Simulation of ionospheric currents and geomagnetic field variations of Sq for different solar activity

Abstract Variations of ionospheric Sq electric currents and fields caused by changes in electric conductivity due to changes in solar activity are studied using the International Reference Ionosphere (IRI) model. Calculations are made for R (sunspot number) = 35 and 200 on the assumption of constant (1, −2)mode tidal winds. It is shown that electric fields grow when solar activity is high, because the ratio of the conductivity in the F -region to that in the E -region increases. Currents in the F -region become stronger than those in the E -region, and nocturnal currents are not negligible when solar activity becomes high. F -region currents also play an important role in the westward currents on the high latitude side of the current vortex. The calculated geomagnetic H component at the equator has a depression around 1600 LT for R = 35, while it decreases smoothly from 1100 LT to 1900 LT for R = 200. This difference is consistent with the observed geomagnetic field variation. The ratio of total Sq currents obtained by our simulation is about 3.5, which is a little larger than is found in the observed results.