Relation of bursty bulk flows in the magnetotail and substorms

By using the data of three satellites of Cluster from 2001 to 2002, we study BBF in the magnetotail and its relationship to substorm. One or two of three satellites have already observed the BBF, but the rest haven't sometimes. When the peak value of bulk velocity satisfies condition requested in the selection rule, the satellite isn't in the region requested in the rule. When the satellite is in the requested region, the peak value of bulk velocity doesn't satisfy. Due to the complicated structure and motion of the neutral sheet, all the rules can't be satisfied simultaneously. Since BBF is high localized, it is very difficult to be observed. From the point of statistical view, there are some limiting factors in the results obtained by one single satellite. The whole duration of BBF observed by C1, C3, C4 account for 55.07, 77.48, and 55.52 percents of that observed by three satellites jointly. Statistical studies indicate that most substorms are accompanied by one or more BBF events. Only a few substorms are not accompanied by BBF events. The main reasons are as follows. The orbit of satellite isn't in the region requested in the selection rule. The structure and motion of neutral sheet are complicated. The BBF selection criteria are limited. BBF events are high localized.