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Evolution and decay of an active region: Magnetic shear, flare and CME activity  

Marcelo Lopez Fuentes   Submitted: 2000-08-09 21:03

An activity complex was observed on the solar disk between April, 1996 and February, 1997. This complex reached its highest level of activity during the the birth of AR 7978. Our observations extend over six solar rotations, from the emergence of AR 7978 (July 1996) until the decay and dispersion of its flux (November 1996). Multi-wavelength observations, provided by instruments aboard the Solar and Heliospheric Observatory (SOHO) and the Japanese spacecraft Yohkoh, follow the evolution of the region from the photosphere to the corona. Using full disk magnetograms obtained by the Michelson Doppler Imager (SOHO/MDI) as boundary condition, we calculate the coronal magnetic field and determine its shear by fitting the computed field lines to the observed soft X-ray loops. We discuss the evolution of the coronal field shear and its probable relation to flare and coronal mass ejection activity.

Authors: Mandrini, C.H., van Driel-Gesztelyi, L., Thompson, B., Plunkett, S., Demoulin, P., Aulanier, G.

Publication Status: Geofis. Inter. 39, N1, 73-80
Last Modified: 2000-08-09 21:03
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Observation and analysis of a 3B/X3 solar flare  

Marcelo Lopez Fuentes   Submitted: 2000-07-13 20:04

We analyze the evolution of active region (AR) NOAA 7070 and relate it to a 3B/X3 solar flare that ocurred on February 27, 1992. The soft X-ray flare observations were obtained by the SXT (Soft X-ray Telescope) on board of the Yohkoh satellite, and those in Hα come from the Udaipur Observatory (India). The location of the Hα kernels and ribbons, and the shape of soft X-ray loops are compared with the magnetic field model of the AR. Both, observations and model, suggest that the coronal loops are too sheared before the flare and that the configuration relaxes after energy release. We compute the magnetic free energy using the virial theorem, finding a lower limit of 2x1032 erg; this value is in good agreement with those that are typical for the energy released by solar flares.

Authors: M.C. Lopez Fuentes, C.H. Mandrini, M.G. Rovira, P. Demoulin

Publication Status: Geofis. Inter., Vol.39, 1, p.65
Last Modified: 2000-07-13 20:04
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Evolution and decay of an active region: Magnetic shear, flare and CME activity
Observation and analysis of a 3B/X3 solar flare

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