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 CMEs are a rare case of an astronomical phenomenon with practical importance

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

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

Coronal Faraday rotation measurements with the VLA Simultaneous L band measurements at 1465 and 1665 MHz Easy measurements of RM ~ 1 rad/m 2 Imaging extended radio sources allows measurements of “differential Faraday rotation”

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

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

Polarization position angle time series for and MHz C2 frames

Rotation measure transient No change for D(RM)=10 rad/m 2 (25 deg pa at 1465 MHz) D(RM) apparently started before occultation of source by outer loop

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. Model predictions for CME-Faraday Rotation at 10 solar radii Prediction of 9 rad/sqm At greater solar elongation, so in the ballpark

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