The gradual and impulsive reconnection and the preheating of solar flares

✍ Scribed by Hong-Wei Li; R. Pallavicini; Chung-Chieh Cheng

• Publisher: Springer
• Year: 1987
• Tongue: English
• Weight: 680 KB
• Volume: 107
• Category: Article
• ISSN: 0038-0938
• DOI: 10.1007/bf00152025

✦ Synopsis

We discuss the preheating phase of solar flares triggered by emerging magnetic flux. We consider the development of microinstabilities in the diffusion region during the emergence process and we propose four different types of reconnection, by which we explain the preheating, as well as the impulsive phase of flares. We find that during the emergence of new magnetic flux the current sheet will not 'jump' from the initial classical state to a fully turbulent one, but will remain in a marginally turbulent state which may develop either gradually or impulsively depending on the conditions of emergence. As a consequence of this, we find that four cases of reconnection are indeed possible: a week gradual heating, a weak impulsive process, a gradual preheating followed by an impulsive phase, and violent bursty reconnection.

The expansion rate of the diffusion region, the duration of the gradual phase, the magnetic energy release, and the energy deposition rate in coronal loops during the gradual phase are derived under simplifying assumptions and applied to X-ray and UV observations of flares from the Solar Maximum Mission.