Relatively low‐latitude wave aurora and substorms

Abstract

Wave aurora produces broadband particle acceleration. For many years, this type of signature was anecdotally but widely thought to occur primarily at the poleward edge of the auroral oval. Recent statistical work has found that, on the contrary, for strong solar wind driving, broadband aurora is common throughout the auroral oval. Of particular interest is the occurrence of wave aurora below 68 degrees MLAT. We have studied the dependence of such signatures, both as a function of solar wind driving, and as a function of substorm cycle. A set of about 1800 substorm onsets identified by Polar UVI, along with 116 isolated substorm onsets, were used for superposed epoch analysis. The results show that the wave aurora has a very strong substorm cycle dependence, rising dramatically in the first few minutes after onset, and peaking about 10–15 minutes later. By contrast, wave aurora has no easily identifiable solar wind driving peak, although the general trend is for wave aurora to become more common with higher driving (as do substorms themselves). This evidence adds to previous circumstantial evidence associating wave aurora particularly with substorms (for example, wave auroral power is much more strongly peaked in the premidnight region than is monoenergetic or “inverted‐V” aurora).