The large magnetic storm of February 1986 provides a unique opportunity to assess whether existing open-closed theories of the magnetosphere can consistently account for precipitating particle signatures measured at 840 km under a wide variety of solar wind and solar particle conditions. Here we report the simultaneous observation of relativistic electrons associated with a solar proton event and of auroral ions and electrons associated with a polar cap arc event, made across the central polar cap using detectors on board the Defense Meteorological Satellite Program (DMSP) satellites. On February 7 while a solar proton event was still in progress, polar cap arc activity (interplanetary magnetic field (IMF) Bz large and positive, Kp=3+) occurred prior to a prolonged period of oval arc activity (IMF Bz large and negative, Kp=6-).

Throughout these periods the following are identified: the equatorward edge of the relativistic electron precipitation; the outer zone electron poleward and equatorward boundaries; the equatorward auroral electron and ion boundaries; and the auroral electron transition boundary. The history of the boundaries is presented as the transition from intense polar cap activity to intense auroral oval activity takes place. The data clearly show that the polar cap region of relativistic electron precipitation does not change significantly as the sign of Bz changes. On the other hand, the boundary layer population, which contains auroral arcs and 1- to 10-keV ion precipitations, expands to fill most of the polar cap for Bz northward and greatly contracts as Bz turns southward. The expansion is not symmetric between poles. The fact that in a broad region of the central polar cap, auroral arcs and relativistic electrons are found on the same field lines presents some difficulty for jointly maintaining theories that propose the formation of polar cap arcs strictly on closed field lines and theories that explain relativistic electron entry by means of direct access along open field lines. We argue that the data support polar cap arc formation on open field lines and present a scenario in which the tail lobe boundary plasma is the source of auroral particles at high lattitudes.