Day-to-day variability of the bottomside ionosphere

This study is focused on investigating how well the day-to-day variability of HF propagation in the bottomside ionosphere can be simulated using a state-of-the-art ionosphere model coupled to a whole atmosphere model driven by the lower atmosphere. The SAMI3 ionosphere model has been coupled to the WACCM-X whole atmosphere model, which was nudged with NAVGEM-HA to incorporate the effects of lower atmospheric weather. The resulting ionospheric specifications were used as input for an HF propagation model (MoJo) in order to compare to observations from the NOAA ionosphere network. The results indicate that the amount of variability at the F-region peak can be successfully reproduced by the model, but that the simulations do not show enough variability in the bottomside of the F-region, particularly below 200 km altitude. Further comparisons with data and a simple modeling study are used to demonstrate that the most likely source of this missing variability are low-altitude ion transport terms, which are not currently included in the standard SAMI3 model. These transport terms are required to simulate the motion perpendicular to the magnetic field in regions where the motion becomes strongly dominated by ion-neutral collisions.