A Statistical Study on Wide‐Amplitude Kinetic Alfvénic Pulse at 8–12RE in the Magnetotail by THEMIS Spacecraft From 2008 to 2010

Abstract

AbstractUsing THEMIS spacecraft observations from 2008 to 2010, we perform statistical study on the wide‐amplitude kinetic Hall‐like Alfvénic wave (KAW) pulse in the near‐Earth tail region of 8–12 RE. The KAW pulse is identified by Ez‐By pulse with parallel‐predominantly Poynting flux (|P///PT| > 0.7) and large Ez/By ratio (|∆Ez/∆By | > VA, VA is Alfvénic velocity). Three typical events are presented. Therein, the KAW pulse on 24 March 2009 at the magnetic dipolarization is accompanied by the ion/electron dispersed structure (IDS/EDS; time of flight effect from reconnection source). Statistical study shows that the near‐Earth KAW pulse has a typical temporal scale of ∼15–25 s. The KAW pulses are mainly distributed in the plasma sheet boundary layer (PSBL) and tail lobe regions of β < 0.1 (β is the ratio of thermal pressure to magnetic pressure). The KAW pule at the PSBL/lobe has a wide distribution in the dawn‐dusk direction (−10 RE < |Y| < 10 RE), with the maximum occurrence at the midnight (|Y| < 4 RE). The KAW pulses at the PSBL/lobe are predominantly earthward‐propagating. Only a small number of the KAW pulses are tailward‐propagating. The earthward‐propagating pulse has a higher Poynting flux (PT) than tailward‐propagating pulse. The KAW pulse occurs during quiet time (AE < 200 nT) as well as substorm interval (AE > 200 nT). The substorm‐interval pulse has a higher Poynting flux than the quiet‐time pulse. Finally, tail reconnection is likely the significant source of the near‐Earth KAW pulses at 8–12 RE.