Global scale-invariance of small-scale magnetic fluctuations in solar wind turbulence as seen by CLUSTER

Details Global scale-invariance of small-scale magnetic fluctuations in solar wind turbulence as seen by CLUSTER Global scale-invariance of small-scale magnetic fluctuations in solar wind turbulence as seen by CLUSTER

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsh52a..05k&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #SH52A-05

Physics

Plasma Physics

[7827] Space Plasma Physics / Kinetic And Mhd Theory, [7836] Space Plasma Physics / Mhd Waves And Instabilities, [7863] Space Plasma Physics / Turbulence, [7868] Space Plasma Physics / Wave/Wave Interactions

Scientific paper

Spacecraft measurements of magnetic fluctuations of collisionless plasma turbulence in the solar wind typically show an ‘inertial range’ of MHD turbulence with a power-law power spectra. At higher frequencies a spectral break is seen around the ion-gyroscale with a subsequent steeper power-law, indicating a cross-over to spatial-temporal scales where kinetic effects become important. Theories for this second scaling range, also known as the “dissipation/dispersion” range focus on the spectral slope and the associated scaling exponents. We will present some results from very high-frequency magnetic field data from the four Cluster II spacecraft in intervals where the spacecraft were in quasi-stationary ambient solar wind and where the instruments were operating in burst mode. The magnetic field data are from the fluxgate and search-coil magnetometers from the Cluster FGM experiment (~67Hz), and the STAFF experiment (~450 Hz). These data sets provide observations of this dissipation/dispersion range over approximately two decades in frequency. This high cadence allows a better determination of the statistics at these small scales; especially the estimation of scaling exponents. We present a robust multiscale statistical analysis focusing on power spectra, PDFs of field fluctuations and higher-order statistics to quantify the scaling of fluctuations; as well as describing the degree of anisotropy in the fluctuations parallel and perpendicular to the average magnetic field. Both neutral fluid and MHD turbulence share a ‘‘classic’’ statistical signature - namely an intermittent multifractal scaling seen in the higher-order statistics. We test the statistical properties of the dissipation range and find in contrast monoscaling behavior, i.e., a global scale invariance. This provides a strong discriminator for the physics and phenomenology of the dissipation range in collisionless plasmas. Reference article: K. H. Kiyani, S. C. Chapman, Yu. V. Khotyaintsev, M. W. Dunlop, and F. Sahraoui, Phys. Rev. Lett. 103, 075006 (2009)

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