Computer Science
Scientific paper
Aug 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006iaujd...3e..18k&link_type=abstract
Solar Active Regions and 3D Magnetic Structure, 26th meeting of the IAU, Joint Discussion 3, 16-17 August, 2006, Prague, Czech R
Computer Science
Scientific paper
The purpose of the report is to consider possibility of formation of small-scale plasma structures in the turbulent flows of photospheric gas and to analyse the dependence of their spectrum and intensity on height and the strength of magnetic field. Results of observations with high spatial resolution clearly show that the solar photospheric flows include both organized and stochastic motions. The spectra associated with the stochastic velocity fields obey power laws, which are close to the law of Kolmogorov turbulence. Since the degree of photospheric gas ionization is small, then electrically charged particles can be regarded as passive contaminants embedded in motions of the gas. Taking these facts into account, the present consideration was based on the macroscopic description of the charged particle behaviour in the ambipolar diffusion approximation, and under the given velocity field of the neutral gas. Length-scales of the plasma structures were restricted to an inertial range of the turbulence, where the random velocity field of the gas is homogeneous and isotropic one with the known statistical properties. An analytic expression for the spatial spectrum of the structures was derived as well as the formula for estimation of the RMS level of their intensity. The plasma structure formation was analysed in the height range from 150 to 350 km. It was shown that in spite of changes in parameters of the photosphere and the turbulence with altitude (e.g., an increase in the kinematic viscosity of the gas, and decrease in the rate of turbulent energy dissipation), the shape of the spectrum and the intensity of the structures remain almost unchanged in our calculations. At the same time the increase in the magnetic field from 5 to 250 G results in the increase in the intensity of deviation from the mean plasma density from 2.5 to 6% for the length-scales of structures smaller than 300 km, and in the slope of the spectrum, if it is approximated by a power law, then power index takes values from -1.2 to -1.6. The obtained result seems to be important for better understanding of basic solar phenomena, such as generation of the random component of magnetic field or chaotic excitation of solar oscillations.
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