-1- Coronal Faraday Rotation of Coronal Faraday Rotation of Occulted Radio Signals Occulted Radio Signals M. K. Bird Argelander-Institut für Astronomie, Universität Bonn International Colloquium on Scattering and Scintillation in Radio Astronomy Pushchino, Russia Monday, 19 June 2006
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-1- Coronal Faraday Rotation of Occulted Radio Signals M. K. Bird Argelander-Institut für Astronomie, Universität Bonn International Colloquium on Scattering.
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Coronal Faraday Rotation ofCoronal Faraday Rotation of Occulted Radio Signals Occulted Radio Signals
M. K. BirdArgelander-Institut für Astronomie, Universität Bonn
International Colloquium on
Scattering and Scintillation in Radio Astronomy
Pushchino, Russia
Monday, 19 June 2006
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OutlineOutline Coronal Faraday Rotation – Definition Coronal FR using Various Radio Sources
– Pulsars
– Extended Continuum Sources
– Spacecraft (Helios E12: 1975-1984)
FR Variations over Different Time Scales– Background Coronal Magnetic Field
Simultaneous FR Spectra with QHCSimultaneous FR Spectra with QHC
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Rapid Sequence of Rapid Sequence of FR SpectraFR Spectra
QHC comes…… and goes!
[Chashei et al., 1999]
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FR Variations over Different Time Scales FR Variations over Different Time Scales … FR Signature of Coronal Mass Ejections … FR Signature of Coronal Mass Ejections
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CME Passing throughCME Passing through Helios-2 Ray Path Helios-2 Ray Path
Solwind CoronagraphImages recorded during Helios Solar Occultations
In Oct/Nov 1979
[Bird et al., 1985]
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CME Height-Time Diagram, 24 Oct 1979CME Height-Time Diagram, 24 Oct 1979
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CME Magnetic Field Estimates, 24 Oct 1979CME Magnetic Field Estimates, 24 Oct 1979
UT Solar Offset
(RS)
I
(hexems)
(deg)
<BS>
(mG)
08:00 5.1 1.8 ±10 ±2
08:30 5.1 1.8 +20 +4
09:00 5.0 1.9 +40 +8
09:30 5.0 1.9 +55 +11
10:00 4.9 2.0 +35 +7
10:30 4.9 2.0 ±5 ±1
11:00 4.8 2.0 -45 -9
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Coronal FR Mapping – the Future?Coronal FR Mapping – the Future?
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One line of sight to a linearly polarized sourceOne line of sight to a linearly polarized source
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Simulated Coronal FR for CR 1751Simulated Coronal FR for CR 1751
[J. Kasper, priv. comm, 2004.]
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Transient Simulations: October 2003 CMEsTransient Simulations: October 2003 CMEs
Faraday Rotation measurements provide a unique tool for investigating coronal magnetic structure…– Emperical model for the magnitude and radial dependence of the
background coronal magnetic field
– Evidence for outward (and inward) propagating Alfvén waves
– Evidence for dominance of magnetic fluctuations over density fluctuations
FR Mapping of CMEs is a difficult, but not hopeless, task.