Observations of the chromospheric Evershed flow of sunspot penumbra

The sunspot penumbra is usually observed in the photosphere and it is of particular interest for its magneto-convection which seems to transport the heat from the top of the convection zone into the solar atmosphere. It is well known that the penumbra magnetic field extends in the upper layers of the solar atmosphere forming the so called super-penumbra. Thanks to the application of the Self Organizing Map technique to a spectral dataset containing monochromatic images acquired along the Ca II 854.2 nm and H$\alpha$ 656.28 nm lines, we were able to segment the penumbra and to measure the plasma velocity along the chromospheric portions of penumbral filaments. We found that the head, body and tail of penumbral filaments show vertical flows compatible with the persistence of the Evershed flow. Instead, the inverse Evershed flow has been observed only in the outer portion of the super-penumbra. We found that two opposite Evershed regimes work next to each other, without overlapping and both contribute to the downflow around sunspots. These results confirm the uncombed model of the sunspot penumbra and provide some hints that the downflow around sunspots may be ascribed to the magnetic field dragging the plasma down

Historical solar Ca II K observations at the Rome and Catania observatories

Here we present the little explored Ca II K archives from the Rome and the Catania observatories and analyse the digitised images from these archives to derive plage areas.Comment: 5 pages, 3 figures, to be published in "Nuovo Cimento C" as proceeding of the Third Meeting of the Italian Solar and Heliospheric Communit

Continuum enhancements, line profiles and magnetic field evolution during consecutive flares

During solar flares, magnetic energy can be converted into electromagnetic radiation from radio waves to $\gamma$ rays. Enhancements in the continuum at visible wavelengths give rise to white-light flares, as well as continuum enhancements in the FUV and NUV passbands. In addition, the strong energy release in these events can lead to the rearrangement of the magnetic field at the photospheric level, causing morphological changes in large and stable magnetic structures like sunspots. In this context, we describe observations acquired by satellite instruments (IRIS, SDO/HMI, Hinode/SOT) and ground-based telescopes (ROSA/DST) during two consecutive C7.0 and X1.6 flares occurred in active region NOAA 12205 on 2014 November 7. The flare was accompanied by an eruption. The results of the analysis show the presence of continuum enhancements during the evolution of the events, observed both in ROSA images and in \textit{IRIS} spectra. In the latter, a prominent blue-shifted component is observed at the onset of the eruption. We investigate the role played by the evolution of the $\delta$ sunspots of the active region in the flare triggering, and finally we discuss the changes in the penumbrae surrounding these sunspots as a further consequence of these flares.Comment: 19 pages, accepted for ApJ; some figures are in B/W to accomplish size limit

Quantifying Properties of Photospheric Magnetic Cancellations in the Quiet Sun Internetwork

We analyzed spectropolarimetric data from the Swedish 1-meter Solar Telescope to investigate physical properties of small-scale magnetic cancellations in the quiet Sun photosphere. Specifically, we looked at the full Stokes polarization profiles along the Fe I 557.6 nm and of the Fe I 630.1 nm lines measured by CRisp Imaging SpectroPolarimeter (CRISP) to study temporal evolution of the line-of-sight (LOS) magnetic field during 42.5 minutes of quiet Sun evolution. From this magnetogram sequence, we visually identified 38 cancellation events. We then used Yet Another Feature Tracking Algorithm (YAFTA) to characterize physical properties of these magnetic cancellations. We found on average $1.6\times10^{16}$ Mx of magnetic flux cancelled in each event with an average cancellation rate of $3.8\times10^{14}$ Mx s$^{-1}$. The derived cancelled flux is associated with strong downflows, with an average speed of $V_\mathrm{LOS}\approx1.1$ km s$^{-1}$. Our results show that the average lifetime of each event is $9.2$ minutes with an average $44.8\%$ of initial magnetic flux being cancelled. Our estimates of magnetic fluxes provide a lower limit since studied magnetic cancellation events have magnetic field values that are very close to the instrument noise level. We observed no horizontal magnetic fields at the cancellation sites and therefore can not conclude whether the events are associated structures that could cause magnetic reconnection.Comment: 19 pages, 18 figures, 2 tables, accepted into ApJ on 06/08/202

Long-term optical monitoring of the solar atmosphere in Italy

Probably, the long-term monitoring of the solar atmosphere started in Italy with the first telescopic observations of the Sun made by Galileo Galilei in the early 17th century. His recorded observations and science results, as well as the work carried out by other following outstanding Italian astronomers inspired the start of institutional programs of regular solar observations at the Arcetri, Catania, and Rome Observatories. These programs have accumulated daily images of the solar photosphere and chromosphere taken at various spectral bands over a time span larger than 80 years. In the last two decades, regular solar observations were continued with digital cameras only at the Catania and Rome Observatories, which are now part of the INAF National Institute for Astrophysics. At the two sites, daily solar images are taken at the photospheric G-band, Blue (λ = 409.4 nm), and Red (λ = 606.9 nm) continua spectral ranges and at the chromospheric Ca II K and Hα lines, with a 2'' spatial resolution. Solar observation in Italy, which benefits from over 2500 hours of yearly sunshine, currently aims at the operational monitoring of solar activity and long-term variability and at the continuation of the historical series as well. Existing instruments will be soon enriched by the SAMM double channel telescope equipped with magneto-optical filters that will enable the tomography of the solar atmosphere with simultaneous observations at the K I 769.9 nm and Na I D 589.0 nm lines. In this contribution, we present the available observations and outline their scientific relevance

On the Evolution of a Sub-C Class Flare: A Showcase for the Capabilities of the Revamped Catania Solar Telescope

Solar flares are occasionally responsible for severe space-weather events, which can affect space-borne and ground-based infrastructures, endangering anthropic technological activities and even human health and safety. Thus, an essential activity in the framework of space-weather monitoring is devoted to the observation of the activity level on the Sun. In this context, the acquisition system of the Catania Solar Telescope has been recently upgraded in order to improve its contribution to the European Space Agency (ESA) - Space Weather Service Network through the ESA Portal, which represents the main asset for space weather in Europe. Here, we describe the hardware and software upgrades of the Catania Solar Telescope and the main data products provided by this facility, which include full-disk images of the photosphere and chromosphere, together with a detailed characterization of sunspot groups. As a showcase of the observational capabilities of the revamped Catania Solar Telescope, we report the analysis of a B5.4 class flare that occurred on 7 December 2020, simultaneously observed by the Interface Region Imaging Spectrograph and the Solar Dynamics Observatory satellites...

Report EduINAF anno 2021/2022

Il periodo a cui fa riferimento questo Report (Anno scolastico 2021/2022: Settembre 2021-Agosto 2022) è stato caratterizzato dal protrarsi dell’emergenza COVID in Italia con conseguenti difficoltà delle scuole e periodi di ricorso alla Didattica a Distanza (DaD). Il 2021/2022 è stato anche il terzo anno di attività della testata registrata EduINAF, il magazine di Didattica e Divulgazione dell’Istituto Nazionale di Astrofisica. In questo periodo, la redazione di EduINAF, oltre a pubblicare risorse didattiche e contenuti informativi sul mondo della Didattica e Divulgazione della scienza, ha organizzato e contribuito a organizzare numerose iniziative a sostegno della scuola e della società, come le dirette osservative della Serie “Il Cielo in Salotto”, i concorsi per le scuole e altre campagne di engagement. In questo Report si presentano le attività svolte nell’arco di tempo indicato e si analizzano i risultati ottenuti in termini di audience, di comportamento e di gradimento del pubblico. L’obiettivo è quello di fornire il contesto per strutturare il Piano Editoriale 2022/2023 che conterrà le linee guida per la programmazione del prossimo anno scolastico

Analysis of high resolution observations of sunspots fine structures

This Ph.D. thesis deals with the study of the interaction between plasma and magnetic fields on the Sun. Observations acquired during two observing campaigns, one at the Solar Swedish Tower and the other at the Richard B. Dunn Solar Telescope, provided high-resolution data which were used to study the details of some phenomena occurring in the Sun. In particular, this work aims to extend and consolidate our knowledge on the formation and evolution of sunspots observed in the solar photosphere. The first aspect which was investigated concerns the study of the mechanism of the penumbra formation in a sunspot. In this regard, I give my contribution in explaining the behaviour of the magnetic field forming the penumbral filaments. A second aspect concerns the study of the kinematic and magnetic properties of a light bridge separating into two parts the umbra of a sunspot. I found that there is a relationship between the upflow motions in the light bridge dark lane and the magnetic field configuration. The third aspect concerns the study of the properties of granules in a light bridge and in the quiet Sun using a new algorithm developed in collaboration with the Department of Mathematics of the University of Catania. In particular, I compared the size, mean continuum intensity and Doppler velocity between the granules forming the light bridge and those of the quiet Sun. In the conclusion, I give my interpretation of the observed phenomena and suggest future observations to confirm these results and support theoretical models

Solar flare forecasting using morphological properties of sunspot groups

We describe a new tool developed for solar flare forecasting on the base of some sunspot group properties. Assuming that the flare frequency follows the Poisson statistics, this tool uses a database containing the morphological characteristics of the sunspot groups daily observed by the Equatorial Spar of INAF – Catania Astrophysical Observatory since January 2002 up today. By means of a linear combination of the flare rates computed on the base of some properties of the sunspot groups, like area, number of pores and sunspots, Zurich class, relative importance between leading spot and density of the sunspot population, and type of penumbra of the main sunspot, we determine the probability percentages that a flare of a particular energy range may occur. Comparing our forecasts with the flares registered by GOES satellites in the 1–8 Å X-ray band during the subsequent 24 h we measured the performance of our method. We found that this method, which combines some morphological parameters and a statistical technique, has the best performances for the strongest events, which are more interesting for their implications in the Earth environment

High-resolution observations of a light bridge in a decaying sunspot

Light brigde are small-scale structures observed in the solar photosphere which separate the umbra of a sunspot in two or more parts. On 6 August 2011, we observed at the Swedish 1-m Solar Telescope a large sunspot of the Active Region NOAA 11263 with a light bridge. We acquired full Stokes profiles over the Fe I line at 630.25 nm and spectroscopic data along the Fe I line profile at 557.6 nm for about an hour, from 09:53:32 UT to 10:48:43 UT. Data in the core of the Ca II H line at 396.8 nm were simultaneously acquired. The Active Region was also observed by SDO and SOT/HINODE to study the dynamics and the magnetic evolution of the light bridge. Thanks to these high-resolution observations the fine structure of this element and its properties are better studied to determine the physical processes behind its formation