Wavelet analysis of the ionospheric response at mid-latitudes during the April 200 storm using magnetograms and vTEC from GPS

In this work we pursue the idea of computing a parameter that allows us to estimate the local ionospheric response to a geospheric event that triggers an ionospheric storm. For that, wavelet technique has been chosen because of its ability to analyze non-stationary signals. The advantage of the time-frequency analysis method called Wavelet Transform resides in providing information not only about the frequencies of the event but also about its location in the time series. Specifically, we compute the Scale Average Wavelet Power (SAWP) of two parameters that describe the local geomagnetic field variation at the Earth surface caused by a geospheric storm and ionospheric response to the storm event. In particular, we propose the time delay between the maximum values of SAWP applied to the vTEC (vertical Total Electron Content) and the horizontal component of the geomagnetic field (H) variations as parameters to characterize the local behavior of the ionospheric storm. We applied the parameter to the geomagnetic and ionospheric disturbances caused by a coronal mass ejection (CME) that took place on April 4, 2000. We used vTEC values computed from GPS observations and H at the surface of the Earth, measured in stations near to each GPS station chosen. The vTEC values used came from the GPS permanent stations belonging to the global IGS (International GNSS Service) network. We chose stations located at magnetic mid-latitudes. Moreover, three-longitude bands representing the ionospheric behavior at different local times (LT) were studied. Because the April 2000 storm has been extensively studied for many authors, the results are compared with those in the literature and we found a very good agreement as expected.En este trabajo perseguimos la idea de estimar un parámetro que nos permita calcular la respuesta ionosférica local a un evento geosférico desencadenante de una tormenta ionosférica. Para ello, se eligió la aplicación de la técnica ondeleta debido a su capacidad para analizar señales no estacionarias. La ventaja del método de análisis en tiempo y frecuencia llamada Transformada Ondeleta reside en el hecho de que provee información, no sólo acerca de las frecuencias del evento, sino también sobre su ubicación en la serie de tiempo. En concreto, se calcula el promedio por escalas de la potencia de la transformada ondeleta (SWAP, de su sigla en inglés Scale Average Wavelet Power) para dos parámetros que describen la respuesta local de la magnetosfera y la ionosfera a una tormenta. En particular, se propone el retraso de tiempo entre los valores máximos de SAWP aplicadas al vTEC (Contenido Electrónico Total en dirección Vertical) y la componente horizontal del campo geomagnético (H), como parámetros cuyas variaciones caracterizan el comportamiento local de la tormenta ionosférica. El parámetro propuesto se aplicó a las perturbaciones geomagnética e ionosférica causadas por una eyección de masa coronal (CME, Coronal Mass Ejection), que tuvo lugar el 4 de abril de 2000. Se utilizaron valores vTEC calculados a partir de las observaciones GPS y H en la superficie de la Tierra, medida en las estaciones cercanas a cada estación de GPS elegida. Los valores de vTEC utilizados provinieron de las estaciones GPS permanentes que pertenecen a la red del servicio internacional IGS (International GNSS Service). Entre todas, elegimos estaciones situadas en latitudes magnéticas medias. Por otra parte, estudiamos tres bandas de longitud que representan el comportamiento de la ionosfera a distintas horas locales (LT). Debido a que la tormenta de abril de 2000 ha sido ampliamente estudiada por muchos autores, los resultados se comparan con los de la literatura y nos encontramos con un muy buen acuerdo entre los datos publicados y nuestros resultados, tal y como se esperaba.Fil: Fernandez, Laura Isabel. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Meza, Amalia Margarita. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Van Zele, Maria Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas; Argentin

Annual and semiannual VTEC effects at low solar activity based on GPS observations at different geomagnetic latitudes

The aim of this work is the analysis of the annual, semiannual, and seasonal effects in the total electron content (TEC) of the terrestrial atmosphere during low solar activity. Spatial and temporal ionospheric variability are investigated from global International Global Navigation Satellite System Service (IGS) VTEC maps during low solar activity in 2006. Two different techniques, principal component analysis (PCA) and Fourier analysis, are applied to the data set. Applying the PCA technique on a time series of global IGS VTEC maps gives us a method to analyze the main ionospheric anomalies on a global scale. The Fourier series provide us a comparison with the results obtained with PCA. The behavior of VTEC variations at 2 h periods centered at 1200 and 2200 local time (LT) are analyzed. Particular characteristics associated with each period and with the geomagnetic region are highlighted. All the stations show an annual behavior, which means that the maxima variations of the VTEC occur in summer while minimum variations are in winter, except in the stations located at the Northern Hemisphere at noon. Some regions show patterns of the semiannual anomaly during local noon, and it is also possible to see a higher peak of VTEC during spring rather than autumn in the Northern Hemisphere. However, if we analyze the pattern in the Southern Hemisphere, both peaks in equinox are of the same magnitude. Results obtained with Fourier series are comparable with the ones mentioned above.Facultad de Ciencias Astronómicas y Geofísica

Generación de mapas vTEC a tiempos casi real : Contribución al estudio del “space weather” en Latinoamérica

El tema de presentación en esta escuela se centra en un breve repaso de los observables GNSS que vinculamos con la información atmosférica; en la descripción de la generación de mapas regionales del contenido de electrones totales verticales ionosféricos (VTEC) con una alta resolución espacial, destacando su gran importancia tanto para aplicaciones civiles como para la comunidad investigadora (Meza et al 2009, Meza & Fernández 2009, Meza et al 2012, Natali & Meza 2017). Estos mapas se basan en la infraestructura pública de los sistemas globales de navegación por satélite (GNSS) en América del Sur, incorporando datos de múltiples constelaciones (actualmente GPS, GLONASS, Galileo y BeiDou), empleando múltiples frecuencias y generando mapas VTEC de todo el continente con una latencia de solo unos minutos (Mendoza el al., 2019, Costa, J E R et al, 2020).Facultad de Ciencias Astronómicas y Geofísica

Annual and semiannual VTEC effects at low solar activity based on GPS observations at different geomagnetic latitudes

The aim of this work is the analysis of the annual, semiannual, and seasonal effects in the total electron content (TEC) of the terrestrial atmosphere during low solar activity. Spatial and temporal ionospheric variability are investigated from global International Global Navigation Satellite System Service (IGS) VTEC maps during low solar activity in 2006. Two different techniques, principal component analysis (PCA) and Fourier analysis, are applied to the data set. Applying the PCA technique on a time series of global IGS VTEC maps gives us a method to analyze the main ionospheric anomalies on a global scale. The Fourier series provide us a comparison with the results obtained with PCA. The behavior of VTEC variations at 2 h periods centered at 1200 and 2200 local time (LT) are analyzed. Particular characteristics associated with each period and with the geomagnetic region are highlighted. All the stations show an annual behavior, which means that the maxima variations of the VTEC occur in summer while minimum variations are in winter, except in the stations located at the Northern Hemisphere at noon. Some regions show patterns of the semiannual anomaly during local noon, and it is also possible to see a higher peak of VTEC during spring rather than autumn in the Northern Hemisphere. However, if we analyze the pattern in the Southern Hemisphere, both peaks in equinox are of the same magnitude. Results obtained with Fourier series are comparable with the ones mentioned above.Facultad de Ciencias Astronómicas y Geofísica

Observed and Intrinsic Properties of Binary Stars Orbits

We have analyzed the effects that the process of spectroscopic binary detection can introduce on the known statistics of these stars. Performing a Monte Carlo simulation, we have studied the possibility of having a 100% spectroscopic binarity. We show the biases in the period and mass ratio distribution introduced by a search for binaries on such a population.Hemos analizado los efectos que el proceso de detección de binarias espectroscópicas introduce en las estadísticas conocidas de dichas estrellas. Por medio de una simulación numérica, hemos estudiado la posibilidad de que exista un 100% de binaridad en un grupo estelar. Mostramos los efectos de selección en las distribuciones de períodos y cocientes de masa introducidos por la búsqueda de binarias dentro de nuestra población.Facultad de Ciencias Astronómicas y Geofísica

PCA and vTEC climatology at midnight over mid-latitude regions

The effect of the thermospheric vertical neutral wind on vertical total electron content (vTEC) variations including longitudinal anomaly, remaining winter anomaly, mid-latitude summer night anomaly, and semiannual anomaly is studied at mid-latitude regions around zero magnetic declination at midnight during high solar activity. By using the principal component analysis (PCA) numerical technique, this work studies the spatial and temporal variations of the ionosphere at midnight over mid-latitude regions during 2000–2002. PCA is applied to a time series of global vTEC maps produced by the International Global Navigation Satellite System (GNSS) Service. Four regions were studied in particular, each located at mid-latitude and approximately centered at zero magnetic declination, with two in the northern hemisphere and two in southern hemisphere, and all are located near and far from geomagnetic poles in each case. This technique provides an effective method to analyze the main ionospheric variabilities at mid-latitudes. PCA is also applied to the vTEC computed using the International Reference Ionosphere (IRI) 2012 model, to analyze the capability of this model to represent ionospheric variabilities at mid-latitude. Also, the Horizontal Wind Model 2007 (HWM07) is used to improve our climatology interpretation, by analyzing the relationship between vTEC and thermospheric wind, both quantitatively and qualitatively. At midnight, the behavior of mean vTEC values strongly responds to vertical wind variation, experiencing a decrease of about 10–15% with the action of the positive vertical component of the field-aligned neutral wind lasting for 2 h in all regions except for Oceania. Notable results include: a significant increase toward higher latitudes during summer in the South America and Asia regions, associated with the mid-latitude summer night anomaly, and an increase toward higher latitudes in winter in the North America and Oceania regions, highlighting the remnant effect of the winter anomaly. Finally, the longitudinal variations of east–west differences, named longitudinal anomaly, show maximum values in March for North America, in December for South America and Oceania, and are not shown for Asia. Our results show that at mid-latitudes regions, the IRI model represents midnight ionospheric mean values with a similar spatial distribution, but the values are always lower than those obtained by GNSS. The differences between IRI and GNSS results include: the longitudinal anomaly is characterized by a stronger semiannual variation in both North America and South America, with a maximum in the equinoxes, while for the Asian region, the behavior is almost constant throughout the years, and finally, there is an absence of the winter anomaly remnant.Facultad de Ciencias Astronómicas y Geofísica

Analysis of the winter and semiannual ionospheric anomalies in 1999-2009 based on GPS global International GNSS Service maps

Our work is focused on the analysis of seasonal and semiannual ionospheric anomalies using vertical total electron content (VTEC) measurements obtained by the International GNSS Service (IGS). For this study we use principal component analysis (PCA) and wavelet transform (WT) because both numerical tools allow us to isolate principal components of the VTEC variability as much spatially as temporally. The IGS VTEC maps are reorganized, and from each daily global data set, two maps were constructed: one at 12:00 LT and the other at 22:00 LT. From these two series of VTEC maps covering the period 1999-2009 for each local time, we found that the semiannual anomaly is globally recorded at noon, especially at mid and low geomagnetic latitudes, and its amplitude has a close relationship with the solar activity, and at night this anomaly is recorded during high solar activity and the larger values are located in the South American region. The values of VTEC at the March equinox exceed that of the September equinox, especially during high solar activity; the winter anomaly is recorded at noon near the geomagnetic poles region, and the effect is more important during high solar activity. At night this anomaly is present during the ascending and descending phases and minimum of the solar cycle. Thus, the night winter anomaly effect is clearly evidenced from our results.Facultad de Ciencias Astronómicas y Geofísica

Analysis of the winter and semiannual ionospheric anomalies in 1999-2009 based on GPS global International GNSS Service maps

Our work is focused on the analysis of seasonal and semiannual ionospheric anomalies using vertical total electron content (VTEC) measurements obtained by the International GNSS Service (IGS). For this study we use principal component analysis (PCA) and wavelet transform (WT) because both numerical tools allow us to isolate principal components of the VTEC variability as much spatially as temporally. The IGS VTEC maps are reorganized, and from each daily global data set, two maps were constructed: one at 12:00 LT and the other at 22:00 LT. From these two series of VTEC maps covering the period 1999-2009 for each local time, we found that the semiannual anomaly is globally recorded at noon, especially at mid and low geomagnetic latitudes, and its amplitude has a close relationship with the solar activity, and at night this anomaly is recorded during high solar activity and the larger values are located in the South American region. The values of VTEC at the March equinox exceed that of the September equinox, especially during high solar activity; the winter anomaly is recorded at noon near the geomagnetic poles region, and the effect is more important during high solar activity. At night this anomaly is present during the ascending and descending phases and minimum of the solar cycle. Thus, the night winter anomaly effect is clearly evidenced from our results.Facultad de Ciencias Astronómicas y Geofísica

Annual and semiannual VTEC effects at low solar activity based on GPS observations at different geomagnetic latitudes

The aim of this work is the analysis of the annual, semiannual, and seasonal effects in the total electron content (TEC) of the terrestrial atmosphere during low solar activity. Spatial and temporal ionospheric variability are investigated from global International Global Navigation Satellite System Service (IGS) VTEC maps during low solar activity in 2006. Two different techniques, principal component analysis (PCA) and Fourier analysis, are applied to the data set. Applying the PCA technique on a time series of global IGS VTEC maps gives us a method to analyze the main ionospheric anomalies on a global scale. The Fourier series provide us a comparison with the results obtained with PCA. The behavior of VTEC variations at 2 h periods centered at 1200 and 2200 local time (LT) are analyzed. Particular characteristics associated with each period and with the geomagnetic region are highlighted. All the stations show an annual behavior, which means that the maxima variations of the VTEC occur in summer while minimum variations are in winter, except in the stations located at the Northern Hemisphere at noon. Some regions show patterns of the semiannual anomaly during local noon, and it is also possible to see a higher peak of VTEC during spring rather than autumn in the Northern Hemisphere. However, if we analyze the pattern in the Southern Hemisphere, both peaks in equinox are of the same magnitude. Results obtained with Fourier series are comparable with the ones mentioned above.Facultad de Ciencias Astronómicas y Geofísica

PCA and vTEC climatology at midnight over mid-latitude regions

The effect of the thermospheric vertical neutral wind on vertical total electron content (vTEC) variations including longitudinal anomaly, remaining winter anomaly, mid-latitude summer night anomaly, and semiannual anomaly is studied at mid-latitude regions around zero magnetic declination at midnight during high solar activity. By using the principal component analysis (PCA) numerical technique, this work studies the spatial and temporal variations of the ionosphere at midnight over mid-latitude regions during 2000–2002. PCA is applied to a time series of global vTEC maps produced by the International Global Navigation Satellite System (GNSS) Service. Four regions were studied in particular, each located at mid-latitude and approximately centered at zero magnetic declination, with two in the northern hemisphere and two in southern hemisphere, and all are located near and far from geomagnetic poles in each case. This technique provides an effective method to analyze the main ionospheric variabilities at mid-latitudes. PCA is also applied to the vTEC computed using the International Reference Ionosphere (IRI) 2012 model, to analyze the capability of this model to represent ionospheric variabilities at mid-latitude. Also, the Horizontal Wind Model 2007 (HWM07) is used to improve our climatology interpretation, by analyzing the relationship between vTEC and thermospheric wind, both quantitatively and qualitatively. At midnight, the behavior of mean vTEC values strongly responds to vertical wind variation, experiencing a decrease of about 10–15% with the action of the positive vertical component of the field-aligned neutral wind lasting for 2 h in all regions except for Oceania. Notable results include: a significant increase toward higher latitudes during summer in the South America and Asia regions, associated with the mid-latitude summer night anomaly, and an increase toward higher latitudes in winter in the North America and Oceania regions, highlighting the remnant effect of the winter anomaly. Finally, the longitudinal variations of east–west differences, named longitudinal anomaly, show maximum values in March for North America, in December for South America and Oceania, and are not shown for Asia. Our results show that at mid-latitudes regions, the IRI model represents midnight ionospheric mean values with a similar spatial distribution, but the values are always lower than those obtained by GNSS. The differences between IRI and GNSS results include: the longitudinal anomaly is characterized by a stronger semiannual variation in both North America and South America, with a maximum in the equinoxes, while for the Asian region, the behavior is almost constant throughout the years, and finally, there is an absence of the winter anomaly remnant.Facultad de Ciencias Astronómicas y Geofísica