Influences of the Ionosphere, Thermosphere and Magnetosphere on Ion Outflows

Abstract

Ion outflows from the auroral and polar cap ionosphere are highly variable in composition, energy, space and time, and constitute an important source of plasma in the magnetosphere. The variety of ion outflows fall into two categories: bulk ion flows, including the polar wind and auroral bulk ion up-flow; and suprathermal ion outflows, including ion beams, ion conics, transversely accelerated ions and upwelling ions. The bulk ion flows constitute an important source of low-energy plasma for suprathermal ion outflows above the topside ionosphere, where transverse ion acceleration results in the generation of ion conics, and parallel electric field and magnetic folding contribute to the formation of ion beams at high altitudes. Both ion outflow categories are strongly influenced by the solar EUV irradiance and solar wind energy input and the state of the magnetosphere-ionosphere-thermosphere. The acceleration of the polar wind and auroral up-flow is much larger and the ion flux of the up-flow is much lower at topside ionospheric altitudes at solar minimum than at solar maximum. Compared with H+ and He+, O+ ion beams and conics exhibit a much stronger dependence on magnetic and solar activity: the active-to-quiet time and solar maximum-to-minimum ratios of the O+ ion outflow rate being ∼20 and ∼5, respectively, compared with the ratios of 4 and 0.5 for H+, and resulting in a factor of 10 increase in O+/H+ ratio at solar maximum.