Three dimensional anisotropic k-spectra of turbulence at sub-proton scales in the solar wind

Details Three dimensional anisotropic k-spectra of turbulence at sub-proton scales in the solar wind Three dimensional anisotropic k-spectra of turbulence at sub-proton scales in the solar wind

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsh43d..08s&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #SH43D-08

Physics

Plasma Physics

[7827] Space Plasma Physics / Kinetic And Mhd Theory, [7863] Space Plasma Physics / Turbulence

Scientific paper

Large scale solar wind turbulence, where the MHD approximation is valid, has been extensively studied over the past decades. A general consensus exists that turbulence at those scales is dominated by strongly nonlinear Alfv’en waves, yielding power law spectra with the Kolmogorov scaling k-5/3. In contrast, electron scales have been only recently explored using data from the four Cluster satellites. Sahraoui et al., PRL [2009] have indeed shown the first evidence of dissipation range of SW turbulence at electron scales. Here we go further by measuring directly the first three dimensional dispersion relations and k-spectra of magnetic turbulence in the solar wind at the sub-proton scales. Taking advantage of the short separations of the Cluster spacecraft (d ˜ 200~km) we applied the k-filtering technique to the frequency range where the transition to sub-proton scales occurs. We show that the cascade is carried by highly oblique Kinetic Alfvén Waves with ω plas≤ 0.1ω ci down to k⊥&rho_i; ˜ 2. Each k-spectrum in the direction perpendicular to B0 shows two scaling ranges separated by a breakpoint (in the interval [0.4,1] k⊥ ρ i): a Kolmogorov spectrum k⊥-1.7 followed by a steeper spectrum ˜ k⊥-4.5. No clear cascade was evidenced on the parallel direction. We conjecture that the turbulence undergoes a transition-range, where part of energy is dissipated into proton heating via Landau damping, and the remaining energy cascades down to electron scales where electron Landau damping may predominate. Implications of the results on the heating problem of the solar wind will be discussed.

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