Effect of solar cycle 23 in foF2 trend estimation

The effect of including solar cycle 23 in foF2 trend estimation is assessed using experimental values for Slough (51.5°N, 359.4°E) and Kokobunji (35.7°N, 139.5°E), and values obtained from two models: (1) the Sheffield University Plasmasphere-Ionosphere model, SUPIM, and (2) the International Reference Ionosphere, IRI. The dominant influence on the F2 layer is solar extreme ultraviolet (EUV) radiation, evinced by the almost 90% variance of its parameters explained by solar EUV proxies such as the solar activity indices Rz and F10.7. This makes necessary to filter out solar activity effects prior to long-term trend estimation. Solar cycle 23 seems to have had an EUV emission different from that deduced from traditional solar EUV proxies. During maximum and descending phase of the cycle, Rz and F10.7 seem to underestimate EUV solar radiation, while during minimum, they overestimate EUV levels. Including this solar cycle in trend estimations then, and using traditional filtering techniques, may induce some spurious results. In the present work, filtering is done in the usual way considering the residuals of the linear regression between foF2 and F10.7, for both experimental and modeled values. foF2 trends become less negative as we include years after 2000, since foF2 systematically exceeds the values predicted by a linear fit between foF2 and F10.7. Trends become more negative again when solar cycle 23 minimum is included, since for this period, foF2 is systematically lower than values predicted by the linear fit. foF2 trends assessed with modeled foF2 values are less strong than those obtained with experimental foF2 values and more stable as solar cycle 23 is included in the trend estimation. Modeled trends may be thought of as a ‘zero level’ trend due to the assumptions made in the process of trend estimation considering also that we are not dealing with ideal conditions or infinite time series.Fil: Elias, Ana Georgina. Universidad Nacional de Tucuman. Facultad de Ciencias Exactas y Tecnologia. Departamento de Fisica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: de Haro Barbás, Blas F.. Universidad Nacional de Tucuman. Facultad de Ciencias Exactas y Tecnologia. Departamento de Fisica; ArgentinaFil: Shibasaki, Kiyoto . Nobeyama Solar Radio Observatory; JapónFil: Souza, Jonas R.. Centro de Previsao de Tempo E Estudos Climaticos. Instituto Nacional de Pesquisas Espaciais; Brasi

Filtering ionosphere parameters to detect trends linked to anthropogenic effects

The great concern about the global warming observed in the troposphere has generated a large interest in the study of long-term trends in the ionosphere since the early 1990s, which has now become a significant topic in global change investigations. Some research works link ionosphere trends to anthropogenic sources such as the increase in greenhouse gas concentration, and others to natural causes such as solar and geomagnetic activity long-term changes, and secular variations in the Earth´s main magnetic field. In all the cases, in order to analyze ionospheric trends, solar activity effect must be filtered out first since around 90% of ionosphere parameter variance is due to solar variations. The filtering process can generate ?spurious? trends in the filtered data series which may lead to erroneous conclusions. foF2 data series which include solar cycle 23 are analyzed in the present work in order to detect the effect of different filtering procedures on the determination of long-term trends. In particular, solar cycle 23 seems to have had an extreme ultraviolet (EUV) emission greater than that deduced from traditional solar EUV proxies during the maximum epoch and lower during the minimum epoch. When solar activity is filtered assessing the residuals of a linear regression between foF2 and Rz, or between foF2 and F10.7, this fact may bias trend values especially because it is at the end of the time series. The length of the period considered for trend assessment, the saturation and hysteresis effect of some ionosphere parameters, and the solar EUV proxy used are also considered in this study in order to quantify a possible spurious trend that may result as a by-product of a filtering process. Since trends expected as a consequence of anthropogenic effects are relatively small, these spurious effects may surely mask, or enhance, trends expected from anthropogenic origins.Fil: Elias, Ana Georgina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnologia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán; Argentin

Which solar EUV indices are best for reconstructing the solar EUV irradiance ?

The solar EUV irradiance is of key importance for space weather. Most of the time, however, surrogate quantities such as EUV indices have to be used by lack of continuous and spectrally resolved measurements of the irradiance. The ability of such proxies to reproduce the irradiance from different solar atmospheric layers is usually investigated by comparing patterns of temporal correlations. We consider instead a statistical approach. The TIMED/SEE experiment, which has been continuously operating since Feb. 2002, allows for the first time to compare in a statistical manner the EUV spectral irradiance to five EUV proxies: the sunspot number, the f10.7, Ca K, and Mg II indices, and the He I equivalent width. Using multivariate statistical methods such as multidimensional scaling, we represent in a single graph the measure of relatedness between these indices and various strong spectral lines. The ability of each index to reproduce the EUV irradiance is discussed; it is shown why so few lines can be effectively reconstructed from them. All indices exhibit comparable performance, apart from the sunspot number, which is the least appropriate. No single index can satisfactorily describe both the level of variability on time scales beyond 27 days, and relative changes of irradiance on shorter time scales.Comment: 6 figures, to appear in Adv. Space. Re

The response of the ionospheric peak electron density (NmF2) to solar activity)

The ionospheric peak electron density NmF2, simulated with the Coupled Thermosphere Ionosphere Plasmasphere electrodynamics (CTIPe) model was used to study the ionospheric response to solar flux in years of low (2008) and high (2013) solar activity. The CTIPe NmF2 was compared to the Whole Atmosphere Community Climate Model with Thermosphere and Ionosphere Extension (WACCM-X) and the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) NmF2 in March and July of 2008 and 2013. The comparison shows that the CTIPe NmF2 is lower than the COSMIC andWACCM-X NmF2. Both models successfully reproduce the semi-annual variations seen in the COSMIC observations. Analysis of the 27-day variations of the CTIPe NmF2 shows that the midnight NmF2 deviations are stronger than the midday deviations. In addition, at low solar activity, the 27-day variations of NmF2 are larger in the Southern Hemisphere, while at high solar activity, the 27-day variations of NmF2 are larger at the equator and in the Northern Hemisphere. An ionospheric delay was estimated with CTIPe simulated NmF2 at the 27-day solar rotation period during low and high solar activity. During low (high) solar activity, an ionospheric delay of about 12 (34) hours is predicted indicating an increasing ionospheric delay with solar activity.Die maximale ionosphärische Elektronendichte NmF2, die mit dem Coupled Thermosphere Ionosphere Plasmasphere electrodynamics (CTIPe) Modell simuliert wurde, wurde zur Untersuchung der ionosphärischen Reaktion in Jahren mit geringer (2008) und hoher (2013) Sonnenaktivität verwendet. CTIPe vorhergesagte NmF2 wurde mit derjenigen des Whole Atmosphere Community Climate Model with Thermosphere and Ionosphere Extension (WACCM-X) und Messwerten des Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) im März und Juli der Jahre 2008 und 2013 verglichen. Der Vergleich zeigt, dass NmF2 aus CTIPe geringer ist als das COSMIC gemessene und von WACCM-X simulierte. Beide Modelle reproduzieren erfolgreich die von COSMIC beobachteten halbjährlichen Schwankungen. Die Analyse der 27-tägigen Schwankungen des CTIPe NmF2 zeigt, dass die mitternächtlichen NMF2-Abweichungen stärker sind als diejenigen am Mittag. Außerdem sind bei geringer Sonnenaktivität die 27-Tage-Abweichungen von NmF2 in der Südhemisphäre größer, während bei hoher Sonnenaktivität die 27-Tage-Abweichungen von NmF2 am Äquator und in der Nordhemisphäre größer sind. Die ionosphärische Verzögerung während geringer und hoher Sonnenaktivität wurde für die 27-tägige Sonnenrotation mit CTIPe simuliert. Bei geringer (hoher) Sonnenaktivität wird eine ionosphärische Verzögerung von etwa 12 (34) Stunden beobachtet, was auf eine zunehmende ionosphärische Verzögerung mit zunehmender Sonnenaktivität hinweist

Ionospheric response during low and high solar activity

We analyse solar extreme ultraviolet (EUV) irradiance observed by the Solar EUV Experiment (SEE) onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite, and solar proxies (the F10.7 index, and Mg-II index), and compare their variability with the one of the global mean Total Electron Content (GTEC). Cross-wavelet analysis confirms the joint 27 days periodicity in GTEC and solar proxies. We focus on a comparison for solar minimum (2007-2009) and maximum (2013-2015) and find significant differences in the correlation during low and high solar activity years. GTEC is delayed by approximately 1-2 days in comparison to solar proxies during both low and high solar activity at the 27 days solar rotation period. To investigate the dynamics of the delay process, Coupled Thermosphere Ionosphere Plasmasphere electrodynamics model simulations have been performed for low and high solar activity conditions. Preliminary results using cross correlation analysis show an ionospheric delay of 1 day in GTEC with respect to the F10.7 index during low and high solar activity.Wir analysieren vom Solar Extreme Ultraviolet Experiment (SEE) an Bord des Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) Satelliten gemessene solare EUV-Irradianzen, solare Proxies (den F10.7-Index und denMg-II-Index), und vergleichen deren Variabilität mit derjenigen des global gemittelten Gesamtelektronengehalts (GTEC). Kreuzwaveletanalysen bestätigen eine gemeinsame Variabilität im Periodenbereich der solaren Rotation (27 Tage). Wir vergleichen insbesondere den Zusammenhang während des solaren Minimums (2007- 2009) und Maximums (2013-2015), wobei signifikante Unterschiede der Korrelation zwischen solaren und ionosphärischen Parametern auftreten. Es tritt eine Verzögerung der Maxima und Minima von GTEC gegenüber denjenigen der solaren Proxies von einem Tag sowohl im solaren Minimum als auch im solaren Maximum auf

Delayed Ionospheric Response to Solar EUV/UV Radiation Variations

The variability of the thermosphere-ionosphere (T-I) system and its complex behavior is strongly dependent on the continuously changing solar extreme ultraviolet (EUV) and ultraviolet (UV) radiation. The ionospheric electron density (or ion density) is mainly controlled by photoionization, loss by recombination, and transport processes. Transport processes play a significant role in the T-I composition and are responsible for the plasma distribution. The ionospheric response to solar activity has been investigated using total electron content (TEC) and solar EUV observations, as well as various solar proxies. An ionospheric delay of about 1-2 days in the daily TEC on the time scale of 27 days solar rotation period has been reported. It has also been shown that the He-II index is one of the best solar proxies to represent the solar activity at different time scales. The ionospheric delay in relation to solar radiation variations has attracted less attention in the past, especially with respect to its possible mechanisms. However, such studies, are of great importance for a better understanding of the complex interactions between solar radiation and the ionosphere that affect radio communications and navigation systems such as GNSS. Since the T-I region is affected not only by solar radiation, but also by lower atmospheric forcings, geomagnetic activity, and space weather events. Therefore, numerical modeling provides an opportunity to interpret the possible physical mechanism. To shed more light on this issue, a global, 3-D, time-dependent, physics-based numerical model was used in this thesis. It is a comprehensive numerical study to investigate the ionospheric response to solar flux changes during the 27 days solar rotation period. Satellite observations were used for comparison with the model simulations. The average delay for the observed (modeled) TEC is about 17 (16) h againest high-resolution solar EUV flux. The study confirms the capabilities of the model to reproduce the delayed ionospheric response with daily and hourly resolution. These results are in close agreement with previous studies. For the first time, the model simulations were performed to understand the role of eddy diffusion. The study shows that eddy diffusion is an important factor affecting the ionospheric delay and highlights the influence of the lower atmospheric forcing. Eddy diffusion was found to cause a change in thermospheric composition, which induces changes in atomic oxygen by modifying loss and photoionization rates. Atomic oxygen contributes significantly to ionization. Enhanced eddy diffusion leads to a decrease in atomic oxygen ion density and consequently TEC. Therefore, TEC decreases due to enhanced eddy diffusion, showing that the ionospheric delay is reduced. Thus, slow transport leads to maximum ionospheric delay.:Bibliographische Beschreibung Bibliographic Description Acronyms 1 General introduction 1.1 Introduction: Ionospheric delayed response 1.2 Objectives and structure of the thesis 1.3 Model description and data 1.3.1 CTIPe model description 1.3.2 Data 2 Paper 1: Ionospheric delayed response: preliminary results Vaishnav, R., Jacobi, C., Berdermann, J., Schmölter, E., and Codrescu, M.: Ionospheric response to solar EUV variations: Preliminary results 3 Paper 2: Long term trends of ionospheric response to solar EUV variations Vaishnav, R., Jacobi, C., and Berdermann, J.: Long-term trends in the iono- spheric response to solar extreme-ultraviolet variations 4 Paper 3: Comparison between CTIPe model simulations and satellite measurements Vaishnav, R., Schmölter, E., Jacobi, C., Berdermann, J., and Codrescu, M.: Ionospheric response to solar extreme ultraviolet radiation variations: com- parison based on CTIPe model simulations and satellite measurements 5 Paper 4: Role of eddy diffusion in the ionospheric delayed response Vaishnav, R., Jacobi, C., Berdermann, J., Codrescu, M., and Schmölter, E.: Role of eddy diffusion in the delayed ionospheric response to solar flux changes 6 Conclusions 7 Outlook References Acknowledgements Curriculum Vitae AffirmationDie Veränderungen des Thermosphäre-Ionosphäre (T-I) Systems und dessen Komplexität werden entscheidend durch die sich ständig ändernde extreme ultraviolette (EUV) und ultraviolette (UV) Sonnenstrahlung geprägt. Hierbei wird die ionosphärische Elektronendichte (oder Ionendichte) hauptsächlich durch Photoionisation, Rekombination und Transportprozesse gesteuert. Insbesondere Transportprozesse spielen eine wichtige Rolle für die Zusammensetzung des T-I-Systems und sind für die Plasmaverteilung verantwortlich. Die ionosphärische Reaktion auf Veränderungen der Sonnenaktivität wurde mithilfe des Gesamtelektronengehalts (englisch total electron content, TEC) und Messdaten des solaren EUV-Spektrums sowie solaren Proxys untersucht. Eine ionosphärische Verzögerung von 1 bis 2 Tagen für Tageswerte von TEC wurde für die 27-Tage-Sonnenrotation gefunden. Es wurde auch gezeigt, dass der He-II-Index einer der besten solaren Proxys ist, um die Sonnenaktivität auf verschiedenen Zeitskalen zu beschreiben. Die ionosphärische Verzögerung in Bezug auf Variationen der Sonnenstrahlung wurde in der Vergangenheit wenig Aufmerksamkeit gewidmet. Insbesondere die zugrundenliegenden Mechanismen wurden nicht untersucht. Solche Studien sind jedoch von entscheidender Bedeutung für ein besseres Verständnis der komplexen Wechselwirkungen zwischen Sonnenstrahlung und Ionosphäre, die unteranderem die Leistung von Radiokommunikation und globalen Navigationssystemen beeinflussen. Das T-I-System wird jedoch nicht nur von der solaren EUV-Strahlung kontrolliert. Prozesse der unteren Atmosphäre, geomagnetische Aktivität und Weltraumwettereignisse haben ebenfalls einen Einfluss auf diese Region. Daher bietet sich numerische Modellierung als Möglichkeit für die Interpretation der physikalischen Prozesse an. Zur Klärung der offenen Fragen wurde in dieser Arbeit ein globales, dreidimensionales, zeitabhängiges physikalisches Modell verwendet und eine umfangreiche Studie der ionosphärischen Reaktion auf Veränderungen der Sonnenstrahlungen während der 27-Tage-Sonnenrotation wurde durchgeführt. Hierfür wurden Messdaten von Satellitenmissionen mit den Modellsimulationen verglichen. Im Mittel ergibt sich eine Verzögerung von 16 Stunden aus der Analyse der Messdaten und eine Verzögerung von 17 Stunden aus den Modellsimulationen. Die Studie bestätigt demnach die Fähigkeit des Modells, die verzögerte ionosphärische Reaktion in stündlicher und täglicher Auflösung zu simulieren. Diese Ergebnisse stimmen gut mit vorangegangenen Studien überein. Im Rahmen dieser Arbeit wurden zum ersten Mal Simulationen zum Einfluss der Eddy-Diffusion durchgeführt. Diese Analyse zeigt, dass die Eddy-Diffusion ein wichtiger Faktor für die Ausprägung der ionosphärischen Verzögerung ist und dass der Einfluss von Prozessen der unteren Atmosphäre eine entscheidende Rolle spielt. Es wurde festgestellt, dass die Eddy-Diffusion eine erhebliche Veränderung der thermosphärischen Zusammensetzung verursacht, was wiederum zu Veränderung der Menge des atomaren Sauerstoffs führt. Dies beeinflusst dann die Ionisations- und Verlustrate. Da der atomare Sauerstoff erheblich zur Ionisierung beiträgt. Zunehmender Eddy-Diffusion folgen damit auch verkleinert der atomarer Sauerstoff Ionendichte und TEC. Daher nimmt TEC mit zunehmender Eddy-Diffusion ab und auch die Verzögerung wird kleiner. Andersherum führt ein langsamer Transport zu einem Maximum der ionosphärischen Verzögerung. Diese Dissertation gibt eine umfangreiche Zusammenfassung für das Verständnis der ionosphärischen Verzögerung zu Variationen der solaren EUV-Strahlung. Dafür werden TEC-Messungen mit numerischen Simulationen kombiniert. Weiterhin werden durch Vergleich die besten solaren Proxys für die Beschreibung der solaren Aktivität in T-I-Modellen bestimmt. Dies ist von entscheidender Bedeutung, um den Fokus auf die Verbesserung dieser Modelle zu lenken.:Bibliographische Beschreibung Bibliographic Description Acronyms 1 General introduction 1.1 Introduction: Ionospheric delayed response 1.2 Objectives and structure of the thesis 1.3 Model description and data 1.3.1 CTIPe model description 1.3.2 Data 2 Paper 1: Ionospheric delayed response: preliminary results Vaishnav, R., Jacobi, C., Berdermann, J., Schmölter, E., and Codrescu, M.: Ionospheric response to solar EUV variations: Preliminary results 3 Paper 2: Long term trends of ionospheric response to solar EUV variations Vaishnav, R., Jacobi, C., and Berdermann, J.: Long-term trends in the iono- spheric response to solar extreme-ultraviolet variations 4 Paper 3: Comparison between CTIPe model simulations and satellite measurements Vaishnav, R., Schmölter, E., Jacobi, C., Berdermann, J., and Codrescu, M.: Ionospheric response to solar extreme ultraviolet radiation variations: com- parison based on CTIPe model simulations and satellite measurements 5 Paper 4: Role of eddy diffusion in the ionospheric delayed response Vaishnav, R., Jacobi, C., Berdermann, J., Codrescu, M., and Schmölter, E.: Role of eddy diffusion in the delayed ionospheric response to solar flux changes 6 Conclusions 7 Outlook References Acknowledgements Curriculum Vitae Affirmatio