Dayside ionospheric response to recurrent geomagnetic activity during the extreme solar minimum of 2008

Global observations of electron density profiles from the COSMIC satellites are used to investigate, for the first time, the altitudinal dependence of the ionospheric response to the recurrent geomagnetic activity at different latitudinal regions during the extreme solar minimum period of 2008. Our results show that the 9-day oscillations in N_mF2 are out of phase with those in Kp at high latitudes, whereas they are in phase at low-middle latitudes. This is consistent with changes in neutral composition associated with the recurrent geomagnetic activity. Meanwhile, the 9-day perturbations in the h _mF2 and the thickness parameter (H_T) exhibit good correspondence with the perturbations in Kp from pole to pole, suggesting that the ionospheric response is global and undergoes periodic expansion/contraction. Further, the ionospheric response to the recurrent geomagnetic activity strongly depends on altitude. The density perturbations are generally in phase with Kp above the F2 peak, while they are out of phase around the F2 peak at high latitudes. These changes in electron density at different altitudes are explained by different physical processes, such as photoionization-chemistry, particle precipitation, and dynamic and diffusion transport.