Gilda González

En el presente trabajo se analiza la periodicidad de valores promedio del contenido electrónico total (TEC) para cinco estaciones GPS de la región ecuatorial durante 90 días del año 2008 (día 32 a día 122). El análisis espectral indica la existencia de periodos de 9, 13-14.5 y 21-22 días para las cinco estaciones. Estas periodicidades están asociadas fundamentalmente a cambios en las corrientes de viento solar; sin embargo, también es importante el efecto de las oscilaciones de la componente Bz del campo magnético interplanetario (IMF). Por otra parte, el pico espectral de 21- 22 días no se observa en el viento solar, ni en IMF ni en el índice Kp, lo que sugiere que probablemente esta periodicidad no tiene relación con la actividad geomagnética ni con las condiciones del viento solar, sino que tiene origen en los efectos meteorológicos en la ionosfera.In this paper we analyze day-to-day variability in Total Electron Content (TEC) values measured at five GPS stations at the equatoria...

The generation and development of ionospheric irregularities is an important topic of study in space weather, mainly because of their adverse effects on navigation and positioning systems, as well as in trans-ionospheric communications. To improve our prediction capabilities, it is necessary to better understand their variabilities during different geomagnetic conditions. The purpose of this research is to analyse the occurrence characteristics of ionospheric irregularities over South America during geomagnetic storms. Using data from six ionosondes and GPS stations in Brazil and Perú, observations from the JULIA radar and Swarm in situ electron density measurements, we examined the presence of irregularities during three intense storms (October 12, 2016, October 7, 2015 and August 25, 2018). Our data show that during the geomagnetic storms that occurred in October 2016 and October 2015, in the Brazilian region, the generation of ionospheric irregularities was usually inhibited during the storm recovery phase. During the main phase, spread-F was generated over the stations located close to the northern crest of the EIA, and it was inhibited over Cachoeira Paulista, a station near the southern crest. During the August 2018 storm, local winter, the geomagnetic activity may have helped generate the irregularities in all the stations analysed regardless of the phase of the storm. We suggest that the generation (inhibition) of irregularities is related to the effect of eastward (westward) storm time electric fields—disturbance dynamo electric fields and prompt penetration electric fields—that created favourable (unfavourable) conditions for the generation of irregularities by uplifting (lowering) the F region.

The generation and development of ionospheric irregularities is an important topic of study in space weather, mainly because of their adverse effects on navigation and positioning systems, as well as in trans-ionospheric communications. To improve our prediction capabilities, it is necessary to better understand their variabilities during different geomagnetic conditions. The purpose of this research is to analyse the occurrence characteristics of ionospheric irregularities over South America during geomagnetic storms. Using data from six ionosondes and GPS stations in Brazil and Perú, observations from the JULIA radar and Swarm in situ electron density measurements, we examined the presence of irregularities during three intense storms (October 12, 2016, October 7, 2015 and August 25, 2018). Our data show that during the geomagnetic storms that occurred in October 2016 and October 2015, in the Brazilian region, the generation of ionospheric irregularities was usually inhibited during the storm recovery phase. During the main phase, spread-F was generated over the stations located close to the northern crest of the EIA, and it was inhibited over Cachoeira Paulista, a station near the southern crest. During the August 2018 storm, local winter, the geomagnetic activity may have helped generate the irregularities in all the stations analysed regardless of the phase of the storm. We suggest that the generation (inhibition) of irregularities is related to the effect of eastward (westward) storm time electric fields—disturbance dynamo electric fields and prompt penetration electric fields—that created favourable (unfavourable) conditions for the generation of irregularities by uplifting (lowering) the F region.

This work presents the study of the variability of foF2 and hmF2 at a low latitude station in South America (Tucuman, 26.9°S, 294.6°E; magnetic latitude 15.5°S, Argentina). Ground based ionosonde measurements obtained during different seasonal and solar activity conditions (a year of low solar activity, 2009 and one of high solar activity, 2016) are considered in order to compare the ionospheric behavior. The parameters used to analyze the variability are the median, upper and lower quartiles. In addition, the foF2 values are compared with those estimated by the International Reference Ionosphere (IRI) - 2016 model. It is found that: a) A clear dependence on solar activity is observed in foF2 and hmF2, both increase with increase in solar activity. b) the variability of foF2 is higher at low solar activity, this behavior is not observed in hmF2 that present similar variability during both periods. c) the variability of foF2 is larger at night than during the day, this behavior is mo...

<b><i>This poster was presented in the 20th International Beacon Satellite Symposium (19 – 23 August 2019, University of Warmia and Mazury, Olsztyn, Poland).</i></b>We present the study of the occurrence of ionospheric irregularities during geomagnetic storms at a low latitude station in the Southern American longitudinal sector (Tucuman – Argentina, 26.9 ° S, 294.6 ° E; magnetic latitude 15.5 ° S), near the southern crest of the equatorial ionization anomaly (EIA). We analyze data recorded during three moderate geomagnetic storms; May 27, 2017 (a month of low occurrence rates of spread – F), October 12, 2016 (a month of transition from low to high occurrence rates of spread-F) and November 7, 2017 (a month of high occurrence rates of spread-F) from Global Positioning System (GPS) receivers and ionosondes. The Total electron content (TEC) estimated with a GPS-TEC calibration technique, GPS Ionospheric L-band scintillation, the virtual height of the F-layer bottom side (h'F) and the critical frequency of the F2- layer (foF2) scaled from the ionograms, are considered. Furthermore, each ionogram is manually examined for the presence of spread-F signatures.The main results are:• For the storm occurred on May 27, range spread-F (RSF) is present during the second part of the main phase, between 23 - 5 LT in coincidence with a rapid F layer uplift and a positive ionospheric storm effect. GPS-TEC present wave-like oscillations on May 28 at ~ 22 – 4 LT for all the satellites in view, the Fast Fourier Transform (FFT) analysis of the TEC perturbations for each satellite-receiver pair shows dominant periods of ~70 and ~40 minutes. Besides, a weak scintillation activity was observed during the day of the storm, with S4 values between 0.1 and 0.3.The spread-F generation is likely associated with the presence of eastward disturbance dynamo electric fields (DDEF) driven by disturbed thermospheric winds. The DDEF during nighttime can cause large increase in plasma vertical drift and lead to instability growth by the Rayleigh-Tayl [...]

This work presents, for the first time, the analysis of the occurrence of ionospheric irregularities during geomagnetic storms at Tucumán, Argentina, a low latitude station in the Southern American longitudinal sector (26.9°S, 294.6°E; magnetic latitude 15.5°S) near the southern crest of the equatorial ionization anomaly (EIA). Three geomagnetic storms occurred on May 27, 2017 (a month of low occurrence rates of spread-F), October 12, 2016 (a month of transition from low to high occurrence rates of spread-F) and November 7, 2017 (a month of high occurrence rates of spread-F) are analyzed using Global Positioning System (GPS) receivers and ionosondes. The rate of change of total electron content (TEC) Index (ROTI), GPS Ionospheric L-band scintillation, the virtual height of the F-layer bottom side (h'F) and the critical frequency of the F2 layer (foF2) are considered. Furthermore, each ionogram is manually examined for the presence of spread-F signatures.

The results show that, for the three events studied, geomagnetic activity creates favorable conditions for the initiation of ionospheric irregularities, manifested by ionogram spread-F and TEC fluctuation. Post-midnight irregularities may have occurred due to the presence of eastward disturbance dynamo electric fields (DDEF). For the May storm, an eastward over-shielding prompt penetration electric field, (PPEF) is also acting. A possibility is that the PPEF is added to the DDEF and produces the uplifting of the F region that helps trigger the irregularities. Finally, during October and November, strong GPS L band scintillation is observed associated with strong range spread-F (SSF), that is, irregularities extending from the bottom-side to the topside of the F region.

Ionospheric irregularities can severely degrade radio communication and navigation systems. Geomagnetic storms may affect the generation of these irregularities in a way that is not yet fully understood. To improve the forecasting of this phenomenon, we need to study the ionosphere in different regions of the world, and in particular in the equatorial ionization anomaly (EIA) where irregularities are usually more intense. This study analyses the effect of geomagnetic storms on ionospheric irregularities. We examined the occurrence of irregularities at the southern crest of the EIA in Argentina (Tucumán, 26.9°S, 294.6°E, dip latitude 15.5°S) during three intense and one moderate geomagnetic storm of different solar sources, between 2015 and 2018. We used data from an ionosonde, a Global Positioning System receiver and magnetometers. Ionogram spread-F, the F-layer bottom side (h'F), the critical frequency of the F2-layer (foF2), the rate of TEC index and the S4 scintillation index were analysed. The data show irregularities were present as range spread-F and moderate TEC fluctuations in one storm: 27 May 2017 (a coronal mass ejection CME-driven storm occurred on local winter), and were absent in the other events. We suggest that eastward disturbance dynamo electric field and over-shielding prompt penetration electric fields may create favourable conditions for developing these irregularities, whereas westward storm time electric fields might inhibit the growth of irregularities during the other storms considered. During co-rotating interaction region CIR-driven storms, the westward disturbance dynamo electric field may be associated with the non-occurrence of irregularities.

Ionospheric F-region irregularities can acutely affect navigation and communication systems. To develop predictive capabilities on their occurrence, it is key to understand their variabilities in a wide range of time scales. Previous studies at low latitudes in South America have been performed mostly in the eastern region. However, there are still few reports on the spread-F over Argentina owing to a lack of ionosonde data. This work presents the analysis of the spread-F (range spread-F and frequency spread-F) and plasma bubble occurrence characteristics near the southern crest of the Equatorial Ionization Anomaly in Argentina (Tucumán, 26.8°S, 65.2°W; magnetic latitude 15.5°S). We used ionosonde and Global Positioning System (GPS) data from November 2014 to December 2019 for different solar and geomagnetic conditions. The data show that spread-F and plasma bubble occurrence rates peak in local summer and are minimum in equinox and winter, respectively. There is a negative correlation between each type of spread-F and solar activity, whereas the opposite happens for plasma bubbles. Geomagnetic activity suppresses the generation of spread-F in equinox and summer and enhances it in winter. Plasma bubble occurrence is higher during disturbed days than during quiet days, but under medium solar activity, summer months register more plasma bubbles in quiet conditions. Range spread-F observed in winter under low solar activity is not associated with plasma bubbles originated at the magnetic equator. These results contribute to the knowledge necessary to improve the prediction of the spatial and temporal distribution of the night-time ionospheric irregularities.

This work presents, for the first time, the analysis of the occurrence of ionospheric irregularities during geomagnetic storms at Tucuma
´n, Argentina, a low latitude station in the Southern American longitudinal sector (26.9
S, 294.6
E; magnetic latitude 15.5
S) near the
southern crest of the equatorial ionization anomaly (EIA). Three geomagnetic storms occurred on May 27, 2017 (a month of low occurrence
rates of spread-F), October 12, 2016 (a month of transition from low to high occurrence rates of spread-F) and November 7, 2017
(a month of high occurrence rates of spread-F) are analyzed using Global Positioning System (GPS) receivers and ionosondes. The rate
of change of total electron content (TEC) Index (ROTI), GPS Ionospheric L-band scintillation, the virtual height of the F-layer bottom
side (h’F) and the critical frequency of the F2 layer (foF2) are considered. Furthermore, each ionogram is manually examined for the
presence of spread-F signatures.
The results show that, for the three events studied, geomagnetic activity creates favorable conditions for the initiation of ionospheric
irregularities, manifested by ionogram spread-F and TEC fluctuation. Post-midnight irregularities may have occurred due to the presence
of eastward disturbance dynamo electric fields (DDEF). For the May storm, an eastward over-shielding prompt penetration electric field
(PPEF) is also acting. A possibility is that the PPEF is added to the DDEF and produces the uplifting of the F region that helps trigger
the irregularities. Finally, during October and November, strong GPS L band scintillation is observed associated with strong range
spread-F (SSF), that is, irregularities extending from the bottom-side to the topside of the F region.