23 research outputs found
The pre-penumbral magnetic canopy in the solar atmosphere
Penumbrae are the manifestation of magnetoconvection in highly inclined (to the vertical direction)
magnetic field. The penumbra of a sunspot tends to form, initially, along the arc of the umbra
antipodal to the main region of flux emergence. The question of how highly inclined magnetic field
can concentrate along the antipodal curves of umbrae, at least initially, remains to be answered.
Previous observational studies have suggested the existence of some form of overlying magnetic canopy
which acts as the progenitor for penumbrae. We propose that such overlying magnetic canopies are
a consequence of how the magnetic field emerges into the atmosphere and are, therefore, part of the
emerging region. We show, through simulations of twisted flux tube emergence, that canopies of
highly inclined magnetic field form preferentially at the required locations above the photosphere
IRIS observations of magnetic interactions in the solar atmosphere between pre-existing and emerging magnetic fields. II. UV emission properties
Multi-wavelength ultraviolet (UV) observations by the IRIS satellite in
active region NOAA 12529 have recently pointed out the presence of long-lasting
brightenings, akin to UV bursts, and simultaneous plasma ejections occurring in
the upper chromosphere and transition region during secondary flux emergence.
These signatures have been interpreted as evidence of small-scale, recurrent
magnetic reconnection episodes between the emerging flux region (EFR) and the
pre-existing plage field. Here, we characterize the UV emission of these
strong, intermittent brightenings and we study the surge activity above the
chromospheric arch filament system (AFS) overlying the EFR. We analyze the
surges and the cospatial brightenings observed at different wavelengths. We
find an asymmetry in the emission between the blue and red wings of the Si IV
1402 \AA{} and Mg II k 2796.3 \AA{} lines, which clearly outlines the dynamics
of the structures above the AFS that form during the small-scale eruptive
phenomena. We also detect a correlation between the Doppler velocity and
skewness of the Si IV 1394 \AA{} and 1402 \AA{} line profiles in the UV burst
pixels. Finally, we show that genuine emission in the Fe XII 1349.4 \AA{} line
is cospatial to the Si IV brightenings. This definitely reveals a pure coronal
counterpart to the reconnection event.Comment: 19 pages, 8 figures + 3 figures in the Appendix; accepted in Ap
PENUMBRAL-LIKE FILAMENTS IN THE SOLAR PHOTOSPHERE AS A MANIFESTATION OF FLUX EMERGENCE
Rare observations of the solar photosphere show the appearance of orphan penumbrae, filamentary structures very similar to a bundle of sunspot penumbral filaments not connected to any umbra. Lim et al. found an orphan penumbra in active region NOAA 11391 near a mature sunspot. We analyze a different data set to study the same structure using the Solar Optical Telescope on board the Hinode satellite. Spectropolarimetric measurements along the Fe I 630.2 nm pair, complemented by G-band and Ca II H filtergrams, show the evolution of this penumbral-like structure and reveal that an emerging flux region is its ancestor. We find new evidence for the interaction between the emerging flux and the pre-existing field that leads to a brightening observed near the base of the chromosphere. Our analysis suggests that as a result of the combination of photospheric flux emergence and magneto-convection in inclined fields the horizontal component of the emerging field can be trapped in the photosphere by the overlying fields and form a structure resembling penumbral filaments
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 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 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
Evolution of the Magnetic Field Inclination in a Forming Penumbra
We describe the evolution of the magnetic and velocity fields in the annular zone around a pore a few hours before the formation of its penumbra. We detected the presence of several patches at the edge of the annular zone, with a typical size of about 1''. These patches are characterized by a rather vertical magnetic field with polarity opposite to that of the pore. They correspond to regions of plasma upflow up to 2.5 km s–1 and are characterized by radially outward displacements with horizontal velocities up to 2 km s–1. We interpret these features as portions of the pore magnetic field lines returning beneath the photosphere being progressively stretched and pushed down by the overlying magnetic fields. Our results confirm that the penumbra formation results from changes in the inclination of the field lines in the magnetic canopy overlying the pore, until they reach the photosphere
VELOCITY AND MAGNETIC FIELD DISTRIBUTION IN A FORMING PENUMBRA
We present results from the analysis of high-resolution spectropolarimetric and spectroscopic observations of the solar photosphere and chromosphere, obtained shortly before the formation of a penumbra in one of the leading polarity sunspots of NOAA active region 11490. The observations were performed at the Dunn Solar Telescope of the National Solar Observatory on 2012 May 28, using the Interferometric Bidimensional Spectrometer. The data set is comprised of a 1 hr time sequence of measurements in the Fe I 617.3 nm and Fe I 630.25 nm lines (full Stokes polarimetry) and in the Ca II 854.2 nm line (Stokes I only). We perform an inversion of the Fe I 630.25 nm Stokes profiles to derive magnetic field parameters and the line-of-sight (LOS) velocity at the photospheric level. We characterize chromospheric LOS velocities by the Doppler shift of the centroid of the Ca II 854.2 nm line. We find that, before the formation of the penumbra, an annular zone of 3''-5'' width is visible around the sunspot. In the photosphere, we find that this zone is characterized by an uncombed structure of the magnetic field although no visible penumbra has formed yet. We also find that the chromospheric LOS velocity field showsmore » several elongated structures characterized by downflow and upflow motions in the inner and outer parts of the annular zone, respectively.« les
The Solar Particle Acceleration Radiation and Kinetics (SPARK) Mission Concept
© 2023by the authors. Licensee MDPI, Basel, Switzerland. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/Particle acceleration is a fundamental process arising in many astrophysical objects, including active galactic nuclei, black holes, neutron stars, gamma-ray bursts, accretion disks, solar and stellar coronae, and planetary magnetospheres. Its ubiquity means energetic particles permeate the Universe and influence the conditions for the emergence and continuation of life. In our solar system, the Sun is the most energetic particle accelerator, and its proximity makes it a unique laboratory in which to explore astrophysical particle acceleration. However, despite its importance, the physics underlying solar particle acceleration remain poorly understood. The SPARK mission will reveal new discoveries about particle acceleration through a uniquely powerful and complete combination of γ-ray, X-ray, and EUV imaging and spectroscopy at high spectral, spatial, and temporal resolutions. SPARK’s instruments will provide a step change in observational capability, enabling fundamental breakthroughs in our understanding of solar particle acceleration and the phenomena associated with it, such as the evolution of solar eruptive events. By providing essential diagnostics of the processes that drive the onset and evolution of solar flares and coronal mass ejections, SPARK will elucidate the underlying physics of space weather events that can damage satellites and power grids, disrupt telecommunications and GPS navigation, and endanger astronauts in space. The prediction of such events and the mitigation of their potential impacts are crucial in protecting our terrestrial and space-based infrastructure.Peer reviewe