A comparison of mid-latitude and equatorial-latitude spread-F characteristics |
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| Affiliation: | 1. Climate Change and BioAdaptation, South African National Biodiversity Institute (SANBI), Kirstenbosch Research Centre, Cape Town, South Africa;2. DST-NRF Centre of Excellence at the Percy FitzPatrick Institute of African Ornithology, Department of Biological Sciences, University of Cape Town, South Africa;3. African Climate & Development Initiative (ACDI), University of Cape Town, South Africa;4. Centre for Statistics in Ecology, the Environment and Conservation (SEEC), Department of Statistical Sciences, University of Cape Town, South Africa;5. Custodians of Rare and Endangered Wildflowers (CREW), South African National Biodiversity Institute, Kirstenbosch Research Centre, Cape Town, South Africa;6. Animal Demography Unit (ADU), Department of Biological Sciences, University of Cape Town, South Africa |
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| Abstract: | Experimental evidence using a fast-swept-gain technique on an ionosonde is presented to support the idea that mid-latitude spread-F irregularities are large-scale wave-like structures. Also,diurnal and annual distributions of spread-F occurrence at an equatorial station at times of low sunspot activity are shown to be similar to those found for mid-latitude stations. The sunspot-cycle variation of post-midnight spread-F occurrence is also found to be similar in the two latitude regions. The similarity of certain spread-F characteristics at both mid- and equatorial-latitude regions is discussed. An attempt is made to reconcile current spread-F models for these two latitude regions by proposing that the primary spread-F structures for equatorial regions are large-scale wave-like structures. It is further proposed that the small-scale plasma instabilities have a role of modifying the traces resulting from specular reflections from the large-scale structures. |
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