Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsm43b1769r&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #SM43B-1769
Astronomy and Astrophysics
Astrophysics
[2149] Interplanetary Physics / Mhd Waves And Turbulence, [2721] Magnetospheric Physics / Field-Aligned Currents And Current Systems, [7509] Solar Physics, Astrophysics, And Astronomy / Corona, [7526] Solar Physics, Astrophysics, And Astronomy / Magnetic Reconnection
Scientific paper
Coronal loops are threaded by a strong magnetic field. As they are so strongly magnetically dominated a first simplification in modeling their dynamics is to neglect the velocity field. This is in fact supposed to be very small in comparison with the Alfvén velocity associated with the DC magnetic field. Setting the velocity equal to zero u=0 leads to a static force-free solution for the magnetic field in the MHD equations. The overall dynamics are then supposed to evolve through a series of equilibria, where each equilibrium configuration is successively destabilized by magnetic reconnection. We simulate the Parker problem in the framework of reduced MHD, where a coronal loop is modeled as an elongated Cartesian box threaded by a strong magnetic field, whose footpoints are stirred by a velocity mimicking photospheric motions. We confirm that the velocity and magnetic field fluctuations induced in the computational box are very small compared with the strong axial magnetic field, and that velocity fluctuations are smaller than magnetic fluctuations. Both energy spectra develop well-defined power-laws. We show that the presence of a small but finite velocity field allows for transfers of energy among shells in Fourier space, that would be impossible if u=0 exactly. A staggering difference with 3-periodic MHD simulations with no average magnetic field is that energy flows along the velocity field are negligible, while the cross-field (between shells of u and b) energy flows contribute equally as the flows among shells of b. Locality and non-locality will be quantitatively discussed.
Rappazzo A. F.
Velli M. M.
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