A2 5 Equatorial Auroras

Abstract

Auroral emission is normally restricted to high latitudes, reflecting the boundary between closed and open geomagnetic field lines. Using a simple dipole model of Earth's magnetic field, we compute the total open magnetic flux in a polar cap as a function of its boundary latitude. We then apply a visibility criterion to determine how much open flux would be required for aurora to reach low latitudes or the equator. The model shows that equatorward auroras require 14.5 times more open flux than typical geomagnetic conditions.