Strong geomagnetic disturbances and induced currents on Earth surface

Long-term variations in strong geomagnetic storms are analyzed and linked to electric fields induced on Earth. In fact, geomagnetic disturbances generate electric fields that drive currents in the Earth which may have significant effects on electrical systems and pipelines. The present study will be carried out using aa, AE and Dst index data to estimate long-term variations in strong geomagnetic disturbances. The results are extended then to the space weather topic through a rough assessment of the expected Earth electric field from measured horizontal components of the surface magnetic field, and also through a qualitative estimation of the consequent currents and voltages induced in a pipeline using the distributed source transmission line (DSTL) theory.Fil: Elias, Ana Georgina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; ArgentinaFil: Silbergleit, Virginia Mabel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ingeniería; Argentin

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

Reflection and transmission in the ionosphere considering collisions in a first approximation

Reflection and transmission coefficients (R and T) of high frequency waves propagating in the ionosphere are studied taking collisions into account. This was done approximating the expression in the refractive index using binomial expansion and neglecting terms of order higher than is the ratio between the electron collision frequency and the wave frequency. R and T height profiles were assessed using the International Reference Ionosphere, IRI, to estimate the ionosphere plasma parameters. Although no significant differences are found between the estimation with and without collisions, the method employed to include collisions may be useful for other purposes where collisions should be taken into account.Fil: Yesil, Ali. Firat University; TurquíaFil: Aydogdu, Mehmet. Firat University; TurquíaFil: Elias, Ana Georgina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Latitudinal variation of foF2 hysteresis of solar cycles 20, 21 and 22 and its application to the analysis of long-term trends

F2 monthly median values for equinoctial months of solar cycles 20, 21 and 22, were analyzed for 37 worldwide stations. For each solar cycle and for a given , the difference between F2 in the falling branch of the cycle and the corresponding value of the rising branch is evaluated. The maximum difference, considered as the hysteresis magnitude, varies systematically with geomagnetic latitude. The pattern is similar for every cycle, with greater hysteresis magnitudes for stronger solar cycles. It is positive between 45S and 45N, with minimum values at equatorial latitudes and maximum at around 25-30 on either side of the equator. For latitudes greater than 50 negative values are observed. At around 25?30 and at high latitudes the hysteresis magnitude reaches 2MHz for solar cycle with high activity levels, which represents around 20% of F2. The effects of F2 hysteresis on the analysis of long-term data sequences is analyzed. In the case of long-term trend analysis, the hysteresis behavior may induce spurious trends as a consequence of the filtering processes applied to F2 time series previous to trend values estimation. This problem may be solved by considering time series covering several solar cycles. F2 monthly median values for equinoctial months of solar cycles 20, 21 and 22, were analyzed for 37 worldwide stations. For each solar cycle and for a given Rz, the difference between F2 in the falling branch of the cycle and the corresponding value of the rising branch is evaluated. The maximum difference, considered as the hysteresis magnitude, varies systematically with geomagnetic latitude. The pattern is similar for every cycle, with greater hysteresis magnitudes for stronger solar cycles. It is positive between 45S and 45N, with minimum values at equatorial latitudes and maximum at around 25?30 on either side of the equator. For latitudes greater than 50 negative values are observed. At around 25?30 and at high latitudes the hysteresis magnitude reaches 2MHz for solar cycle with high activity levels, which represents around 20% of F2. The effects of F2 hysteresis on the analysis of long-term data sequences is analyzed. In the case of long-term trend analysis, the hysteresis behavior may induce spurious trends as a consequence of the filtering processes applied to F2 time series previous to trend values estimation. This problem may be solved by considering time series covering several solar cycles.Fil: Ortiz de Adler, Nieves del Carmen. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología; ArgentinaFil: Elias, Ana Georgina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentin

A search for an association between the equatorial stratospheric QBO and solar UV irradiance

The QBO of the zonal wind in the equatorial stratosphere between 15 and 70 hPa is analyzed in connection to the solar UV flux. F10.7 is used as a UV proxy after filtering out its long‐term variations. A running correlation between F10.7 filtered values and the equatorial zonal wind was estimated. A clear oscillation of around 11 years can be noticed in the running correlation coefficients, with maximum negative and positive values around maximum and minimum solar activity respectively, between 50 and 15 hPa. In coincidence with other authors, during maximum solar activity, higher (lower) UV levels occur during the QBO easterly (westerly) phase. During minimum solar activity this relationship is reversed. A link between these results and the association between the equatorial QBO and the polar winter is suggested together with a mechanism of association between the UV QBO and the zonal equatorial wind in the stratosphereFil: Elias, Ana Georgina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología; Argentina. Universidad Nacional de Tucumán. Instituto de Física del Noroeste Argentino. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Noa Sur. Instituto de Física del Noroeste Argentino; ArgentinaFil: Zossi Artigas, Marta Maria. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología; Argentina. Universidad Nacional de Tucumán. Instituto de Física del Noroeste Argentino. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Noa Sur. Instituto de Física del Noroeste Argentino; Argentin

Pedersen ionic contribution in different time scales

Pedersen conductivity is one of the main parameters in atmospheric electrodynamics, magnetosphere-ionosphere-thermosphere coupling, and several other geophysical processes. It is determined by the collision frequency between charged and neutral components and the Earth´s magnetic field intensity through the gyrofrequency. This work analyzes the contribution of different ionic species to the variability of Pedersen conductance in time scales from hours to years within the period 1964?2008 based on the results of various atmospheric and ionospheric models. The main results are (1) there is a positive correlation between O+ density and Pedersen conductance, (2) Pedersen conductance of F layer has a larger increase with the solar activity than that of E layer, (3) Pedersen conductance has a long-term trend that is determined by Earth´s magnetic field intensity and electron density, and (4) at midlatitudes trends are mainly governed by the Earth´s magnetic field and modulated by the electron density, while at high latitudes both are important.Fil: Zossi, Bruno Santiago. Universidad Nacional de Tucumán; Argentina. Universidad Nacional de Tucumán. Instituto de Física del Noroeste Argentino. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Noa Sur. Instituto de Física del Noroeste Argentino; ArgentinaFil: Fagre, Mariano. Universidad Nacional de Tucumán; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; ArgentinaFil: Elias, Ana Georgina. Universidad Nacional de Tucumán. Instituto de Física del Noroeste Argentino. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Noa Sur. Instituto de Física del Noroeste Argentino; Argentina. Universidad Nacional de Tucumán; Argentin

foF2 long-term trends at the southern crest of the equatorial anomaly

Long-term trends in the electron density of the ionosphere for the period 1957-1986 is studied using foF2 monthly median hourly data measured at Tucuman (26.9S, 65.4W), a station located at the southern crest of the equatorial anomaly. The linear trend for each hour and each month is estimated after filtering out the effects of solar activity. For the intervals 0-2 LT and 9-23 LT, during equinoxes and summer solstice, the trend is negative. Statistically null or slightly positive trends are observed for the interval 3-8 LT for every season, and for every hour of winter months. The daily amplitude of foF2 decreases since 1957 due to the decreasing trend in the maximum daily values and almost null-trended minimum daily values. A rough estimate, based on the dip angle trend (which in Tucuman has increased during the 30-year interval at a rate of 0.35%/year), indicates that negative foF2 trends should be expected during daytime hours, and positive trends during night-time hours, behaviour observed in the foF2 data here analyzed.Fil: Elias, Ana Georgina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; ArgentinaFil: Ortiz de Adler, Nieves del Carmen. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología; Argentin

Sky-wave over-the-horizon radar simulation tool

This work deals with the entire process of target detection and ranging by a sky-wave over-the-horizon radar (OTHR) computational model simulation. The different processing stages of the transmitted signal along its space-time trajectory from transmission to digital signal processing are modelled. With this simulation tool a moving target present over the sea can be detected according to a set of given initial conditions together with the ionosphere model inputs and the target electromagnetic model. Initial conditions as well as the modulation and filtering options among other parameters of the model can be set easily. The present work is intended to be a further contribution to OTHR studies, providing a user-friendly tool of easy application in order to improve a radar design, facilitate its implementation, as well as for debugging algorithms and signal processing techniques.Fil: Saavedra, Zenon. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Electricidad, Electrónica y Computación. Laboratorio de Telecomunicaciones; ArgentinaFil: Zimmerman, Diego. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Electricidad, Electrónica y Computación. Laboratorio de Telecomunicaciones; ArgentinaFil: Cabrera, Miguel Angel. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Electricidad, Electrónica y Computación. Laboratorio de Telecomunicaciones; ArgentinaFil: Elias, Ana Georgina. Universidad Nacional de Tucumán. Instituto de Física del Noroeste Argentino. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Noa Sur. Instituto de Física del Noroeste Argentino; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología; Argentin

Effects of Earth's magnetic field variation on high frequency wave propagation in the ionosphere

The ionosphere is an anisotropic, dispersive medium for the propagation of radio frequency electromagnetic waves due to the presence of the Earth?s intrinsic magnetic field and free charges. The detailed physics of electromagnetic wavepropagation through a plasma is more complex when it is embedded in a magnetic field. In particular, the ground range of waves reflecting in the ionosphere presents detectable magnetic field effects. Earth?s magnetic field varies greatly, with the most drastic scenario being a polarity reversal. Here the spatial variability of the ground range is analyzed using numerical ray tracing under possible reversal scenarios. Pattern changes of the ?spitze?, a cusp in the ray path closely related to the geomagnetic field, are also assessed. The ground range increases with magnetic field intensity and ray alignment with the field direction. For the present field, which is almost axial dipolar, this happens for Northward propagation at the magnetic equator, peaking in Indonesia where the intensity is least weak along the equator. A similar situation occurs for a prevailing equatorial dipole with Eastward ray paths at the corresponding magnetic equator that here runs almost perpendicular to the geographic equator. Larger spitze angles occur for smaller magnetic inclinations, and higher intensities. This is clearly observed for the present field and the dipole rotation scenario along the corresponding magnetic equators. For less dipolar configurations the ground range and spitze spatial variabilities become smaller scale. Overall, studying ionospheric dynamics during a reversal may highlight possible effects of dipole decrease which is currently ongoing.Fil: Fagre, Mariano. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Electricidad, Electrónica y Computación. Laboratorio de Telecomunicaciones; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; ArgentinaFil: Zossi, Bruno Santiago. Universidad Nacional de Tucumán. Instituto de Física del Noroeste Argentino. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Noa Sur. Instituto de Física del Noroeste Argentino; ArgentinaFil: Yiğit, Erdal. George Mason University; Estados UnidosFil: Amit, Hagay. Cnrs- S, Laboratoire de Planetologie Et de Geodyn; FranciaFil: Elias, Ana Georgina. Universidad Nacional de Tucumán. Instituto de Física del Noroeste Argentino. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Noa Sur. Instituto de Física del Noroeste Argentino; Argentin

Performance of CHIRPS dataset for monthly and annual rainfall-indices in Northern Argentina

In this study, we analyze the performance of CHIRPS in comparison with data from 50 rain gauges (OBS) in Northern Argentina (NA) for the 1982–2019 period. The methodology consists in a point-to-pixel comparison using the correlation coefficient (RHO), the mean relative error (MRE), the mean absolute error (MAE) and the Nash-Sutcliffe efficiency (NSE). We analyze monthly rainfall, annual rainfall indices and their trends, differentiating between anchor and no-anchor stations. A comparative analysis is performed further between two NA sub-regions: Northwestern Argentina (NWA) and Northeastern Argentina (NEA). Results indicate that CHIRPS dataset better represents the interannual variability in wetter (drier) months in NWA (NEA). For all months, RHO values are higher in NEA than NWA. For annual rainfall indices, RHO values in most of the stations of NA are non-significant or low for some number-days (with threshold of 1 mm) and very extreme indices, with the exception of the eastern extreme of NA. The less extreme indices (PRCPTOT, R95pad and R99pad) are observed to have higher RHO values (> 0.5 in all cases) in NA, as well as better MRE, MAE and NSE values. Monthly values and annual indices are underestimated in general, especially in NWA no-anchor stations. Most of the significant linear trends observed in rainfall indices are not detected with CHIRPS. As an exception, a relatively better performance for the maximum number of consecutive dry days (CDD) is observed in the sense that CHIRPS detect the positive linear trends in NWA but do not locate them with precision in comparison with OBS data. CHIRPS is not recommended for studies in NA related with the aspects (mean values, interannual variability, linear trends) of rainfall analyzed in this work, especially for the extreme rainfall.Fil: Medina, Franco Dario. Universidad Nacional de Tucumán. Instituto de Física del Noroeste Argentino. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Noa Sur. Instituto de Física del Noroeste Argentino; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física; ArgentinaFil: Zossi, Bruno Santiago. Universidad Nacional de Tucumán. Instituto de Física del Noroeste Argentino. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Noa Sur. Instituto de Física del Noroeste Argentino; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física; ArgentinaFil: Bossolasco, Adriana Gabriela. Universidad Nacional de Tucumán. Instituto de Física del Noroeste Argentino. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Noa Sur. Instituto de Física del Noroeste Argentino; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física; ArgentinaFil: Elias, Ana Georgina. Universidad Nacional de Tucumán. Instituto de Física del Noroeste Argentino. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Noa Sur. Instituto de Física del Noroeste Argentino; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física; Argentin