Other
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsh41a1600a&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #SH41A-1600
Other
7524 Magnetic Fields, 7529 Photosphere, 7839 Nonlinear Phenomena (4400, 6944), 7863 Turbulence (4490)
Scientific paper
We propose a proxy for horizontal electric currents in the solar photosphere based on spectral and spatial distributions of magnetic energy dissipation. For a set of evolving active regions (ARs) observed with SOHO/MDI in the high resolution mode, the dissipation spectrum, k2E(k), and the spatial structure of dissipation, i.e., the Stokes dissipation function ɛ(x,y), were calculated from the observed line-of-sight component of the magnetic field. These functions allowed us to calculate (a part of) the horizontal electric current density in the photosphere. We found that as an active region emerges, large-scale horizontal electric currents are gradually generated and they determine the bulk of dissipation. When an active region decays, the large-scale horizontal currents decay faster than the small-scale currents. The density of transverse currents in active regions is in the range of < jh > ~ (0.008 - 0.028) A/m2, that is comparable with the density of vertical currents in active regions. We estimated the upper boundary of the plasma conductivity to be σ < 5× 10-8 s/m2, which is four orders of magnitude lower than the classical ohmic conductivity for the photosphere. We suggest two possible mechanisms for generation of these horizontal currents in the photosphere. One of them is the horizontal drift of charged particles in the medium of varying plasma pressure gradient at the periphery of a sunspot. Such drift can produce quasi-circular closed horizontal currents around sunspots. Another possibility could be the existence of horizontal axial current within a highly twisted horizontal magnetic structure laying in the photosphere along the magnetic neutral line. The horizontal currents may contribute significantly to the dynamics of the photosphere/corona coupling, as well as the estimation of non-potentiality of ARs.
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