Cause of postterminator flux transfer events

The local time at which flux transfer events (FTEs) are observed affects the interplanetary magnetic field (IMF) dependence of their occurrence [Kawano and Russell, 1997]. Subsolar FTEs occur mainly during southward IMF, consistent with the dayside reconnection model. Postterminator FTEs occur during both southward and northward IMF but are not simply generated by pressure pulses convected to the magnetopause from the foreshock. This paper evaluates other possible generation mechanisms of these postterminator FTEs. We attribute the generation of the postterminator FTEs when IMF B_z < 0 to an "equatorial reconnection line," which is tilted according to the IMF B_y, just as we do for subsolar FTEs. When IMF B_z > 0, we find it unlikely that the postterminator FTEs are generated by local reconnection. Two possible sources are cusp reconnection and the "equatorial reconnection," with re-reconnection in the subsolar region [Nishida, 1989]. When the IMF is northerly directed but mostly equatorial, the "equatorial reconnection line" model fits better with observations. When the IMF is more northward, both models can explain observations we have at hand.