Equatorial spread-F at Ibadan, Nigeria

Lyon, A. J.; Skinner, N.J.; Wright, Robert

doi:10.1016/0021-9169(61)90104-0

Cited by 65 publications

(34 citation statements)

References 9 publications

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“…From the start of the first satellite trace it took about 45 min for the appearance of RSF. These observations indicate that the satellite traces, indicative of LSWS, appear to be a precursor for the generation of ESF over Sanya, which are similar to those observed at equatorial [e.g., Lyon et al , 1961; Abdu et al , 1981] and other low latitude stations [ Abdu et al , 2009b]. Specifically, using conjugate station Digisonde observations, Abdu et al [2009b]observed a tendency for the LSWS to occur simultaneously at low latitude conjugate points and found a time delay in their occurrence of about 20–45 min with respect to the equatorial LSWS.…”

Section: Resultsmentioning

confidence: 98%

Precursor signatures and evolution of post‐sunset equatorial spread‐F observed over Sanya

Ning

Abdu

et al. 2012

J. Geophys. Res.

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[1] Recent case studies on the precursor signatures of equatorial spread-F (ESF) have shown a one-to-one correspondence between the large-scale wave structures (LSWS) and ESF development at equatorial latitude. In this study, the LSWS and the onset and development of the ESF are investigated over Sanya (18 N, 109 E), a station located at 13 north of the magnetic equator, during both geomagnetic quiet and disturbed conditions in September-October 2011. High-time-resolution ionograms from Digisonde Portable Sounder (DPS-4D) provided the satellite trace measurements that were used to indicate the occurrence of the LSWS. The development of local ESF activity was identified using GPS scintillation and VHF coherent radar echo measurements from the same site, together with the range type spread-F (RSF) in ionograms. Additionally, the Sanya VHF radar five-beam scanning measurements in east-west direction were used to characterize the longitudinal difference in establishing the initial conditions for ESF development. Correlative studies between the LSWS and ESF activities during the observational period offer consolidated evidence that the LSWS is a necessary precursor for the ESF development. It is shown that the LSWS and ESF have nearly a one-to-one relationship when the F layer undergoes an abrupt post-sunset rise (PSSR), revealing that the magnitude of the pre-reversal enhancement in zonal electric field (PRE) that elevates the F layer to a high enough altitude is an important parameter controlling the generation of post-sunset ESF. However, in the absence of the PSSR, the ESF and GPS scintillation did not always occur following the appearance of LSWS. Sometimes the LSWS events preceded the generation of bottom type spread-F (BSF) that did not develop vertically into ESF and radar plumes. This result may indicate that under inexpressive, weak, or even moderate PRE conditions, the appearance of the LSWS alone may not be sufficient to produce the post-sunset F region irregularities responsible for ionospheric scintillations. More factors, other than the LSWS, could play crucial roles favoring the growth of ESF instabilities responsible for ionospheric scintillations.

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Section: Resultsmentioning

confidence: 98%

Precursor signatures and evolution of post‐sunset equatorial spread‐F observed over Sanya

Ning

Abdu

et al. 2012

J. Geophys. Res.

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“…Satellite traces in equatorial ionograms appear as one or more quasi replicas of the Flayer trace at displaced virtual heights prior to the ESF onset, and are probably produced by oblique reflections from upwelling walls, that is, corrugations in the isodensity surfaces. This issue was very well illustrated by Tsunoda (2008) who provided further evidence, besides those advanced by Wright (1959), Lyon (1961), Abdu et al (1981), andMcNamara et al (2008), that STs are a characteristic precursor of ESF over the equatorial belt. Fagundes et al (2009a, b), as well, showed that PSSR can be strongly modulated by traveling planetary wave ionospheric disturbance oscillations.…”

Section: Introductionmentioning

confidence: 89%

Satellite traces, range spread-F occurrence, and gravity wave propagation at the southern anomaly crest

et al. 2010

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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.

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“…Few early papers [ Lyon et al , 1961; Rastogi , 1977; Abdu et al , 1981] showed observational evidences that ‘satellite’ traces seen in the ionograms preceded the onset of RSF. It was seen that the time between the first appearance of the satellite trace and the RSF onset varied from zero to 45 min.…”

Section: Introductionmentioning

confidence: 99%

Ionogram signatures of large‐scale wave structure and their relation to equatorial spread F

Thampi¹,

Tsunoda²,

Jose³

et al. 2012

J. Geophys. Res.

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[1] Observations of signatures of the large-scale wave structure (LSWS) and subsequent development of equatorial spread F (ESF) by using data from a newly installed digital ionosonde at Trivandrum (8.5 N; 77 E; 0.5 N magnetic dip latitude) are presented. The LSWS signatures are observed using the ionograms with echo directions. The 'satellite' traces are shown as echoes from oblique directions, when an upwelling (associated with LSWS) is not directly over the ionosonde location. When an upwelling is centered overhead, and the radius of curvature of the isodensity contours matches the height of reflection, signals from various directions can add in phase to enhance the ionospheric reflection coefficient, and produce another ionogram signature, referred to as multireflected echoes (MREs). It is also shown that the generation of ESF is related to the presence of LSWS. The skymaps also show the presence of small-scale wave structures in the bottomside F region. The investigation also indicates that the range spread F (RSF) occurs because of the reflections from the embedded smaller-scale structures within the large-scale upwelling.

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Equatorial spread-F at Ibadan, Nigeria

Cited by 65 publications

References 9 publications

Precursor signatures and evolution of post‐sunset equatorial spread‐F observed over Sanya

Precursor signatures and evolution of post‐sunset equatorial spread‐F observed over Sanya

Satellite traces, range spread-F occurrence, and gravity wave propagation at the southern anomaly crest

Ionogram signatures of large‐scale wave structure and their relation to equatorial spread F

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