Abstract
Abstract. Range spread-F (RSF) and occurrence of "satellite" traces prior to RSF onset were studied at the southern peak of the ionospheric equatorial anomaly (EA). Ionograms recorded in September 2007 at the new ionospheric station of Tucumán, Argentina (26.9° S, 294.6° E, dip latitude 15.5° S), by the Advanced Ionospheric Sounder (AIS) developed at the Istituto Nazionale di Geofisica e Vulcanologia (INGV), were considered. Satellite traces (STs) are confirmed to be a necessary precursor to the appearance of an RSF trace on the ionograms. Moreover, an analysis of isoheight contours of electron density seems to suggest a relationship between RSF occurrence and gravity wave (GW) propagation.
Highlights
Spread-F signatures on ionograms are the manifestation of ionospheric irregularities in the F-region
Our results show that Range spread-F (RSF) signatures on the ionograms do not seem to be due to equatorial plasma bubbles coming from the magnetic equator where they were generated around sunset, but rather to plasma instabilities that were locally generated
This suggests the two following considerations: 1) the observed RSF do not seem to be signature of equatorial plasma bubble (EPB) generated around sunset at the magnetic equator; instead they may be considered signatures of plasma instabilities that were locally generated; 2) the post-sunset rise (PSSR), that can extend under the southern crest of the equatorial anomaly (EA) as was shown by Klausner et al (2009) and by Abdu et al (2009), cannot be considered itself as the only cause of RSF appearance on the ionogram, and a triggering process associated with PSSR is needed to cause instabilities responsible for RSF development
Summary
Spread-F signatures on ionograms are the manifestation of ionospheric irregularities in the F-region. Tsunoda (2005, 2008, 2009) and Tsunoda and Ecklund (2007) pointed out that large-scale wave structure (LSWS), in the bottomside F-layer, is an important contributor to be taken into account in solving this puzzle These authors showed how the LSWS upwelling may evolve into a plume and into an equatorial plasma bubble (EPB), and they demonstrated, using incoherent scatter radar data and ionosonde data from Kwajalein Atoll, Marshall Islands, that STs and multi-reflected echoes can be considered as ionogram signatures for LSWS. Our results show that RSF signatures on the ionograms do not seem to be due to equatorial plasma bubbles coming from the magnetic equator where they were generated around sunset, but rather to plasma instabilities that were locally generated
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