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Ann. Geophys., 23, 25-37, 2005
www.ann-geophys.net/23/25/2005/
© European Geosciences Union 2005
Spatial structure of summertime ionospheric plasma near magnetic noon
R. W. Sims1,*, S. E. Pryse1, and W. F. Denig2
1Institute of Mathematical and Physical Sciences, University of Wales Aberystwyth, SY23 3BZ, UK
2Space Vehicles Directorate, Air Force Research Laboratory, Hanscom AFB, Massachusetts, USA
*now at: Medical Physics Directorate, University Hospital of North Staffordshire, ST4 7LN, UK
Abstract. Results are presented from a multi-instrument study of the spatial
distribution of the summertime, polar ionospheric electron density
under conditions of relatively stable IMF Bz<0. The EISCAT
Svalbard radar revealed a region of enhanced densities near
magnetic noon that, when comparing radar scans from different
local times, appeared to be spatially confined in longitude. This
was identified as the tongue-of-ionisation (TOI) that comprised
photoionisation of sub-auroral origin that is drawn poleward into
the polar cap by the anti-sunward flow of the high-latitude
convection. The TOI was bounded in longitude by high-latitude
troughs; the pre-noon trough on the morning side with a minimum
near 78° N and the post-noon trough on the afternoon side
with a minimum at 80° N. Complementary measurements by
radio tomography, the SuperDARN radars, and a DMSP satellite,
together with comparisons with earlier modelling work, provided
supporting evidence for the interpretation of the density
structuring, and highlighted the role of plasma convection in the
formation of summertime plasma distribution. Soft particle
precipitation played only a secondary role in the modulation of
the large summertime densities entering the polar cap.
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