that allowed us to explain a lot of observational data. In particular, it has been extensively applied to Saturn (Alexeev et al, 2006;Belenkaya et al, 2006bBelenkaya et al, , 2007Belenkaya et al, , 2010Belenkaya et al, , 2011Belenkaya et al, , 2013Belenkaya et al, , 2014. The advantages of the model relate to its block structure; i.e., the magnetic field of each magnetospheric current system is calculated using its own program (block).…”

“…The Alexeev et al (2006) model was used in papers by Belenkaya et al (2006bBelenkaya et al ( , 2007Belenkaya et al ( , 2010Belenkaya et al ( , 2011Belenkaya et al ( , 2013Belenkaya et al ( , 2014 to compare the high-latitude edge of Saturn's auroral oval with the model open-closed ionospheric field line boundary, the results of which supported the idea that these boundaries are located rather close to each other Cowley et al, 2004a;Bunce et al, 2008). The IMF data used in these studies were obtained from Cassini magnetometer data when available, while the auroral boundaries were determined from Hubble Space Telescope (HST) UV images.…”

“…The open paraboloid model of Saturn's magnetospheric magnetic field was constructed and described by Alexeev et al (2006) and has been used by Belenkaya et al (2006bBelenkaya et al ( , 2007Belenkaya et al ( , 2010Belenkaya et al ( , 2011Belenkaya et al ( , 2013Belenkaya et al ( , 2014 in a number of subsequent investigations. The sources of magnetic field in this model are (i) the planetary magnetic field, (ii) the tail current system, (iii) the ring current, and (iv) the magnetopause shielding currents.…”

Auroral Processes at the Giant Planets: Energy Deposition, Emission Mechanisms, Morphology and Spectra

“…These field aligned currents are responsible for Saturn's main auroral emission and lie close to the boundary between open and closed field lines, driven by the flow shear between anti-sunward open and outer magnetosphere flux tubes, and the sub-corotating middle and inner magnetospheric flux tubes (Cowley et al 2004b. The auroral oval maps to the outer magnetosphere, beyond the ring current, with the poleward boundary of the aurora mapping to the vicinity of the magnetopause on the dayside (Carbary et al 2008;Belenkaya et al 2011).…”

Optimization of Saturn paraboloid magnetospheric field model parameters using Cassini equatorial magnetic field data

“…In this study, however, we focus on the global "paraboloid model" of Saturn's magnetosphere, in which the outer magnetopause boundary is taken to form a paraboloid of revolution about the planet-Sun line (Alexeev et al, 2006). This model has been used, in particular, to investigate the dependence of the magnetospheric magnetic structure and the origins of the aurorae on the direction and strength of the interplanetary mag-642 E. S. Belenkaya et al: Optimization of Saturn paraboloid magnetospheric field model parameters netic field (IMF), employing data from the Cassini spacecraft and the Hubble Space Telescope as inputs (Belenkaya et al, 2006a(Belenkaya et al, , 2007(Belenkaya et al, , 2010(Belenkaya et al, , 2011(Belenkaya et al, , 2013. In addition to the internal planetary field, taken to be the three-term axisymmetric model derived by Burton et al (2010) in the most recent work, this model contains representations of the field due to the ring current and the tail current, all contained within the paraboloid magnetopause by the surface current flowing on that boundary, to which a penetrating field due to the IMF can be added.…”