Theoretical study of new plasma structures in the low-latitude ionosphere during a major magnetic storm

When the arch forms during the day, a new F₂ layer is created at the original altitude by photoionization, and a density hole can be created between this new F₂ layer and the arch.

When the arch forms during the night, the F₂ layer is not recreated and no hole forms. In a vertical profile of electron density, the daytime elevated ionospheric layer can appear distinctly from the recreated F₂ layer, in which case the elevated layer is called the F₃ layer. A latitude cut through the night-side arch shows the characteristics of an equatorial electron density trough, bounded to the north and south by enhanced densities associated with plasma that has diffused down along the geomagnetic field from the elevated layer.