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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.

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Radio Scattering Observations of Turbulence in the Solar Wind and the Interstellar Medium

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  1. Radio Scattering Observations of Turbulence in the Solar Wind and the Interstellar Medium Steven R. Spangler University of Iowa

  2. 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.

  3. Example: Phase Scintillations of a VLBI Interferometer

  4. Types of Scintillation Phenomena • Frequency scintillation • Intensity cross-correlation

  5. 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

  6. 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

  7. Turbulence properties Bamert, Kallenbach, et al, 2004

  8. Shocks in the Heliosphere: Radio Remote Sensing • Woo and Schwenn, JGR 96, 21227, 1991 (e.g.) • Measurements made of Doppler fluctuations • The data

  9. Results from Woo and Schwenn, JGR 96, 21227, 1991

  10. MHD Shocks in the Solar Wind Comparison and compatibility between two sets of observations not thoroughly explored. There is much to learn.

  11. 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

  12. A method of probing supernova remnants Spitler and Spangler, ApJ 632, 932, 2005

  13. 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

  14. 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

  15. Radio Results on Coronal Turbulence I: Speed of irregularities << VA : Irregularities are non-propagating or oblique AIC waves

  16. Radio Results on Coronal Turbulence II: Density spectrum power law with “bulge” at ion inertial length (Coles and Harmon, 1989ff)

  17. Radio Results on Coronal Turbulence III: Smooth variation of turbulent intensity with heliocentric distance; no coronal “Kumasphere”. Not unanimous; see Lotova

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