Home » Solar physics

Category Archives: Solar physics

Magnetic Energy Balance in the Quiet Sun on Supergranular Spatial and Temporal Scales

Papers from SWICo members

F. Giannattasio, G. Consolini, F. Berrilli, and D. Del Moro

Small-scale magnetic fields are ubiquitous in the quiet solar photosphere and may store and transfer huge amounts of energy to the upper atmospheric layers giving rise to a chain of phenomena that are relevant for Space Weather. For this reason, it is fundamental to constrain the energetics of the quiet Sun.

Mean energy variation rate in the Field of View saturated between −1.5 and 1.5 erg/cm−3 s. The superposed green lines are contour plots of the longest magnetic decorrelation times (>120 min).

By taking advantage of a 24 hr long with 90 s cadence magnetogram time series acquired by the Hinode mission without interruption, we computed, for the first time, the average photospheric electric field, the average current density, and starting from these, the rate of change of magnetic energy density on supergranular spatial and temporal scales. The main result is that, on average, the energy provided by photospheric electric and magnetic fields and current density can sustain the magnetic fields in the network.

Publication: F. Giannattasio, G. Consolini, F. Berrilli, and D. Del Moro, Magnetic Energy Balance in the Quiet Sun on Supergranular Spatial and Temporal Scales, The Astrophysical Journal, 904, 1, 2020.

Detection Capability of Flux Ropes during the Solar Orbiter Mission

Papers from SWICo members

Telloni, Daniele; D’Amicis, Raffaella; Bruno, Roberto; Carbone, Francesco; Perrone, Denise; Zank, Gary P.; Zhao, Lingling; Nakanotani, Masaru; Adhikari, Laxman

Flux ropes are interplanetary magnetic helical structures that are receiving increasing attention because of their likely role in magnetohydrodynamic (MHD) processes as well as their impact on space weather science. A very promising and powerful approach to address their investigation and characterization is based on wavelet spectrograms of the invariants of the ideal MHD equations.

The accuracy of this method to infer flux rope properties depends on the proper evaluation of the direction of propagation of the flux rope itself, which is often difficult to assess. We present a numerical test of the reliability of this diagnostic technique, by simulating a synthetic flux rope of fixed size and propagation direction along the Solar Orbiter orbit, that is very elongated and inclined with respect to the orbital plane. We find that when the flux rope is crossed for less than 50% of its width, the procedure becomes unreliable. Quantitative information on how to properly recover the flux-rope intrinsic properties is provided.

Publication: Telloni D., D’Amicis R., Bruno R., Carbone F., Perrone D., Zank G. P., Zhao L., et al., 2020, ApJL, 899, L25.

Study of the Influence of the Solar Wind Energy on the Geomagnetic Activity for Space Weather Science

Papers from SWICo members

Telloni, Daniele; Carbone, Francesco; Antonucci, Ester; Bruno, Roberto; Grimani, Catia; Villante, Umberto; Giordano, Silvio; Mancuso, Salvatore; Zangrilli, Luca

This paper addresses the investigation of the interaction of the solar wind energy with the Earth’s magnetosphere, by studying its correlation with the disturbance storm time (Dst) index, a proxy of the geomagnetic activity. Some relevant parameters of the solar wind (the bulk speed and the z-component of the interplanetary magnetic field) are explored in the energy-Dst space.

It results that (I) the solar wind energy and the geomagnetic activity are strictly related, with the coronal mass ejections representing the most energetic and geoeffective driver; (II) the slow solar wind has negligible effects on Earth regardless of its energy content, whereas high-speed streams may induce severe geomagnetic storming depending on the advected energy; and (III) while at low and mid energies, geomagnetic disturbances are induced provided the magnetic reconnection between the interplanetary and terrestrial magnetic fields occurs, high-energy solar wind plasma can impact Earth even without reconnecting with the geomagnetic field at the dayside magnetopause. The most significant result in the framework of space weather science resides in the observational evidence that the Earth’s magnetosphere has a maximum response to the energetic content of the solar wind, which leads to the derivation of an empirical law allowing the proper forecast of the upper limit of the intensity of any geomagnetic disturbance on the basis of the solar wind energy derived in situ at the Lagrangian point L1.

Publication: Telloni D., Carbone F., Antonucci E., Bruno R., Grimani C., Villante U., Giordano S., et al., 2020, ApJ, 896, 149.

Detection of Coronal Mass Ejections at L1 and Forecast of Their Geoeffectiveness

Papers from SWICo members

Daniele Telloni , Ester Antonucci, Alessandro Bemporad, Tiziano Bianchi, Roberto Bruno, Silvano Fineschi, Enrico Magli, Gianalfredo Nicolini, and Roberto Susino

A novel tool aimed to detect solar coronal mass ejections (CMEs) at the Lagrangian point L1 and to forecast their geoeffectiveness is presented in this paper. This approach is based on the analysis of in situ magnetic field and plasma measurements to compute some important magnetohydrodynamic quantities of the solar wind (the total pressure, the magnetic helicity, and the magnetic and kinetic energy), which are used to identify the CME events, that is their arrival and transit times, and to assess their likelihood for impacting the Earths magnetosphere.

The method is essentially based on the comparison of the topological properties of the CME magnetic field configuration and of the CME energetic budget with those of the quasi-steady ambient solar wind. The algorithm performances are estimated by testing the tool on solar wind data collected in situ by the Wind spacecraft from 2005 to 2016. In the scanned 12 yr time interval, it results that (i) the procedure efficiency is of 86% for the weakest magnetospheric disturbances, increasing with the level of the geomagnetic storming, up to 100% for the most intense geomagnetic events, (ii) zero false positive predictions are produced by the algorithm, and (iii) the mean delay between the potentially geoeffective CME detection and the geomagnetic storm onset if of 4 hr, with a 98% 2-8 hr confidence interval. Hence, this new technique appears to be very promising in forecasting space weather phenomena associated to CMEs.

Publication: Telloni D., Antonucci E., Bemporad A., Bianchi T., Bruno R., Fineschi S., Magli E., et al., 2019, ApJ, 885, 120. doi:10.3847/1538-4357/ab48e9

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

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