Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008apj...685..606n&link_type=abstract
The Astrophysical Journal, Volume 685, Issue 1, pp. 606-621.
Astronomy and Astrophysics
Astronomy
5
Plasmas, Sun: Activity, Sun: Corona
Scientific paper
The energy balance at large scales in a coronal loop is investigated, using an analytical approach based on the reduced magnetohydrodynamic equations and a simplified model of the loop. The dynamics is regulated by two phenomena: the resonance excited by motions at the loop basis, which stores energy within the loop; and nonlinear couplings, which move energy toward smaller scales. The former phenomenon is studied using a linearized dissipative model; the properties of resonant modes are derived, and the input energy flux is found to be independent of dissipation. The spectral energy flux to small scales is calculated assuming local mode interactions and taking into account the space and time dependence of resonant modes. This flux is determined by interactions among fluctuations at the same order of resonance and the zero-frequency (DC) velocity fluctuation. The DC magnetic field fluctuations do not influence the spectral flux, although they dominate the large-scale fluctuations. An estimate for the velocity fluctuation in the loop is derived from the energy balance, finding an agreement with measures of nonthermal velocity in the solar corona. A peculiar form of the fluctuation spectrum is inferred, formed by an injection range at large scales, a preinertial range where magnetic energy dominates kinetic energy, an inertial range where the turbulence behaves as in an unbounded system, and a dissipative range. These analytical results are compared with those of a numerical model, finding a good agreement, and are discussed with respect to those of previous works.
Malara Francesco
Nigro Giuseppina
Veltri Pierluigi
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