Download - Radio Scattering Observations of Turbulence in the Solar Wind and the Interstellar Medium
Radio Scattering Observations of Turbulence in the Solar Wind and the
Interstellar Medium
Steven R. Spangler
University of Iowa
Basic physics of extracting information on astrophysical plasma turbulence: the radio
refractive index
• Radio propagation effects primarily diagnose density fluctuations.• Are secondary indicators of B.
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Scintillation Contributions to Heliospheric Physics
• Radial evolution in turbulence
• Velocity structure of the solar wind
• Possible identification of coronal kinetic Alfven waves (Harmon and Coles 2005)
• Remote sensing of heliospheric shocks
Shocks in the Heliosphere: Direct Measurements
• Bamert, Kallenbach, et al, ApJ 609, L99, 2004• Studied dependence of turbulence and cosmic ray
intensities on distance upstream of shock (< 0.11 au)
• Two order of magnitude enhancement in turbulence level before crossing shock jump
• Additional factor of 10 jump in turbulence at shock
Shocks in the Heliosphere: Radio Remote Sensing
• Woo and Schwenn, JGR 96, 21227, 1991 (e.g.)
• Measurements made of Doppler fluctuations
• The data
MHD Shocks in the Solar Wind
Comparison and compatibility between two sets of observations not thoroughly explored. There is much to learn.
The Interstellar Medium
The ISM has powerful shock waves (supernova remnants) that accelerate the cosmic rays. Image from Univ. of Wisconsin WHAM instrument, R. Reynolds,
M. Haffner, et al
Radio sources viewed through supernova
remnants show minimal “blurring” due to
turbulence
• Intensity of turbulence in downstream region enhanced by less than a factor of 30,000 (G127) and 2000 (S147) relative to undisturbed ISM
Present Results and Open Questions
• Radio scattering observations provide good diagnostics of heliospheric shocks.
• A detailed comparison of radio and in-situ measurements would be an interesting astrophysical exercise.
• Similar scattering effects not yet seen for supernova remnants. Work by Bamert and Kallenbach indicates further inquiries are of interest.
Thanks
Radio Results on Coronal Turbulence I:
Speed of irregularities << VA : Irregularities are non-propagating or
oblique AIC waves
Radio Results on Coronal Turbulence II:
Density spectrum power law with “bulge” at ion inertial length (Coles and Harmon, 1989ff)