A statistical study of optical signatures of high-latitude Pc5 waves

We present the first large scale study of optical signatures associated with ultra-low frequency (ULF) waves using an automated detection method at high-latitudes in the northern hemisphere winter. We classify these waves as ULF wave driven auroral arcs (UAAs). We have detected 198 UAAs in optical keograms of the 630.0 nm channel of the Meridian Scanning Photometer (MSP) located in Longyearbyen, Svalbard. Some of the detected UAAs have accompanying signatures in the 557.7 nm channel. The 198 UAAs can be divided into different populations based on magnetic local time: dawn (129) and dusk (69), or propagation direction: poleward (126) and equatorward (72). The poleward-propagating population partly consists of field line resonance driven auroral arcs (FAAs), which have been extensively studied before and are generally well understood. In our case, solar wind data suggests that the FAAs are most likely externally generated through the Kelvin–Helmholtz instability on the flanks of the magnetopause. Furthermore, they exhibit a dawn-dusk asymmetry favoring the dawn flank as reported previously in literature. Another part of the poleward-propagating population seems to consist of internally generated small-scale waves. On the other hand, the equatorward-propagating population is less known with only three previous reports of optical signatures. The data suggest that they correspond to small-scale, internally generated, ULF waves, which potentially have an energy source formed by substorm-injected energetic particles. Possibly, the high-latitude position of Svalbard at the border between the auroral oval and the polar cap, explains why most known occurrences of equatorward-propagating waves have been observed around Svalbard.