The Impact of Geomagnetic Activity on the Height-Dependent Ionospheric Delay in Relation to Solar Activity

Previous research has indicated that geomagnetic activity plays an important role in influencing the ionospheric delayed response to solar activity variations at the solar rotation time scale depending on solar activity conditions. In this study, we employed the Thermosphere-Ionosphere-Electrodynamic General Circulation Model to investigate the vertically resolved impact of geomagnetic activity on the ionospheric delay over the solar rotation period from 29 April to 25 May 2015. This time period was chosen due to its representative moderate solar and geomagnetic activity conditions. Our analysis revealed that the ionospheric delay increases with altitude due to geomagnetic activity and is more pronounced in the Southern Hemisphere than in the Northern Hemisphere. To further understand the underlying mechanisms responsible for the observed changes in ionospheric delay, we examined neutral species ($O$ and $N_2$), their ratio $\left(O/N_2\right)$, and neutral temperature. The results show that thermosphere-ionosphere composition varies both vertically and horizontally in response to geomagnetic activity, and that these composition changes contribute to vertical variations in ionospheric delay.