Influence of the Magnetic Field Strength and Solar Activity on the Thermospheric Zonal Wind

Based on Thermosphere-Ionosphere Electrodynamics General Circulation Model simulation and CHAllenging Minisatellite Payload observations, the effects of the geomagnetic field intensity and solar activity on the thermospheric zonal wind and the related physical mechanisms are investigated. The weakening of the magnetic field results in an increase in the westward wind during the daytime and a decrease in the eastward wind at night, and leading to a decreasing superrotation. The weakening solar activity causes a reduction in the zonal wind and superrotation. The theoretical term analysis shows that when the magnetic field is weakened, the vertical upward drift velocity of the plasma increases, resulting in a decrease in the electron density and ion drag in the F layer. The weakening of eastward acceleration of the viscous force and ion drag results in an enhanced westward wind. The downward drift velocity of ions increases at night, resulting in an increase in the electron density at the F layer, while the ion-neutral velocity difference decreases. The weakening of eastward acceleration of the pressure gradient and viscous force at night are the main reasons for the decreased eastward wind. The reduced solar activity leads to a decrease in the pressure gradient and ion drag. Combined with the change of viscous force, these processes cause the decrease in the superrotation. The geomagnetic field configuration is the main reason for the variation in the superrotation with UT. When the magnetic field is weakened, although the average neutral wind decreases, the Pedersen conductivity of the F-layer is quadrupled. Therefore, the meridional current system driven by the F-layer dynamo is enhanced accordingly. Due to obvious longitudinal difference in the magnetic field intensity, the longitudinal variation of superrotation is expected.