Articles | Volume 31, issue 2
Ann. Geophys., 31, 153–162, 2013
Ann. Geophys., 31, 153–162, 2013

Regular paper 05 Feb 2013

Regular paper | 05 Feb 2013

Low-latitude equinoctial spread-F occurrence at different longitude sectors under low solar activity

M. Pezzopane1, E. Zuccheretti1, P. Abadi2, A. J. de Abreu3, R. de Jesus3, P. R. Fagundes3, P. Supnithi4, S. Rungraengwajiake4, T. Nagatsuma5, T. Tsugawa5, M. A. Cabrera6,7,8, and R. G. Ezquer7,8,9 M. Pezzopane et al.
  • 1Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy
  • 2Division of Ionosphere and Telecommunication, Space Science Center, Indonesian National Institute of Aeronautics and Space (LAPAN), Indonesia
  • 3Universidade do Vale do Paraíba, São José dos Campos, Brazil
  • 4Faculty of Engineering, King Mongkut's Institute of Technology Ladkrabang (KMITL), Bangkok 10520, Thailand
  • 5Space Weather and Environment Informatics Laboratory, National Institute of Information and Communications Technology, Tokyo 184-8795, Japan
  • 6Laboratorio de Telecomunicaciones, DEEC, FACET, Universidad Nacional de Tucumán, Tucumán, Argentina
  • 7Laboratorio de Ionósfera, Departamento de Física, FACET, Universidad Nacional de Tucumán, Tucumán, Argentina
  • 8CIASUR, Facultad Regional Tucumán, Universidad Tecnológica Nacional, Tucumán, Argentina
  • 9Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina

Abstract. We present the results of a comparative study of spread-F signatures over five low-latitude sites: Chiangmai (CGM; 18.8° N, 98.9° E, mag. Lat. 8.8° N), Thailand; Tanjungsari (TNJ; 6.9° S, 107.6° E, mag. Lat. 16.9° S), Indonesia; Palmas (PAL; 10.2° S, 311.8° E, mag. Lat. 0.9° S) and São José Dos Campos (SJC; 23.2° S, 314.1° E, mag. Lat. 14.0° S), Brazil; and Tucumán (TUC; 26.9° S, 294.6° E, mag. Lat. 16.8° S), Argentina. The investigation was based on simultaneous ionograms recorded by an FMCW (frequency-modulated continuous-wave) at CGM, an IPS-71 (digital ionosonde from KEL aerospace) at TNJ, a CADI (Canadian Advanced Digital Ionosonde) at PAL and SJC, and an AIS-INGV (Advanced Ionospheric Sounder – Istituto Nazionale di Geofisica e Vulcanologia) at TUC, during the equinoctial periods March–April (R12 = 2.0 and R12 = 2.2) and September–October (R12 = 6.1 and R12 = 7.0) 2009, for very low solar activity. Spread-F signatures were categorized into two types: the range spread-F (RSF) and the frequency spread-F (FSF). The study confirms that the dynamics and the physical processes responsible for these phenomena are actually complicated. In fact, the features that arise from the investigation are different, depending on both the longitude sector and on the hemisphere. For instance, TUC, under the southern crest of the ionospheric equatorial ionization anomaly (EIA), shows a predominance of RSF signatures, while both SJC, under the southern crest of EIA but in a different longitude sector, and CGM, under the northern crest of EIA, show a predominance of FSF signatures. Moreover, the spread-F occurrence over the longitude sector that includes CGM and TNJ is significantly lower than the spread-F occurrence over the longitude sector of PAL, SJC, and TUC.