Effect of Vertical Shear in the Zonal Wind on Equatorial Electrojet Sidebands: An Observational Perspective Using Swarm and ICON Data

The wind dynamo in the ionosphere leads to differential motion of ions and electrons, which in turn sets up electric fields and currents. Observations show that daytime lower thermospheric horizontal winds have large vertical gradients. Numerical modeling conducted approximately 50 years ago demonstrated that the zonal wind shears in the ∼130–180 km altitude range can generate off-equatorial relative minima (dips) in the daytime height-integrated eastward current density, appearing as westward sidebands north and south of the equatorial electrojet (EEJ). This study observationally confirms this connection for the first time by combining Ionospheric CONnection explorer zonal wind profiles and Swarm latitudinal zonal currents. We demonstrate observationally that the magnitude of the EEJ sideband current is proportional to the strength of westward turning winds with altitude in the Pedersen conductivity dominated region. Additional numerical experiments explain the importance of wind shear in different altitude regions in generating the sideband current. This study contributes to the better understanding of the neutral wind effect on the local current generation.