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Continuum Enhancements, Line Profiles, and Magnetic Field Evolution during Consecutive Flares

Papers from SWICo members

Zuccarello, Francesca; Guglielmino, Salvo L.; Capparelli, Vincenzo; Mathioudakis, Mihalis; Keys, Peter H.; Criscuoli, Serena; Falco, Mariachiara; Murabito, Mariarita

The occurrence of very energetic solar flares can give rise to Space Weather phenomena impacting on the circum-terrestrial environment.It is well known that, during solar flares, magnetic energy can be converted into electromagnetic radiation from radio waves to γ-rays. Enhancements in the continuum at visible wavelengths, as well as continuum enhancements in the FUV and NUV passbands, give rise to the so-called white-light (WL) flares. Moreover, the strong energy release taking place during these events can lead to the rearrangement of the magnetic field at the photospheric level, causing morphological changes in sunspots.

Left: Map showing the details of the δ-spot hosting the flares (the arrow indicates the WL ribbon). The blue, orange, and green circles indicate the IRIS slit positions used to determine the line profiles shown on the Right for Si IV 140.28 nm (top row) and C II 133.575 nm (bottom row). In each row, the line profiles for successive times are overplotted on the relevant spectrograms. The dashed vertical lines indicate the position of the line center, while the blue, orange, and green circles show the slit positions relative to the profiles indicated with the same colors.

In this paper, we describe the results of the analysis performed using data acquired by satellite instruments (Interface Region Imaging Spectrograph (IRIS), Solar Dynamics Observatory/Helioseismic and Magnetic Imager, Hinode/Solar Optical Telescope) and ground-based telescopes (Rapid Oscillations in the Solar Atmosphere (ROSA)/Dunn Solar Telescope) during two consecutive C7.0 and X1.6 flares (accompanied by an eruption) that occurred in active region NOAA 12205 on 2014 November 7. The analysis shows the presence of continuum enhancements during the evolution of the events, observed both in ROSA images and in IRIS spectra. We also investigate the role played by the evolution of the δ sunspots in the flare triggering, as well as the changes in the penumbrae surrounding these sunspots as a further consequence of these flares.

Publication: Zuccarello F., Guglielmino S. L., Capparelli V., Mathioudakis M., Keys P. H., Criscuoli S., Falco M., et al., 2020, ApJ, 889, 65. doi:10.3847/1538-4357/ab621f

The ionosphere prediction service prototype for GNSS users

Papers from SWICo members

Sreeja Vadakke Veettil, Claudio Cesaroni, Marcio Aquino, Giorgiana De Franceschi, Francesco Berrili, Filippo Rodriguez, Luca Spogli, Dario Del Moro, Alice Cristaldi, Vincenzo Romano, Roberto Ronchini, Stefano Di Rollo, Eric Guyader, Angela Aragon-Angel

The effect of the Earth’s ionosphere represents the single largest contribution to the Global Navigation Satellite System (GNSS) error budget and harsh ionospheric conditions can impact seriously on GNSS system functionality, including integrity, accuracy and availability. With the growing reliance on GNSS for many modern technological applications, reliable ionospheric forecasts can contribute to the understanding and mitigation of the impact of the ionosphere on our technology based society.

Diagram of the IPS architecture

With this aim, the Ionosphere Prediction Service (IPS) project was set up to design and develop a prototype platform to translate the forecast of the ionospheric conditions into a service customized for different GNSS user communities. To achieve this overarching aim, four different product groups dealing with solar activity, ionospheric activity, GNSS receiver performance and service performance have been developed and integrated into a service chain, which is made available through an innovative and fully customizable web based platform. This paper provides an overview of the IPS project describing its overall architecture, products and platform.

Publication: Veettil, S. V., Cesaroni, C., Aquino, M., De Franceschi, G., Berrili, F., Rodriguez, F., … & Ronchini, R. (2019). The ionosphere prediction service prototype for GNSS users. Journal of Space Weather and Space Climate9, A41.

Neural network based model for global Total Electron Content forecasting

Papers from SWICo members

Claudio Cesaroni, Luca Spogli, Angela Aragon-Angel, Michele Fiocca, Varuliator Dear, Giorgiana De Franceschi, Vincenzo Romano

We describe a novel empirical model to forecast, one day in advance, the Total Electron Content (TEC) at global scale. The technique is based on the Global Ionospheric Map (GIM), provided by the International GNSS Service (IGS), and exploits a nonlinear autoregressive neural network with external input (NARX) applied to selected TEC time series for soma particular GIM grid points (24 h single-point TEC forecasting), taking into account the actual and forecasted geomagnetic conditions. To extend the forecasting at a global scale, the technique leverages of the NeQuick2 Model fed by an effective sunspot number R12 (R12eff), calculated by minimizing the root mean square error (RMSE) between NARX output and NeQuick2 applied at the same GIM grid points. This new approach is able to reproduce the behavior of the ionosphere especially during disturbed periods.

Validation by using Final Global TEC product provided by the Universitat Politècnica de Catalunya (UPC) for the geomagnetic storm occurred 7–11 September 2017: (a) distribution of TEC difference (forecast-actual), statistical parameters are reported together with a red line indicating the mean; (c) map of the mean values of the TEC difference (forecast-actual); (b) time profile of the RGEC parameter (right y axis) and Dst (left y axis), the black dashed line indicates the zero reference value; (d) map of the standard deviation of the TEC difference (forecast-actual).

The performance of the forecasting model is extensively validated under different geospatial conditions, against both TEC maps products by UPC (Universitat Politècnica de Catalunya) and independent TEC data from Jason-3 spacecraft. The validation gives very satisfactory results in terms of RMSE, as it has been found to range between 3 and 5 TECu. RMSE depend on the latitude sectors, time of the day, geomagnetic conditions, and provide a statistical estimation of the accuracy of the 24-h forecasting technique even over the areas poorly covered by GNSS receivers (i.e. the oceans). The validation of the forecasting during five geomagnetic storms reveals that the model performance is not deteriorated during disturbed periods. This 24-h empirical approach is currently implemented on the Ionosphere Prediction Service (IPS), a prototype platform to support different classes of GNSS users in order to support the mitigation of the ionospheric effects on GNSS based technologies.

Publication: Cesaroni, C., Spogli, L., Aragon-Angel, A., Fiocca, M., Dear, V., De Franceschi, G., & Romano, V. (2020). Neural network based model for global Total Electron Content forecasting. Journal of Space Weather and Space Climate, 10, 11.

On the Analytical Description of the Topside Ionosphere by NeQuick: Modeling the Scale Height through COSMIC/FORMOSAT-3 Selected Data

Papers from SWICo members

Alessio Pignalberi, Michael Pezzopane, David R. Themens, Haris Haralambous, Bruno Nava, Pierdavide Coïsson

The topside part of the ionosphere extends from the F2-layer peak, corresponding to the ionospheric electron density maximum, to the plasmasphere. Developing a reliable model of the topside ionosphere is one of the most difficult tasks because instruments commonly used to probe the ionosphere, namely ionosondes, are only capable of sounding the region below the F2-layer peak. The topside ionosphere is characterized by a monotonic decrease of the electron density as the ion population smoothly transitions from the heavy O+ ions to the lighter H+ and He+ ions. This behavior is described by means of monotonically decreasing analytical functions dependent on a parameter called topside scale height whose exact description is the most challenging task for the topside ionosphere modeling.

In this paper, the analytical description of the topside ionosphere included in the NeQuick model is deeply analyzed. The NeQuick modeled scale height behavior is first studied at infinity and then for the lowest part of the topside region through an expansion in Taylor series near the F2-layer peak. The significant influence of the NeQuick topside parameters in the modeling of the topside profile is investigated in detail and, in particular, it is shown that for the lowest part of the topside the model assumes a linearly increasing trend of the topside scale height. Afterwards, the NeQuick topside formulation is inverted to derive a fully analytical expression of the topside scale height as a function of the electron density and F2-layer peak parameters. This expression has been applied to a selected and very reliable dataset of COSMIC/FORMOSAT-3 Radio Occultation profiles. The performed statistical analyses strongly support the supposed linear trend of the topside scale height for the lowest part of the topside ionosphere, as embedded in NeQuick; thus, the developed technique might be relevant for Space weather modeling purposes.

Publication: A. Pignalberi, M. Pezzopane, D. R. Themens, H. Haralambous, B. Nava and P. Coïsson, “On the Analytical Description of the Topside Ionosphere by NeQuick: Modeling the Scale Height Through COSMIC/FORMOSAT-3 Selected Data,” in IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, vol. 13, pp. 1867-1878, 2020, doi: 10.1109/JSTARS.2020.2986683.

The ionospheric irregularities climatology over Svalbard from solar cycle 23

Papers from SWICo members

Giorgiana De Franceschi, Luca Spogli, Lucilla Alfonsi, Vincenzo Romano, Claudio Cesaroni, Ingrid Hunstad

An unprecedented climatology of the ionospheric irregularities over the Svalbard (NO) derived from the longest Global Navigation Satellite Systems (GNSS) scintillation data series ever collected. Two receivers for scintillation monitoring are working at Ny-Ålesund, the first of which has been installed in late September 2003.

Climatological maps of occurrence of sigma_phi and S4 above the moderate to strong scintillation threshold. Maps are sorted according different level of Kp: quiet (left plots), minor/moderate G1-G2 (middle plots) and strong/severe/extreme G3-G4-G5 (right plots).

They are able to investigate auroral and cusp/cap regions and the length of the data series allows describing the Arctic ionosphere along about two solar cycles, from the descending phase of cycle 23 to almost the end of cycle 24. A detailed assessment of the long-term behaviour of the ionosphere under solar maximum and solar minimum conditions is provided including several periods of perturbed ionospheric weather caused by unfavourable heliogeophysical conditions. Since November 2015, a multi-constellation GNSS receiver has been deployed in Ny-Ålesund, providing the opportunity to perform the ionospheric climatology from Galileo signals. The results offer realistic features of the high latitude ionosphere, providing a broad spectrum of ionospheric reactions to different space weather conditions.

Publication: De Franceschi, G., Spogli, L., Alfonsi, L., Romano, V., Cesaroni, C., & Hunstad, I. (2019). The ionospheric irregularities climatology over Svalbard from solar cycle 23. Scientific reports, 9(1), 1-14.

Role of the external drivers in the occurrence of low-latitude ionospheric scintillation revealed by multi-scale analysis

Papers from SWICo members

Luca Spogli, Mirko Piersanti, Claudio Cesaroni, Massimo Materassi, Antonio Cicone, Lucilla Alfonsi, Vincenzo Romano, and Rodolfo Gerardo Ezquer

By leveraging on the modal analysis provided by the Adaptive Local Iterative Filtering (ALIF) technique, this study focuses on the multi-scale variability of the amplitude scintillation on Global Navigation Satellite Systems (GNSSs) recorded over San Miguel de Tucumán (Argentina).

Relative energy of each intrinsic mode function as a function of the period (in days) calculated for (a) S4, (b) Equatorial Electrojet,(c) AL index, (d) AE index, (e) IMF-Bz, (f) IEF-Ex and (g) epsilon parameter. Red curves are for 1–15 March 2011, while green curves for the period 16–31 March 2011. Shaded colors (yellow, red, green) indicate three different intervals of periods: low periods (yellow), middle periods (red) and high periods (green). Black dashed box indicates the range of scales in which correspondence between S4 and epsilon parameter is found.

The site is nominally located below the expected position of the southern crest of the Equatorial Ionospheric Anomaly (EIA). The considered period is 1–31 March 2011, during which one minor and one moderate storm characterize the first half of the month, while generally quiet conditions of the geospace stand for the second half. The multiscale analysis is extended to helio-geophysical parameters to speculate on the possible relationship between forcing factors from the geospace and the ionospheric response. Resonant modes in the Akasofu (e) parameter are identified as likely related to the frequency components in the time evolution found for the amplitude scintillation index, hence modulating the scintillation itself. The analysis shows how the time-frequency structure of the amplitude scintillation can be characterized in terms of the resonant modes found in the combination of the Akasofu parameter. When assessed statistically, the proposed study can support models driven by interplanetary parameters aimed at characterizing the low latitude scintillation. The detection of resonant modes in the identified parameters can be used to define the Space Weather impact on GNSS signals recorded at ground.

Publication: Spogli, L., Piersanti, M., Cesaroni, C., Materassi, M., Cicone, A., Alfonsi, L., … & Ezquer, R. G. (2019). Role of the external drivers in the occurrence of low-latitude ionospheric scintillation revealed by multi-scale analysis. Journal of Space Weather and Space Climate9, A35

A Preliminary Risk Assessment of Geomagnetically Induced Currents over the Italian Territory

Papers from SWICo members

Roberta Tozzi, Paola De Michelis, Igino Coco, Fabio Giannattasio

A sketch representing the chain of events leading to the generation of GICs.

Major geomagnetic storms drive rapid intensification and variability of magnetospheric and ionospheric current systems that give rise to large ground geomagnetically-induced currents (GIC). Space weather associated GIC pose a serious threat to the reliability of power-transmission systems and other electrically conducting infrastructures such as oil and gas pipelines. The most severe effects are observed at high latitudes due to ionospheric currents associated with the aurora. However, as power transmission grid and pipeline infrastructures continue to grow at middle and low-latitudes, GIC hazards are no longer just concerns of high-latitude regions.

On the left: maximum daily GIC indices estimated from CTS geomagnetic data (blue line); thresholds between the different risk levels (coloured dashed lines); monthly averaged sunspot number (grey line). On the right: table of the threat and risk levels.

We provide a preliminary characterisation of the general risk to which the Italian power grid network is exposed. Due to limited direct GIC measurements, a proxy of the geoelectric field is used, i.e. the GIC index. This is calculated for a time interval of approximately 20 years using data from the two longest running Italian magnetic observatories, i.e. Castello Tesino and L’Aquila. Results show that during periods of high geomagnetic activity, potentially detrimental GICs could flow through the power network, especially at the highest Italian latitudes that are characterized by a low conductivity lithosphere.

Publication:  Tozzi, R., De Michelis, P., Coco, I., Giannattasio, F., 2019. A Preliminary Risk Assessment of Geomagnetically Induced Currents over the Italian Territory, Space Weather, 17, 46-58, doi: 10.1029/2018SW002065. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018SW002065

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Single-spacecraft Identification of Flux Tubes and Current Sheets in the Solar Wind

Papers from SWICo members


F. Pecora, A. Greco, Q. Hu, S. Servidio, A. Chasapis, W. H. Matthaeus

In this work we present a novel technique, based on two consolidated models, for describing and visualising the local topology of the magnetic field solar wind using single-spacecraft data. The Grad-Shafranov (GS) reconstruction method provides a two-dimensional map of the magnetic field surrounding the spacecraft trajectory, while the Partial Variance of Increments (PVI) technique is able to identify coherent magnetic structures, such as current sheets. We applied this combined technique to one month of magnetic field data measured by Wind satellite at 1 AU. In this stream we selected the flux rope events, that are structures with cylindrical symmetry and a relatively strong magnetic field along the symmetry axis. These flux tubes are quite large structures (a fraction of AU) and have a complex inner structure and they interact each other while moving in the Solar Wind.

On the left a sketch of interacting flux tubes with the path of a spacecraft passing through them. On the right reconstructed flux ropes for Wind January 2016 in the local frame (x,y), with the z-axis representing the cylindrical axis of the flux rope. Magnetic potential contour lines with filled colour plots of the current density J[A/m2] in the z-direction. The dashed lines at y = 0 are the projection of the spacecraft path on the flux rope cross section. The yellow stars and the green circles represent the start and the end time of current sheets, respectively. The x-axis of the figures represent the observation period, that can be transformed into spatial dimensions (see the ruler inside the plots) applying Taylor hypothesis.

These inner and outer interactions can possibly generate sites of magnetic reconnection where strong current sheets appear. What we observed from the reconstruction is that a quasi-two-dimensional turbulence emerges as a sea of nested magnetic islands with current sheets located mostly at their boundaries. The method shows great promise for visualising and analysing single-spacecraft data from missions such as Parker Solar Probe and Solar Orbiter, as well as 1 AU SpaceWeather monitors such as ACE, Wind, and IMAP.

Publication: Pecora F., Greco A., Hu Q., Servidio S., Chasapis A. G., Matthaeus W. H., 2019, ApJL, 881, L11. doi:10.3847/2041-8213/ab32d9

Forecasting the 2018 February 12th CME propagation with the P-DBM model: a fast warning procedure

Papers from SWICo members

Dario Del Moro, Gianluca Napoletano, Roberta Forte, Luca Giovannelli, Ermanno Pietropaolo, Francesco Berrilli

The forecast of the time of arrival of a Coronal Mass Ejection (CME) to Earth is of critical importance for our high−technology society and for the Earth’s upper atmosphere status and LEO satellites. We realized a procedure based on the Drag−Based Model which uses probability distributions, rather than exact values, as input parameters, and allows the evaluation of the uncertainty on the forecast. The P−DBM belongs to a family of models that apply a somewhat simplified description of the main interaction the ICME is subject to during its interplanetary journey. The drag−based models (DBMs) assume that beyond a certain heliospheric distance, a simple aerodynamic drag equation can describe the interaction between the ICME and the solar
wind environment.

Ensemble modeling incorporate the intrinsic limitation of information due to measure errors or due to the lack of measure at all, in form of probability distributions. In practice, instead of a single run to forecast an ICME propagation, a set of runs, driven with input parameters extracted from suitable distributions are used to retrieve a distribution of output parameters. We tested this approach using a set of CMEs whose transit times are known, obtaining extremely promising results.

We realized a real−time implementation of this algorithm which ingests the outputs of automated CME tracking algorithms as inputs to provide early warning for those CME approaching Earth. We present the results of this real−time fast warning procedure for the case of the 2018 February 12th

Publication: DEL MORO, Dario et al. Forecasting the 2018 February 12th CME propagation with the P-DBM model: a fast warning procedure. Annals of Geophysics, [S.l.], v. 62, n. 4, p. GM456, dec. 2019. ISSN 2037-416X.

Can superflares occur on our Sun?

Papers from SWICo members


Paolo Romano, Abouazza Emhamdi, Ayman Kordi

Two strong homologous white light flares of X-GOES class occurred on the Sun on Sept. 06, 2017, providing a rare exceptional opportunity to study the mechanisms responsible for the formation of the magnetic field configurations suitable for the manifestation of such yet enigmatic eruptive events and their effects in the lower layers of the solar atmosphere.

Using photospheric vector magnetograms, taken before the beginning of the two X-class events, as boundary conditions to reconstruct the non−linear coronal magnetic field configuration, we identified two related 3D null points located at low heights above the photosphere (i.e. in very low corona). These null points are most likely responsible for the triggering of the two strong X-GOES class flares. We deduced that their formation at such low altitudes may plausibly be ascribed to the peculiar photospheric horizontal motions of the main magnetic structures of the hosting Active Region NOAA 12673.

These events can be adopted as a hint for a possible interpretation of the activity of young G-type stars, recently reported by the Kepler mission, and can shed light on the probability that superflares occur on our Sun.

Publication: Two Strong White-Light Solar Flares in AR NOAA 12673 as Potential Clues for Stellar Superflares, Solar Physics, 294, 4, 2019