Navegando por Autor "Roberto, Marisa"

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    Ionospheric GPS-TEC responses from equatorial region to the EIA crest in the South American sector under intense space weather conditions
    (Elsevier) Abreu, Alessandro José de; Correia, Emilia; Denardini, Clezio Marcos; Jesus, Rodolfo de; Venkatesh, Kavutarapu; Roberto, Marisa; Abalde, José Ricardo; Fagundes, Paulo Roberto; Bolzan, Maurício José Alves; Gende, Maurício Alfredo
    We present and discuss the ionospheric F-region observations from equator to the equatorial ionization anomaly (EIA) regions over the South American sector during an intense space weather event occurred between 27 and May 29, 2017. During this geomagnetic storm, the symmetric-H (SYM-H) reached a minimum of − 142 nT at ~0700 UT on May 28, 2017. For this investigation, we analyze the vertical total electron content (VTEC) observations from a chain of nearly 120 Global Positioning System (GPS) stations. Magnetometer measurements obtained at two stations in the low latitude regions are also presented. The observations do not indicate prompt penetration electric field (PPEF) effects in the VTEC variations. Magnetometer’s observations over Cuiaba ´ (CBA) and Cachoeira Paulista (CXP) in central west and south parts of Brazil, respectively, have shown a strong crosscorrelation with SYM-H in the period between 3 and 48 h. The results also show positive ionospheric storm phase during the recovery phase on May 28, 2017. Positive effect during the recovery phase of the geomagnetic storm is possibly associated with effects of disturbances winds. During the recovery phase, a strong intensification of the EIA took place, possibly related to an additional ionization effect. The VTEC values show differences between the west and east sectors. This indicates that the EIA crest is stronger in the east sector than in the west sector, possibly due to the combination of disturbance wind effects and geomagnetic field geometry where in the east sector the field lines are more inclined.
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    Observation and simulation studies of ionospheric F-region in the South American and Antarctic sectors in the intense geomagnetic storm of August 2018
    (Elsevier) Abreu, Alessandro José de; Correia, Emilia; Jonah, Olusegun Folarin; Venkatesh, Kavutarapu; Thomas, Evan G.; Jesus, Rodolfo F. de; Roberto, Marisa; Abalde, José Ricardo; Fagundes, Paulo Roberto
    In this investigation, we present and discuss the ionospheric F region observations in the equatorial, low-, mid-, and near high-latitude regions in the South American and Antarctic sectors during the intense geomagnetic storm that occurred on 25–27 August 2018. The geomagnetic storm reached a minimum Dst of − 175 nT at ~0700 UT on 26 August. We present the variations of vertical total electron content (VTEC) from a chain of almost 200 GPS stations, covering the South American and Antarctic sectors. A comparison with model simulations from the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIE-GCM) is realized. The results ob- tained show that during the main phase of the storm, a southward Bz component of the interplanetary magnetic field (IMF) and an eastward prompt penetration electric field (PPEF) can be observed, but they had no significant impact on the ionospheric plasma. A long recovery phase a predominance of positive phase is observed during daytime. The observations show the effects of an unusual case of multiple PPEF, occurred on 26 August, and effects of thermospheric winds disturbances, occurred on 27 August, resulting in increased VTEC values on both days. The TIE-GCM model reproduces the VTEC increases during the main and recovery phases from mid- latitudes to the equatorial region, but it underestimates the observed values near high-latitudes.
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    Statistical analysis on the ionospheric response over South American mid- and near high-latitudes during 70 intense geomagnetic storms occurred in the period of two decades
    (Elsevier) Abreu, Alessandro José de; Correia, Emilia; Jesus, Rodolfo de; Venkatesh, Kavutarapu; Macho, Eduardo Perez; Roberto, Marisa; Fagundes, Paulo Roberto; Gende, Maurício Alfredo
    The first-time statistical response of the positive and negative ionospheric storms phases using Vertical Total Electron Content (VTEC) measurements during 70 geomagnetic storms at near high- and mid-latitudes regions in the Antarctic and Argentine/Chilean sectors in the Southern hemisphere are investigated. The study covers the years between 1999 and 2018 of solar cycles 23 and 24, using the Dst ≤ −100 nT as a criterion for all 70 storms selected. Significant features of solar cycle, seasonal and local time of ionospheric storms are showed. Our results indicate that the occurrence of geomagnetic storms follows a pattern of solar activity dependence, and also indicate a predominance of positive and positive-negative phases during autumn, winter, and spring at mid-latitudes and winter at near high-latitudes. Negative and negative-positive phases occur during all seasons at near high- and mid-latitudes. In addition, positive phases occur more frequently during the daytime while the negative phases occur predominantly in nighttime. There is also a predominance of positive and positive-negative phases simultaneously at near high- and mid-latitudes in the Antarctic and Argentine/Chilean sectors. The percentages of occurrence of positive and positive-negative phases are of 50% and 19%, respectively, at mid-latitude and 60% and 22%, respectively, at near high-latitudes. Negative and negative-positive phases are below 9% at both latitudes.