Ion distribution isosurfaces after interaction with a magnetic "island" or O-type magnetic neutral line in the geomagnetic tail. The long axes are velocity parallel and perpendicular to the magnetic field, while the short (horizontal) axis is gyrophase, which indicates where the particle is in its rotation about the field line.

The "tubes" near the center indicate maxima in the probability density for detecting particles with the given velocity. The tube which is offset from the central tube indicates a beam of ions, and one can see as the plot rotates, that this beam only exists for some phases, but not all - i.e. this feature is non-gyrotropic- a common occurence observed in the tail current sheet region, and of the reasons this part of the magnetosphere is so interesting.