Evidence for solar-production as a source of polar-cap plasma

S. E. Pryse*, R. W. Sims, J. Moen, L. Kersley, D. Lorentzen, W. F. Denig

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

14 Citations (Scopus)


The focus of the study is a region of enhanced ionospheric densities observed by the EISCAT Svalbard radar in the polar F-region near local magnetic noon under conditions of IMF Bz<0. Multi-instrument observations, using optical, spacecraft and radar instrumentation, together with radio tomographic imaging, have been used to identify the source of the enhancement and establish the background ionospheric conditions. Soft-particle precipitation was ruled out as a candidate for the production. Tomographic observations identified a latitudinally restricted region of enhanced densities at sub-auroral latitudes, distinct from the normal mid-latitude ionosphere, which was likely to be the source. The evidence suggested that the increased sub-auroral densities were photoionisation produced at the equatorward edge of the afternoon high-latitude cell, where the plasma is exposed to sunlight for an extended period as it flows slowly sunward toward magnetic noon. It is proposed that this plasma, once in the noon sector, was drawn antisunward by the high-latitude convection toward polar latitudes where it was identified by the EISCAT Svalbard radar. The observations are discussed in terms of earlier modelling studies of polar patch densities.

Original languageEnglish
Pages (from-to)1093-1102
Number of pages10
JournalAnnales Geophysicae
Issue number4
Publication statusPublished - 2004


  • Ionosphere (polar ionosphere; plasma temerature; plasma convection)


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