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Probing Coronal Mass Ejections with Faraday Rotation Measurements

Probing Coronal Mass Ejections with Faraday Rotation Measurements. Steven R. Spangler and Catherine A. Whiting University of Iowa. Importance of CMEs. Associated with destabilization of coronal loops Basic physics questions remain as to how this occurs

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Probing Coronal Mass Ejections with Faraday Rotation Measurements

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  1. Probing Coronal Mass Ejections with Faraday Rotation Measurements Steven R. Spangler and Catherine A. Whiting University of Iowa

  2. Importance of CMEs • Associated with destabilization of coronal loops • Basic physics questions remain as to how this occurs • CMEs are a rare case of an astronomical phenomenon with practical importance

  3. Measuring Magnetic Fields in CMEs Radioastronomical polarization observations at GHz frequencies, and solar elongations of 1-3 degrees

  4. Literature on Faraday Rotation Observations of Coronal Mass Ejections • M. Bird et al 1985, Solar Physics 98, 341 • Y. Lui et al 2007, ApJ 665, 1439 (model predictions for theoretical CMEs) • Ingleby, Spangler, Whiting 2007, ApJ 668, 520

  5. Coronal Faraday rotation measurements with the VLA • Simultaneous L band measurements at 1465 and 1665 MHz • Easy measurements of RM ~ 1 rad/m2 • Imaging extended radio sources allows measurements of “differential Faraday rotation”

  6. VLA observations of CME-associated, Faraday Rotation anomaly on March 12, 2005 Constellation of radio sources LASCO coronagraph image during observing session

  7. Progress of the March 12, 2005 CME Position of CME relative to radio sources 23:12 UT 22:36 UT

  8. Polarization position angle time series for 2337-025 and 2335-015 2335-015 C2 frames 1465 MHz 2337-025

  9. Rotation measure transient • No change for 2335-015 • D(RM)=10 rad/m2 (25 deg pa at 1465 MHz) • D(RM) apparently started before occultation of source by outer loop

  10. Model predictions for CME-Faraday Rotation at 10 solar radii Prediction of 9 rad/sqm At greater solar elongation, so in the ballpark Fig. 6.— Mapping of the rotation measure corresponding to the four configurations of a flux rope onto the sky. The color shading indicates the value of the rotation measure. The arrows show the directions of the azimuthal and axial magnetic fields, from which a left‐handed (LH) or right‐handed (RH) helicity is apparent. Each configuration of the flux rope has a distinct rotation measure pattern.

  11. Future radioastronomical CME studies • VLA/LASCO C2 CME patrol (exploiting dynamic scheduling • Mileura Widefield Array (80-300 MHz) could see CMEs at great heliocentric distances. Issue is polarization of extragalactic sources at these frequencies

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