A statistical study of the relative locations of electron and proton auroral boundaries inferred from meridian scanning photometer observations

Abstract

We present the results of a statistical study of the absolute and relative locations of the equatorward boundaries of the proton and diffuse electron auroras. The boundaries were analyzed using latitude scans of 630.0 and 486.0 nm (“Hβ”) emissions obtained with the meridian scanning photometers at Gillam and Pinawa, Canada with DMSP overflights. The aurora data were classified into three different steady geomagnetic activity states, one being long‐duration quiet intervals and the other two being moderate and active steady magnetospheric convection (SMC) events. Both case and statistical studies show that the quiet times dusk‐premidnight proton aurora extends slightly equatorward of the electron aurora. This is reversed on the dawnside. In contrast, the electron aurora during moderate and active SMC intervals lies equatorward of the proton aurora throughout the entire nightside covered in this work (20–03 MLT). There is a dawn‐dusk offset in the auroral oval location, with the proton aurora shifting toward premidnight and the electron aurora toward postmidnight. Moreover, with increasing geomagnetic activity, both of the auroras intrude to lower latitude. The penetration of the electron boundary equatorward of the proton precipitation across this MLT range has not been previously identified. We attribute this to the fact that the equatorward part of the diffuse electron aurora is produced by lower energy electrons to which the 630.0 nm emission is more responsive and so marks a more realistic location of the electron equatorward boundary than do the 557.7 nm and UV emissions used in previous intercomparisons of these boundaries.