25 research outputs found
On the fine structure of the quiet solar \Ca II K atmosphere
We investigate the morphological, dynamical, and evolutionary properties of
the internetwork and network fine structure of the quiet sun at disk centre.
The analysis is based on a 6 h time sequence of narrow-band filtergrams
centred on the inner-wing \Ca II K reversal at 393.3 nm. The results
for the internetwork are related to predictions derived from numerical
simulations of the quiet sun. The average evolutionary time scale of the
internetwork in our observations is 52 sec. Internetwork grains show a tendency
to appear on a mesh-like pattern with a mean cell size of 4-5 arcsec.
Based on this size and the spatial organisation of the mesh we speculate that
this pattern is related to the existence of photospheric downdrafts as
predicted by convection simulations. The image segmentation shows that typical
sizes of both network and internetwork grains are in the order of 1.6 arcs.Comment: 8 pages, 9 figure
Science with Large Solar Telescopes: Overview of SpS 6
With several large aperture optical and IR telescopes just coming on-line, or scheduled for the near future, solar physics is on the verge of a quantum leap in observational capabilities. An efficient use of such facilities will require new and innovative approaches to both observatory operations and data handling.
This two-days long Special Session discussed the science expected with large solar telescopes, and started addressing the strategies necessary to optimize their scientific return. Cutting edge solar science as derived from state-of-the-art observations and numerical simulations and modeling was presented, and discussions were held on the role of large facilities in satisfying the demanding requirements of spatial and temporal resolution, stray-light correction, and spectro-polarimetric accuracy. Building on the experience of recently commissioned telescopes, critical issues for the development of future facilities were discussed. These included operational issues peculiar to large telecopes as well as strategies for their best use
Magnetic fields and plasma heating in the Sun's atmosphere
We use the first publically available data from the Daniel K. Inouye Solar
Telescope (DKIST) to track magnetic connections from the solar photosphere into
the corona. We scrutinize relationships between chromospheric magnetism and
bright chromospheric, transition region and coronal plasmas. In June 2022, the
Visible Spectro-Polarimeter (ViSP) instrument targeted unipolar network within
a decaying active region. ViSP acquired rastered scans with longitudinal Zeeman
sensitivities of 0.25 Mx/cm2 (Fe I 630.2 nm) and 0.5 Mx/cm2 (Ca II 854.2 nm).
ViSP was operated in a "low" resolution mode (0.214" slit width, spectral
resolution R ~ 70,000) to produce polarization maps over a common area of 105"
x 50". Data from SDO and IRIS are combined to ask: Why is only a fraction of
emerging flux filled with heated plasma? What is the elemental nature of the
plasmas? No correlations were found between heated plasma and properties of
chromospheric magnetic fields derived from the WFA, on scales below
supergranules. Processes hidden from our observations control plasma heating.
While improved magnetic measurements are needed, these data indicate that "the
corona is a self-regulating forced system" (Einaudi et al. 2021). Heating
depends on the state of the corona, not simply on boundary conditions. Heating
models based upon identifiable bipolar fields, including cool loops, tectonics
and observable magnetic reconnection, are refuted for these regions with
unipolar chromospheric magnetic fields
Spectral Signatures of Penumbral Transients
In this work we investigate the properties of penumbral transients observed in the upper photospheric and chromospheric region above a sunspot penumbra using two-dimensional spectroscopic observations of the Ca II 854.21 nm line with a 5 s cadence. In our 30 minutes of observations, we identify several penumbral-micro jets (PMJs) with cotemporal observations from Dunn Solar Telescope/IBIS and Hinode/SOT. We find that the line profiles of these PMJ events show emission in the two wings of the line (±0.05 nm), but little modification of the line core. These are reminiscent of the line profiles of Ellerman bombs observed in plage and network regions. Furthermore, we find evidence that some PMJ events have a precursor phase starting 1 minute prior to the main brightening that might indicate initial heating of the plasma prior to an acoustic or bow shock event. With the IBIS data, we also find several other types of transient brightenings with timescales of less than 1 minute that are not clearly seen in the Hinode/SOT data. The spectral profiles and other characteristics of these events are significantly different from those of PMJs. The different appearances of all these transients are an indicator of the general complexity of themore » chromospheric magnetic field and underscore the highly dynamic behavior above sunspots. It also highlights the care that is needed in interpreting broadband filter images of chromospheric lines, which may conceal very different spectral profiles, and the underlying physical mechanisms at work.« les