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.

2 22 22

2

/1

1

p

e

k cn

Example: Phase Scintillations of a VLBI Interferometer

Types of Scintillation Phenomena

(i) Frequency scintillation

(ii) Intensity cross-correlation

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

Bamert, Kallenbach, et al, 2004

Turbulence

properties

Shocks in the Heliosphere: Radio Remote Sensing

• Woo and Schwenn, JGR 96, 21227, 1991 (e.g.)

• Measurements made of Doppler fluctuations

• The data

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

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

A method of probing supernova remnants

Spitler and Spangler, ApJ 632, 932, 2005

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)

Radio Results on Coronal Turbulence III:

Smooth variation of turbulent intensity with heliocentric distance;

no coronal “Kumasphere”. Not unanimous; see Lotova