Statistical Characteristics of Giant Undulations During Geomagnetic Storms

Abstract

In this letter, the statistical characteristics of the structures of giant undulations (GUs) during geomagnetic storms are studied for the first time, based on aurora images during 2005–2019. The GUs mainly occur within ∼4 h following the beginning of the storm main phase and finish in ±4 h around the storm peak. The most interesting feature is that the anti-sunward edge of GUs is quasi-stable (18–19 h MLT) during their lifetime. The latitudinal amplitudes of GUs (AGU) peak at 200–300 km while the azimuthal wavelengths (WGU) occupy several discrete values between 100 and 900 km. Both AGU and WGU are quasi-proportional to the strength of the storms, and AGU is also proportional to WGU. There are some differences in the characteristics of AGU and WGU between pre- and post dusk sectors. These results would provide both statistical insight for mechanisms of dynamic auroral structures and data sources for validating magnetosphere-plasmasphere-ionosphere coupling models.