Seasonal and local time variations of auroral electrojet: CHAMP observation

The auroral electrojet is an important element of the polar current system and an essential subject in space weather research. Based on the scalar magnetic field data from CHAMP satellite, we studied the influences of solar illumination and the dipole tilt angle (DTA) on the auroral electrojet as well as its seasonal variations. Furthermore, the auroral electrojet measured by satellite was compared with the auroral electrojet indices derived from the ground stations. It is shown that on the dayside, the auroral electrojet is more intense at a smaller solar zenith angle (SZA), whereas it’s more intense on the nightside when the SZA is larger. The daytime current is mainly controlled by the solar illumination, while the nighttime current is affected by the substorm. Compared with the solar illumination, the dipole tilt angle plays a minor role. The auroral electrojet shows an obvious annual and semiannual variation. The eastward electrojet and the dayside westward electrojet are more intense in summer than in winter, while the nightside westward electrojet is more intense in winter than in summer. The daytime westward electrojet is more intense at solstices, whereas the nighttime westward electrojet is more intense at equinoxes. The westward electrojet shows a good correlation with AL and SML indices. The eastward electrojet correlates well with the SMU index, but shows obvious difference with the AU index. The discrepancy can be attributed to the fact that the peak eastward electrojet is located outside the detection range of the auroral electrojet stations.