The CEDAR High Latitude Plasma Structures (HLPS) initiative has carried out several observational campaigns to acquire comprehensive data bases on Sun-aligned polar cap arcs (SA). At USU, two distinct modeling efforts have produced models that pertain to polar cap Sun-aligned arcs, namely, an upgraded Time Dependent Ionospheric Model with embedded Sun-aligned polar cap arcs (TDIM-SA) and an MHD coupled magnetosphere-ionosphere polar cap Sun-aligned arc model (M-I SA). The PIs propose to use these two models in five specific collaborative investigations utilizing these CEDAR-HLPS data lets, each investigation having a specific scientific goal. The first and second investigations pertain to understanding the dawn-dusk (or vice versa) drift associated with SA and their multiple arc, striated, nature. Both of these studies use the M-I SA model which exhibits both of these features. The third is to use the HLPS observations of many electrodynamic and plasma parameters to validate the TDIM-SA model, especially the model prediction that the cross arc drift speed is a key parameter. Our fourth study is to understand the strong convection rotation observed in the vicinity of polar cap and auroral arcs during times when the arc is changing. Again, this type of feature is present in the M-I SA simulations. Strong plasma depletions have been observed adjacent to SAs and have been tentatively associated with electrodynamic current closure requirements. For this fifth study, we will use the TDIM-SA to quantify all the electrodynamic parameters and evaluate if this hypothesis is the source of the plasma depletions.
