Global TEC Response to the November 2021 Geomagnetic Storm

This work reports the global ionospheric total electron content (TEC) distribution using global ionosphere maps (GIM) and Swarm satellite observations one day before and one day after the November 2021 geomagnetic storm. The November 2021 storm was the first intense storm of solar cycle 25, resulting from a cannibalistic coronal mass ejection, which is a combination of two coronal mass ejections. The main features observed were the enhancement of the equatorial ionization anomaly for up to 8 h post-storm sudden commencement (SSC), and the depletion of TEC along the equator compared to the post-storm day. Additionally, a hemispherical asymmetry was observed 8 h post-SSC in the form of an enhancement of TEC along the high-latitude northern hemisphere and depletion along the high-latitude southern hemisphere compared to the pre-storm day. This asymmetry lasted for more than 8 h. The maximum upper ionosphere (above the F2 layer peak) TEC observed by Swarm satellites started decreasing 6 h post-SSC and reached levels lower than that of pre-storm day. Additionally, the mean TEC of the upper ionosphere observed by Swarm satellites was lower for the entire post-storm day than the pre-storm day. This feature contradicts what was observed from GIM, where an enhancement of TEC was observed post-storm, particularly along low latitudes, and northern hemisphere high latitudes. This decrease of TEC in the upper ionosphere can be attributed to the lowering of the post-storm ionospheric F-region height on the dayside of the globe, as reported in previous work and confirmed empirically in this work.