Local Time Variations of the Equatorial Electrojet in Simultaneous Response to Subauroral Polarization Streams During Quiet Time

Based on 1-year equatorial electrojet (EEJ) measurements from Swarm, and ion velocity from the Defense Meteorological Satellite Program, this study first examines the simultaneous effects of the subauroral polarization streams (SAPS) on EEJ during quiet time. The changes in EEJ (ΔEEJ) vary significantly with local time. ΔEEJ flows westward at dawn and is gradually enhanced to eastward at dusk. The eastward ΔEEJ at post-noon might be driven indirectly by the upward electric field associated with SAPS electric field at SAPS channel, whereas ΔEEJ at pre-noon might be directly attributed to the penetrating SAPS-related polarization electric field. Under stronger geomagnetic forcing, a stronger intensity of westward ΔEEJ at dawn and noon is produced, whereas a stronger eastward ΔEEJ at dusk is generated because of a faster SAPS velocity.