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

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 (<I>R</I><sub>12</sub> = 2.0 and <I>R</I><sub>12</sub> = 2.2) and September–October (<I>R</I><sub>12</sub> = 6.1 and <I>R</I><sub>12</sub> = 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

The occurrence of equatorial spread-F at conjugate stations in Southeast Asia

“…The most striking feature coming out from their paper is that the spread-F occurrences in the Asian longitude sector are lower than those recorded in the American longitude sector. Similarly to what was shown by Pezzopane et al (2013), also this paper highlights that the FSF type is the dominant type at Chiangmai. In addition, Pezzopane et al (2013) found that satellite traces (STs), caused by gravity waves (GWs) propagation, are precursor to the RSF appearance at Chiangmai, and also at TUC, Argentina, and TNJ, Indonesia, which are located in the southern hemisphere.…”

“…Similarly to what was shown by Pezzopane et al (2013), also this paper highlights that the FSF type is the dominant type at Chiangmai. In addition, Pezzopane et al (2013) found that satellite traces (STs), caused by gravity waves (GWs) propagation, are precursor to the RSF appearance at Chiangmai, and also at TUC, Argentina, and TNJ, Indonesia, which are located in the southern hemisphere. Also, Cabrera et al (2010), by using ionograms recorded at Tucuman, Argentina, in September 2007, previously found that STs are precursor to the RSF appearance.…”

“…This can be explained by taking into account that the ESF prediction routine of the IRI model was computed on the basis of the data observed at the magnetic equator and at low-latitudes over the Brazilian region (Abdu et al, 2003). The differences of spread-F characteristics and occurrences at different regions can be, however, in general attributed to the differences in latitudes, longitudes, magnetic declinations, season and solar activity (Abdu et al, 1998(Abdu et al, , 2000Abdu, 2001;Maruyama et al, 2002;Maruyama, 2006, 2007;Hoang et al, 2010;Pezzopane et al, 2013;Rungraengwajiake et al, 2013).…”

“…For instance, the issues in the equatorial ionosphere-thermosphere electrodynamics over American and Southeast Asia sectors (Abdu, 2001;Cabrera et al, 2010;Candido et al, 2011;Maruyama et al, 2007) or the investigations to find out the relation between the spread-F occurrence and the sporadic-E (Es) characteristics over the Brazilian conjugate point equatorial experiment (COPEX) (Batista et al, 2008). The statistics of spread-F occurrence over different regions confirm that at the different geomagnetic declinations, latitudinal and longitudinal regions, ESF occurrence and intensity have distinct annual or seasonal patterns (Abdu et al, 1981;Maruyama and Matuura, 1984;Sastri, 1999;Maruyama et al, 2002Maruyama et al, , 2007Saito and Maruyama, 2007;Wang et al, 2008Wang et al, , 2010Hoang et al, 2010;Amabayo et al, 2011;Pezzopane et al, 2013).…”

Statistical characteristics of ionogram spread-F and satellite traces over a Chinese low-latitude station Sanya

“…Afterwards, many aspects of SF including the occurrence statistics, longitudinal/latitudinal and seasonal distributions, the dependence on solar and magnetic activity, and their associated ionospheric scintillations (e.g., Abdu et al, 1985Abdu et al, , 2006Cabrera et al, 2010;Li et al, 2010b;Hu et al, 2013;Pezzopane et al, 2013;Upadhayaya and Gupta, 2014), have been extensively studied. The SF has been usually categorized into two main types, the range spread-F (RSF) and frequency spread-F (FSF).…”