The Seasonal Dependence of the Unexpected Afternoon Westward Equatorial Electrojet During Quiet Time

AbstractThe equatorial electrojet is a strong ionospheric current along the dip equator at 110 km. It usually flows eastward and peaks at noon. However, it sometimes reverses westward. Using 10 years of horizontal geomagnetic field observations from a ground station, this work investigated the counter electrojet (CEJ) in the afternoon at Indian longitudes during geomagnetically quiet time, which has a substantial occurrence rate of 46.7%. A total of 41.7% of the afternoon CEJ is related to the westward electric field during substorms. The intensity of the afternoon CEJ has significant seasonal dependences: peaks in June‐September and December‐February. A similar seasonal variation is established in the westward electric field, indicating its key roles. The occurrence rate reaches its peak solely in June‐September, which might also be attributed to the activity of substorms.