Drift-resonance resonance between electrons and ultralow frequency waves are characterized by energy-dependent phase differences between electron flux and electromagnetic oscillations. In the initial wave cycles, however, such characteristic differs from observations. The differences are found to be imprints of impulse-excited waves before they transform into more typical standing waves. Our identification of such imprints provides a new understanding of how energy couples in the inner magnetosphere, and a new diagnostic for the generation of hydromagnetic waves
Dipolarization fronts (DFs) in the magnetotail are typically asymmetric with a small Bz dip followed by a sharp Bz enhancement. Using THEMIS observations of hundreds of DFs, we find that the depth of the Bz dip as a function of the front azimuth depends on DF propagation speed and ambient plasma density. These statistical signatures support the hypothesis that the Bz dip is caused by ion reflection and suggest that secondary currents carried by these reflected ions can reshape the front significantly.
During a substorm on 27 January 2004, energetic particle injections associated with ULF waves have been detected by Cluster satellites. The observed ULF waves with the period of 1 minutes are probably the third harmonic mode, which can simultaneously interact with both substorm injected "hot" particles from the magnetotail and cold outflow ions from the Earth's ionosphere.