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Ann. Geophys., 24, 3139-3150, 2006
www.ann-geophys.net/24/3139/2006/
© European Geosciences Union 2006
Linear prediction studies for the solar wind and Saturn kilometric radiation
U. Taubenschuss1, H. O. Rucker1, W. S. Kurth2, B. Cecconi2, P. Zarka3, M. K. Dougherty4, and J. T. Steinberg5
1Space Research Institute, Austrian Academy of Sciences, A-8042 Graz, Austria
2Department of Physics and Astronomy, The University of Iowa, Iowa City, Iowa 52242, USA
3Laboratoire d'Etudes Spatiales et d'Instrumentation en Astrophysique, Observatoire de Paris, 92195 Meudon, France
4Blackett Laboratory, Imperial College of Science and Technology, London SW7 2BZ, UK
5Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
Abstract. The external control of Saturn kilometric radiation (SKR) by the
solar wind has been investigated in the frame of the Linear
Prediction Theory (LPT). The LPT establishes a linear filter
function on the basis of correlations between input signals, i.e.
time profiles for solar wind parameters, and output signals, i.e.
time profiles for SKR intensity. Three different experiments onboard
the Cassini spacecraft (RPWS, MAG and CAPS) yield appropriate data
sets for compiling the various input and output signals. The time
period investigated ranges from DOY 202 to 326, 2004 and is only
limited due to limited availability of CAPS plasma data for the
solar wind. During this time Cassini was positioned mainly on the
morning side on its orbit around Saturn at low southern latitudes.
Four basic solar wind quantities have been found to exert a clear
influence on the SKR intensity profile. These quantities are: the
solar wind bulk velocity, the solar wind ram pressure, the magnetic
field strength of the interplanetary magnetic field (IMF) and the
y-component of the IMF. All four inputs exhibit nearly the same
level of efficiency for the linear prediction indicating that all
four inputs are possible drivers for triggering SKR. Furthermore,
they act at completely different lag times ranging from ~13 h
for the ram pressure to ~52 h for the bulk velocity. The lag
time for the magnetic field strength is usually beyond ~40 h
and the lag time for the y-component of the magnetic field is
located around 30 h. Considering that all four solar wind
quantities are interrelated in a corotating interaction region, only
the influence of the ram pressure seems to be of reasonable
relevance. An increase in ram pressure causes a substantial
compression of Saturn's magnetosphere leading to tail collapse,
injection of hot plasma from the tail into the outer magnetosphere
and finally to an intensification of auroral dynamics and SKR
emission. So, after the onset of magnetospheric compression at least
~1.2 rotations of the planet elapse until intensified SKR
emission is visible in a Cassini-RPWS dynamic spectrum.
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