Evidence of Interhemispheric Asymmetry in Swarm Geomagnetic Activity Indices Using Complexity Measures

Swarm data can be used to derive spaceborne indices of geomagnetic activity, capturing the same dynamic processes and exhibiting the same behaviour as ground-based geomagnetic indices traditionally used to monitor magnetic storm (SYM-H index) and substorm (AE index) activity. Given the fact that the official ground-based index for the substorm activity (i.e., the Auroral Electrojet – AE index) is constructed by data from 12 ground stations, solely in the northern hemisphere, it can be said that this index is predominantly northern, while the Swarm-derived AE index may be more representative of a global state, since it is based on measurements from both hemispheres. A few studies have addressed the question of whether the auroras are symmetric, between the northern and southern hemispheres. Therefore, the possibility to have different Swarm-derived AE indices for the northern and southern hemispheres respectively, may provide, under appropriate time series analysis techniques based on information theoretic approaches, an opportunity to further confirm the recent findings on interhemispheric asymmetry. Here, we also provide evidence for interhemispheric energy asymmetry in the ionosphere based on the analyses of Swarm-derived auroral indices AE North and AE South.