Multipoint observations of Pi2 pulsations and correlation with dynamic processes in the near-Earth magnetotail on March 18, 2009

Simultaneous measurements from THEMIS spacecraft, GOES-11 and ground stations (Canadian Array for Realtime Investigations of Magnetic Activity or CARISMA, and 210° magnetic meridian or MM) on March 18, 2009 allow the study of dynamic processes in the near-Earth magnetotail and corresponding Pi2 pulsations on the ground in great detail. Fast earthward flows along with traveling Alfvén waves and fast mode waves in the Pi2 band were observed by three Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes (P3, P4 and P5) in the near-Earth plasmasheet. At the mid- to high-latitude nightside, the CARISMA stations located near the foot points of the three probes recorded Pi2s with two periods, about 80 s after the earthward fast flows observed by the P4 probe. The long-period Pi2 (140–150 s) belongs to the transient response Pi2 (TR Pi2), since the travel time of the Alfvén waves between the plasma sheet and CARISMA stations is very close to half the period of the long-period Pi2. The short-period Pi2 (60–80 s) has the same period band as the perpendicular velocity of the fast flows, which indicates that it may relate to the inertial current caused by periodic braking of the earthward fast flows. The 210° MM stations located at the low-latitude duskside also observed Pi2s with the same start time, waveform and frequency, about ～120 s after the earthward fast flows. Strong poloidal oscillations are shown by GOES-11 (～23 MLT) and the compressional component (Bb) is highly correlated with H components of the 210° MM stations, whereas the other two components (Br and Be) are not. These results confirm that the low-latitude Pi2s are generated by cavity mode resonance, which is driven by an impulsive broadband source in the near-Earth magnetotail.