Electron Density Trough in the Topside Ionosphere & Its Relationship with the Plasmapause Position

Abstract

The ionospheric trough observed around 60^o latitude has been suggested by several earlier workers to be a field-aligned extension of the magnetospheric 'knee' (or 'plasmapause') phenomenon. The Langmuir probe data obtained from the Tiros-7 satellite are used in the present work to study this relationship. These ionospheric data are compared with published whistler data for the same period. The trough is observed to move to higher <i>L </i> values during night-time in response to increasing scale heights in the topside ionosphere. The discrepancy between the trough and knee positions is, however, reduced for moderately high magnetic activity. The theoretically predicted plasmapause position from plasma convection speed considerations shows better agreement with Tiros-7 observations than with the whistler data during quiet and disturbed periods.