The ionospheric electron density is a highly variable quantity and significantly affects the propagation of radio signals that pass through or are reflected by the ionosphere. Ionospheric troughs refer to regions of very low plasma density comparing with that of the surrounding regions. Based on the relative location of the trough to the auroral oval, the trough can be classified as mid-latitude or high-latitude trough. Their characteristics and generation mechanisms differ from each other. The characteristics and formation mechanisms of ionospheric mid- and high-latitude troughs during storms and substorms have been studied [e.g., Zou et al., 2011, Zou et al., 2013, Heine et al., 2017, Aa et al., 2020].
