Discrete aurora

spaceweb@oulu.fi - last update: 25 November 1998, 2230 UT (RR)

Discrete auroras are the most intense auroral types where field-aligned acceleration play an important role, forming the so-called inverted-V precipitation.

Discrete auroral types include

• Quiet auroral arcs
• Spirals, curls, and folds
• Auroral bulge
• Omega bands

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. 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

• Sun-aligned arcs
• Afternoon auroral spots
• Mantle aurora (open field lines!)

See also:

• Space Physics Text Book of Oulu