Characteristics of Counter Electrojet Using Multi-Spacecraft Swarm Observations

The characteristics of the westward ionospheric current flowing at the geomagnetic equator, known as Counter Electrojet (CEJ), are studied here using multi-satellite Swarm mission magnetic field data collected during January 2014 to March 2021. For the first time, the simultaneous measurements from multiple satellites are used to investigate the various features of the CEJ, including its longitudinal extent. The CEJ events occur in ∼19.8% of quiet-time electrojet profiles during the period of study. The local time, seasonal, and longitudinal variations of the CEJ amplitude and occurrence percentage during geomagnetically quiet days confirm many of the earlier reported observations. It is found that the CEJ is more prone to occur during morning and less frequent at noon, while the amplitude of CEJ peaks during noon hours. Longitudinal pattern of CEJ occurrence shows distinct four-peaks at ∼50°E, ∼150°E, ∼230°E and ∼310°E longitudes. Also, CEJ occurrence peaks from June to August. The CEJ occurrence and meteorite ablation rates are found to be moderately correlated on a monthly scale, and no one-to-one correlation found in the Indian region. For the first time, the longitudinal extent of CEJ is estimated using simultaneous observations from Swarm A and B. It is found that the CEJ has predominant longitudinal extent of 15°–25°, although it can also have larger longitudinal coverage more than or up to 165°, under the assumption of temporal and spatial stability of CEJ.