Width and brightness of auroral arcs driven by inertial Alfven waves

Abstract

Alfven waves with scale sizes perpendicular to the geomagnetic field of the order of an electron skin depth (λe), or electron inertial length, and larger are often observed by polar orbiting spacecraft above the aurora. Using observations from the FAST spacecraft, predictions from an MHD simulation, and theoretically derived results for the efficiency of light production from auroral electron spectra characteristic of those found in Alfven waves, the width and brightness distribution of auroral arcs driven by linear inertial Alfven waves are determined. It is shown that inertial Alfven waves can drive aurora to optical intensities as high as 100 kR over widths in the ionosphere of the order of 1 km. It is also shown that while linear inertial Alfven waves can cause auroral arcs of widths less than 100 m, it is unlikely that these waves can account for the optically observed distribution of narrow arc widths reported in the literature.