Grossly-distorted isoionic contours associated with spread-F occurrence at mid-latitudes |
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| Affiliation: | 1. Mbarara University of Science and Technology, Mbarara, Uganda;2. South African National Space Agency (SANSA) Space Science, 7200 Hermanus, South Africa;3. Department of Physics and Electronics, Rhodes University, 6140 Grahamstown, South Africa;1. Saint-Petersburg State University of Aerospace Instrumentation, 67, Bolshaya Morskaya, Saint-Petersburg 190000, Russia;2. SCiESMEX, LANCE, Instituto de Geofisica, Unidad Michoacan, Universidad Nacional Autonoma de Mexico, Antigua carretera a Patzcuaro 8701, Morelia, Michoacan C.P.58089, Mexico;3. CONACYT, Instituto de Geofisica, Unidad Michoacan, Universidad Nacional Autonoma de Mexico, Antigua carretera a Patzcuaro 8701, Morelia, Michoacan, C.P.58089 Mexico;1. Muş Alparslan University, Faculty of Education, Department of Classroom Teaching, Muş, Turkey;2. Muş Alparslan University, Faculty of Science and Art, Department of Physics, Muş, Turkey;1. National Remote Sensing Centre, Hyderabad, India;2. SPL, VSSC, ISRO, Trivandrum, India;3. Andhra University, Vishakhapatnam, India;1. Virginia Polytechnic Institute and State University, Blacksburg, VA, USA;2. Cooperative Institute for Research in Environmental Sciences, NOAA/NCEI, Boulder, CO, USA;3. Toronto, ON, M9B 2L9, Canada;1. Department of Physics, Mbarara University of Science and Technology, Mbarara, Uganda;2. Department of Physics, Busitema University, Tororo, Uganda;3. South African National Space Agency (SANSA) Space Science, P.O. Box 32, Hermanus 7200, South Africa |
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| Abstract: | A directional ionosonde has been used to investigate a mid-latitude travelling ionospheric disturbance which passed over Brisbane, Australia, on the night of 31 July/1 August 1981. The analyses have revealed what appears to be a large-scale frontal height rise (about 300 km wide) travelling in a north-west direction with a speed of 93 ms−1. Smaller-scale frontal structures with wavelengths of some tens of kilometres appeared near the crest of this large-scale upwelling and have the same frontal orientations. These are responsible for the spread-F seen on ionograms during the passage of the disturbance. Also, associated with the disturbance was a tongue of ionization which extended down from the crest of the upwelling more than 100 km. It appeared to be drifting with the same speed and in the same direction as the upwelling. Near the lowest extremity of the tongue the ionization density was at least 35% greater than elsewhere in the ionosphere. The lowest extremity of the tongue was located 240 km from the recording station as the large-scale frontal structure passed overhead. Statistical analyses using 19 tongue events in 1979 have shown that ionospheric height rises seem to be generally associated with these events not only at the recording station, but also in the conjugate hemisphere. Certain characteristics of the mid-latitude disturbance which have been investigated in this paper are compared with the characteristics of similar disturbances in equatorial regions. |
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