Discrete auroral types include
All these are nighttime, auroral oval, arc related phenomena (the three last ones are deformed arcs that appear with increasing activity, e.g., auroral substorms). They are more pronounced premidnight than postmidnight, and reflect the dynamics of the Earth's magnetotail (see magnetosphere). They are located on the poleward part of the auroral oval, in the region of the so-called boundary plasma sheet (BPS) precipitation mapping to plasma sheet and its boundary layer (PSBL). Studies of isotropic boundary have indicated that the source region is always within the current sheet (Bz < 5 nT), i.e., non-dipolar field lines.
Other discrete auroras include