Speaker
Bogdan Hnat
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I1.J101.pdf
Scaling and intermittency of the solar wind turbulence on MHD scales
B. Hnat1, S. C. Chapman1, K. T. Osman1, K. H. Kiyani1
1 CFSA, Department of Physics, University of Warwick, Coventry, UK
The solar wind magnetic Reynolds number has been estimated to be as high as 105. This
makes the solar wind an effective turbulence laboratory for collisional plasma, spanning
many temporal and spatial scales of interest. The last two decades have seen a rapid
progress in the solar wind studies, due to many space missions providing in situ
measurements, with ever increasing temporal resolution, and with multi-point spatial
measurements. Quantifying solar wind fluctuations has direct implications for our
understanding of MHD turbulence. Here we focus on quantification of three aspects of
MHD turbulence: its anisotropy, intermittency and the role of compressive fluctuations. We
review the phenomenological models of anisotropic MHD turbulence and discuss scaling
properties of power spectra derived from in situ fluctuations of solar wind velocity and of
magnetic field. Intermittency, considered as departure of scaling exponents of the higher
order moments from mono-fractal values, can be quantified via structure functions and by
examining distribution function of fluctuations on different scales. We show that this
scaling can be strongly affected by the presence of long-lived coherent structures, for
different quantities. Differences in the intermittent scaling of the magnetic field magnitude
and density fluctuations suggest that the solar wind plasma cannot be treated as
incompressible. We discuss different models for the compressible fluctuations in the inertial
range of MHD fluctuations.
