External and Internal Causes of the Dawnside Current Wedge Formation During Geomagnetic Storms

The dawn-dusk asymmetry of ground magnetic depression is a characteristic feature of the storm main phase. Recently Ohtani (2021) found that this asymmetry is highly correlated with the intensity of the dawnside westward auroral electrojet (AEJ), but not with that of the duskside eastward AEJ. The author therefore suggested that a wedge-shaped electric current system, dawnside current wedge (DCW), forms in the dawn sector, which may be envisioned as a westward magnetospheric current short-circuiting through the dawnside auroral zone. However, the cause of the DCW formation still remains to be understood. In this study we consider the enhancement of the dawnside AEJ in terms of the driving of the M-I system and the enhancement of ionospheric conductance. For the former, (i) substorm and (ii) global convection are two candidates. For the latter, we can consider (iii) the injection of energetic electrons and (iv) solar wind compression; both processes intensify electron precipitation through the subsequence enhancement of wave-particle interactions. In this presentation we show how solar wind, magnetospheric, and ionospheric conditions change in association with the dawnside AEJ enhancement, and discuss their sequence in terms of the aforementioned four processes (i - iv).