Abstract
Abstract. Magnetic reconnection is the crucial process in the release of magnetic energy associated with magnetospheric substorms and with solar flares. On the basis of three-dimensional resistive MHD simulations we investigate similarities and differences between the two scenarios. We address in particular mechanisms that lead to the onset of reconnection and energy release, transport, and conversion mechanisms. Analogous processes might exist in the motion of field line footpoints on the sun and in magnetic flux addition to the magnetotail. In both cases such processes might lead to a loss of neighboring equilibrium, characterized by the formation of a very thin embedded current sheet, which acts as trigger for reconnection. We find that Joule (or ohmic) dissipation plays only a minor role in the overall energy transfer associated with reconnection. The dominant transfer of released magnetic energy occurs to electromagnetic energy (Poynting) flux and to thermal energy transport as enthalpy flux. The former dominates in low-beta, specifically initially force-free current sheets expected for the solar corona, while the latter dominates in high-beta current sheets, such as the magnetotail. In both cases the outflow from the reconnection site becomes bursty, i.e. spatially and temporally localized, yet carrying most of the outflow energy. Hence an analogy might exist between bursty bulk flows (BBFs) in the magnetotail and pulses of Poynting flux in solar flares. Further similarities might exist in the role of collapsing magnetic flux tubes, as a consequence of reconnection, in the heating and acceleration of charged particles.
Highlights
Analogies between magnetospheric substorms and solar eruptions, coronal mass ejections (CMEs) and solar flares, have been invoked for a long time (e.g., Kuperus, 1976)
Using ideal and resistive MHD simulations, we have investigated similarities and differences between magnetic reconnection scenarios in the magnetotail and the solar corona, related to magnetospheric substorms and solar flares
The initial configurations consisted of stretched closed field line models typical for the magnetotail and, in the solar case, representing the expected structure below a departing CME (e.g., Forbes, 1996). Since it is not clear whether the current sheet in the stretched field configuration below the CME is force-free, and for comparison with the magnetotail, we have investigated both force-free and non-force-free configurations
Summary
Analogies between magnetospheric substorms and solar eruptions, coronal mass ejections (CMEs) and solar flares, have been invoked for a long time (e.g., Kuperus, 1976). A central process in either case is the release of previously stored magnetic energy and its conversion into particle energy in the form of heating, bulk plasma kinetic energy, and accelerated particles with suprathermal energies. The ejection of a plasmoid or flux rope is a central part of substorms as well as CMEs. In this paper we focus on additional similarities that may exist in the mechanisms for initiating reconnection and the details of the energy release and conversion processes. 2 with a brief description of the basic approach and the numerical procedure, followed by simulation results on the early phase preceding the onset of reconnection We investigate the energy transfer after the onset of reconnection, based on three-dimensional MHD simulations 5), complemented by more localized, two-dimensional particlein-cell simulations of reconnection The mechanisms that govern dissipation and transfer are addressed in more detail in Sect.
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