Example of a VLF saucer

This figure shows the electron and fields signatures of a very low frequency (VLF) saucer measured by FAST instruments in the morning auroral oval (6.6 MLT) at an altitude of approximately 3400 km. Panel (a) shows the perpendicular electric field in the spin plane and nearly along the spacecraft path (mostly North). The negative electric field signal followed by a positive signal corresponds to a diverging electric field structure indicative of a downward parallel electric field. Panel (b) shows the magnetic perturbations to the global magnetic field, DB, along the spacecraft spin axis (mostly West). A negative slope indicates upward current; a positive slope indicates downward current. The electric field spectral power density is shown in panel (c). The spectra power density signature with multiple-arms stemming from a narrow region is known as a VLF saucer. The electron differential energy flux versus energy and time as well as pitch-angle and time associated with the VLF saucer is shown in panels (d) and (e). At the vertex of the VLF saucer, intense, low-energy, up-going (180^o) electron fluxes dominate the electron spectra shown in panels (d) and (e).

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