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

Abstract

AbstractBased 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 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 in the F layer. The weakening of eastward acceleration of 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, while the ion‐neutral velocity difference decreases. The weakening of eastward acceleration of pressure gradient and viscous force at night are 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 responsible for the UT variation (potential longitudinal change) in the superrotation. 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.