Abstract
Lacuna on ionograms indicate conditions where the usual ionospheric reflections of vertically propagating radio waves transmitted from and subsequently received by an ionosonde are missing over a range of frequencies. Reflections from the lowermost E-region should still be observable contrary to the more usual cases where absorption processes in the underlying D-region removes the low-frequency part of the ionospheric reflections appearing in ionograms. It is emphasized below that lacuna cases related to E-region processes should be distinguished from lacunae related to processes in the F1 and F2 regions. This distinction appears to have been neglected in a recent paper.
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Stauning, P. Polar lacuna on ionograms. E- or F-region processes?. Annales Geophysicae 13, 450–453 (1995). https://doi.org/10.1007/s00585-995-0450-z
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DOI: https://doi.org/10.1007/s00585-995-0450-z