Effects of high-latitude forcing uncertainty on the low- and mid-latitude ionosphere

Ensemble simulations are performed in the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM) in order to understand the role of high-latitude forcing uncertainty on the low- and mid-latitude ionosphere response to the April 2010 geomagnetic storm. The ensemble is generated by perturbing either the Assimilative Mapping for Ionosphere Electrodynamics (AMIE) high-latitude electric potential or auroral energy flux. Simulations with perturbed high-latitude electric potential result in substantial intra-ensemble variability in the low- and mid-latitude ionosphere response to the geomagnetic storm, and the ensemble standard deviation for the change in NmF2 reaches 50-100% of the mean change. Such large intra-ensemble variability is not seen when perturbing the auroral energy flux. In this case, the effects of the forcing uncertainty are primarily confined to high-latitudes. We therefore conclude that uncertainty in the specification of high-latitude electric fields is the primary source of uncertainty for modeling the low- and mid-latitude ionosphere response to a geomagnetic storm. A multiple linear regression analysis of the results indicates that uncertainty in the storm time changes in the equatorial electric fields, neutral winds, and neutral composition can all contribute to the uncertainty in the ionosphere electron density. The initial uncertainty is dominated by electric field uncertainty, and neutral winds and composition dominate on longer time scales, at least for the April 2010 storm. The imposed intra-ensemble variability in high-latitude electric fields is commensurate with observed high-latitude electric field variability. The results of the present study therefore provide a reasonable depiction of the uncertainty in simulations of the low- and mid-latitude ionosphere response to geomagnetic storms due to imperfect knowledge of the high-latitude forcing.