Magnetosphere-Ionosphere Coupling on Multiple Scales Associated with Magnetotail Flow Bursts: Event Study

Abstract:

Magnetosphere-ionosphere (M-I) coupling in the auroral region is achieved, essentially, by field-aligned currents (FAC) and ultra-low frequency (ULF) waves, covering a broad range of spatial and temporal scales. Current systems of various sizes and intensities, often embedded in each other, connect the auroral ionosphere to the equatorial magnetosphere, while changes in these current systems, like their setup or intensification, are naturally associated with ULF waves. Even if addressed by somewhat different communities, field-aligned currents and ULF waves complement each other in providing M-I coupling paths, whose most spectacular effect is the aurora. The present investigation addresses an M-I coupling event during a relatively quiet time interval, when conjugate data from THEMIS and Cluster spacecraft, ground based observations, as well as data from GOES spacecraft, show dynamic features on multiple scales, associated with magnetotail flow bursts. Thus, on small scale, the flow bursts in the tail, probed by THEMIS D and E, are related to episodes of Alfvenic acceleration, probed by conjugate Cluster 1 observations near the auroral acceleration region. On meso-scale, the THEMIS plasma flow data show evidence for vortical motion (known to be associated with field-aligned current), whose low altitude end is explored by ground magnetic field and optical data. Finally, on large to global scale, the flow bursts in the tail are associated with Pi2 geomagnetic pulsations, examined closely in a companion presentation by THEMIS, GOES, and ground data.