On the Scaling of Magnetic Field Strength with Loop Length in Solar Active Regions

MANDRINI, C.H.; JAIN, R.

Katlenburg-Lindau, Alemania

Conferencia; International Scientific Conference on Chromospheric and Coronal Magnetic Fields; 2005

Max Plank Institut - Lindau

Recognizing that loops are the main structures of the solar corona, we investigate how the magnetic field strength of coronal flux tubes depends on the end-to-end length of the tube for a sample of active regions. We use photospheric magnetograms from the Michelson Doppler Imager, aboard the Solar and Heliospheric Observatory, and compute potential and linear force-free extrapolation models. The free parameter of the models is adjusted so as to match the soft X-ray loops observed by the Solar Xray Telescope that flew aboard Yohkoh. For each model, we determine the average coronal field strength, <B>, in approximately one thousand individual flux tubes with regularly spaced footpoints, and obtain scatter plots of  <B> versus length, L. We determine the dependence of <B> for a wide range of flux-tube lengths and, then, we restrict to the range which is meaningful for the soft X-ray emission. For this range we find that <B> = L^{delta}, with {delta} = -1.3 +/- 0.5.  We compare our results with those of Mandrini et al. (2000), and find that both are fully consistent. Such studies have important implications for solar coronal heating models.