Small-Scale Dynamic Aurora

Small-scale dynamic auroras have spatial scales of a few km or less, and temporal scales of a few seconds or less, which visualize the complex interplay among charged particles, Alfvén waves, and plasma instabilities working in the magnetosphere-ionosphere coupled regions. We summarize the observed properties of flickering auroras, vortex motions, and filamentary structures. We also summarize the development of fundamental theories, such as dispersive Alfvén waves (DAWs), plasma instabilities in the auroral acceleration region, ionospheric feedback instabilities (IFI), and the ionospheric Alfvén resonator (IAR).

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11214-021-00796-w.

Laboratory realization of an Alfvén wave maser

It is demonstrated that a frequency selective Alfvén-wave resonator can be realized by applying a nonuniform magnetic field to a plasma region bounded between a cathode and a semitransparent mesh anode. When a current threshold is exceeded, selective amplification results in a highly coherent, large amplitude wave that propagates into an adjacent plasma column.