Using VERB-4D to Model Ring Current Ions and Their Sensitivity to Plasmasphere Density

We extend the Versatile Electron Radiation Belt (VERB) code to model ring current ions. We validate our simulation results against observations from the Van Allen Probes mission for the St. Patrick's Day storm in 2013. We study the sensitivity to plasma density of the modeled losses from Coulomb collisions. To this end, we compare the Coulomb energy deposition rate, and trapped particle fluxes from simulations coupled to different models of plasmaspheric density: an empirical, a physics-based, and a machine learning model. The results show that cold plasma density plays an important role in the spatial distribution of Coulomb heating. Therefore, an accurate description of plasmasphere density is vital for modeling magnetosphere-ionosphere coupling. The impact of cold plasma density on the modeled ring current ion fluxes remains small.