Response of the equatorial and low-latitude ionosphere during the space weather events of April 2002

Lima, W. L. C.; Becker‐Guedes, F.; Sahai, Y.; Fagundes, P. R.; Abalde, J. R.; Crowley, G.; Bittencourt, J. A.

doi:10.5194/angeo-22-3211-2004

Cited by 29 publications

(38 citation statements)

References 39 publications

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“…Figure 1 also shows the second reflection of the transmitted frequencies above about 450 km altitude and E and E S layer reflections around 100 km. Becker‐Guedes et al [2004] and Lima et al [2004] have used similar isofrequency plots to study the response of the ionospheric F layer during geomagnetically disturbed periods.…”

Section: Data Analysis and Discussionmentioning

confidence: 99%

Observations of F layer electron density profiles modulated by planetary wave type oscillations in the equatorial ionospheric anomaly region

Fagundes¹,

Pillat²,

Bolzan³

et al. 2005

J. Geophys. Res.

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A digital ionosonde of the type known as the Canadian Advanced Digital Ionosonde (CADI) is operational at São José dos Campos (23.2°S, 45.9°W), Brazil. This ionospheric sounding station is located under the southern crest of the ionospheric equatorial anomaly. The F layer electron density profile presents considerable day‐to‐day variability, even during undisturbed conditions, and this variability is still one of the less understood aspects of the physics of the ionosphere. The propagation of waves into the ionosphere may play an important role in this day‐to‐day ionospheric variability. In this paper we present a new technique that uses multifrequency virtual height variations, from ionospheric sounding observations at this low‐latitude station, to investigate how the F layer is modulated by planetary wave type oscillations. We have also considered the possible influence of oscillations due to solar origin (solar rotation variation). In the present study, observations during the months of June to September 2003 (season of low‐range type equatorial spread F occurrence at this location) have been used. The present study indicates the presence of 2‐day (the observed 3‐day periods are possibly associated with the quasi 2‐day oscillations), 5‐day, 10‐day, and 16‐day periods related to planetary wave type oscillations due to tropospheric sources during all the day. Also, it appears that during the day and dusk times, the longer periods 24–30 days are related to solar rotation (27 days), whereas the shorter periods 9–17 days have possibly some influence from half solar rotation (13.5 days). During the nighttime, possibly the short period oscillations 3–9 days may have some influence from the geomagnetic disturbances.

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Section: Data Analysis and Discussionmentioning

confidence: 99%

Observations of F layer electron density profiles modulated by planetary wave type oscillations in the equatorial ionospheric anomaly region

Fagundes¹,

Pillat²,

Bolzan³

et al. 2005

J. Geophys. Res.

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“…The use of the parameter hpF2 has been reported by many authors (e.g. Danilov and Morozova 1985;Lima et al 2004;Becker-Guedes et al 2007) to be more reliable during nighttime, when it is close to the actual height of the F2-peak layer (hmF2). D 0 in the second term of Eq.…”

Section: Observation Sites and Experiments Datamentioning

confidence: 97%

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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“…A number of studies have been conducted on low latitudinal ionospheic responses during magnetic storm periods that have significantly advanced our knowledge on this subject (Kelley et al, 1979;Dabas and Jain, 1985;Abdu et al, 1990Abdu et al, , 1995Fejer, 1991;Lakshmi el al., 1997;de Medeiros et al, 1997;Sobral et al, 1997;Abdu, 1997;Sastri et al, 2000;Abdu, 2001;Sastri et al, 2002;Pincheira et al, 2002;Pavlov, 2002a, 2002b;Pavlov et al, 2004;Lynn et al, 2004 andLima et al, 2004). Evidence has been provided by Fesen et al (1989) for the effect of winds blowing across the magnetic equator transporting plasma along the nearly horizontal field lines.…”

Section: Introductionmentioning

confidence: 97%

“…Also, season-dependent meridional/transequatorial winds can significantly alter the EIA response to disturbance electric fields. Lima et al (2004) studied the response of the equatorial and low latitude ionosphere during a storm in April 2002 and the observed F-region parameters when compared with the TIMEGCM model show reasonable agreement during magnetic disturbances. Lynn et al (2004), using a combination of TOPEX/Poseidon TEC and ionosonde observations, studied the cases of storms showing a strong depression in daytime foF2 values at low latitudes which are caused by the suppression in the equatorial ionization anomaly.…”

Section: Introductionmentioning

confidence: 99%

Space weather impact on the equatorial and low latitude F-region ionosphere over India

et al. 2006

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Abstract. For a detailed study of the space weather impact on the equatorial and low latitude F-region, the ionospheric response features are analysed during the periods of three recent and most severe magnetic storm events of the present solar cycle which occurred in October and November 2003, and November 2004. The F-layer base height (h'F), peak height (hmF2) and critical frequency (foF2) data, from Trivandrum, an equatorial station and Delhi, a low latitude location, are examined during the three magnetic storm periods. The results of the analysis clearly shows that the height of the F-region (both h'F and hmF2), at the equator and low latitude, simultaneously increases by 200 to 300 km, in association with maximum negative excursion of Dst values around the midnight hours with a large depletion of ionization over the equator, which is followed by an ionization enhancement at low latitude during the recovery phase of the storm. At Delhi, fast variations up to 200 m/s are also observed in the F-layer vertical upward/downward velocity, calculated using Doppler shifts, associated with the maximum negative excursion of Dst. This shows that during magnetic disturbances, the equatorial ionization anomaly (EIA) expands to a much wider latitude than the normal fountain driven by the E/F-layer dynamo electric fields. It is also observed that during the main phase of the storm, at low latitude there is generally an enhancement of F-region ionization with an increase in h'F/hmF2 but in the equatorial region, the ionization collapses with a decrease in h'F/hmF2, especially after sunset hours. In addition, at the equator the normal pre-sunset hours' enhancement in h'F is considerably suppressed during storm periods. This might be due to changes in magnitude and direction of the zonal electric field affecting the upward E×B drift and hence the plasma distribution in the form of a decrease in electron density in the equatorial region and an increase in the low latitude region. In association with disturbance electric fields, the enhanced storm-induced equatorward meridional winds in the thermosphere can also further amplify the F-layer height rise at low latitudes during the post-midnight hours, as observed in two of the storm periods.

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Response of the equatorial and low-latitude ionosphere during the space weather events of April 2002

Cited by 29 publications

References 39 publications

Observations of F layer electron density profiles modulated by planetary wave type oscillations in the equatorial ionospheric anomaly region

Observations of F layer electron density profiles modulated by planetary wave type oscillations in the equatorial ionospheric anomaly region

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

Space weather impact on the equatorial and low latitude F-region ionosphere over India

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