On the nature of homogeneous auroral arcs

The nature of homogeneous auroral arcs is discussed. It is shown that the system of magnetospheric-ionospheric currents might prove to be unstable with regard to delamination in the regions where the longitudinal currents flow out of the ionosphere. Then the Larmor radius of hot ions in the vicinity of the equator plane should exceed the reverse wave number of instability, whereas the density of the longitudinal currents in the ionosphere should exceed a certain critical value determined by the geometry of the problem, ionospheric conductivity and hot ion temperature, Tsub(i). The instability evolution becomes substantially easier, if the hot ion distribution function versus speeds has a maximum, and the potential step between the magnetosphere and ionosphere is close to αTsub(i)/e, where α approximately 0.5 to 1