New kinetic evidence for the near‐Earth reconnection

An anomalously large southward Bz (−23 nT) is detected in association with tailward jet (1600 km/s) by GEOTAIL at X GSM = −46 R E . Variations of MHD parameters suggest that the large southward Bz is caused by piling‐up of reconnected field lines by the jet against the standing plasma sheet. In addition, the ion distribution at the time of the large southward Bz is found to show a counter streaming ions (CSI) feature. A hybrid simulation of a reconnection process not only reproduces this feature, but also proves that the CSI ions are from both the lobes. Taking this CSI feature as new kinetic evidence that both the lobes are magnetically connected, we firmly conclude that the event is interpreted in terms of near‐Earth reconnection.