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Anisotropic Angular Broadening in the Solar Wind

Published online by Cambridge University Press:  12 April 2016

K.R. Anantharamaiah ,
Pradeep Gothoskar  and
T.J. Cornwell
K.R. Anantharamaiah
Affiliation:
Raman Research Institute, Bangalore 560 080, INDIA
Pradeep Gothoskar
Affiliation:
National Center for Radio Astrophysics, Pune 411 007, INDIA
T.J. Cornwell
Affiliation:
National Radio Astronomy Observatory, Socorro, NM 87801, USA

Abstract

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We present Very Large Array observations at wavelengths of 2, 3.5, 6, and 20 cm, of angular broadening of radio sources due to the solar wind in the region 2-16 solar radii. Angular broadening is anisotropic with axial ratios in the range 2-16. Larger axial ratios are observed preferentially at smaller solar distances. Assuming that anisotropy is due to scattering blobs elongated along magnetic field lines, the distribution of position angles of the elliptically broadened images indicates that the field lines are non-radial even at the largest heliocentric distances observed here. At 5R⊙, the major axis scattering angle is ~ 0.7" at λ = 6 cm and it varies with heliocentric distance as R−1.6. The level of turbulence, characterized by the wave structure function at a scale of 10 km along the major axis, normalized to λ = 20 cm, has a value 20±7 at 5R⊙ and varies with heliocentric distance as R−3. Comprison with earlier results suggest that the level of turbulence is higher during solar maximum. Assuming a power-law spectrum of electron density fluctuations, the fitted spectral exponents have values in the range 2.8–3.4 for scales sizes between 2–35 km. The data suggests temporal fluctuations (of up to 10%) in the spectral exponent on a time scale of a few tens of minutes. The observed structure functions at different solar distances do not show any evidence for an inner scale; the upper limits are 1 km at 2R⊙ and 4 km at 13R⊙. These upper limits are in conflict with earlier determinations and may suggest a reduced inner scale during solar maximum.

Type
Coronal Heating and Solar Wind Acceleration
Information
International Astronomical Union Colloquium , Volume 154: Solar and Interplanetary Transients , 1996 , pp. 77 - 81
Copyright
Copyright © Kluwer 1997

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