High-Speed Plasma Flows Observed in the Magnetotail during Geomagnetically Quiet Times: Relationship between Magnetic Reconnection, Substorm and High-Speed Plasma Flows

It has been widely accepted that a major mechanism for generating the high-speed plasma flows (HSPFs) observed in the magnetotail is the magnetic reconnection. Furthermore, these magnetotail HSPFs are observed during both geomagnetically quiet and active times. However, it has been open question and controversial whether the magnetic reconnection is main mechanism to produce the magnetotail HSPFs as observed even during geomagnetically quiet times, and how the relationship between the HSPFs and substorm is. In this study, we focused on the 4 events of the magnetotail HSPFs observed by THEMIS (the details are listed in Table), where the value of the GSM-X component for the plasma velocity (|Vx|) was higher than 300 km/s and that of the velocity perpendicular to the local magnetic field (|V⊥x| and |V⊥|) ranged between about 200 km/s and 500 km/s during which simultaneous AL and AU indices were lower than 40 nT and the range of the Kp index was between -1 and 1. Simultaneous all magnetic field components were varying and magnetic field intensity showed the enhancement in almost all events, suggesting that the HSPFs induced some magnetic perturbations, and the magnetic flux was transported and piled up by the HSPFs in the magnetotail even during geomagnetically quiet times. Interestingly, some HSPF events were associated with the Pi 2 waves, but the others were not. Based on this result, the magnetic reconnection might not always play a crucial role for producing the HSPFs during geomagnetically quiet times. Furthermore, the striking auroral activation was not observed in all events. This result suggests that the HSPFs during geomagnetically quiet times can occur in association with not only "substorm" but also "substorm-like phenomena", such as pseudo-substorm.<br />4 Events of "Magnetotail High-Speed Plasma Flows during Geomagnetically Quiet Times"
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