A mechanism of dissipation of the perpendicular turbulent cascade in the solar wind

Details A mechanism of dissipation of the perpendicular turbulent cascade in the solar wind A mechanism of dissipation of the perpendicular turbulent cascade in the solar wind

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmsh44a..02m&link_type=abstract

American Geophysical Union, Fall Meeting 2004, abstract #SH44A-02

Physics

2149 Mhd Waves And Turbulence, 2159 Plasma Waves And Turbulence, 2164 Solar Wind Plasma

Scientific paper

We discuss a mechanism of dissipation that allows us to explain several key features of the turbulent fluctuations in the solar wind. The observational data suggest that the solar wind turbulence is dominated by fluctuations with wavevectors nearly perpendicular to the background magnetic field. This is in agreement with numerical simulations showing that the turbulent cascade tends to produce small spatial scales across the magnetic field rather than along it. The dissipation of the turbulent fluctuations is thought to be responsible for the observed perpendicular heating of the solar wind protons. The problem, however, is that the perpendicular heating is usually a signature of the cyclotron resonance, while the cross-field fluctuations cannot be immediately cyclotron-resonant with the protons. We suggest that the velocity shear associated with the cross-field fluctuations can excite a proton cyclotron instability. These unstable waves will then transfer the energy from the cross-field fluctuations to the protons thus dissipating the cascade and producing the perpendicular heating. We analyze the observed turbulence spectra and show that the threshold of the instability is consistent with the spectral break separating the inertial and dissipation ranges of the turbulence. In particular, during the periods of strong variation of the plasma beta in the solar wind, the threshold scales as the proton inertial length rather than the proton gyroradius, in agreement with the prediction of the theory. The observed turbulence spectra often have power-law dissipation ranges with an average spectral index of -3. We demonstrate that this fact is simply a consequence of a marginal state of the instability in the dissipation range.

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