MOP 2011, BOSTON, MA, USAJuly 14, 2011 Norbert Krupp Open-Close Field line Boundary Characterization of Saturn‘s magnetosphere using Cassini MIMI-LEMMS data and auroral observations from HST and Cassini-UVIS Norbert Krupp, Elias Roussos MPS, Katlenburg-Lindau, Germany Aikaterini Radioti, Denis Grodent LPAP, Liege, Belgium Donald G. Mitchell JHUAPL, Laurel, MD, USA Michele K. Dougherty Imperial College, London, UK

MOP 2011, BOSTON, MA, USAJuly 14, 2011 Norbert Krupp Previous work : Mitchell et al, 2009 electron beam width < 3 deg acceleration region < 1 RS electron beams associated with ion conics

MOP 2011, BOSTON, MA, USAJuly 14, 2011 Norbert Krupp Previous work : Belenkaya et al, 2011 HST UV images of Saturn’s southern auroras, projected onto a spheroidal surface 1100 km above the atmospheric 1 bar level, The locations of the poleward and equatorward boundaries of the emission in each image are shown by red crosses, The superposed solid orange lines show the open field regions Mappings of field lines ito quatorial plane (blue and purple squares for the equatorward and poleward boundaries) the two inner circles centred on the planet (black dot) show the inner and outer boundaries of the equatorial ring current, the red line corresponds to the boundary between open and closed field lines.

MOP 2011, BOSTON, MA, USAJuly 14, 2011 Norbert Krupp Previous work: Gurnett et al. GRL 2010 low-energy electron density drop auroral hiss ratio of diff. intensities from field-aligned energetic electrons with the same energy but oppositie directions is a proxy of open- closed field line configuration: ratio = 1 (CLOSED) ratio ≠ 1 (OPEN) Indications for open-closed field line boundary:

MOP 2011, BOSTON, MA, USAJuly 14, 2011 Norbert Krupp Cassini MIMI/LEMMS orientation and pitch angle coverage HE LE

MOP 2011, BOSTON, MA, USAJuly 14, 2011 Norbert Krupp Cassini MIMI/LEMMS orientation and pitch angle coverage HE LE

MOP 2011, BOSTON, MA, USAJuly 14, 2011 Norbert Krupp Example 1 65 deg S R = 5 RS L = MIMI/LEMMS pointing along field direction during whole period S/C staring large asymmetry in intensities measured in low-energy end compared to high-energy end pitch angle 180 degrees in the south possible crossing of open- closed field line boundary intensity increase by 3 orders of magnitude !!  electrons move along the open field line away from the planet‘s south pole towards the S/C closed open ???

MOP 2011, BOSTON, MA, USAJuly 14, 2011 Norbert Krupp Example 2 40 deg N R = 18 RS L = 40 MIMI/LEMMS pointing along field direction only shortly during S/C rotation S/C rotating large asymmetry in high energy end pitch angle 0 degrees in the north beams only every second S/C rotation (?)  electrons move along the open field line away from the north pole towards the S/C  highly collimated beams

MOP 2011, BOSTON, MA, USAJuly 14, 2011 Norbert Krupp Example 3 53 deg N R = 23 RS L = 65 MIMI/LEMMS pointing along field direction only shortly during S/C rotation lS/C rotating large asymmetry in low- energy end first then in high energy end pitch angle 0 degrees in the north  electrons move along the open field line away from the planet‘s north pole

MOP 2011, BOSTON, MA, USAJuly 14, 2011 Norbert Krupp Time periods of asymmetries in field-aligned electron intensities in Saturn‘s magnetosphere Cassini MIMI/LEMMS data July 2004-July time periods interpreted as periods when Cassini was on open field lines

MOP 2011, BOSTON, MA, USAJuly 14, 2011 Norbert Krupp Locations of open field lines in Saturn‘s magnetosphere using offset dipole (green) or Khurana field model (red) noon-midnight cutdawn-dusk cut

MOP 2011, BOSTON, MA, USAJuly 14, 2011 Norbert Krupp Traces of the open field line locations in the auroral zone Northern hemisphere Southern hemisphere questionable

MOP 2011, BOSTON, MA, USAJuly 14, 2011 Norbert Krupp 2008_195 NORTH 2008_129 NORTH2008_334 NORTH 2008_195 NORTH Emissions that are associated with open field lines (bifurcations: signatures of reconnection at the magnetopause, Radioti et al, submitted ) The location of the main ring of emission varies, but mainly the tracing is poleward of the emission, thus on open field lines 08/07/ _197 SOUTH RED: Current sheet model GREEN: dipole BLUE: Khurana 12 LT 18 LT

MOP 2011, BOSTON, MA, USAJuly 14, 2011 Norbert Krupp Comparison with recent Cassini/CAPS results: mapping of the cold and hot beam-like populations down to the ionosphere using a dipole within 20 RS NorthernSouthern see Poster by Arridge et al.

MOP 2011, BOSTON, MA, USAJuly 14, 2011 Norbert Krupp Conclusions and next steps 50 events of highly collimated field-aligned electrons are found in Cassini MIMI/LEMMS data  interpreted as open line regions in Saturn‘s high latitude magnetosphere Observations of open field lines when Cassini was at S and N degrees latitudes  open field lines map nicely poleward of the main auroral oval when compared with Cassini/UVIS images To do list: –include closed field line tracing when looking along the field for a better determination of open-closed boundary –Determine width of electron beams –Comparison with other data sets