Author name code: merenda ADS astronomy entries on 2022-09-14 author:"Merenda, Laura" ------------------------------------------------------------------------ Title: Configuración magnética preeruptiva de la región NOAA 12127 mediante extrapolación no lineal del campo Authors: Merenda, L. A.; Iglesias, F. A.; Mandrini, C. H.; Cremades, H. Bibcode: 2021BAAA...62...19M Altcode: We studied the magnetic properties of active region NOAA 12127 previous to a M1.5-class flare, that was accompanied by a coronal mass ejection, on the August 1, 2014. We estimated the pre-eruptive coronal magnetic field using a non-linear force-free extrapolation, and compared the results with images in Hα and 171 Å. The extrapolated field is able to reproduce the general morphology of the magnetic configurations linked to a filament and several coronal loops identified. Title: Asymmetric expansion of coronal mass ejections in the low corona Authors: Cremades, H.; Iglesias, F. A.; Merenda, L. A. Bibcode: 2020A&A...635A.100C Altcode: 2020arXiv200110085C
Aims: Understanding how magnetic fields are structured within coronal mass ejections (CMEs), and how they evolve from the low corona into the heliosphere, is a major challenge for space weather forecasting and for solar physics. The study of CME morphology is a particularly auspicious approach to this problem, given that it holds a close relationship with the CME magnetic field configuration. Although earlier studies have suggested an asymmetry in the width of CMEs in orthogonal directions, this has not been inspected using multi-viewpoint observations.
Methods: The improved spatial, temporal, and spectral resolution, added to the multiple vantage points offered by missions of the Heliophysics System Observatory, constitute a unique opportunity to gain insight into this regard. We inspect the early evolution (below ten solar radii) of the morphology of a dozen CMEs occurring under specific conditions of observing spacecraft location and CME trajectory, favorable to reduce uncertainties typically involved in the 3D reconstruction used here. These events are carefully reconstructed by means of a forward modeling tool using simultaneous observations of the Solar-Terrestrial Relations Observatory (STEREO) Extreme Ultraviolet Imager and the Solar Dynamics Observatory Atmospheric Imaging Assembly as input when originating low in the corona, and followed up in the outer fields of view of the STEREO and the Solar and Heliospheric Observatory coronagraphs. We then examine the height evolution of the morphological parameters arising from the reconstructions.
Results: The multi-viewpoint analysis of this set of CMEs revealed that their initial expansion - below three solar radii - is considerably asymmetric and non-self-similar. Both angular widths, namely along the main axes of CMEs (AWL) and in the orthogonal direction (AWD, representative of the flux rope diameter), exhibit much steeper change rates below this height, with the growth rate of AWL found to be larger than that of AWD, also below that height. Angular widths along the main axes of CMEs are on average ≈1.8 times larger than widths in the orthogonal direction AWD. The ratios of the two expansion speeds, namely in the directions of CMEs main axes and in their orthogonal, are nearly constant in time after ∼4 solar radii, with an average ratio ≈1.6. Heights at which the width change rate is defined to stabilize are greater for AWL than for AWD. Title: Expansión y autosimilitud de eyecciones coronales de masa a partir de observaciones estereoscópicas Authors: Cremades, H.; Iglesias, F. A.; Merenda, L. A.; López, F. M.; Cabello, I. Bibcode: 2019BAAA...61...41C Altcode: Coronal mass ejections (CMEs) constitute the most spectacular dynamic events in the solar system, and are key players in determining space weather conditions. Given that the ocurrence of a CME has so far been impossible to predict, the best attempt at forecasting is then to assess their impact with the best possible accuracy. In this respect, understanding how magnetic fields are organized within CMEs, and how they evolve from the low corona into the heliosphere, is crucial. Exceptional ongoing solar missions, such as STEREO, SOHO, and SDO, provide a unique opportunity to shed light into this aspect. The STEREOscopic-view images provided by the STEREO/SECCHI suite in combination with images from Earth’s perspective recorded by SDO/AIA and SOHO/LASCO enable the analysis of CME evolution from their birth in the low corona. The set of CMEs uder study arises from an appropriate combination of spacecraft vantage points and CME propagation direction, which is helpful to reduce uncertainties in their forward modeling. These events are carefully analyzed as they originate low in the corona by means of simultaneous observations of STEREO/EUVI and SDO/AIA, and followed up to the outer fields of view of the STEREO and SOHO coronagraphs. In particular, we examine the evolution of their global magnetic field configuration, and how CMEs expand along the direction of their main symmetry axis and orthogonal to it. Title: A long-duration active region: Evolution and quadrature observations of ejective events Authors: Cremades, H.; Mandrini, C. H.; Fuentes, M. C. López; Merenda, L.; Cabello, I.; López, F. M.; Poisson, M. Bibcode: 2017IAUS..327...60C Altcode: Unknown aspects of the initiation, evolution, and associated phenomena of coronal mass ejections (CMEs), together with their capability of perturbing the fragile technological equilibrium on which nowadays society depends, turn them a compelling subject of study. While space weather forecasts are thus far not able to predict when and where in the Sun will the next CME take place, various CME triggering mechanisms have been proposed, without reaching consensus on which is the predominant one. To improve our knowledge in these respects, we investigate a long-duration active region throughout its life, from birth until decay along five solar rotations, in connection with its production of ejective events. We benefit from the wealth of solar remote-sensing data with improved temporal, spatial, and spectral resolution provided by the ground-breaking space missions STEREO, SDO, and SOHO. During the investigated time interval, which covers the months July - November 2010, the STEREO spacecraft were nearly 180 degrees apart, allowing for the uninterrupted tracking of the active region and its ensuing CMEs. The ejective aspect is examined from multi-viewpoint coronagraphic images, while the dynamics of the active region photospheric magnetic field are inspected by means of SDO/HMI data for specific subintervals of interest. The ultimate goal of this work in progress is to identify common patterns in the ejective aspect that can be connected with the active region characteristics. Title: Erratum:"Convective Nature of Sunspot Penumbral Filaments: Discovery of Downflows in the Deep Photosphere" (2011, ApJ, 734, L18) Authors: Joshi, Jayant; Pietarila, A.; Hirzberger, J.; Solanki, S. K.; Aznar Cuadrado, R.; Merenda, L. Bibcode: 2011ApJ...740L..55J Altcode: No abstract at ADS Title: The height of chromospheric loops in an emerging flux region Authors: Merenda, L.; Lagg, A.; Solanki, S. K. Bibcode: 2011A&A...532A..63M Altcode: 2012arXiv1202.1113M Context. The chromospheric layer observable with the He i 10 830 Å triplet is strongly warped. The analysis of the magnetic morphology of this layer therefore requires a reliable technique to determine the height at which the He i absorption takes place.
Aims: The He i absorption signature connecting two pores of opposite polarity in an emerging flux region is investigated. This signature is suggestive of a loop system connecting the two pores. We aim to show that limits can be set on the height of this chromospheric loop system.
Methods: The increasing anisotropy in the illumination of a thin, magnetic structure intensifies the linear polarization signal observed in the He i triplet with height. This signal is altered by the Hanle effect. We apply an inversion technique incorporating the joint action of the Hanle and Zeeman effects, with the absorption layer height being one of the free parameters.
Results: The observed linear polarization signal can be explained only if the loop apex is higher than ≈ 5 Mm. Best agreement with the observations is achieved for a height of 6.3 Mm.
Conclusions: The strength of the linear polarization signal in the loop apex is inconsistent with the assumption of a He i absorption layer at a constant height level. The determined height supports the earlier conclusion that dark He 10 830 Å filaments in emerging flux regions trace emerging loops. Title: Convective Nature of Sunspot Penumbral Filaments: Discovery of Downflows in the Deep Photosphere Authors: Joshi, Jayant; Pietarila, A.; Hirzberger, J.; Solanki, S. K.; Aznar Cuadrado, R.; Merenda, L. Bibcode: 2011ApJ...734L..18J Altcode: 2011arXiv1105.1877J We study the velocity structure of penumbral filaments in the deep photosphere to obtain direct evidence for the convective nature of sunspot penumbrae. A sunspot was observed at high spatial resolution with the 1 m Swedish Solar Telescope in the deep photospheric C I 5380 Å absorption line. The Multi-Object Multi-Frame Blind Deconvolution method is used for image restoration and straylight is filtered out. We report here the discovery of clear redshifts in the C I 5380 Å line at multiple locations in sunspot penumbral filaments. For example, bright head of filaments show larger concentrated blueshift and are surrounded by darker, redshifted regions, suggestive of overturning convection. Elongated downflow lanes are also located beside bright penumbral fibrils. Our results provide the strongest evidence yet for the presence of overturning convection in penumbral filaments and highlight the need to observe the deepest layers of the penumbra in order to uncover the energy transport processes taking place there. Title: Internetwork Horizontal Magnetic Fields in the Quiet Sun Chromosphere: Results from a Joint Hinode/VTT Study Authors: Lagg, A.; Ishikawa, R.; Merenda, L.; Wiegelmann, T.; Tsuneta, S.; Solanki, S. K. Bibcode: 2009ASPC..415..327L Altcode: We present results from a joint Hinode/VTT campaign (May 2008). Spectropolarimetric data of a quiet Sun super-granular network cell at a heliocentric angle of 28° in the He I 10830 Å line were analyzed using an inversion code incorporating Hanle and Zeeman effects (HeLIx^+) to retrieve magnetic field strength and direction in the upper chromosphere. Simultaneously recorded Hinode SOT/SP data reveal the photospheric magnetic field morphology, clearly showing magnetic flux concentrations in the internetwork. The photospheric magnetic field maps are used to feed potential field extrapolations similar to the work by Schrijver & Title (2003). The extrapolated magnetic field structure is compared with the magnetic field configuration resulting from the He 10830 inversions. These inversions also reveal horizontal magnetic structures extending over a length of up to 20 Mm above the internetwork, indicative of the presence of a magnetic canopy. The photospheric magnetic flux concentrations in the internetwork are obviously not sufficiently strong to prevent the formation of a canopy at chromospheric heights. Title: Diagnóstico de campos magnéticos en estructuras de la cormosfera y corona del sol mediante los efectos Hanle y Zeeman Title: Diagnóstico de campos magnéticos en estructuras de la cormosfera y corona del sol mediante los efectos Hanle y Zeeman Title: Diagnosis of magnetic fields in structures of the solar cormosphere and corona through the Hanle and Zeeman effects; Authors: Merenda, Laura Bibcode: 2008PhDT.......407M Altcode: No abstract at ADS Title: A Magnetic Map of a Solar Filament Authors: Merenda, L.; Trujillo Bueno, J.; Collados, M. Bibcode: 2007ASPC..368..347M Altcode: One of the most useful diagnostic tools for the detection of inclined magnetic fields in solar chromospheric and coronal structures is that based on the fact that the Hanle effect in forward scattering at the solar disk center creates linear polarization in some spectral lines, such as those of the He I 10830 Å multiplet. Here we show the preliminary results of an ongoing investigation on the magnetic field of a solar filament, based on the inversion of spectropolarimetric observations obtained with the Tenerife Infrared Polarimeter. Title: The Magnetic Field of Solar Chromospheric Spicules Authors: Trujillo Bueno, J.; Ramelli, R.; Merenda, L.; Bianda, M. Bibcode: 2007ASPC..368..161T Altcode: A suitable diagnostic tool for investigating the magnetism of the solar chromosphere is the observation and theoretical modeling of the Hanle and Zeeman effects in solar spicules. In our presentation we highlighted the great scientific interest of this new diagnostic window by showing how the magnetic field vector can be inferred from spectropolarimetric observations of solar chromospheric spicules in several spectral lines, such as those of the 10830 Å and 5876 Å multiplets of neutral helium. Our off-limb spectropolarimetric observations of the He I 10830 Å multiplet were obtained with the Tenerife Infrared Polarimeter (TIP) attached to the Vacuum Tower Telescope at the Observatorio del Teide (Tenerife), while those of the 5876 Å multiplet resulted from observations with the Zurich Imaging Polarimeter (ZIMPOL) at the Gregory Coudé Telescope of the Istituto Ricerche Solari Locarno. The application of a Stokes profiles inversion technique led to the following conclusion. In quiet Sun spicules the magnetic field vector at a height of about 2000 km above the solar visible ``surface" has a typical strength of the order to 10 G and is inclined by approximately 35° with respect to the solar local vertical direction. In spicules observed close to active regions the strength of the magnetic field was of the order of 50 G. The two figures below show the off-limb Stokes profiles of the He I 5876 Å multiplet observed in a quiet region (upper figure) and close to an active region (lower figure). Note that in both cases Stokes U is non-zero, which is the observational signature of the Hanle effect of an inclined magnetic field. The change of sign in Stokes U along the spatial direction of the spectrograph's slit can be explained by variations in the azimuth of the magnetic field vector. Interestingly, while the Stokes V profiles corresponding to the observed quiet region are caused by the alignment-to-orientation transfer mechanism (see, e.g., page 607 of Landi Degl'Innocenti & Landolfi 2004), that observed in the spicules close to the active region is dominated by the longitudinal Zeeman effect. The interested reader will find more information in the papers by Trujillo Bueno et al. (2005) and by Ramelli et al. (2006). Title: Spectro-Polarimetry of Solar Prominences Authors: Ramelli, R.; Bianda, M.; Trujillo Bueno, J.; Merenda, L.; Stenflo, J. O. Bibcode: 2006ASPC..358..471R Altcode: 2009arXiv0906.2342R A large set of high-precision, full-Stokes spectro-polarimetric observations of prominences in He I D3, Hα, and Hβ lines has been recorded with the ZIMPOL polarimeter at the Gregory-Coudé Telescope in Locarno. The observational technique allows us to obtain measurements free from seeing-induced spurious effects. The instrumental polarization is well under control and taken into account in the data analysis. We present our observational results for each of the lines mentioned above. Of particular interest is that most of our Hα measurements show

antisymmetric V profiles that are a characteristic signature of the Zeeman effect in the prominence plasma. A Stokes inversion technique based on the quantum theory of the Hanle and Zeeman effects is being applied on observed Stokes profiles in the He I D3 line in order to obtain information on the magnetic field vector that confines the prominence plasma. Title: The Hanle and Zeeman Effects in Solar Spicules Authors: Ramelli, R.; Bianda, M.; Merenda, L.; Trujillo Bueno, T. Bibcode: 2006ASPC..358..448R Altcode: 2009arXiv0906.2340R A large set of high precision full-Stokes spectro-polarimetric observations of the He I D3 line in spicules has been recorded with the ZIMPOL polarimeter at the Gregory-Coudé Telescope in Locarno. The observational technique allows us to obtain measurements free from seeing-induced spurious effects. The instrumental polarization is well under control and taken into account in the data analysis. The observed Stokes profiles are interpreted according to the quantum theory of the Hanle and Zeeman effects with the aim of obtaining information on the magnetic field vector. To this end, we make use of a suitable Stokes inversion technique. The results are presented giving emphasis on a few particularly interesting measurements which show clearly the operation of the Hanle and Zeeman effects in solar chromospheric spicules. Title: Determination of the Magnetic Field Vector via the Hanle and Zeeman Effects in the He I λ10830 Multiplet: Evidence for Nearly Vertical Magnetic Fields in a Polar Crown Prominence Authors: Merenda, L.; Trujillo Bueno, J.; Landi Degl'Innocenti, E.; Collados, M. Bibcode: 2006ApJ...642..554M Altcode: The magnetic field is the key physical quantity responsible for the formation, stability, and evolution of solar prominences (ribbons of cool dense gas embedded in the hot tenuous corona). Therefore, it is important to obtain good empirical knowledge of the three-dimensional structure of prominence magnetic fields. Here we show how the magnetic field vector can be inferred via the physical interpretation of spectropolarimetric observations in the He I λ10830 multiplet. To this end, we have developed an inversion code based on the quantum theory of the Hanle and Zeeman effects and on a few modeling assumptions. We show an application to full Stokes vector observations of a polar crown prominence that, in the slit-jaw Hα image, showed nearly vertical plasma structures. Our results provide evidence for magnetic fields on the order of 30 G inclined by about 25° with respect to the local solar vertical direction. Of additional interest is that the inferred nearly vertical magnetic field vector appears to be slightly rotating around a fixed direction in space as one proceeds along the direction of the spectrograph's slit. While these results provide new light on the three-dimensional geometry of the magnetic fields that confine the plasma of polar crown prominences, they also urge us to develop improved solar prominence models and to pursue new diagnostic investigations. Title: Determination of the Magnetic Field Vector in a Polar Crown Prominence via the Hanle and Zeeman Effects in the He I 10830 Å Multiplet. Authors: Merenda, L.; Trujillo Bueno, J.; Landi Degl'Innocenti, E.; Collados, M. Bibcode: 2005ESASP.596E..18M Altcode: 2005ccmf.confE..18M No abstract at ADS Title: Spectropolarimetric Observations of Prominences and Spicules, and Magnetic Field Diagnostics Authors: Ramelli, R.; Bianda, M.; Trujillo Bueno, J.; Merenda, L.; Stenflo, J. O. Bibcode: 2005ESASP.596E..82R Altcode: 2005ccmf.confE..82R No abstract at ADS Title: The Hanle and Zeeman Effects in Solar Spicules: A Novel Diagnostic Window on Chromospheric Magnetism Authors: Trujillo Bueno, J.; Merenda, L.; Centeno, R.; Collados, M.; Landi Degl'Innocenti, E. Bibcode: 2005ApJ...619L.191T Altcode: 2005astro.ph..1533T; 2005astro.ph..1533B An attractive diagnostic tool for investigating the magnetism of the solar chromosphere is the observation and theoretical modeling of the Hanle and Zeeman effects in spicules, as shown in this Letter for the first time. Here we report on spectropolarimetric observations of solar chromospheric spicules in the He I λ10830 multiplet and on their theoretical modeling accounting for radiative transfer effects. We find that the magnetic field in the observed (quiet-Sun) spicular material at a height of about 2000 km above the visible solar surface has a strength of the order of 10 G and is inclined by approximately 35deg with respect to the local vertical direction. Our empirical finding based on full Stokes vector spectropolarimetry should be taken into account in future magnetohydrodynamical simulations of spicules. Title: Selective absorption processes as the origin of puzzling spectral line polarization from the Sun Authors: Trujillo Bueno, J.; Landi Degl'Innocenti, E.; Collados, M.; Merenda, L.; Manso Sainz, R. Bibcode: 2002Natur.415..403T Altcode: 2002astro.ph..1409T Magnetic fields play a key role in most astrophysical systems, from the Sun to active galactic nuclei. They can be studied through their effects on atomic energy levels, which produce polarized spectral lines. In particular, anisotropic radiation `pumping' processes (which send electrons to higher atomic levels) induce population imbalances that are modified by weak magnetic fields. Here we report peculiarly polarized light in the HeI 10,830-Å multiplet observed in a coronal filament located at the centre of the solar disk. We show that the polarized light arises from selective absorption from the ground level of the triplet system of helium, and that it implies the presence of magnetic fields of the order of a few gauss that are highly inclined with respect to the solar radius vector. This disproves the common belief that population imbalances in long-lived atomic levels are insignificant in the presence of inclined fields of the order of a few gauss, and opens up a new diagnostic window for the investigation of solar magnetic fields. Title: A study of AE UMa: Is it a δ Scuti variable? Authors: Martín-Luis, F.; García, A.; Rey, M.; Merenda, L. Bibcode: 2001hsa..conf..388M Altcode: No abstract at ADS