Magnetic reconnection produces oppositely directed, bidirectional high-speed flows (called reconnection jets) emanating from the reconnection point. The velocity of reconnection jet is given by the Alfvén velocity in Equation (22). In the case of the Sweet–Parker-type reconnection, the width of reconnection jet is nearly constant, comparable to the width of the diffusion region (see Figure 26)9 cm. On the other hand, the Petschek-type reconnection gives
Magnetic reconnection mainly converts magnetic energy into thermal and kinetic energy, and part of the kinetic energy is used for plasmoid ejection. An observational result on plasmoid ejection and its comparison to theoretical modeling are presented in Figure 43. The dynamics of an ejecting plasmoid has been investigated in numerical simulations (Magara et al., 1997; Choe and Cheng, 2000; Shibata and Tanuma, 2001).
Figure 43a shows a result from a two-dimensional MHD simulation, in which magnetic reconnection produces an ejecting magnetic island (two-dimensional counterpart of a plasmoid). The time variation of the convective electric field defined by Equation (16) is also plotted at this panel. Figure 43b shows the height-time relations of an observed plasmoid as well as hard X-ray intensity (Ohyama and Shibata, 1997). When comparing these simulation and observation, we assume that the time variation of the convective electric field is closely related to the time variation of hard X-ray emissions because the electric field can accelerate particles which contribute to producing hard X-ray emissions. The comparison suggests that the plasmoid ejection drives fast magnetic reconnection. More detailed investigations of plasmoid ejection are given by Choe and Cheng (2000), where multiple ejection of plasmoids and associated HXR bursts are discussed (see Figure 43c).
Shibata and Tanuma (2001) gives a rough estimate on the velocity of an ejecting plasmoid as follows:
Living Rev. Solar Phys. 8, (2011), 6
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