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.

In this letter, we report the correlations between giant undulations (GUs) and plasmapause (PP) configurations based on GUs' images and corresponding PP crossings of satellites between 2005 and 2019. Typically, GUs occur when the plasmasphere is eroded to form a thin and sharp PP during the storm main phase and early recovery phase. The thicknesses of the PP are usually comparable with the azimuthal wavelengths of the GUs and are smaller than the radial amplitudes of the GUs. The amplitudes and wavelengths are quasi‐proportional to the thicknesses of the PP and are inversely quasi‐proportional to the ion density gradients around the PP. The radial centers of GUs are typically aligned with the PP surfaces and their radial geocentric locations show positive correlations for different geomagnetic storms. These results would provide both physical insights and model constrains on the magnetosphere‐plasmasphere‐ionosphere energy coupling and the generation mechanisms of the GUs and plasmapause surface waves.