300 research outputs found
H-alpha features with hot onsets. II. A contrail fibril
The solar chromosphere observed in H-alpha consists mostly of narrow fibrils.
The longest typically originate in network or plage and arch far over adjacent
internetwork. We use data from multiple telescopes to analyze one well-observed
example in a quiet area. It resulted from the earlier passage of an
accelerating disturbance in which the gas was heated to high temperature as in
the spicule-II phenomenon. After this passage a dark H-Halpha fibril appeared
as a contrail. We use Saha-Boltzmann extinction estimation to gauge the onset
and subsequent visibilities in various diagnostics and conclude that such
H-alpha fibrils can indeed be contrail phenomena, not indicative of the
thermodynamic and magnetic environment when they are observed but of more
dynamic happenings before. They do not connect across internetwork cells but
represent launch tracks of heating events and chart magnetic field during
launch, not at present.Comment: Accepted for Astronomy & Astrophysic
Characterization and formation of on-disk spicules in the Ca II K and Mg II k spectral lines
We characterize, for the first time, type-II spicules in Ca II K 3934\AA\
using the CHROMIS instrument at the Swedish 1-m Solar Telescope. We find that
their line formation is dominated by opacity shifts with the K minimum
best representing the velocity of the spicules. The K features are either
suppressed by the Doppler-shifted K or enhanced via an increased
contribution from the lower layers, leading to strongly enhanced but un-shifted
K peaks, with widening towards the line-core as consistent with
upper-layer opacity removal via Doppler-shift. We identify spicule spectra in
concurrent IRIS Mg II k 2796\AA\ observations with very similar properties.
Using our interpretation of spicule chromospheric line-formation, we produce
synthetic profiles that match observations.Comment: 10 pages, 8 figures, accepted for publication in Astronomy and
Astrophysics Letter
Surges and Si IV bursts in the solar atmosphere. Understanding IRIS and SST observations through RMHD experiments
Surges often appear as a result of the emergence of magnetized plasma from
the solar interior. Traditionally, they are observed in chromospheric lines
such as H 6563 \AA and Ca II 8542 \AA. However, whether there is a
response to the surge appearance and evolution in the Si IV lines or, in fact,
in many other transition region lines has not been studied. In this paper we
analyze a simultaneous episode of an H surge and a Si IV burst that
occurred on 2016 September 03 in active region AR12585. To that end, we use
coordinated observations from the Interface Region Imaging Spectrograph (IRIS)
and the Swedish 1-m Solar Telescope (SST). For the first time, we report
emission of Si IV within the surge, finding profiles that are brighter and
broader than the average. Furthermore, the brightest Si IV patches within the
domain of the surge are located mainly near its footpoints. To understand the
relation between the surges and the emission in transition region lines like Si
IV, we have carried out 2.5D radiative MHD (RMHD) experiments of magnetic flux
emergence episodes using the Bifrost code and including the non-equilibrium
ionization of silicon. Through spectral synthesis we explain several features
of the observations. We show that the presence of Si IV emission patches within
the surge, their location near the surge footpoints and various observed
spectral features are a natural consequence of the emergence of magnetized
plasma from the interior to the atmosphere and the ensuing reconnection
processes.Comment: 13 pages, 8 figures. The Astrophysical Journal (Accepted
Ellerman Bombs at high resolution: I. Morphological evidence for photospheric reconnection
High-resolution imaging-spectroscopy movies of solar active region NOAA 10998
obtained with the CRisp Imaging SpectroPolarimeter (CRISP) at the Swedish 1-m
Solar Telescope show very bright, rapidly flickering, flame-like features that
appear intermittently in the wings of the Balmer H-alpha line in a region with
moat flows and likely some flux emergence. They show up at regular H-alpha
blue-wing bright points that outline magnetic network, but flare upward with
much larger brightness and distinct "jet" morphology seen from aside in the
limbward view of these movies. We classify these features as Ellerman bombs and
present a morphological study of their appearance at the unprecedented spatial,
temporal, and spectral resolution of these observations. The bombs appear along
magnetic network with footpoint extents up to 900km. They show apparent travel
away from the spot along the pre-existing network at speeds of about 1 km/s.
The bombs flare repetitively with much rapid variation at time scales of
seconds only, in the form of upward jet-shaped brightness features. These reach
heights of 600-1200km and tend to show blueshifts; some show bi-directional
Doppler signature, and some seem accompanied with an H-alpha surge. They are
not seen in the core of H-alpha due to shielding by overlying chromospheric
fibrils. The network where they originate has normal properties. The morphology
of these jets strongly supports deep-seated photospheric reconnection of
emergent or moat-driven magnetic flux with pre-existing strong vertical network
fields as the mechanism underlying the Ellerman bomb phenomenon.Comment: 13pages, 10 figures, 2 tables. Accepted for publication in the
Astrophysical Journa
- …