Outflow from the ionosphere in the vicinity of the cusp

Abstract

Low-energy ion outflows from the ionosphere are known to be an important source of plasma for the magnetosphere. The objective of this study is to describe the spatial relationships between low-energy ionospheric outflows and the cusp. The analysis is similar to that used in superposed epoch analyses, except that a spatial reference is used instead of a temporal one. Data from the Thermal Ion Dynamics Experiment (TIDE) supported by data from the Toroidal Imaging Mass-Angle Spectrograph (TIMAS) and Hydra, during low-altitude, perigee passes over the South Pole by the Polar spacecraft are used. The presence of isotropic ions from the magnetosheath is used to define the equatorward boundary of the cusp. By using this magnetospheric boundary as a reference point instead of invariant latitude, the temporal variability of the cusp location with respect to the Earth is removed. Poleward of this boundary in the cusp proper, observations show ionospheric outflow in addition to the isotropic magnetosheath ions. A technique used to separate the ion distributions originating from the two sources is presented and applied in order to calculate moments of the outflowing ion distribution. Ionospheric outflow is found to occur in the cleft region that extends approximate to1.5degrees equatorward of the low-latitude cusp boundary and in the cusp that extends approximate to5degrees poleward of this boundary. Both the parallel and perpendicular temperatures of the outflowing ions are found to be approximately a factor of 3 larger on the equatorward side of this cusp boundary, i.e., in the cleft.