Equatorial spread-F occurrence statistics in the American longitudes: Diurnal, seasonal and solar cycle variations

Abdu, M. A.; Sobral, J. H. A.; Batista, I. S.; Ríos, V. H.; Medina, Catalina

doi:10.1016/s0273-1177(98)00111-2

Cited by 67 publications

(53 citation statements)

References 21 publications

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“…Sultan, 1996;Sekar and Kelley, 1998), during the recent years, are known as trans-equatorial plasma bubbles associated with strong range spread-F and have the highest disruptive levels of trans-ionospheric communications. As pointed out by Abdu et al (1998;see also Whalen, 2002) the spread-F in equatorial ionograms represent bottomside plasma irregularities that either could be associated, or not, with the equatorial plasma bubbles, whereas the spread-F in low-latitude ionograms are indicative of equatorial plasma bubbles or macroscopic bubbles (Whalen, 2002). The equatorial plasma bubbles are formed in the post-sunset period, at the magnetic equator, due to the Rayleigh-Taylor gravitational instability process operational on the steep upward gradient in the bottomside F-region.…”

Section: Introductionmentioning

confidence: 83%

“…Abdu et al, 1998;Fejer et al, 1999;Palmroth et al, 2000;Sahai et al, 2000;Whalen, 2002;Huang et al, 2002), as well as theoretical ones (e.g. Sultan, 1996;Sekar and Kelley, 1998), during the recent years, are known as trans-equatorial plasma bubbles associated with strong range spread-F and have the highest disruptive levels of trans-ionospheric communications.…”

Section: Introductionmentioning

confidence: 99%

“…In the Brazilian sector it is now known that there are distinct strong spread-F (EPBs) seasons (Sahai et al, 1994(Sahai et al, , 1998(Sahai et al, , 2004Abdu et al, 1998), with high occurrence during the D months, low occurrence during the J months, and the equinox E months showing transition characteristics from high to low and vice versa. The observed seasonal dependence of the EPBs in the Brazilian sector is associated with the magnetic declination control (about 20 • W) (Tsunoda, 1985;Maruyama, 1988;Abdu et al, 1992).…”

Section: Introductionmentioning

confidence: 99%

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Geomagnetic storm and equatorial spread-F

et al. 2004

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Abstract. In August 2000, a new ionospheric sounding station was established at Sao Jose dos Campos (23.2° S, 45.9° W; dip latitude 17.6° S), Brazil, by the University of Vale do Paraiba (UNIVAP). Another ionospheric sounding station was established at Palmas (10.2° S, 48.2° W; dip latitude 5.5° S), Brazil, in April 2002, by UNIVAP in collaboration with the Lutheran University Center of Palmas (CEULP), Lutheran University of Brazil (ULBRA). Both the stations are equipped with digital ionosonde of the type known as Canadian Advanced Digital Ionosonde (CADI). In order to study the effects of geomagnetic storms on equatorial spread-F, we present and discuss three case studies, two from the ionospheric sounding observations at Sao Jose dos Campos (September and November 2000) and one from the simultaneous ionospheric sounding observations at Sao Jose dos Campos and Palmas (July 2003). Salient features from these ionospheric observations are presented and discussed in this paper. It has been observed that sometimes (e.g. 4-5 November 2000) the geomagnetic storm acts as an inhibitor (high strong spread-F season), whereas at other times (e.g. 11-12 July 2003) they act as an initiator (low strong spread-F season), possibly due to corresponding changes in the quiet and disturbed drift patterns during different seasons.

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Section: Introductionmentioning

confidence: 83%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Geomagnetic storm and equatorial spread-F

et al. 2004

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“…The objective was to study the influence that sporadic E-layers at the field line footprints may have on the formation of ESF at Cachimbo. Major characteristics of ESF in the South American longitude sector, and especially over Brazil, have been studied during the last two decades (see, for example, Abdu et al, 1998;Batista et al, 1990).…”

Section: Introductionmentioning

confidence: 99%

Multistation digisonde observations of equatorial spread F in South America

et al. 2004

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Abstract. Directional ionogram and F -region drift observations were conducted at seven digisonde stations in South America during the COPEX campaign from October to December 2002. Five stations in Brazil, one in Argentina, and one in Peru, monitored the ionosphere across the continent to study the onset and development of F -region density depletions that cause equatorial spread F (ESF). New ionosonde techniques quantitatively describe the prereversal uplifting of the F layer at the magnetic equator and the eastward motion of the depletions over the stations. Three of the Brazilian stations were located along a field line with a 350-km apex over the equator to investigate the relation of the occurrence of ESF and the presence of sporadic E-layers at the two Eregion intersections of the field line. No simple correlation was found.

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“…Since the L-band scintillation occurrence is largely controlled by the EPB occurrence, the differences in its occurrence during August and September are directly associated to the seasonal variation in the plasma bubble occurrence. August is winter in the Southern Hemisphere, whereas September is more like Equinox when the occurrence of spread F increases over Brazil (Abdu et al 1998;Muella et al 2009). It is also seen from Fig.…”

Section: Resultsmentioning

confidence: 99%

Thermospheric Meridional Wind Control on Equatorial Scintillations and the Role of the Evening F-Region Height Rise, E × B Drift Velocities and F2-Peak Density Gradients

et al. 2010

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The possible role, on L-band scintillation activity, played by the nighttime magnetic meridional component of the thermospheric horizontal neutral winds, the postsunset F-layer base height, the electrical field pre-reversal enhancement (PRE) and the latitudinal gradients of the F2-layer peak density is analyzed, considering different cases of scintillation occurrence (and their latitudinal extent) during August and September 2002. The meridional winds were derived over low-latitudes from a modified form of the nonlinear time-dependent servo-model. A chain of two scintillation monitors and three digital ionosondes was operational in Brazil and used to collect, respectively, global positioning system signal amplitude scintillation and ionospheric height (h 0 F; hpF2) and frequency (foF2) parameters. From the overall behavior in the 2 months analyzed, the results suggest that high near sunset upward vertical plasma drifts are conducive for the generation of spread-F irregularities, whereas large poleward meridional winds tend to suppress the development of plasma bubble irregularities and the occurrence of their associated scintillations. Even when generated, a reduced fountain effect, due to weak electric field PRE, acts for the bubbles to be expanded less effectively to higher latitudes. The results also reveal that high F-layer base and peak heights (at equatorial and off-equatorial latitudes), and intense gradients in the F2-peak density between the dip equator and the equatorial anomaly crests, are favorable conditions for the generation of F-region irregularities and increased scintillation activity. Other distinct features of the controlling factors in the cases of occurrence and non-occurrence of equatorial scintillations are presented and discussed.

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Equatorial spread-F occurrence statistics in the American longitudes: Diurnal, seasonal and solar cycle variations

Cited by 67 publications

References 21 publications

Geomagnetic storm and equatorial spread-F

Geomagnetic storm and equatorial spread-F

Multistation digisonde observations of equatorial spread F in South America

Thermospheric Meridional Wind Control on Equatorial Scintillations and the Role of the Evening F-Region Height Rise, E × B Drift Velocities and F2-Peak Density Gradients

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