A theory of patchy and intermittent reconnections for magnetospheric flux transfer events

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Abstract
We propose that the elbow‐shaped flux transfer events (FTEs) of Russell and Elphic (1979) are initiated by a specific normal mode of three‐dimensional tearing of the magnetopause current sheet, resulting in a three‐dimensional component reconnection driven by the solar wind. The patchy nature of the proposed three‐dimensional tearing reconnection is determined by the structure of the three‐dimensional tearing on the dayside magnetopause, leading to isolated reconnection sites; the intermittent nature is governed externally by the fluctuation of the interplanetary magnetic field (IMF) and internally regulated by the ionospheric line‐tying effect. The proposed 3DT reconnection can occur simultaneously with the single x line intermittent or quasi‐steady reconnection if the IMF drapes over the dayside magnetopause, which takes place when the solar wind speed exceeds the MHD fast‐mode speed. Magnetic field signatures of the 3DT reconnection are consistent with the elbow‐shaped FTE signatures. Electric fields associated with the elbow‐shaped FTEs can be expected to be spiky, peaking near the center of the localized FTE reconnection sites. The spiky electric field of FTEs is expected to produce channels of enhanced magnetospheric convection. The observed multiple field‐aligned current sheets and auroral arcs fanning out from the cusp region along enhanced convection channels can be expected as consequences of the proposed 3DT reconnection on the dayside magnetopause. The polar cap potential due to the elbow‐shaped FTEs is predicted to have a dependence on the IMF polar angle somewhat different from that of the single x line reconnection.