Alfvenic Turbulence Dissipation Near the Sun as Inferred From Radio Scattering Observations

Details Alfvenic Turbulence Dissipation Near the Sun as Inferred From Radio Scattering Observations Alfvenic Turbulence Dissipation Near the Sun as Inferred From Radio Scattering Observations

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmsh44a..04h&link_type=abstract

American Geophysical Union, Fall Meeting 2004, abstract #SH44A-04

Physics

7509 Corona, 7863 Turbulence, 2149 Mhd Waves And Turbulence, 2159 Plasma Waves And Turbulence

Scientific paper

Radio scattering and scintillation (IPS) observations offer a powerful technique for studying dissipation-range plasma turbulence in the near-Sun solar wind. Although the physical mechanism responsible for the low-frequency, power-law component of the density fluctuation spectrum remains uncertain, we can show that the enhanced high-frequency end of the spectrum is almost certainly the direct signature of the linear compressibility of obliquely propagating Alfven waves in the ion-cyclotron regime. The evidence for this is (1) the enhancement is just as expected from an R-4 inward extrapolation of spacecraft magnetic spectra, and (2) IPS observations close to the Sun show large parallel ``random" velocities and an apparent wave bias that is consistent with the shear-Alfven dispersion relation. An important implication is that the observed density spectrum inner scale must be the direct signature of the dissipation of Alfven waves or Alfvenic turbulence. A passive damped-WKB model for the wave spectrum evolution is inadequate, as it predicts a stronger erosion of the spectrum by electron Landau damping than is consistent with radio and spacecraft data. Invoking a Kolmogorov cascade can counteract this erosion and push the spectral cutoff back out to near the ion inertial scale, where proton cyclotron damping becomes important. The wave energy dissipation in our damped cascade model is substantial, amounting to an equivalent base power flux of 5× 105 erg/cm2-s available for extended heating between 5--20 solar radii. For a cascade at the nominal Kolmogorov rate, the electron Landau and proton cyclotron heating are about equal. The estimated proton cyclotron contribution diminishes rapidly for weaker cascades and hence can be very sensitive to the precise inner scale size.

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