Statistical characteristics of plasma flow in the magnetotail

The characteristics of plasma flow are studied statistically by using the IMP 6 plasma and magnetic field data. The analysis was performed by dividing the data set according to flow direction and flow velocity. Fast tailward flows (those with a tailward component of velocity exceeding 300 km/s) are observed only within a few RE of the estimated neutral sheet position and are associated with southward polarity of the magnetic field. They can therefore be interpreted as a product of reconnection operating at a location earthward of the spacecraft. On the other hand, slow tailward flows (those with a tailward component less than 300 km/s) are not associated with southward field polarity and are very similar to slow earthward flows (those with an anti‐tailward component less than 300 km/s) in such characteristics as association to northward inclination of the field and occurrence over a wide range of distance (± several RE) from the neutral sheet. These results suggest that there exist at least two source mechanisms of plasma flow in the magnetotail; X type neutral line in the near‐earth plasma sheet is likely to be the source of the fast tailward flows but other driving mechanisms are responsible for slow flows.