mop 2011, boston, ma, usajuly 14, 2011 norbert krupp open-close field line boundary characterization...
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MOP 2011, BOSTON, MA, USA July 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, USA July 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, USA July 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 atmospheric1 bar level,
The locations of the polewardand equatorward boundaries of the emission in each imageare 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, USA July 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, USA July 14, 2011 Norbert Krupp
Cassini MIMI/LEMMS orientation and pitch angle coverage
HE LE
MOP 2011, BOSTON, MA, USA July 14, 2011 Norbert Krupp
Cassini MIMI/LEMMS orientation and pitch angle coverage
HE
LE
MOP 2011, BOSTON, MA, USA July 14, 2011 Norbert Krupp
Example 1
65 deg SR = 5 RSL = 30-40
• 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, USA July 14, 2011 Norbert Krupp
Example 2
40 deg NR = 18 RSL = 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, USA July 14, 2011 Norbert Krupp
Example 3
53 deg NR = 23 RSL = 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, USA July 14, 2011 Norbert Krupp
Time periods of asymmetries in field-aligned electron intensities in Saturn‘s magnetosphere
Cassini MIMI/LEMMS data July 2004-July 2011
50 time periods interpreted as periods when Cassini was on open field lines
MOP 2011, BOSTON, MA, USA July 14, 2011 Norbert Krupp
Locations of open field lines in Saturn‘s magnetosphere using offset dipole (green) or Khurana field model (red)
noon-midnight cut dawn-dusk cut
MOP 2011, BOSTON, MA, USA July 14, 2011 Norbert Krupp
Traces of the open field line locations in the auroral zone
Northern hemisphere
Southern hemisphere
questionable
MOP 2011, BOSTON, MA, USA July 14, 2011 Norbert Krupp
2008_195 NORTH
2008_129 NORTH 2008_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
08/07/2011
2008_197 SOUTH
RED: Current sheet modelGREEN: dipoleBLUE: Khurana
12 LT
18 LT
MOP 2011, BOSTON, MA, USA July 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
Northern Southern
see Poster by Arridge et al.
MOP 2011, BOSTON, MA, USA July 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 35-75 S and 20-72 N degrees latitudesopen 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