Long term studies of equatorial spread F using the JULIA radar at Jicamarca |
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| Institution: | 1. PG - Ciência dos Materiais, Universidade Federal do Vale do São Francisco, 48902-300 Juazeiro, BA, Brazil;2. Instituto de Física, Universidade Federal Fluminense, 24210-346 Niterói, RJ, Brazil;1. Data Analysis Center for Geomagnetism and Space Magnetism, Graduate School of Science, Kyoto University, Japan;2. Research Institute for Sustainable Humanosphere, Kyoto University, Japan;3. Space and Upper Atmospheric Science Group, National Institute of Polar Research, Japan;4. Solar-Terrestrial Environment Laboratory, Nagoya University, Japan;5. Solar-Planetary Electromagnetism Laboratory, Graduate School of Science, Kyoto University, Japan;1. Saint-Petersburg State University of Aerospace Instrumentation, 67, Bolshaya Morskaya street, Saint-Petersburg 190000, Russia;2. Institute for Physics, Southern Federal University, Stachki, 194, Rostov-on-Don 344090, Russia;3. Physical Department, Southern Federal University, Sorge, 5 Rostov-on-Don 344090, Russia;4. SCiESMEX, Instituto de Geofisica, Unidad Michoacan, Universidad Nacional Autonoma de Mexico, Morelia, Michoacan, CP 58190, Mexico;5. Arctic and Antarctic Research Institute, 38 Bering street, Saint-Petersburg 199397, Russia;1. German Aerospace Center (DLR), German Remote Sensing Data Center (DFD), 82234 Wessling, Germany;2. Augsburg University, 86135 Augsburg, Germany;1. Pwani University College, School of Pure and Applied Sciences, Department of Mathematics and Physics, P.O Box 195, 80108 Kilifi, Kenya;2. Kenya Polytechnic University College, School of Pure and Applied Sciences, Department of Physics, P.O Box 52428, 00200 City Square Nairobi, Kenya;3. South African National Space Agency, Space Science Directorate, P.O Box 32, Hermanus, South Africa;4. Institute for Scientific Research, Boston College, 201 Foster Street, Brighton, MA 02135, USA;5. The Abdus Salam International Centre for Theoretical Physics, Trieste, Italy;6. University of Cape Town, Cape Town, South Africa |
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| Abstract: | Jicamarca unattended long term investigations of the ionosphere and atmosphere radar observations of equatorial spread F (ESF) plasma irregularities made between August 1996 and April 2000 are analyzed statistically. Interpretation of the data is simplified by adopting a taxonomy of echo types which distinguishes between bottom-type, bottomside, topside, and post-midnight irregularities. The data reveal patterns in the occurrence of ESF in the Peruvian sector that are functions of season, solar flux, and geomagnetic activity. We confirm earlier work by Fejer et al. (J. Geophys. Res. 104 (1999) 19,859) showing that the quiet-time climatology of the irregularities is strongly influenced by the climatology of the zonal ionospheric electric field. Under magnetically quiet conditions, increasing solar flux implies greater pre-reversal enhancement amplitudes and, consequently, irregularity appearances at earlier times, higher initial altitudes, and higher peak altitudes. Since the post-reversal westward background electric field also grows stronger with increasing solar flux, spread F events also decay earlier in solar maximum than in solar minimum. Variation in ESF occurrence during geomagnetically active periods is consistent with systematic variations in the electric field associated with the disturbance dynamo and prompt penetration described by Fejer and Scherliess (J. Geophys. Res. 102 (1997) 24,047) and Scherliess and Fejer (J. Geophys. Res. 102 (1997) 24,037). Quiet-time variability in the zonal electric field contributes significantly to variability in ESF occurrence. However, no correlation is found between the occurrence of strong ESF and the time history of the zonal electric field prior to sunset. |
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