Abstract
JOURNAL OF GEOPHYSICAL RESEARCH,
VOL. 113,
A10210,
18 PP., 2008
doi:10.1029/2008JA013276
An empirical model of Saturn's bow shock: Cassini observations of shock location and shape
Space and Atmospheric Physics Group, The Blackett Laboratory, Imperial College London, London, UK
Atmospheric Physics Laboratory, Department of Physics and Astronomy, University College London, London, UK
Space and Atmospheric Physics Group, The Blackett Laboratory, Imperial College London, London, UK
Heliophysics Science Division, NASA GSFC, Greenbelt, Maryland, USA
Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa, USA
Mullard Space Science Laboratory, Department of Space and Climate Physics, University College London, Dorking, UK
Centre for Planetary Sciences, University College London, London, UK
Mullard Space Science Laboratory, Department of Space and Climate Physics, University College London, Dorking, UK
Centre for Planetary Sciences, University College London, London, UK
We present a new empirical model of Saturn's bow shock that utilizes observations from the Cassini spacecraft. Shock crossings
are identified in magnetic field and plasma observations made by Cassini between June 2004 and August 2005. The Cassini crossings
are then combined with the crossings made during the Saturn flybys of Pioneer 11, Voyager 1, and Voyager 2. Solar wind dynamic
pressures for the Cassini crossings are estimated using upstream electron densities determined from Langmuir wave observations
made by the Radio and Plasma Wave System. The crossing positions are rotated into aberrated coordinates to correct for the
effect of the planet's orbital motion. In the case of Saturn this rotation is by ∼1°. To correct for solar wind dynamic pressure
variations, the crossing positions are normalized to the average pressure
PSW
= 0.048 nPa. The model is then obtained by fitting a conic section to the crossings using a nonlinear least squares technique.
To validate the assumptions made in constructing the model, we treat the parameters previously assumed to be constants as
variables and fit their values using an optimization routine; this leads to a conic section that is within the positional
uncertainty of the model. The spacecraft trajectories are considered, and we conclude that they do not significantly bias
the model. The new model is compared to the existing models, and the similarities and differences are discussed. We suggest
that the new model gives the most accurate empirical representation of the shape and location of Saturn's bow shock.
Received 7 April 2008; accepted 23 July 2008; published 17 October 2008.
Citation: (2008), An empirical model of Saturn's bow shock: Cassini observations of shock location and shape, J. Geophys. Res., 113, A10210, doi:10.1029/2008JA013276.
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