Relationship between plasma flows and the near-Earth tail dipolarizations

The magnetic dipolarizations at the tail are often, if not always, associated with plasma flows of some magnitude. The associated flow direction is known to be earthward most often but not necessarily always. It is the primary goal of this paper to clarify the association between dipolarizations and the associated flow characteristics in general, but with a primary emphasis on tailward flow cases. Based on a number of dipolarizations that we identify at the near-Earth tail using the THEMIS tail observations we first confirm that dipolarizations can in general initiate in association with both earthward and tailward flows. Also, the main direction of the plasma flow, whether being earthward or tailward, is not critical in determining the intensity of the dipolarizations. We actually identify some events of tailward flow-associated dipolarizations that are as much intense as the earthward flow-associated events. The occurrence rate of the tailward flow-associated dipolarizations is mainly concentrated in the radial region of < 10 RE and in the local time region of 22-01 hr. However, its relative occurrence rate is rather low, ~19 % in the radial region and ~15.3 % in the local time region, as compared to that for the events associated with all other types of flows. Furthermore, the flow direction often changes no matter whether it is initially earthward or tailward near the onset time. As a consequence, the net transport of the magnetic flux during the main duration of the dipolarization process is earthward for nearly all of the dipolarizations that initiate with dominantly tailward flows near the onset, as is the case for those that initiate with dominantly earthward flows.