Computer Science – Sound
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsh21a0722h&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #SH21A-0722
Computer Science
Sound
2159 Plasma Waves And Turbulence, 2164 Solar Wind Plasma, 2169 Sources Of The Solar Wind
Scientific paper
Recent modeling results by Coles on near-Sun IPS velocities has led us to revive an earlier suggestion (Harmon, 1989) that obliquely propagating Alfvén waves produce observable effects at the high-frequency end of the plasma density spectrum inferred from radio scattering. The idea that the high-frequency flattening of the density spectrum is an Alfvén compressibility effect is consistent with (1) the absence of such flattening in spacecraft B-field spectra and (2) the degree of flattening expected based on an inward extrapolation of Helios B-field spectra. This presumes that the density spectrum is a composite of a high-frequency Alfvén compressibility component and a Kolmogorov component (e.g., pressure balance or pseudosound fluctuations) riding on the Alfvénic turbulence. Our wave damping calculations show that passive erosion of outgoing WKB Alfvén waves produces an inner scale larger than that observed. However, we find that introducing a turbulent cascade at the Kolmogorov rate pushes the inner scale out to the ion inertial length, in better agreement with observations. Associated with this is substantial energy dissipation from both proton cyclotron damping and electron Landau damping. The field-aligned anisotropy of the near-Sun density fluctuations can be explained if the Alfvén wave angular spectrum starts out in highly oblique propagation. The radial drop in anisotropy can then be explained by wavefront turning from the Völk-Alpers effect. Such oblique Alfvén waves (unlike oblique fast waves) are also consistent with the IPS velocities, as they would give the observed radially-directed bias to the pattern velocity.
Coles William A.
Harmon John K.
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