Ionospheric signatures of magnetospheric boundaries in the post-noon sector

Spatial structures in ionospheric electron density revealed in a tomographic image have been identi®ed with auroral forms and related to their sources in precipitating particles observed by DMSP satellites. The observations of plasma enhancements relate to discrete auroral arcs seen in the post-noon sector, identi®ed by both redand green-line emissions measured by a meridional scanning photometer. The features lie within a very narrow latitudinal band on L-shells where the satellite detectors observed electron precipitation classi®ed as from the boundary plasma sheet (BPS). The harder particles are identi®ed with an E-region structure, while further north the precipitation is softer, resulting in a localised F-layer blob and 630.0 nm emissions. A steep gradient in plasma density represent a signature in the ionosphere of the central plasma sheet (CPS)/BPS boundary. A transition to a less-structured F-layer is found on crossing the convection reversal boundary.