AbstractIn this paper we present a new mechanism of the main energy conversion of the solar flare. Since a flare inducing prominence (flux tube) rises Vz300kms−1, the plasmas below it cannot continuously eject with Alfvén speeds of VA=3000kms−1 but probably with Vz≈±100kms−1. Plasma up and downflows with VA will within a short duration be blocked between the chromosphere where reconnected flux tubes are piling up, and the slowly rising flux rope. Hence the Petschek slow shock mechanism is difficult to be realized as a major energy converting mechanism.Adopting a conventional reconnecting morphology, we assume a magnetic component parallel to the photospheric neutral line, i.e. sheared fields of By≠0. Then Gauss’s law leads to non-vanishing electric charges σ; 4πσ=−div(V×B/c)≈By∂Vz/c∂x where the horizontal inflow velocity Vx changes to vertical down-flow Vz (e.g. By≈Bz=40G and Δx≈104km). Then the electric field parallel to the magnetic fields E∥ calculated from Coulomb’s law from this σ is found to be far greater than the Dreicer field, and accelerates electrons and protons. Thus the horizontally inflowing Poynting energy flux in area Sx is immediately converted to the kinetic energy of electron beams along the magnetic field in area Sz; with Sx/Sz≈4. The particle beam energy flux cannot exceed the Poynting energy flux however large E∥ may be. The total energy can be supplied by 10keV electrons and nbeam=2×107cm−3 for Vx=40kms−1. This inflow velocity Vx, though restricted by the rising prominence speed, explains the short flare duration consistent to observations. The electron beam flux nbeamVbeam will be simultaneously and co-spatially compensated by the slowly back-flowing bulk electrons, avoiding possible enormous charge pile-up.Instead of the conventional diffusion region, which contains serious difficulties if there is the shear as one should normally expect, we propose a reconnecting small region in the potential magnetic fields. The latter may be created by unwinding motions to erase the shear and to minimize energy, and the time scale is given only from the outside condition free from any diffusive processes such as the anomalous resistivity, because no electric currents may exist.
Energy conversion of the flare due to direct electric fields from the sheared reconnection
Advances in Space Research ; 41 , 6 ; 914-925
2007-04-18
12 pages
Aufsatz (Zeitschrift)
Elektronische Ressource
Englisch
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