Polar cap Sporadic-E: Part 1, Observations |
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| Institution: | 1. Department of Electrical Engineering, University of Western Ontario, London, Ont, Canada N6A 5B9;2. School of Environmental Sciences, University of East Anglia, Norwich, UK;1. Space Sciences Laboratory, University of California, Berkeley, CA 94720, USA;2. MIT Haystack Observatory, Westford, MA, USA;3. Institute of Ionosphere, National Academy of Sciences of Ukraine, Ministry of Education and Science of Ukraine, Kharkov, Ukraine;4. Jicamarca Radio Observatory, Instituto Geofisico del Peru, Lima, Peru;5. Leibniz Institute of Atmospheric Physics at the Rostock University, Germany;6. Electrical and Computer Engineering Department, Miami University, Oxford, OH, USA;7. Center for Geospace Studies SRI International, 333 Ravenswood Avenue, Menlo Park, USA;8. Applied Physics Laboratory, Johns Hopkins University, Laurel, MD, USA;1. University of Saint Petersburg, Saint Petersburg, Russia;2. Arctic and Antarctic Research Institute, Saint Petersburg, Russia |
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| Abstract: | Sporadic E (Es) is reasonably common in the central polar cap where some of the mechanisms that produce Es at lower latitudes should become inoperative. There is some occasional auroral Es but this is readily identifiable. The other types of Es that are observed have different properties in winter and summer. The characteristic winter type is a “height-spread”, short-lived layer that tends to occur in the middle and upper E region. The common summer type is in the form of a “thin”, long-lived layer in the lower E region. Both summer and winter types are associated with positive IMF By. We explain the initial formation of Es by gravity waves that move ionization out of the lower F region into the E region and concentrate it at reversals of vertical gravity wave motion. These concentrations are seen in winter as transient Es layers. In summer, these transient layers persist and change into long-lived thin Es layers because of metallic ions that are maintained in an ionized state by charge exchange of neutral metal atoms with the ambient E region NO+ and O2+ ions produced by photo-ionization. |
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