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Found 18 entries in the Bibliography.

Showing entries from 1 through 18

2022

Occurrence of Ionospheric irregularities over Brazil and Africa during the 2019 Antarctic minor sudden stratospheric warming

The influence of sudden stratospheric warming (SSW) on the ionosphere and ionospheric irregularities has been studied extensively over the years. However, majority of these

Agyei-Yeboah, Ebenezer; Fagundes, Paulo; Tardelli, Alexandre; Pillat, Valdir; Vieira, Francisco; Arcanjo, Mateus;

Published by: Advances in Space Research Published on:

YEAR: 2022 DOI: 10.1016/j.asr.2022.08.065

2016

Positive and negative GPS-TEC ionospheric storm effects during the extreme space weather event of March 2015 over the Brazilian sector

We studied the response of the ionosphere (F region) in the Brazilian sector during extreme space weather event of 17 March 2015 using a large network of 102 GPS- total electron content (TEC) stations. It is observed that the vertical total electron content (VTEC) was severely disturbed during the storm main and recovery phases. A wavelike oscillation with three peaks was observed in the TEC diurnal variation from equator to low latitudes during the storm main phase on 17\textendash18 March 2015. The latitudinal extent of the wavelike oscillation peaks decreased from the beginning of the main phase toward the recovery phase. The first peak extended from beyond 0\textdegreeS to 30\textdegreeS, the second occurred from 6\textdegreeS to 25\textdegreeS, whereas the third diurnal peaks was confined from 13\textdegreeS to 25\textdegreeS. In addition, a strong negative phase in VTEC variations was observed during the recovery phase on 18\textendash19 March 2015. This ionospheric negative phase was stronger at low latitudes than in the equatorial region. Also, two latitudinal chains of GPS-TEC stations from equatorial region to low latitudes in the east and west Brazilian sectors are used to investigate the storm time behavior of the equatorial ionization anomaly (EIA) in the east and west Brazilian sectors. We observed an anomalous behavior in EIA caused by the wavelike oscillations during the storm main phase on 17 March, and suppression of the EIA, resulting from the negative phase in VTEC, in the storm recovery phase.

Fagundes, P.; Cardoso, F.; Fejer, B.; Venkatesh, K.; Ribeiro, B.; Pillat, V.;

Published by: Journal of Geophysical Research: Space Physics Published on: 05/2016

YEAR: 2016 DOI: 10.1002/2015JA022214

2012

Effects observed in the equatorial and low latitude ionospheric F-region in the Brazilian sector during low solar activity geomagnetic storms and comparison with the COSMIC measurements

The main objective of the present investigation has been to compare the ionospheric parameters (NmF2 and hmF2) observed by two ground-based ionospheric sounders (one at PALMAS- located near the magnetic equator and the other at Sao Jose dos Campos-located in the low-latitude region) in the Brazilian sector with that by the satellite FORMOSAT-3/COSMIC radio occultation (RO) measurements during two geomagnetic storms which occurred in December 2006 and July 2009. It should be pointed out that in spite of increasing the latitude (to 10\textdegree) and longitude (to 20\textdegree) around the stations; we had very few common observations. It has been observed that both the peak electron density (NmF2) and peak height (hmF2) observed by two different techniques (space-borne COSMIC and ground-based ionosondes) during both the geomagnetic storm events compares fairly well (with high correlation coefficients) at the two stations in the Brazilian sector. It should be pointed out that due to equatorial spread F (ESF) in the first storm (December 2006) and no-reflections from the ionosphere during nighttime in the second storm (July 2009), we had virtually daytime data from the two ionosondes.

Sahai, Y.; de Jesus, R.; Fagundes, P.R.; Selhorst, C.L.; de Abreu, A.J.; Ram, Tulasi; Aragon-Angel, A.; Pillat, V.G.; Abalde, J.R.; Lima, W.L.C.; Bittencourt, J.A.;

Published by: Advances in Space Research Published on: 11/2012

YEAR: 2012 DOI: 10.1016/j.asr.2012.07.006

COSMIC satellite; F-region; geomagnetic storm; Ionosphere; Low solar activity

The global thermospheric and ionospheric response to the 2008 minor sudden stratospheric warming event

This paper presents a study of thermospheric and ionospheric response to the 2008 minor sudden stratospheric warming (SSW) event. This period was characterized by low solar and geomagnetic activity. The study was performed using the Global Self-consistent Model of Thermosphere, Ionosphere, and Protonosphere (GSM TIP). Model results were compared with ionosonde data from Irkutsk, Kaliningrad, Sao Jose dos Campos, and Jicamarca. The SSW event was modeled by specifying the temperature and density perturbations at the lower boundary of the GSM TIP (80 km altitude). GSM TIP simulation allowed the reproduction of the lower thermosphere temperature disturbances (the occurrence of the quasi-wave 1 structure at 80\textendash130 km altitude with a vertical scale of \~40 km), the negative response of F2 region electron density and the positive response of electron temperature at 300 km during the 2008 minor SSW event. The main formation mechanism of the global ionospheric response is due to the disturbances (decrease) in then(O)/n(N2) ratio. The change in zonal electric field is another important mechanism of the ionospheric response at low latitudes.

Korenkov, Y.; Klimenko, V.; Klimenko, M.; Bessarab, F.; Korenkova, N.; Ratovsky, K.; Chernigovskaya, M.; Shcherbakov, A.; Sahai, Y.; Fagundes, P.; de Jesus, R.; de Abreu, A.; Condor, P.;

Published by: Journal of Geophysical Research Published on: 10/2012

YEAR: 2012 DOI: 10.1029/2012JA018018

Electric field; Ionosphere; sudden stratospheric warming; thermosphere

2011

Studies of ionospheric F-region response in the Latin American sector during the geomagnetic storm of 21--22 January 2005

Sahai, Y.; Fagundes, P.; de Jesus, R.; de Abreu, A.; Crowley, G.; Kikuchi, T.; Huang, C.-S.; Pillat, V.; Guarnieri, F.; Abalde, J.; Bittencourt, J.;

Published by: Annales Geophysicae Published on: Jan-01-2011

YEAR: 2011 DOI: 10.5194/angeo-29-919-2011

Effects of geomagnetic super storms on the ionospheric F-region in the South American sector using a GPS technique: A review

Sahai, Y; De Abreu, AJ; Fagundes, PR; De Jesus, R; Crowley, G; Klimenko, MV; Klimenko, VV; Brunini, C; Gende, M; Pillat, VG; , others;

Published by: Asian Journal of Physics Published on:

YEAR: 2011 DOI:

Numerical modeling of ionospheric effects in the middle-and low-latitude F region during geomagnetic storm sequence of 9--14 September 2005

This study presents the Global Self-Consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) numerical simulations of the 9–14 September 2005 geomagnetic

Klimenko, MV; Klimenko, VV; Ratovsky, KG; Goncharenko, LP; Sahai, Y; Fagundes, PR; De Jesus, R; De Abreu, AJ; Vesnin, AM;

Published by: Radio Science Published on:

YEAR: 2011 DOI:

2010

Seasonal variations in ionospheric F-region parameters during the low solar activity period in the Brazilian sector and comparison with ionospheric models

Sahai, Yogeshwar; de Jesus, Rodolfo; Fagundes, Paulo; de Abreu, Alessandro; Crowley, Geoff; Pillat, Valdir; Guede, Jose; Bittencourt, Jose;

Published by: 38th COSPAR Scientific Assembly Published on:

YEAR: 2010 DOI:

2009

Response of the Ionospheric F-region in the Latin American Sector During the Intense Geomagnetic Storm of 21-22 January 2005

Sahai, Y; Fagundes, PR; De Jesus, R; De Abreu, AJ; Crowley, G; Pillat, VG; Guarnieri, FL; , Abalde; Bittencourt, JA;

Published by: Published on:

YEAR: 2009 DOI:

Effects observed in the Latin American sector ionospheric F region during the intense geomagnetic disturbances in the early part of November 2004

Sahai, Y; Becker-Guedes, F; Fagundes, PR; De Jesus, R; De Abreu, AJ; Paxton, LJ; Goncharenko, LP; Brunini, C; Gende, M; Ferreira, AS; , others;

Published by: Journal of Geophysical Research: Space Physics Published on:

YEAR: 2009 DOI:

2008

Unusual ionospheric effects observed during the intense 28 October 2003 solar flare in the Brazilian sector

Sahai, Y.; Becker-Guedes, F.; Fagundes, P.R.; Lima, W.L.C.; de Abreu, A.J.; Guarnieri, F.L.; Candido, C.M.N.; Pillat, V.G.;

Published by: Published on:

YEAR: 2008 DOI:

2007

Brazilian ionosphere behavior during an intense solar flare

The 28 October 2003 solar flare was one of the most intense solar flares observed in the recent past. In the present investigation we show the ionospheric effects observed in the

Becker-Guedes, F; Sahai, Y; Fagundes, PR; Abreu, A; Pillat, VG; Lima, WLC;

Published by: Published on:

YEAR: 2007 DOI: https://doi.org/10.3997/2214-4609-pdb.172.SBGF0393_07

Unusual ionospheric effects observed during the intense 28 October 2003 solar flare in the Brazilian sector

Sahai, Y; Becker-Guedes, F; Fagundes, PR; Lima, WLC; De Abreu, AJ; Guarnieri, FL; Candido, CMN; Pillat, VG;

Published by: Published on:

YEAR: 2007 DOI:

The ionospheric response in the Brazilian sector during the super geomagnetic storm on 20 November 2003

Becker-Guedes, F; Sahai, Y; Fagundes, PR; Espinoza, ES; Pillat, VG; Lima, WLC; Basu, Su; Basu, Sa; Otsuka, Y; Shiokawa, K; MacKenzie, E.; Bittencourt, J.;