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. Plain Language Summary The winds in the E‐region ionosphere push the plasma in the presence of Earth’s magnetic field, causing ions and electrons to move separately, producing electric current. The low‐latitude ionospheric current system consists of an intense eastward current at the magnetic equator (called Equatorial Electro‐Jet (EEJ)) and off‐equatorial reduced eastward or relative westward currents (EEJ sideband currents) in both hemispheres. Modeling studies have shown that the altitudinal gradient of the zonal wind is related to the strength of the EEJ sideband currents. However, observational studies to validate these results have been missing to this date. This study utilizes simultaneous observations from Ionospheric CONnection explorer and Swarm satellites to provide insights on the connection between low‐latitude winds and currents, which will improve our understanding of the causes of daytime ionospheric variability. Key Points First observational evidence of effect of zonal wind gradients at ∼130–180 km on low‐latitude Equatorial Electro‐Jet sideband currents The altitude variation of the zonal wind gradient modulates the latitudinal variation of EEJ sideband currents With increasing westward wind shear, the strength of low‐latitude Equatorial Electro‐Jet sideband current increases