Energy balance in current sheets: From Petschek to gravity driven reconnection? |
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| Authors: | C Mercier J Heyvaerts |
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| Institution: | (1) Observatoire de Meudon (D.A.S.O.P.), 92190 Meudon, France;(2) Université de Paris VII et Observatoire de Meudon (D.A.F.), 92190 Meudon, France |
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| Abstract: | It has been shown earlier that energy balance processes play a very important role in the determination of the reconnection regime in the central diffusive region of a steady Petschek flow (usually considered elsewhere as isothermal and incompressible): as a consequence of the plasma thermal properties, abrupt transitions in the reconnection regime may occur for special external conditions. The regime becomes then a dynamical one, and it was suggested that onset of plasma microturbulence may result and act as a primary triggering mechanism in solar flares.In this paper we will reexamine the problem of onset of such dynamical transition and conclude that plasma microturbulence does not appear in a straightforward way. However it is possible that the canonical Petschek regime may evolute into a new one in which the dissipative sheet is no longer infinitesimal with respect to the dimensions of the structure, and in which gravity plays an important role. Flare triggering, if related to the reconnection regime, must then proceed by more complex processes, possibly related to tearing mode dynamics, or to more global properties of the magnetic structure of the active region. |
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