Produção Nacional
Solar cycle related range type spread-F occurrence characteristics over equatorial and low latitude stations in Brazil
1985; Elsevier BV; Volume: 47; Issue: 8-10 Linguagem: Inglês
10.1016/0021-9169(85)90065-0
ISSN1878-593X
AutoresM. A. Abdu, J. H. A. Sobral, Osman Rosso Nelson, I. S. Batista,
Tópico(s)Solar and Space Plasma Dynamics
ResumoRange type spread-F occurrence rates from sunset to morning hours over Fortaleza (3.9°S, 38.6°W, dip 3.5°S) and Cachoeira Paulista (22°41′S, 45°W, dip 26°S) during the equinoctial month of October (that presents relatively high rates of occurrence) are analysed for the years 1973–1982. Distinctly different occurrence rates are observed at the two stations, especially in the early post-sunset hours. Over Cachoeira Paulista the spread-F occurrence rate at 20 and 21 LT increased by approximately a factor of 3 from low to high sunspot years, and starting from 22–23 LT this rate of increase diminished and even showed an inverse dependence with sunspot number towards early morning hours. Over Fortaleza, on the other hand, the spread-F occurrence rate in the early post-sunset hours remained very high, 90–100%, during 20–21 LT, with no variation from solar minimum to maximum epochs. The spread-F occurrence rate that appears to be nearly independent of sunspot number remained high up to midnight and fell towards morning hours. These results are interpreted on the bases of solar activity control on plasma bubble generation and its vertical rise velocity and F-region dynamo electric field.
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