257 research outputs found
The dynamics of 3-minute wavefronts and their relation to sunspot magnetic fields
We present a study of wave processes occurring in solar active region NOAA
11131 on 2010 December 10, captured by the Solar Dynamics Observatory in the
1600A, 304A, and 171A channels. For spectral analysis we employed pixelised
wavelet filtering together with a developed digital technique based on
empirical mode decomposition. We studied the 3-minute wave dynamics to obtain
relationships with the magnetic structuring of the underlying sunspot. We found
that during development of wave trains the motion path occurred along a
preferential direction, and that the broadband wavefronts can be represented as
a set of separate narrowband oscillation sources. These sources become visible
as the waves pass through the umbral inhomogeneities caused by the differing
magnetic field inclination angles. We found the spatial and frequency
fragmentation of wavefronts, and deduced that the combination of narrowband
spherical and linear parts of the wavefronts provide the observed spirality.
Maps of the magnetic field inclination angles confirm this assumption. We
detect the activation of umbral structures as the increasing of oscillations in
the sources along the front ridge. Their temporal dynamics are associated with
the occurrence of umbral flashes. Spatial localisation of the sources is stable
over time and depends on the oscillation period. We propose that these sources
are the result of wave paths along the loops extending outwards from the
magnetic bundles of the umbra.Comment: 18 pages, 8 figures, accepted to publication in Royal Society
Philosophical Transactions
Multi-wavelength observations of the 2014 June 11 M3.9 flare:Temporal and spatial characteristics
We present multi-wavelength observations of an M-class flare (M3.9) that
occurred on 2014 June 11. Our observations were conducted with the Dunn Solar
Telescope (DST), adaptive optics, the multi-camera system ROSA (Rapid
Oscillations in Solar Atmosphere) and new HARDcam (Hydrogen-Alpha Rapid
Dynamics) camera in various wavelengths, such as Ca~II~K, Mg~I~b (at 5172.7
Ang), and H narrow-band, and G-band continuum filters. Images were
re-constructed using the Kiepencheuer-Institut Speckle Interferometry Package
(KISIP) code, to improve our image resolution. We observed intensity increases
of 120-150% in the Mg, Ca~K and H narrow band filters during
the flare. Intensity increases for the flare observed in the SDO EUV channels
were several times larger, and the GOES X-rays increased over a factor of 30
for the harder band. Only a modest delay is found between the onset of flare
ribbons of a nearby sympathetic flare and the main flare ribbons observed in
these narrow-band filters. The peak flare emission occurs within a few seconds
for the Ca~K, Mg, and H bands. Time-distance techniques find
propagation velocities of 60 km/s for the main flare ribbon and as
high as 300 km/s for smaller regions we attribute to filament eruptions. This
result and delays and velocities observed with SDO (100 km/s) for
different coronal heights agree well with the simple model of energy
propagation versus height, although a more detailed model for the flaring solar
atmosphere is needed. And finally, we detected marginal quasi-periodic
pulsations (QPPs) in the 40--60 second range for the Ca~K, Mg and H
bands, and such measurements are important for disentangling the detailed
flare-physics.Comment: 16 Pages, 7 Figures, 1 Table (1 video in on-line journal); Accepted
in Research in Astronomy and Astrophysic
Hα and EUV observations of a partial CME
We have obtained Hα high spatial and time resolution observations of the upper solar chromosphere and supplemented these with multi-wavelength observations from the Solar Dynamics Observatory (SDO) and the Hinode Extreme-ultraviolet Imaging Spectrometer. The Hα observations were conducted on 2012 February 11 with the Hydrogen-Alpha Rapid Dynamics Camera instrument at the National Solar Observatory's Dunn Solar Telescope. Our Hα observations found large downflows of chromospheric material returning from coronal heights following a failed prominence eruption. We have detected several large condensations ("blobs") returning to the solar surface at velocities of ≈200 km s−1 in both Hα and several SDO Atmospheric Imaging Assembly band passes. The average derived size of these "blobs" in Hα is 500 by 3000 km2 in the directions perpendicular and parallel to the direction of travel, respectively. A comparison of our "blob" widths to those found from coronal rain, indicate that there are additional, smaller, unresolved "blobs" in agreement with previous studies and recent numerical simulations. Our observed velocities and decelerations of the "blobs" in both Hα and SDO bands are less than those expected for gravitational free-fall and imply additional magnetic or gas pressure impeding the flow. We derived a kinetic energy of ≈2 orders of magnitude lower for the main eruption than a typical coronal mass ejection, which may explain its partial nature.Publisher PDFPeer reviewe
High-resolution wave dynamics in the lower solar atmosphere
The magnetic and convective nature of the Sun's photosphere provides a unique
platform from which generated waves can be modelled, observed, and interpreted
across a wide breadth of spatial and temporal scales. As oscillations are
generated in-situ or emerge through the photospheric layers, the interplay
between the rapidly evolving densities, temperatures, and magnetic field
strengths provides dynamic evolution of the embedded wave modes as they
propagate into the tenuous solar chromosphere. A focused science team was
assembled to discuss the current challenges faced in wave studies in the lower
solar atmosphere, including those related to spectropolarimetry and radiative
transfer in the optically thick regions. Following the Theo Murphy
international scientific meeting held at Chicheley Hall during February 2020,
the scientific team worked collaboratively to produce 15 independent
publications for the current Special Issue, which are introduced here.
Implications from the current research efforts are discussed in terms of
upcoming next-generation observing and high performance computing facilities.Comment: 16 pages, 4 figures, Introduction to the "High-resolution wave
dynamics in the lower solar atmosphere" special issue of the Philosophical
Transactions A: https://walsa.team/u/rst
The Velocity Distribution of Solar Photospheric Magnetic Bright Points
We use high spatial resolution observations and numerical simulations to
study the velocity distribution of solar photospheric magnetic bright points.
The observations were obtained with the Rapid Oscillations in the Solar
Atmosphere instrument at the Dunn Solar Telescope, while the numerical
simulations were undertaken with the MURaM code for average magnetic fields of
200 G and 400 G. We implemented an automated bright point detection and
tracking algorithm on the dataset, and studied the subsequent velocity
characteristics of over 6000 structures, finding an average velocity of
approximately 1 km/s, with maximum values of 7 km/s. Furthermore, merging
magnetic bright points were found to have considerably higher velocities, and
significantly longer lifetimes, than isolated structures. By implementing a new
and novel technique, we were able to estimate the background magnetic flux of
our observational data, which is consistent with a field strength of 400 G.Comment: Accepted for publication in ApJL, 12 pages, 2 figure
Finding the mechanism of wave energy flux damping in solar pores using numerical simulations
Context. Solar magnetic pores are, due to their concentrated magnetic fields,
suitable guides for magnetoacoustic waves. Recent observations have shown that
propagating energy flux in pores is subject to strong damping with height;
however, the reason is still unclear. Aims. We investigate possible damping
mechanisms numerically to explain the observations. Methods. We performed 2D
numerical magnetohydrodynamic (MHD) simulations, starting from an equilibrium
model of a single pore inspired by the observed properties. Energy was inserted
into the bottom of the domain via different vertical drivers with a period of
30s. Simulations were performed with both ideal MHD and non-ideal effects.
Results. While the analysis of the energy flux for ideal and non-ideal MHD
simulations with a plane driver cannot reproduce the observed damping, the
numerically predicted damping for a localized driver closely corresponds with
the observations. The strong damping in simulations with localized driver was
caused by two geometric effects, geometric spreading due to diverging field
lines and lateral wave leakage.Comment: 12 pages (including appendix), 13 figures, accepted for publication
by A&
Accurately constraining velocity information from spectral imaging observations using machine learning techniques
Determining accurate plasma Doppler (line-of-sight) velocities from
spectroscopic measurements is a challenging endeavour, especially when weak
chromospheric absorption lines are often rapidly evolving and, hence, contain
multiple spectral components in their constituent line profiles. Here, we
present a novel method that employs machine learning techniques to identify the
underlying components present within observed spectral lines, before
subsequently constraining the constituent profiles through single or multiple
Voigt fits. Our method allows active and quiescent components present in
spectra to be identified and isolated for subsequent study. Lastly, we employ a
Ca II 8542 {\AA} spectral imaging dataset as a proof-of-concept study to
benchmark the suitability of our code for extracting two-component atmospheric
profiles that are commonly present in sunspot chromospheres. Minimisation tests
are employed to validate the reliability of the results, achieving median
reduced values equal to 1.03 between the observed and synthesised
umbral line profiles.Comment: 23 pages, 8 figures. Improved formatting of abstract and reference
Characterisation of shock wave signatures at millimetre wavelengths from Bifrost simulations
Observations at millimetre wavelengths provide a valuable tool to study the
small scale dynamics in the solar chromosphere. We evaluate the physical
conditions of the atmosphere in the presence of a propagating shock wave and
link that to the observable signatures in mm-wavelength radiation, providing
valuable insights into the underlying physics of mm-wavelength observations. A
realistic numerical simulation from the 3D radiative Magnetohydrodynamic (MHD)
code Bifrost is used to interpret changes in the atmosphere caused by shock
wave propagation. High-cadence (1 s) time series of brightness temperature
(T) maps are calculated with the Advanced Radiative Transfer (ART)
code at the wavelengths mm and mm, which represents opposite
sides of spectral band~ of the Atacama Large Millimeter/submillimeter Array
(ALMA). An example of shock wave propagation is presented. The brightness
temperatures show a strong shock wave signature with large variation in
formation height between to Mm. The results demonstrate that
millimetre brightness temperatures efficiently track upwardly propagating shock
waves in the middle chromosphere. In addition, we show that the gradient of the
brightness temperature between wavelengths within ALMA band can potentially
be utilised as a diagnostics tool in understanding the small-scale dynamics at
the sampled layers.Comment: 16 pages, 6 figures. Accepted for publication in Philosophical
Transactions A of the Royal Societ
- …