Swarm In Situ Observations of F-Region Polar Cap Patches Created by Cusp Ionization

Multi-point in situ measurements from the Swarm spacecraft provide a novel tool to investigate the creation, transport, and evolution of polar cap patches. The string-of-pearls spacecraft configuration allow the motion and dynamics of electron density to be resolved on a one minute timescale. Swarm flew northward through the Scandinavian dayside cusp, passing through auroral features and high frequency radar backscatter. The observations reveal that plasma flow channels, the transport of photoionized plasma, and cusp particle precipitation are all important processes involved in creating the structures which become polar cap patches. Newly created electron density structures are transported across the polar cap via convection. The observed time-history of density structure indicates that particle impact ionization can add structure to both photoionized plasma and lower density polar cap plasma. Newly created and highly structured plasma evolves into lower density, less structured polar cap patches as they transit the polar cap.