Physics – Plasma Physics
Scientific paper
Oct 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001aps..dppli2004c&link_type=abstract
American Physical Society, 43rd Annual Meeting of the APS Division of Plasma Physics October 29 - November 2, 2001 Long Beach, C
Physics
Plasma Physics
Scientific paper
Solar flares are intense, abrupt release of energy in the solar corona. The time evolution of a flare can be divided into three phases. In the preflare phase, lasting tens of minutes before the flare onset, enhanced thermal emissions are detected mostly in soft X-rays (SXR). During the impulsive phase, lasting 1 to 10 minutes, the intensity and area of emissions in all wavelengths rapidly increase, and hard X-rays (HXR) are often observed. In the main phase, the overall emission intensity slowly declines over several hours. Observations of a cusp-shaped SXR emission and an HXR source located above the SXR loop support the conventional idea of magnetic reconnection in an arcade field geometry. However, previous arcade reconnection models do not explain the observation that an X-ray emitting plasma ejecta is launched before the impulsive phase and its rising speed continues to increase throughout this phase. Also, it is not well understood why a series of homologous flares often take place repetitively with some time interval in the same active region. Based on resistive MHD simulations, our model can explain all these observational features. In particular, we show that the rapid merging of a new magnetic island in the lower arcade with a pre-existing island above enhances the reconnection rate in the current sheet below the new island. The enhanced reconnection electric field at this time can accelerate electrons to more than 100 keV to produce hard X-ray emissions. After the island merging is completed, the reconnection rate declines over several hours. With a continuous supply of magnetic shear, these processes can repeat to form a series of homologous flares.
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