Effects of Solar Illumination and Substorms on Auroral Electrojets Based on CHAMP Observations

Abstract We investigate the effects of solar illumination and the substorm process on the auroral electrojets using CHAMP high‐resolution magnetic field data obtained over a period of 10 years. The eastward electrojet was found to be proportional to the ionospheric conductance induced by solar irradiation over the whole day. More notably, a stronger westward current was detected in times of lower fluxtube‐integrated conductance in both hemispheres. The relative spatial distribution and evolution of the westward electrojet and field‐aligned current (FAC) during the substorm periods were also investigated. The position of the westward current coincided with that of the upward FAC in 2000–2200 magnetic local time (MLT), in keeping with the structure of a westward traveling surge. Furthermore, the upward FAC in the local time sector of the poleward of the westward electrojet was supplied mostly by the remote closure current. The downward FACs in the poleward and upward FACs in the equatorward of the westward electrojet existed in the MLT sectors after 2200 h. Finally, the ratio of the peak intensity of the westward electrojet to that of the meridional Pedersen current, in the 2000–2200 MLT sector increased by about 250%, and the value in the 2200–0200 MLT increased by about 10%–20%. These results provide observational evidence of the increased efficiency of the Cowling channel in the night‐time during substorm periods and contribute to our understanding of the formation mechanism of the auroral electrojet.