Testing the Hill model of transpolar potential saturation

Abstract

The Hill model predicts that the transpolar potential (Φ PC ) saturates for strong solar wind electric fields (E SW ) and saturates at higher values for larger solar wind ram pressures (P SW ) and/or lower ionospheric Pedersen conductances (Σ P ). Three months of Defense Meteorological Satellite Program (DMSP) measurements of polar cap potentials have been compared with predictions of the Hill model. Data from representative days that span a wide range of interplanetary and solar‐cycle conditions were selected for presentation. In the comparison we augmented the Hill model by adding a constant term to the magnetospheric potential and expressing Σ P in terms of the 10.7‐cm solar radio flux (F 10.7 ). Temporal variations in observed Φ PC are in good agreement with the predictions of the augmented Hill model. Comparison of two events with significantly different average P SW but similar F 10.7 and E SW found that DMSP observed higher potentials when P SW was larger. DMSP also observed higher potentials when Σ P was lower, when comparing two events with significantly different F 10.7 (solar minimum versus solar maximum) but similar P SW and E SW . Both comparisons agree with the predictions of the Hill model.