A Minimum Energy Fit Method to Reconstruct Photospheric Velocity and Magnetic Diffusivity in Active Regions from Observed Magnetograms and Dopplergrams

作者：Tremblay Benoit; Vincent Alain^*

来源：Solar Physics, 2015, 290(2): 437-466.

DOI：10.1007/s11207-014-0629-0

• Eddy-diffusivity
• Magnetograms
• Minimum energy fit
• Photosphere
• Velocity fields

We introduce MEF-R, a generalization of the minimum energy fit (MEF; Longcope, Astrophys. J. 612, 1181, 2004) to a non-ideal (resistive) gas. The new technique requires both vector magnetograms and Doppler velocities as input fields. However, in the case of active regions observed only with the Michelson-Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory (SOHO) such as AR 9077, we have only access to line-of-sight magnetograms. We reconstruct two-dimensional maps of the magnetic diffusivity eta(x,y) together with velocity components v (x) (x,y), v (y) (x,y), and v (z) (x,y) under the linear force-free magnetic field approximation. Computed maps for v (z) (x,y) very well match the Doppler velocities v (r) (x,y). We find the average value aOE (c)eta > a parts per thousand 10(8) m(2) s(-1) with a standard deviation of a parts per thousand aEuro parts per thousand 10(10) m(2) s(-1). Such high values of eta(x,y) are to be expected at some places since our magnetic diffusivity is actually eddy-diffusivity. Inside AR 9077, the maps of eta(x,y) do not resemble closely the maps from classical models of the magnetic diffusivity, but they are closer to eta as a function of temperature than to eta as a function of electric current density.

• 出版日期2015-2