Wind dynamo effects on ground magnetic perturbations and vertical drifts

The equatorial electrojet (EEJ) flows as an enhanced eastward current in the daytime E region ionosphere between 100 and 120 km height at the Earth's magnetic equator. The flowing currents in the ionosphere induce magnetic perturbations on the ground. Calculating the difference between the horizontal components of magnetic perturbation (H) at magnetometers near the equator and about 6-9 degrees away from the equator, ΔH, provides us an indicator of the strength of the EEJ. However, in this research we show how wind-driven currents can also be an important factor in changing the magnitude of ΔH, using simulations with the NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM). Through modifying the neutral wind and high-latitude electrical potential at the March equinox under moderate solar activity (F_10.7 =140 units), the latitudinal distributions of H, diurnal variations of ΔH, and vertical drift in the Peruvian (75 °W) longitude sector are presented in this paper. The relationship between ΔH and vertical drift is also simulated and discussed, which helps us to understand the importance of both the EEJ and the off-equatorial wind-driven currents in altering the relation. Model results show that the altitude variation of wind velocity in the low-latitude region is capable of modifying the ground magnetic perturbation a few degrees away from the equator. Only by combining the effects of both the EEJ and the off-equatorial wind-driven currents can the magnitude of ΔH and its relation with the vertical drift be accurately estimated.