Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aspc..354..195a&link_type=abstract
Solar MHD Theory and Observations: A High Spatial Resolution Perspective ASP Conference Series, Vol. 354, Proceedings of the Con
Astronomy and Astrophysics
Astronomy
Scientific paper
In this study, turbulence of the magnetic field in the photosphere is explored by means of power spectra of line-of-sight photospheric magnetograms obtained for 16 active regions of different flare activity. Magnetic field measurements were made in the high resolution mode with the Michelson Doppler Imager instrument, onboard the Solar and Heliospheric Observatory. For each active region, we determined the daily soft X-ray flare index, A, which characterizes the flare productivity of an active region, being equal to one when the specific flare productivity is one C1.0 flare per day. The power index, α, of the magnetic power spectrum, E(k) ˜ k^{-α}, averaged over all analyzed magnetograms for a given active region, was then compared with the flare index. Here we report that those active regions which produced X-class flares possessed a steep power spectrum with α > 2.0, while the flare-quiet active regions with small A displayed a Kolmogorov-type spectrum of α ≈ 5/3. The data suggest that the flare index A may be determined from the power index α via the following equation: A(α)= 409.5 (α-5/3)^{2.49}. We also found that the magnitude of the power index at the stage of emergence of an active region is not related to the current flaring level of this active region but instead reflects its future flare productivity, when the magnetic configuration becomes well-evolved. This finding enables us to distinguish, at a very early stage, those solar active regions that are ``born bad'' and have a potential to produce powerful solar flares and significant disturbances in the Earth's magnetosphere.
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